ecological research study

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Peer-reviewed

Research Article

Trends in Ecological Research during the Last Three Decades – A Systematic Review

Affiliation Faculty of Civil and Environmental Engineering, Technion – Israel Institute of Technology, Haifa, Israel

* E-mail: [email protected]

Affiliation Department of Plant Sciences, University of Cambridge, Cambridge, United Kingdom

Affiliation Department of Biology and Environment, University of Haifa at Oranim, Kiryat Tivon, Israel

Affiliation Institute of Evolution, University of Haifa, Haifa, Israel

• Yohay Carmel, 
• Rafi Kent, 
• Avi Bar-Massada, 
• Lior Blank, 
• Jonathan Liberzon, 
• Oded Nezer, 
• Gill Sapir, 
• Roy Federman

• Published: April 24, 2013
• https://doi.org/10.1371/journal.pone.0059813
• Reader Comments

It is thought that the science of ecology has experienced conceptual shifts in recent decades, chiefly from viewing nature as static and balanced to a conception of constantly changing, unpredictable, complex ecosystems. Here, we ask if these changes are reflected in actual ecological research over the last 30 years. We surveyed 750 articles from the entire pool of ecological literature and 750 articles from eight leading journals. Each article was characterized according to its type, ecological domain, and applicability, and major topics. We found that, in contrast to its common image, ecology is still mostly a study of single species (70% of the studies); while ecosystem and community studies together comprise only a quarter of ecological research. Ecological science is somewhat conservative in its topics of research (about a third of all topics changed significantly through time), as well as in its basic methodologies and approaches. However, the growing proportion of problem-solving studies (from 9% in the 1980s to 20% in the 2000 s) may represent a major transition in ecological science in the long run.

Citation: Carmel Y, Kent R, Bar-Massada A, Blank L, Liberzon J, Nezer O, et al. (2013) Trends in Ecological Research during the Last Three Decades – A Systematic Review. PLoS ONE 8(4): e59813. https://doi.org/10.1371/journal.pone.0059813

Editor: Luís A. Nunes Amaral, Northwestern University, United States of America

Received: September 16, 2012; Accepted: February 19, 2013; Published: April 24, 2013

Copyright: © 2013 Carmel et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Funding: This study was funded by the Israel Science Foundation (grant number 486-2010). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.

Introduction

Ecologists often describe ecological science as dynamic. ‘Ecology is a science in transition’ [1] . This transition is characterized by several significant shifts in emphasis and perspective [2] . During most of the 20 th century, the majority of ecologists conceptualized ecological systems as balanced and stable, typically at equilibrium, or as returning to such equilibrium deterministically following rare disturbances [3] . In recent decades, there has been a shift towards an understanding of ecological systems as nonlinear, constantly changing, and unpredictable in time and space [4] , [5] . The concept of equilibrium was replaced by other concepts, for example, the concept of non-equilibrium change, in which the system is often described as rotating between alternative states [6] .

Ecologists are split on the question of whether the changes in ecological science represent a Kuhnian ‘paradigm shift’ [5] , [7] , [8] , [9] , or, alternatively, a gradual accumulation of modifications, better characterized as ‘evolution’ rather than ‘revolution’ [2] , [10] . In contrast, other ecologists maintained that progress in ecology is lacking [11] or limited [12] .

Here, we ask if the topics and methodologies of ecological research as reflected in the literature of the last 30 years provide evidence to support notions of dramatic shifts, or of gradual change. We characterize various aspects of ecological research, using an extensive survey of ecological literature. In particular, we ask three questions regarding general aspects of ecology, and look for possible changes in these aspects over the last 30 years:

• Domains of ecological research : What proportion of research is devoted to the various domains in ecology (population, species, community, and ecosystem)? What are the major topics of ecological study? Has there been a change in the frequency of investigation of any of these topics and, if so, which ones?
• Types of research : Is ecology an experimental science, or a science of observation and measurement? How often are models used in ecological research? To what degree do ecologists use meta-analysis of data from previous studies (vs. collecting new data in each research)?
• Basic science or problem-solving oriented discipline : Is ecology becoming a problem-solving science? In other words, how often does ecology relate to actual, specific environmental problems, in an attempt to provide solutions (or at least new insights on how to make progress towards solutions)?

Preliminary expectations

A. domains of ecological research..

The concepts of ecosystem and community have become increasingly dominant in ecological thinking. In a survey conducted among members of the British Ecological Society, ecosystem was identified as the single most important concept in ecology [13] . More recently, the Ecological Visions Committee of the Ecological Society of America issued a report that listed eight critical environmental issues for prioritizing ecological research [14] . Only two of those topics related to populations and species, while five topics were clearly within the domains of ecosystems and communities . We expected an increase in research conducted at the ecosystem level, and at the community level, accompanied by a proportional decrease in studies of single species. We also expected specific topics to become more frequent subjects of ecological study (such as biodiversity, climate change, biogeochemistry, and scale).

B. Types of research.

Observations and experiments are known to be the two dominant tools of ecological research . In this research, we expected to identify an increase in the frequency of models, for two reasons: (1) the ecosystem has increasingly been described as ‘complex’, and models are often the only tools available for the study of complex systems, and (2) due to the substantial increase in the availability of modelling tools during the last three decades. We also expected an increase in the proportion of meta-analysis studies, for two major reasons: (1) a growing awareness of the incapacity of single studies of specific systems, conducted under narrow ranges of conditions, to provide insights on broader ecological issues [15] , and (2) the increased access to information and data in the age of the Internet.

C. Is ecology a problem-solving science?

In the past, ecologists have been reluctant to engage in applied research [16] . Applied science was considered inferior to basic, ‘pure’ science [17] . Some applied ecological issues, such as conservation, are emotionally charged [2] , and perceived by some ecologists as ‘advocacy’ [18] . More recently, ecologists have become increasingly concerned about the implications of their work to society's problems [15] , [17] , while environmental agencies have expressed an increased demand for ecological solutions to environmental problems [19] . For these reasons, we expected to find an increase in the proportion of applied studies over the last three decades.

In order to attempt to answer these questions, a quantitative survey of ecological research is required. Surprisingly, few attempts have been made to systematically quantify trends in ecological research. Typically, these studies have used an automated count of words in titles and abstracts to assess trends in ecology [20] , [21] , [22] , [23] . Shorrocks [24] used an alternative method to survey trends in ‘the Journal of animal ecology’ –he actually sampled 13 volumes of the journal between 1932 and 1992. Here, we followed that method: we inspected a large sample of the ecological literature, classifying it according to its content. This process is time-consuming, but the resulting analysis is probably more reliable than an automated word count.

Two surveys

One major consideration was our choice of target population within the ecological literature. Two plausible alternatives existed: we could either sample the entire pool of ecological research, or sample only leading journals. There are pros and cons to each choice. Including the entire range of ecological literature may introduce research of varying quality into the analysis. On the other hand, niche journals (the vanguard of novel research) may serve as early indicators of transitions and trends. We therefore decided to conduct two parallel surveys, using identical methods. In survey 1, we included all 136 journals that concern ecology, while in survey 2 we sampled eight ‘core journals’ that were published throughout the entire study period. A brief description of the data collection approach can be found in the Prisma 2009 flow diagram and checklist.

Journal selection

For survey 1, we selected all relevant journals that appeared during at least parts of the study period 1981–2010. This pool consisted of 136 journals. From the entire collection of articles published in these journals during this period, we limited the selection to research articles in English, and received a total of 110,965 articles (see Appendix S1 for a full list of journals sampled for this survey).

For survey 2, we selected eight prominent journals, using the following criteria: (a) high-impact factor (among the top 30 ecological journals, using ISI Web of Science Impact Factor), (b) generality (cover the entire scope of ecological research), and (c) consistency (were published throughout the study period). Not a single journal satisfied all three criteria. We therefore selected eight journals belonging to three major ecological societies that issue their own journals; thus, each group, as such, satisfies all three criteria. The eight journals were those issued by the Ecological Society of America ( Ecological Applications , Ecological Monographs , and Ecology ); the British Ecological Society (Journal of Ecology, Journal of Animal Ecology, and Journal of Applied Ecology), and the Nordic Ecological Society ( Oikos and Ecography ). Ecological Applications , first published in 1991, was an offshoot of Ecology, and Ecography , first published in 1991, was an offshoot of Oikos ; we assumed that the range of topics covered by each of the pairs was similar to that of the parent journal prior to the split. The pool of all research articles published in these journals in the period 1981–2010 consisted of 22,788 articles).

For each of the two surveys, we used a random selection scheme to select 25 articles from each year, totalling 750 articles in each survey. The classification (domain, topics, research type, applied or basic science) was performed by the authors of the current study, based on the articles. In many cases, reading the abstract provided sufficient information for classifying the article. In order to ensure a high degree of consistency between the classifiers, we carried out a pilot exercise, in which the degree of agreement between the classifiers was assessed prior to the research study. A set of 29 articles was classified independently by all classifiers. Classifications were then discussed until consensus was reached for each classification. For each topic and for each classifier, the level of agreement between initial classification and final ‘consensus’ was recorded.

Article characterization

A. ecological domains..

We predefined 20 topics that describe major research fields in ecology, and grouped these 20 topics into five broad ecological domains: (1) Single Species (demography, physiology, distribution, behaviour, evolution, genetics); (2) Species Interactions (grazing, predation, mutualism, parasitism, competition); (3) Community (biodiversity, community structure); (4) Ecosystem (food web, climate change, vegetation dynamics, biomass and productivity, biogeochemistry); and (5) Other topics (scale, statistics). We limited topic-based characterization to three topics per article.

B. Type of research.

We classified the type of ecological research according to four general categories: experiment, observation, model, and data analysis. An article was classified as ‘experiment’ if an actual experiment was conducted in the laboratory, or if a field study included some sort of treatment or manipulation of the natural environment. Where research included both observation and field experiment, the article was labelled ‘experiment’. ‘Observation’ was a study where the major activity was any sort of measurement of ecological phenomena. An article was labelled ‘model’ if its sole activity or the major endeavor was to construct a model. In cases where a model was only a minor part of the research, the article was labelled ‘experiment’ or ‘observation’. Articles that did not present any new data, but used data collected in previous studies, often conducting meta-analysis, were labelled ‘data analysis’. Articles that did not include any of the above types of research, but discussed ecological issues qualitatively were omitted from the survey (and a replacement was added).

C. Problem-solving.

Our goal here was to determine the degree to which ecology is oriented towards problem-solving. We assigned the category of ‘application’ to all articles that either searched for solutions to problems associated with anthropogenic activities, or proposed tools for practical problems (such as practices for conservation, global change mitigation etc.).

Statistical analyses

The number of articles assigned to each ecological topic, label, and variable was recorded for each survey. The differences between surveys in terms of the frequency of each term were analyzed using Chi square test. To evaluate change in the frequency of these variables over time, we used logistic regression [25] , with publication year as a continuous variable and survey type as a fixed variable. In order to account for multiple comparisons, we applied the Bonferroni correction. Fifty comparisons (25 comparisons in each survey) yielded a threshold of p<0.001 . The Bonferroni correction becomes very conservative when the number of comparisons becomes large, as it controls the probability of false positives only, at the cost of increasing the probability of false negatives [26] . We therefore report the results using Bonferroni correction, as well as for less conservative thresholds.

Classification consistency

Classifiers' results were in good agreement with the consensus of the test articles, with an overall average agreement rate of 90%. The average accuracy of parameter classification was high in all cases, ranging from 86% for ‘topics’ and ‘problem solving’, to 93% and 94% for ‘research type’ and ‘domain’, respectively. In what follows, wherever we report two figures, the first figure refers to the ‘all journals’ survey, and the second figure refers to the ‘core journals’ survey.

Domains of ecological research

(1) Single Species was the most frequent domain of study in this survey of ecological research, with 71% (66%) of all the studies involving topics within this domain ( Table 1 ). In both surveys, the four most common topics related to this domain: demography, physiology, behaviour and distribution. Taken together, these topics appeared in 64% (63%) of all articles. Only 4% (3%) of all articles studied evolution. (2) In the Species Interactions domain, predation and competition were the frequent terms, recorded in 5–9% of the articles, while mutualism and parasitism were recorded in 2–4% of the articles. (3) Community-related topics (biodiversity and community structure) appeared in 17% of the studies in both surveys, and (4) Ecosystem-related topics appeared in nearly a quarter of the articles. Among ecosystem topics, biogeochemistry accounted for 11% (8%) of ecological research and 2% of the research concerned climate change studies ( Table 1 ).

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https://doi.org/10.1371/journal.pone.0059813.t001

The frequency of community studies increased significantly (nearly significantly in the ‘core journals’) during the studied period, while the other three domains remained quite constant over time ( Table 2 , Figure 1 ).

White bars denote ‘all journals’ and gray bars denote ‘core journals’. Temporal trend was significant for community studies only (a logistic model, see Table 2 ).

https://doi.org/10.1371/journal.pone.0059813.g001

https://doi.org/10.1371/journal.pone.0059813.t002

There were significant changes in the frequency of several topics over time. The frequency of two topics climate change and biodiversity, increased significantly with time in both surveys ( Table 2 , Figure 2 ). The frequency of three additional topics changed significantly in the ‘all journals’ survey only: physiology and behaviour decreased, while genetics increased. An increase in the frequency of scale was the single significant change that appeared in the ‘core journals’ only. Additionally, five topics revealed a nearly significant frequency change through time in that survey (p<0.05): demography , grazing , and vegetation dynamics decreased, while evolution and parasitism increased in frequency with time ( Table 2 ).

White bars denote ‘all journals’ and gray bars denote ‘core journals’. *** Temporal trend was significant (a logistic model, see Table 2 ), p<0.001. ** p<0.01. * p<0.05.

https://doi.org/10.1371/journal.pone.0059813.g002

Differences between the two surveys

The results of both surveys were quite similar for 14 of the 20 topics, while significant differences between the two surveys were found for six topics: physiology , behaviour and genetics were much more frequent in the ‘all journals’ survey, while demography , grazing , and vegetation dynamics were much more frequent in the ‘core journals’ survey ( Table 1 ). Most domains appeared at similar frequencies in the two surveys, except Species Interactions, which was nearly twice as frequent in the ‘core journals’ survey compared to its frequency in the ‘all journals’ survey ( Table 1 ).

Type of research

Observations constitutes the major type of ecological research (59%, 45%), followed by experiments (28%, 36%), while models (12%, 12%) and data-analysis (9%, 6%) were less frequent ( Table 3 ).

https://doi.org/10.1371/journal.pone.0059813.t003

The proportion of data-analysis studies increased significantly with time in the ‘all journals’ survey. The use of models as a primary research tool slightly decreased in ‘all journals’ and slightly increased (nearly significant) in the ‘core journals’ survey ( Table 4 ).

https://doi.org/10.1371/journal.pone.0059813.t004

Observation studies were significantly more frequent in the ‘all journals’ survey, while experiments were somewhat more frequent in the ‘core journals’ survey.

Is ecology a problem-solving science?

Overall, 17% (15%) of the articles were labelled ‘problem solving’ ( Table 3 ). In both surveys, their proportion increased significantly over time, from 9% (7%) in the 1980s to 21% (21%) in the 2000 s ( Table 4 , Figure 2 ).

Few systematic surveys of ecological literature have been conducted to date, and most have been restricted to a single theme or a narrow branch of ecological science [20] , [21] , [22] , [23] . For example, [22] evaluated relations between the size of the organism and its relative representation in ecological research. Swihart [12] quantified the rates of appearance of new ecological terms and disappearance of old terms. Shorrocks [24] was perhaps the only investigator to quantify various trends in ecological science, using articles published in The Journal of Animal Ecology between 1932 and 1992. To the best of our knowledge, the present study is the first attempt to systematically survey the entire breadth of ecological literature, in order to quantify various characteristics of the science of ecology, as well as their temporal trends. The results suggest that ecology may be substantially less dynamic than is generally acknowledged.

Ecology is mostly a study of single species. Most of the ecological research focused on the demography, physiology and distribution of single species. The proportion of single-species studies has slightly decreased in the past three decades, but still consists of more than 60% of the studies. In comparison, community and ecosystem studies represented a minor fraction of ecological research. This surprising finding seems at odds with the strong emphasis on the community and the ecosystem as major concepts in ecology [27] , [28] . Also surprising was the scarcity of a few topics which are thought to be central in ecology. Two notable examples are evolution, and food-web, each of which appeared as a research topic in 2–4% of the articles. Most of the increase in community studies occurred in the 2000s, probably reflecting the renewed interest in this field, after the neutral theory challenged the prevalence of the niche concept.

The analysis of changes in the frequency of research topics over time provided inconclusive results. Only two topics, climate change and biodiversity, showed a significant change in both surveys. The increase in both topics probably relates to the fact that both were non-issues at the beginning of the period under study. Four other topics changed significantly, and seven other topics changed nearly significantly, in only one of the surveys. Overall, there does not seem to be a drastic transformation in the relative importance of domains and topics in the field of ecology, but the apparent change in topics and research types signifies that ecological science is not entirely stagnant.

The frequency of more than half of the topics and domains was very similar in both surveys, but nearly a third of the topics differed significantly between the surveys. Interestingly, the topics that were significantly more frequent in the ‘all journals’ survey related to the basic and static aspects of a species (genetics and physiology), and the ecosystem (biomass and productivity). In contrast, the topics that were significantly more frequent in the ‘core journals’ related to dynamic processes (demography, vegetation dynamics, and grazing).

Observation and experiment were by far the predominant tools of ecological study, together accounting for 80% of the research; these proportions did not change over time. Interestingly, modelling (∼12% of all studies), is no more common today than it was thirty years ago, despite a drastic increase in the availability of modelling tools during this period. Data-analysis became a more common research tool. Many of the studies in this category were, in fact, meta-analyses (analyses of data from several sources). The major increase in data-analysis studies was in the mid-90s, suggesting that the increased availability of information in the age of the Internet had an important role in this trend.

Comparing the two surveys in terms of type of research revealed a fundamental difference: the ratio of experiments to observations in the ‘all journals’ survey was 1:2, while in the ‘core journals’ survey it was 7:9. The prevalent consensus that ecology has changed during the 20 th century, from an observational to an experimental science, may be somewhat overstated; nevertheless, such a change appeared more prominently in the ‘core journals’ survey.

Ecological research is mostly a basic science, with only a small proportion of ‘problem solving’ studies. Yet, in both surveys we found a significant and consistent increase in the number of ‘problem solving’ articles published during the survey period. If this trend continues in future decades, it may prove to be a major shift in the orientation of ecology.

Is ecology a dynamic science?

Prominent ecologists have claimed that ecology has undergone transitions [29] , and even paradigm shifts [5] in recent decades, and is now a mature and competent science [30] . Our survey reveals that these claims perhaps overstate the case. The science of ecology appears to be changing slowly, in the sense that major research subjects and principal methodologies have not changed dramatically for at least 30 years. In particular, the popular image of ecology as a science in transition [7] , dealing chiefly with ecosystems and communities [1] seems at odds with the major proportion of single species studies reported here.

A contrasting view, put forward by O'Connor [11] , claimed that ecology lags after other life sciences, and makes very little progress. O'Conner's study ignited a debate, wherein various arguments were employed to disprove this claim [31] , [23] , or put it in a balanced perspective [12] . This debate is still ongoing, and is probably driven by emotions no less than by objective evaluations. The current study does not substantiate O'Connor's claim, and it was not meant to evaluate progress. However, it is safe to assume that a major advance in ecology would be accompanied by a major change in the frequency of domains, topics, and types of research; yet, as shown here, these have changed only moderately in the course of three decades.

A major aspect of progress in science is the rate at which basic questions in ecology are being answered [12] , which we have not evaluated, and is very difficult to evaluate quantitatively. Also, we could not detect conceptual shifts, such as network thinking, that do not connect to particular terms or topics. Swihart et al. [12] provide an interesting attempt to quantify progress based on ‘birth rate’ and ‘death rate’ of ecological terms, and claim to show viable progress in ecology. In contrast, the list of 100 fundamental questions in ecology [32] reports profound knowledge gaps regarding the central mechanisms driving ecosystems, communities, and even population dynamics.

Our approach could not, and was not meant to detect changes in particular methods and technologies applied within each research domain or topic. The availability of advanced molecular and genetic tools and the increase in computing power have allowed analyses to become more complex and sophisticated. However, the use of these new technologies and processing power does not imply enhanced knowledge or understanding. Also, such surveys may not detect conceptual shifts, such as network thinking, which do not connect to particular terms or topics.

Perhaps the single and most important change in the study of ecology is the growing proportion of ecological research directed towards problem solving. This trend by itself, if continued, may represent a major transition in ecology in the long run.

Our results may be disturbing to some researchers, insofar as they portray an ecological discipline which is considerably less dynamic than ecologists would like to believe. The value of this research is precisely in reviving the debate and presenting an opportunity for self-assessment to those who strive to advance the discipline, all of which can serve to stimulate the investigation of new and groundbreaking tools, paradigms and perspectives. Only through meta-scale monitoring of the scope of research can we understand, and hope to influence, the trajectory of ecological research in the years to come.

Supporting Information

Appendix s1..

A full list of journals sampled for survey 1.

https://doi.org/10.1371/journal.pone.0059813.s001

Flow Diagram S1.

https://doi.org/10.1371/journal.pone.0059813.s002

Checklist S1.

https://doi.org/10.1371/journal.pone.0059813.s003

Acknowledgments

Curtis Flather, Mark Burgman, Leon Blaustein, Yaacov Garb, Yaron Ziv and Daniel Statman have provided valuable comments on a draft of this manuscript.

Author Contributions

Conceived and designed the experiments: YC AB LB RF. Performed the experiments: YC RK AB LB JL ON RF GS. Analyzed the data: RF YC GS. Wrote the paper: YC RK AB LB RF JL ON.

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Methodology Series Module 7: Ecologic Studies and Natural Experiments

Maninder singh setia.

Epidemiologist, MGM Institute of Health Sciences, Navi Mumbai, Maharashtra, India

In this module, we have discussed study designs that have not been covered in the previous modules – ecologic studies and natural experiments. In an ecologic study, the unit of analysis is a group or aggregate rather than the individual. It may be the characteristics of districts, states, or countries. For example, per capita income across countries, income quintiles across districts, and proportion of college graduates in states. If the data already exist (such as global measures and prevalence of diseases, data sets such as the National Family Health Survey, census data), then ecologic studies are cheap and data are easy to collect. However, one needs to be aware of the “ecologic fallacy.” The researcher should not interpret ecologic level results at the individual level. In “natural experiments,” the researcher does not assign the exposure (as is the case in interventional studies) to the groups in the study. The exposure is assigned by a natural process. This may be due to existing policies or services (example, one city has laws against specific vehicles and the other city does not); changes in services or policies; or introduction of new laws (such helmet for bikers and seat-belts for cars). We would like to encourage researchers to explore the possibility of using these study designs to conduct studies.

Introduction

In the previous modules, we have discussed study designs that are generally used in clinical research. These can be broadly classified into two major categories: Observational and interventional studies. We have discussed cohort studies, cross-sectional studies, and case–control studies in the observational category. Furthermore, we also discussed clinical trials (randomized and nonrandomized) in the experimental category. In this module, we will discuss study designs that have not been covered in the previous modules – ecologic studies and natural experiments.

Ecologic Studies

In an ecologic study, the unit of analysis is a group or aggregate rather than the individual. It may be the characteristics of districts, states, or countries. For example, per capita income across countries, income quintiles across districts, proportion of college graduates in states. Actually, as clinical researchers, we often conduct ecologic studies. However, sometimes, we fail to acknowledge them as being “ecologic” in nature. We have provided some examples of these studies.

Examples of Ecologic Studies

Prentice et al . (1988).

The authors reported that there is strong correlation between dietary intake (of various caloric sources) and breast cancer incidence in 21 countries. They found that there was strong correlation in breast cancer incidence with national estimates of per capita intake of dietary fat in these countries. However, they did not find any such relation between other forms of caloric intake such as proteins and carbohydrates.

Pascal et al . (2013)

In this study, the authors assessed hospitalizations due to cardiovascular diseases, respiratory diseases, and cancers in an industrial region in the South of France. The exposure was the annual mean concentration of sulfur dioxide (SO 2 ) in 29 administrative districts of this region. They found that there was an excess risk of hospitalization for myocardial infarction in men and women who lived in districts with high or medium SO 2 levels compared with those living in reference levels. However, they did not find any excess risk for respiratory diseases. They concluded that industrial air pollution has an effect on the cardiovascular system; thus, there is a need to improve the air quality in this region.

Parkhurst (2010)

In this study, the author assessed the prevalence of human immunodeficiency virus (HIV) and socioeconomic parameters in 12 African countries. The author found that the HIV prevalence increased with wealth; this trend was observed particularly in lower-income countries. In nearly, all countries with gross domestic product (GDP) <US$ 2000, there was a significant trend in HIV prevalence across wealth quintiles. However, there was no such consistent relationship in countries with a GDP >US$ 2000. The author concluded that since both wealth and poverty can lead to change in behaviors, the interventions should be aimed at context-specific risks.

What are the different types of group variables?

In the first example, the group variable was per capita intake of dietary fat. This measure may have been calculated from some nutritional surveys (with the individuals reporting dietary intake). This is an example of “aggregate measure.” Some other examples could be median number of cigarettes per day, proportion of immigrants in districts, or proportion of minorities in cities.

In the second study, the group variable was mean concentration of SO 2. This is an example of “environment measure.” Some other examples could be hardness of water, levels of other pollutants, or hours of sunlight in the country.

A third type of group variable is the “Global measure.” Some examples of this measure are human development index, gender equality measure, and GDP (gross and per capita). Some other global measure could be existing laws in the country (death penalty exists), policies present (example, free education for primary school, free antiretroviral treatment to HIV-infected individuals), etc.

Why ecologic studies?

• If the data already exist (such as global measures and prevalence of diseases, data sets such as National Family Health Survey, census data), these studies are cheap, and data are easy to collect
• These studies may be useful to generate hypotheses. For example, in the first example, the authors found a correlation between per capita intake of dietary fat and breast cancer incidence. This may be used to conduct clinical studies or molecular studies to evaluate the association between fat and breast cancer
• Sometimes, this is the only option available. For example, if we are interested to study the relation between GDP and prevalence of psoriasis (hypothetical example) across countries, we have use ecologic level data and it will be ecologic analysis.

What is the problem with ecologic studies?

• The analyses of ecologic studies may require expertise (such as handling Geographic Information System, confounding variables). Thus, it is important to consultant a methodologist or a statistician before initiating these studies
• Ecologic fallacy: This is an important concern in ecologic studies. Let us understand this fallacy. We have conducted a study to assess the relation between psoriasis and socioeconomic status (SES). We find that districts with a higher proportion of the upper SES individuals have a high prevalence of psoriasis. One should not conclude immediately that higher SES is associated with psoriasis. This will be an example of “ecologic fallacy.” We have interpreted ecologic level analysis at the individual level.

Natural Experiments

Although they are called natural experiments, the researcher does not assign the exposure (as is the case in interventional studies) to the groups in the study. The exposure is assigned by a natural process. This may be due to existing policies or services (example, one city has laws against specific vehicles and the other city does not), changes in services or policies, or introduction of new laws (such helmet for bikers and seat-belts for cars). The difference in outcomes in these groups (two or more with different types or levels of exposure) is assessed. The assessment can be (1) simultaneously between two or more groups with different policies/services/any other form of exposure or (2) pre-post assessment after the change in policy/service/other exposure.

Examples of Natural Experiment Studies

Cole et al . (1987).

The authors evaluated eye injuries in the United Kingdom before and after the introduction of seat belt laws. They evaluated 381 injuries during two time periods (time period one: August 1, 1981–January 31, 1983 - 18 months; time period two: February 1, 1983–July 31, 1984). They found that the proportion of road traffic accidents as a cause of eye injuries reduced from 17.1% in the preseat belt legislation period to 6% in the postseat belt legislation period. Thus, they concluded that “seat belt law” was effective in reducing serious ocular morbidity.

Cheng et al . (1997)

The authors evaluated the changes in health-care utilization in Taiwan after the introduction of Universal Health Insurance. They evaluated physician visits, hospital admissions, and emergency department visits before and after the implementation of the policy in a cohort of individuals. They found that individuals who were insured after the implementation of the program were significantly more likely to make outpatient visits, emergency department visits, and get admitted in the hospitals, and compared with the time period before the implementation of the insurance program. However, there were no significant changes in the hospital admissions and emergency department visits in those that were insured before the National Insurance Programmes. Thus, they concluded that introduction of the program reduced barriers for health-care access.

Evans et al . (2016)

The authors evaluated the association between socioeconomic factors and time to revascularization in patients with acute myocardial infarction after redesigning the services. They analyzed data from two cohorts – 24 months before and after the date of change of services (the cutoff was kept very close to the date of change). They found that in the preintervention period, the adjusted risk for revascularization was significantly lower in the most deprived quintile compared with the least deprived quintile. However, the difference in the rates was not statistically significant between the two quintiles in the postintervention period. Thus, they concluded that access to revascularization was not different in different socioeconomic catergories after redesigning the services.

What are the advantages of natural experiments?

• They can be used in situations when it not ethical to assign exposures. For examples, it will unethical to design an interventional study to assess the role of helmets in prevention of head injuries
• These studies can be used to evaluate policies and laws
• The results from these studies are useful for advocating changes in policies.

Learning points in natural experiments

• The principles of study design should be adhered to. For example, if the researcher wants to compare two groups at the same time (in two different areas/cities), then it is a cross-sectional comparison. However, the researcher may choose to use a cohort design to compare the two groups
• One may also use ecologic data for natural experiments. For example, the researcher can assess the number of outcomes every year before the introduction of policy and compare with the number of outcomes every year after the introduction of policy
• Although these studies may give some evidence of the role of policy change, it may not be enough for causal inference.

Additional Points

In addition to these study designs, another important quantitative study is the diagnostic study. The diagnostic study design can be used to assess the diagnostic properties of a new test or diagnostic algorithms. These properties include sensitivity, specificity, positive predictive value, and negative predictive value. A detailed explanation of these terms and methods for these parameters will be discussed in the biostatistics module.

We would like to encourage researchers to explore the possibility of using these study designs to conduct studies. In some of these studies, data collection and management may be relatively easy. For example, if the researcher proposes to conduct an ecologic study based on published data, the data can be collected in an office (using a computer), addressing ethical issues may be easy, and the study can be completed at a lower cost.

Financial support and sponsorship

Conflicts of interest.

There are no conflicts of interest.

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Ecologic studies in epidemiology: concepts, principles, and methods

Affiliation.

• 1 Department of Epidemiology, University of California, Los Angeles, School of Public Health, USA.
• PMID: 7639884
• DOI: 10.1146/annurev.pu.16.050195.000425

An ecologic study focuses on the comparison of groups, rather than individuals; thus, individual-level data are missing on the joint distribution of variables within groups. Variables in an ecologic analysis may be aggregate measures, environmental measures, or global measures. The purpose of an ecologic analysis may be to make biologic inferences about effects on individual risks or to make ecologic inferences about effects on group rates. Ecologic study designs may be classified on two dimensions: (a) whether the primary group is measured (exploratory vs analytic study); and (b) whether subjects are grouped by place (multiple-group study), by time (time-trend study), or by place and time (mixed study). Despite several practical advantages of ecologic studies, there are many methodologic problems that severely limit causal inference, including ecologic and cross-level bias, problems of confounder control, within-group misclassification, lack of adequate data, temporal ambiguity, collinearity, and migration across groups.

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Ecological studies: advantages and disadvantages

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• Philip Sedgwick , reader in medical statistics and medical education
• 1 Centre for Medical and Healthcare Education, St George’s, University of London, London, UK
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Researchers examined the association between child wellbeing and economic status in rich developed societies. An ecological cross sectional study design was used, with 23 of the richest 50 countries in the world included in the analysis. Child wellbeing was measured by the Unicef index of child wellbeing. Three macro-economic measures were used—material living standards (average income), the scale of differentiation in social status (income inequality), and social exclusion (children in relative poverty). 1

The overall Unicef index has 40 items that measure six dimensions—material wellbeing, health and safety, education, peer and family relationships, behaviours and risks, and young people’s own subjective sense of wellbeing. An item measuring relative poverty was removed before calculating the index of child wellbeing. Low scores indicated worse outcomes. Income inequality was measured as the ratio of the total annual household income received by the richest 20% of the population to that received by the poorest 20%. Therefore, larger values indicated greater inequality between the richest and poorest within a country. Child relative poverty was measured as the proportion of children aged 0-17 years in households with an income equivalent to less than the national median.

It was reported that the overall …

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• Ecology: Definition, Types, Importance & Examples

Ecological Research Methods: Observing, Experimenting & Modeling

Ecology is the study of the relationship between organisms and their environment on earth. Several ecological methods are used to study this relationship, including experimenting and modeling.

Manipulative, natural or observational experiments may be used. Modeling helps analyze the collected data.

What Is Ecology?

Ecology , the study of how organisms interact with their environment and each other, draws upon several other disciplines. The environmental science of ecology incorporates biology, chemistry, botany, zoology, mathematics and other fields.

Ecology examines species interactions, population size, ecological niches, food webs, energy flow and environmental factors. In order to do this, ecologists rely on careful methods to collect the most accurate data they can. Once data is collected, ecologists then analyze it for their research.

The information gained from these research methods can then help ecologists find impacts caused by humans or natural factors. This information can then be used to help manage and conserve impacted areas or species.

Observation and Field Work

Every experiment requires observation. Ecologists must observe the environment, the species within it and how those species interact, grow and change. Different research projects require different types of assessments and observations.

Ecologists sometimes use a desk-based assessment , or DBA, to collect and summarize information about specific areas of interest. In this scenario, ecologists are using information already collected from other sources.

Oftentimes, however, ecologists rely on observation and field work . This entails actually going into the habitat of the subject of interest to observe it in its natural state. By doing field surveys, ecologists can track population growth of species, observe community ecology in action and study the impact of any new species or other introduced phenomena in the environment.

Each field site will differ in nature, in shape or in other ways. Ecological methods allow for such differences so that different tools can be used for observations and sampling. It is crucial that sampling be done in a random fashion to combat bias.

Types of Data Obtained

Data obtained from observation and field work can be either qualitative or quantitative. These two classifications of data vary in distinct ways.

Qualitative data : Qualitative data refers to a quality of the subject or conditions . It is therefore a more descriptive form of data. It is not easily measured, and it is collected by observation.

Because qualitative data is descriptive, it might include aspects such as color, shape, whether the sky is cloudy or sunny, or other aspects for how an observation site might look. Qualitative data is not numerical like quantitative data. It is therefore considered less reliable than quantitative data.

Quantitative data: Quantitative data refers to numerical values or quantities . These kinds of data can be measured and are usually in number form. Examples of quantitative data might include pH levels in soil, the number of mice in a field site, sample data, salinity levels and other information in numeric form.

Ecologists use statistics to analyze quantitative data. It is therefore considered a more reliable form of data than qualitative data.

Types of Field Work Surveys

Direct survey: Scientists can directly observe animals and plants in their environment. This is called a direct survey. Even in places as remote as a seafloor, ecologist can study the underwater environment. A direct survey in this case would entail photographing or filming such an environment.

Some sampling methods used to record images of sea life on the seafloor include video sledges, water curtain cameras and Ham-Cams. Ham-Cams are attached to a Hamon Grab, a sample bucket device used to collect samples. This is one effective way to study animal populations.

The Hamon Grab is a method of collecting sediment from the seafloor, and the sediment is taken onto a boat for ecologists to sort through and photograph. These animals will be identified in a laboratory elsewhere.

In addition to a Hamon Grab, undersea collection devices include a beam trawl, which is used to obtain larger sea animals. This entails attaching a net to a steel beam and trawling from the back of a boat. The samples are brought on board the boat and photographed and counted.

Indirect survey: It is not always practical or desirable to observe organisms directly. In this situation, ecological methods entail observing the traces those species leave behind. These could include animal scat, footprints and other indicators of their presence.

Ecological Experiments

The overarching purpose of ecological methods for research is to get high-quality data. In order to do this, experiments must be carefully planned.

Hypothesis : The first step in any experimental design is to come up with a hypothesis or scientific question. Then, researchers can come up with a detailed plan for sampling.

Factors that affect field work experiments include the size and shape of an area that needs to be sampled. Field site sizes range from small to very large, depending on what ecological communities are being studied. Experiments in animal ecology must take into account potential movement and size of animals.

For example, spiders would not require a large field site for study. The same would be true when studying soil chemistry or soil invertebrates. You could use a size of 15 meters by 15 meters.

Herbaceous plants and small mammals might require field sites of up to 30 square meters. Trees and birds might need a couple of hectares. If you are studying large, mobile animals, such as deer or bears, this could mean needing a quite large area of several hectares.

Deciding upon the number of sites is also crucial. Some field studies might require only one site. But if two or more habitats are included in the study, two or more field sites are necessary.

Tools: Tools used for field sites include transects, sampling plots, plotless sampling, the point method, the transect-intercept method and the point-quarter method. The goal is to get unbiased samples of a high-enough quantity that statistical analyses will be sounder. Recording information on field data sheets aids in the data collection.

A well-designed ecological experiment will have a clear statement of purpose or question. Researchers should take extraordinary care to remove bias by providing both replication and randomization. Knowledge of the species being studied as well as the organisms within them is paramount.

Results: Upon completion, collected ecological data should be analyzed with a computer. There are three types of ecological experiments that can be made: manipulative, natural and observational.

Manipulative Experiments

Manipulative experiments are those in which the researcher alters a factor to see how it affects an ecosystem. It is possible to do this in the field or in a laboratory.

These kinds of experiments provide interference in a controlled manner. They work in cases in which field work cannot occur over an entire area, for various reasons.

The downside of manipulative experiments is they are not always representative of what would happen in the natural ecosystem. Additionally, manipulative experiments might not reveal the mechanism behind any patterns observed. It is also not easy to change variables in a manipulative experiment.

Example : If you wanted to learn about lizard predation of spiders, you could alter the number of lizards in enclosures and study how many spiders resulted from this effect.

A larger and current example of a manipulation experiment is the reintroduction of wolves into Yellowstone National Park. This reintroduction allows for ecologists to observe the effect of wolves returning to what was once their normal range.

Already, researchers have learned that an immediate change in the ecosystem occurred once wolves were reintroduced. Elk herd behaviors changed. Increased elk mortality led to a more stable food supply for both wolves and carrion eaters.

Natural Experiments

Natural experiments, as their name implies, are not directed by humans. These are manipulations of an ecosystem caused by nature. For example, in the wake of a natural disaster, climate change or invasive species introduction, the ecosystem itself represents an experiment.

Of course, real-world interactions such as these are not truly experiments. These scenarios do provide ecologists with opportunities to study the effects natural events have on species in an ecosystem.

Example: Ecologists could take a census of animals on an island to study their population density.

The main difference between manipulative and natural experiments from a data perspective is that natural experiments do not have controls. Therefore it is sometimes harder to determine cause and effect.

Nevertheless, there is useful information to be gained from natural experiments. Environmental variables like moisture levels and density of animals can still be used for data purposes. Additionally, natural experiments can occur across large areas or vast stretches of time. This further distinguishes them from manipulative experiments.

Unfortunately, humanity has caused catastrophic natural experiments across the globe. Some examples of these include habitat degradation, climate change, introduction of invasive species and removal of native species.

Observational Experiments

Observational experiments require adequate replications for high-quality data. The “rule of 10” applies here; researchers should collect 10 observations for each category required. Outside influences can still hamper efforts to collect data, such as weather and other disturbances. However, using 10 replicating observations can prove helpful for obtaining statistically significant data.

It is important to perform randomization, preferably prior to performing observational experiments. This can be done with a spreadsheet on a computer. Randomization strengthens data collection because it reduces bias.

Randomization and replication should be used together to be effective. Sites, samples and treatments should all be randomly assigned to avoid confounded results.

Ecological methods rely heavily on statistical and mathematical models. These provide ecologists with a way to predict how an ecosystem will change over time or react to changing conditions in the environment.

Modeling also provides another way to decipher ecological information when field work is not practical. In fact, there are several drawbacks to relying solely on field work.Because of the typically large scale of field work, it is not possible to replicate experiments exactly. Sometimes even the lifespan of organisms is a rate-limiting factor for field work. Other challenges include time, labor and space.

Modeling, therefore, provides a method in which to streamline information in a more efficient manner.

Examples of modeling include equations, simulations, graphs and statistical analyses. Ecologists use modeling for producing helpful maps as well. Modeling allows for calculations of data to fill in gaps from sampling. Without modeling, ecologists would be hampered by the sheer amount of data that needs to be analyzed and communicated. Computer modeling allows for comparatively rapid analysis of data.

A simulation model, for example, enables the description of systems that would otherwise be extremely difficult and too complex for traditional calculus. Modeling allows scientists to study coexistence, population dynamics and many other aspects of ecology. Modeling can help predict patterns for crucial planning purposes, such as for climate change.

Humanity’s impact upon the environment will continue. It therefore becomes ever more crucial for ecologists to use ecological research methods to find ways to mitigate the effects on the environment.

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• Wessex Archaeology: Explore the Seafloor: Ecological Research Methods
• EcologyandEvolution.org: How to Design a Field Study
• The University of Vermont: Designing Successful Field Studies
• MyYellowstonePark.com: Wolf Reintroduction Changes Ecosystem in Yellowstone
• Oxford Bibliographies: Simulation Modeling
• University of Ohio: Intro to Ecology and Experiments
• Clever ISM: Overview of Qualitative and Quantitative Data Collection Methods

About the Author

J. Dianne Dotson is a science writer with a degree in zoology/ecology and evolutionary biology. She spent nine years working in laboratory and clinical research. A lifelong writer, Dianne is also a content manager and science fiction and fantasy novelist. Dianne features science as well as writing topics on her website, jdiannedotson.com.

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PH717 Module 1B - Descriptive Tools

Descriptive epidemiology & descriptive statistics.

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Ecological Studies (Correlational Studies)

Test yourself.

Ecologic studies assesses the overall frequency of disease in a series of populations and looks for a correlation with the average exposure in the populations. These studies are unique in that the analysis is not based on data on individuals. Instead, the data points are the average levels of exposure and the overall frequency of disease in a series of populations. Therefore, the unit of observation is not a person ; rather, it is an entire population or group.

In the study below investigators used commerce data to compute the overall consumption of meat by various nations. They then calculated the average (per capita) meat consumption per person by dividing total national meat consumption by the number of people in a given country. There is a clear linear trend; countries with the lowest meat consumption have the lowest rates of colon cancer, and the colon cancer rate among these countries progressively increases as meat consumption increases.

Note that in reality, people's meat consumption probably varied widely within each nation, and the exposure that was calculated was an average that assumes that everyone ate the average amount of meat. This average exposure was then correlated with the overall disease frequency in each country. The example here suggests that the frequency of colon cancer increases as meat consumption increases. The characteristic of ecological studies that is most striking is that there is no information about individual people. If the data were summarized in a spread sheet, you would not see data on individual people; you would see records with data on average exposure in multiple groups .

An ecological study correlated per capita alcohol consumption to death rates from coronary heart disease (CHD) in different countries, and it appeared that there was a fairly striking negative correlation as shown in the graph below.

However, a cohort study with data on alcohol consumption in individual subjects showed that there was a J-shaped relationship. People who drank modestly had a lower mortality rates than those who did not drink at all, but among higher levels of individual consumption there was a striking linear increase in mortality, as shown in the graph below.

Source: Adapted from AR Dyer et al. Alcohol consumption and 17-year mortality in the Chicago Western Electric Company Study. Prev. Med . 1980; 9(1):78-90.

The real question was whether individuals who drank heavily had higher or lower mortality rates than those who drank modestly or not all, but the ecologic study led to an incorrect conclusion because it was based on aggregate data. In reality, most people drink modestly, but mortality rates are much greater in the small number of people who drink very heavily. The misleading conclusion from the ecologic study is an example of the ecologic fallacy.

Is the following statement true or false?

For an exposure to cause a health outcome the exposure must precede the outcome in a given person. This is what is observed in ecologic studies.

To see an extraordinary example of an ecologic study, play the video below created by Hans Rosling. This is a magnificent example that examines the correlation between income and life expectancy in the countries of the world over time. It is also a terrific example of a creative, engaging, and powerful way to display a vast quantity of data.

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Content ©2020. All Rights Reserved. Date last modified: September 10, 2020. Wayne W. LaMorte, MD, PhD, MPH

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Salamanders are surprisingly abundant in US northeastern forests, research finds

by United States Geological Survey

Two recent amphibian-focused studies shed light on the ecological importance of red-backed salamanders, while confirming that proactive measures would prevent costly impacts from a wildlife disease spreading across Europe that has not yet reached North America.

Scientists knew that red-backed salamanders were abundant in eastern North America, but a recent study found their densities and biomass across the region were much higher than expected. The study authors estimated an average of 5,300 salamanders in every patch of forest the size of a football field in the Northeast. Even though each individual is a mere 3 inches long, the sheer number of red-backed salamanders means that they also have some of the highest biomass estimated for animals other than insects in the Northeast, similar to or greater than white-tailed deer.

The study, " Range-wide salamander densities reveal a key component of terrestrial vertebrate biomass in eastern North American forests ," conducted by U.S. Geological Survey and many partner institutions, was the first time that the densities and biomass for this common, but rarely seen, species were calculated across the extent of its range. The paper is published in the journal Biology Letters .

The incredible magnitude of red-backed salamander presence in the Northeast captured in this study suggests that red-backed salamanders, and likely amphibians in general, play a more prevalent role in terrestrial temperate ecosystems than previously suspected.

"The very large biomass of red-backed salamanders tells us that they are likely 'small but mighty' in terms of their role in the ecological health of northeastern forests," said Evan Grant, lead author and USGS research wildlife biologist. "If red-backed salamanders disappeared, there would probably be some pretty large ecosystem-level consequences."

Many salamanders, like the red-backed salamander, are tiny and spend the majority of their time underground, so it's easy for most people to overlook them. In fact, Grant commonly refers to salamanders and other amphibians as "hidden biodiversity" because, though they are often abundant, they hide well. But that doesn't mean people should overlook their ecological roles. Salamanders eat things that bigger consumers can't eat and are themselves prey for other animals, meaning salamanders punch above their weight in an ecosystem's food web.

"Salamanders serve a vital function in forest ecosystems," explained David Miller, professor of wildlife ecology at Penn State and co-author of the study. "They are at the top of the food chain on the forest floor, where everything is breaking down into the soil that sustains this entire network of life. In fact, salamanders are so important to this life cycle that we can use them as a barometer for forest health."

Unfortunately, just as scientists are beginning to understand the true magnitude of salamanders' 'hidden biodiversity' and ecological importance, a new wildlife disease that is particularly hard on salamanders is a looming threat and a serious concern for scientists and wildlife managers.

Batrachochytrium salamandrivorans, or Bsal for short, is a fungal disease closely related to the chytrid fungus that is already devastating amphibian populations around the world. It was first found in the Netherlands in 2013. Sadly, since its introduction, Bsal has decimated the salamander populations in central Europe and continues to spread across Europe.

Bsal hasn't been detected in the U.S. yet, so scientists and wildlife managers are preparing for its arrival. There is a North American Bsal Task Force whose mission is to limit the invasion and reduce the impact of Bsal in North America. However, natural resource managers ran into a problem when trying to enact proactive management guidance for a disease that isn't even on U.S. shores yet.

They needed evidence that proactive management would be more effective than waiting to respond until the disease is detected in the wild. So, Grant co-authored another recent paper that tested a series of proactive and reactive management actions to forecast the impact on salamander populations over time.

This study, " Quantitative support for the benefits of proactive management for wildlife disease control ," used computer modeling to confirm what seems intuitively obvious: namely, initiating management of wild populations before Bsal arrives is, in fact, more successful at achieving the management goal of keeping salamanders from disappearing than waiting until after Bsal is detected or not doing anything at all. The findings are published in the journal Conservation Biology .

"If we do nothing to manage Bsal, the model forecasted that the disease would be catastrophic to North American salamander species," said Molly Bletz, assistant professor of disease ecology at Penn State and lead author of the second study. "This study gives strong quantitative support to proactive management actions. Basically, if we want these at-risk salamander species to be around in the future, doing something proactively is our best bet."

The types of proactive management actions considered included:

• making it harder for amphibians to spread the disease among themselves through installing barriers or increasing habitat complexity;
• reducing Bsal fungal spores in aquatic habitats by temporarily raising the water temperatures, increasing the salinity, or increasing the abundance of zooplankton that consume funguses;
• helping amphibians fight off the disease by improving their health through supplemental feeding, etc., increasing the abundance of local, beneficial anti-fungal microbes, or through vaccination.

While this second study did not estimate how proactive management for Bsal may affect other parts of the ecosystem, visitor satisfaction or financial cost, Bletz, Grant and others are already working on estimating these outcomes so that managers have a full account of the relative benefits of proactive versus reactive management.

"With a new understanding of how incredibly prevalent salamanders are in an ecosystem, and with the empirical justification for the benefits of proactive management for salamander populations threatened by Bsal, it is more critical than ever to protect the 'hidden biodiversity' of amphibians," said Bletz.

Molly C. Bletz et al, Quantitative support for the benefits of proactive management for wildlife disease control, Conservation Biology (2024). DOI: 10.1111/cobi.14363

Journal information: Biology Letters

Provided by United States Geological Survey

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Collection  10 March 2022

Top 100 in Ecology

This collection highlights our most downloaded* ecology papers published in 2021. Featuring authors from aroud the world, these papers showcase valuable research from an international community.

*Data obtained from SN Insights which is based on Digital Science's Dimensions.

The first true millipede—1306 legs long

• Paul E. Marek
• Bruno A. Buzatto
• Juanita Rodriguez

Lethal coalitionary attacks of chimpanzees ( Pan troglodytes troglodytes ) on gorillas ( Gorilla gorilla gorilla ) in the wild

• Lara M. Southern
• Tobias Deschner
• Simone Pika

Defining priority areas for blue whale conservation and investigating overlap with vessel traffic in Chilean Patagonia, using a fast-fitting movement model

• Luis Bedriñana-Romano
• Rodrigo Hucke-Gaete
• Daniel M. Palacios

Earliest evidence of herd-living and age segregation amongst dinosaurs

• Adriana C. Mancuso
• Vincent Fernandez

Extreme miniaturization of a new amniote vertebrate and insights into the evolution of genital size in chameleons

• Jörn Köhler
• Miguel Vences

Excess protein enabled dog domestication during severe Ice Age winters

• Maria Lahtinen
• David Clinnick
• Suvi Viranta

Honey bee hives decrease wild bee abundance, species richness, and fruit count on farms regardless of wildflower strips

• G. M. Angelella
• C. T. McCullough
• M. E. O’Rourke

Tracking late Pleistocene Neandertals on the Iberian coast

• Eduardo Mayoral
• Ignacio Díaz-Martínez
• Ricardo Díaz-Delgado

Exposure to foreign gut microbiota can facilitate rapid dietary shifts

• A. M. Fisher

Self-care tooling innovation in a disabled kea ( Nestor notabilis )

• Amalia P. M. Bastos
• Kata Horváth
• Alex H. Taylor

Discovery of a colossal slickhead (Alepocephaliformes: Alepocephalidae): an active-swimming top predator in the deep waters of Suruga Bay, Japan

• Yoshihiro Fujiwara
• Masaru Kawato
• Shinji Tsuchida

Microplastics in fish and fishmeal: an emerging environmental challenge?

• Christina J. Thiele
• Malcolm D. Hudson
• Giovanna Sidaoui-Haddad

An Italian dinosaur Lagerstätte reveals the tempo and mode of hadrosauriform body size evolution

• Alfio Alessandro Chiarenza
• Matteo Fabbri
• Federico Fanti

Seagrasses provide a novel ecosystem service by trapping marine plastics

• Anna Sanchez-Vidal
• Miquel Canals

Mistaken identity may explain why male sea snakes ( Aipysurus laevis , Elapidae, Hydrophiinae) “attack” scuba divers

• Tim P. Lynch
• Ross A. Alford
• Richard Shine

Explainable identification and mapping of trees using UAV RGB image and deep learning

• Masanori Onishi
• Takeshi Ise

The giant panda is cryptic

• Ossi Nokelainen
• Nicholas E. Scott-Samuel

Pivot burrowing of scarab beetle ( Trypoxylus dichotomus ) larva

• Haruhiko Adachi
• Makoto Ozawa
• Shigeru Kondo

Redefining the oceanic distribution of Atlantic salmon

• Audun H. Rikardsen
• David Righton
• Kim Aarestrup

Chest beats as an honest signal of body size in male mountain gorillas ( Gorilla beringei beringei )

• Edward Wright
• Sven Grawunder
• Martha M. Robbins

Powered flight in hatchling pterosaurs: evidence from wing form and bone strength

• Darren Naish
• Mark P. Witton
• Elizabeth Martin-Silverstone

Two wild female bonobos adopted infants from a different social group at Wamba

• Nahoko Tokuyama
• Kazuya Toda
• Shintaro Ishizuka

Multiple pygmy blue whale acoustic populations in the Indian Ocean: whale song identifies a possible new population

• Emmanuelle C. Leroy
• Jean-Yves Royer
• Tracey L. Rogers

Action potentials induce biomagnetic fields in carnivorous Venus flytrap plants

• Anne Fabricant
• Geoffrey Z. Iwata
• Dmitry Budker

North Pacific warming shifts the juvenile range of a marine apex predator

• Kisei R. Tanaka
• Kyle S. Van Houtan
• Salvador J. Jorgensen

Spatial and temporal pattern of wildfires in California from 2000 to 2019

• Tirtha Banerjee

Effects of climate change and land cover on the distributions of a critical tree family in the Philippines

• Sean E. H. Pang
• Jose Don T. De Alban
• Edward L. Webb

African soil properties and nutrients mapped at 30 m spatial resolution using two-scale ensemble machine learning

• Tomislav Hengl
• Matthew A. E. Miller
• Jonathan Crouch

Russian forest sequesters substantially more carbon than previously reported

• Dmitry Schepaschenko
• Elena Moltchanova
• Florian Kraxner

Isotope data from amino acids indicate Darwin’s ground sloth was not an herbivore

• Julia V. Tejada
• John J. Flynn
• Brian N. Popp

Late Pleistocene human paleoecology in the highland savanna ecosystem of mainland Southeast Asia

• Kantapon Suraprasit
• Rasmi Shoocongdej
• Hervé Bocherens

Early Pleistocene faunivorous hominins were not kleptoparasitic, and this impacted the evolution of human anatomy and socio-ecology

• Manuel Domínguez-Rodrigo
• Enrique Baquedano
• Diego González-Aguilera

An ecological niche shift for Neanderthal populations in Western Europe 70,000 years ago

• William E. Banks
• Marie-Hélène Moncel
• Frédéric Santos

Surface slicks are pelagic nurseries for diverse ocean fauna

• Jonathan L. Whitney
• Jamison M. Gove
• Gregory P. Asner

Field measurements of a massive Porites coral at Goolboodi (Orpheus Island), Great Barrier Reef

• Nathan Cook
• Vicki Saylor

Ongoing ecological and evolutionary consequences by the presence of transgenes in a wild cotton population

• Valeria Vázquez-Barrios
• Karina Boege

Novel and disappearing climates in the global surface ocean from 1800 to 2100

• Katie E. Lotterhos
• Áki J. Láruson
• Li-Qing Jiang

Partial shading by solar panels delays bloom, increases floral abundance during the late-season for pollinators in a dryland, agrivoltaic ecosystem

• Maggie Graham
• Serkan Ates
• Chad W. Higgins

The early hunting dog from Dmanisi with comments on the social behaviour in Canidae and hominins

• Saverio Bartolini-Lucenti
• Joan Madurell-Malapeira
• Lorenzo Rook

Comprehensive comparative morphology and developmental staging of final instar larvae toward metamorphosis in the insect order Odonata

• Genta Okude
• Takema Fukatsu
• Ryo Futahashi

G enome-wide data implicate terminal fusion automixis in king cobra facultative parthenogenesis

• Daren C. Card
• Freek J. Vonk
• Warren Booth

New evidence from exceptionally “well-preserved” specimens sheds light on the structure of the ammonite brachial crown

• C. P. A. Smith
• N. H. Landman

Population decline in a ground-nesting solitary squash bee ( Eucera pruinosa ) following exposure to a neonicotinoid insecticide treated crop ( Cucurbita pepo )

• D. Susan Willis Chan
• Nigel E. Raine

Tropical deforestation induces thresholds of reproductive viability and habitat suitability in Earth’s largest eagles

• Everton B. P. Miranda
• Carlos A. Peres
• Colleen T. Downs

Biodiversity and ecosystem functions depend on environmental conditions and resources rather than the geodiversity of a tropical biodiversity hotspot

• Christine I. B. Wallis
• Yvonne C. Tiede
• Jörg Bendix

Summer weather conditions influence winter survival of honey bees ( Apis mellifera ) in the northeastern United States

• Martina Calovi
• Christina M. Grozinger
• Sarah C. Goslee

Evidence that spillover from Marine Protected Areas benefits the spiny lobster ( Panulirus interruptus ) fishery in southern California

• Hunter S. Lenihan
• Jordan P. Gallagher
• Daniel C. Reed

Metal concentrations in coastal sharks from The Bahamas with a focus on the Caribbean Reef shark

• Oliver N. Shipley
• Cheng-Shiuan Lee
• Austin J. Gallagher

First tracks of newborn straight-tusked elephants ( Palaeoloxodon antiquus )

• Carlos Neto de Carvalho
• Zain Belaústegui
• Clive Finlayson

An integrative analysis uncovers a new, pseudo-cryptic species of Amazonian marmoset (Primates: Callitrichidae: Mico ) from the arc of deforestation

• Rodrigo Costa-Araújo
• José S. Silva-Jr.
• Tomas Hrbek

eDNA sampled from stream networks correlates with camera trap detection rates of terrestrial mammals

• Arnaud Lyet
• Loïc Pellissier
• Robin Naidoo

Large-scale variations in the dynamics of Amazon forest canopy gaps from airborne lidar data and opportunities for tree mortality estimates

• Ricardo Dalagnol
• Fabien H. Wagner
• Luiz E. O. C. Aragão

Tipping point realized in cod fishery

• Christian Möllmann
• Xochitl Cormon
• Martin Quaas

Temporal activity patterns suggesting niche partitioning of sympatric carnivores in Borneo, Malaysia

• Miyabi Nakabayashi
• Tomoko Kanamori

No evidence of physiological declines with age in an extremely long-lived fish

• Derek J. Sauer
• Britt J. Heidinger
• Mark E. Clark

International fisheries threaten globally endangered sharks in the Eastern Tropical Pacific Ocean: the case of the Fu Yuan Yu Leng 999 reefer vessel seized within the Galápagos Marine Reserve

• Elisa Bonaccorso
• Nicté Ordóñez-Garza
• Juan M. Guayasamin

Indirect effects of invasive rat removal result in recovery of island rocky intertidal community structure

• Carolyn M. Kurle
• Kelly M. Zilliacus
• Donald A. Croll

Assessing the carbon capture potential of a reforestation project

• David Lefebvre
• Adrian G. Williams

The evolutionary history of manatees told by their mitogenomes

• Érica Martinha Silva de Souza
• Lucas Freitas
• Mariana Freitas Nery

Microplastics accumulate fungal pathogens in terrestrial ecosystems

• Gerasimos Gkoutselis
• Stephan Rohrbach
• Gerhard Rambold

Advances in automatic identification of flying insects using optical sensors and machine learning

• Carsten Kirkeby
• Klas Rydhmer
• Kaare Græsbøll

Aboveground plant-to-plant communication reduces root nodule symbiosis and soil nutrient concentrations

• Yuta Takahashi
• Kaori Shiojiri
• Akira Yamawo

The rhizosphere microbiome plays a role in the resistance to soil-borne pathogens and nutrient uptake of strawberry cultivars under field conditions

• Cristina Lazcano
• Kelly Ivors

Highest risk abandoned, lost and discarded fishing gear

• Eric Gilman
• Michael Musyl
• Brandon Kuczenski

Future thermal regimes for epaulette sharks ( Hemiscyllium ocellatum ): growth and metabolic performance cease to be optimal

• Carolyn R. Wheeler
• Jodie L. Rummer
• John W. Mandelman

Earliest evidence of marine habitat use by mammals

• Anton F.-J. Wroblewski
• Bonnie E. Gulas-Wroblewski

Constraining the chronology and ecology of Late Acheulean and Middle Palaeolithic occupations at the margins of the monsoon

• James Blinkhorn
• Hema Achyuthan
• Jana Ilgner

Neonicotinoids disrupt memory, circadian behaviour and sleep

• Kiah Tasman
• Sergio Hidalgo
• James J. L. Hodge

Evaluation metrics and validation of presence-only species distribution models based on distributional maps with varying coverage

• Kamil Konowalik
• Agata Nosol

Ecosystem response persists after a prolonged marine heatwave

• Robert M. Suryan
• Mayumi L. Arimitsu
• Stephani G. Zador

Rhizobia use a pathogenic-like effector to hijack leguminous nodulation signalling

• Safirah Tasa Nerves Ratu
• Albin Teulet
• Shin Okazaki

Camera trap placement for evaluating species richness, abundance, and activity

• Kamakshi S. Tanwar
• Yadvendradev V. Jhala

Assessing biophysical and socio-economic impacts of climate change on regional avian biodiversity

• Simon Kapitza
• Pham Van Ha
• Brendan A. Wintle

Smell of green leaf volatiles attracts white storks to freshly cut meadows

• Martin Wikelski
• Michael Quetting
• Jonathan Williams

Dinosaur senescence: a hadrosauroid with age-related diseases brings a new perspective of “old” dinosaurs

• Justyna Słowiak
• Tomasz Szczygielski
• Dawid Surmik

Positive effects of COVID-19 lockdown on river water quality: evidence from River Damodar, India

• Baisakhi Chakraborty
• Biswajit Bera
• Pravat Kumar Shit

Snow algae blooms are beneficial for microinvertebrates assemblages (Tardigrada and Rotifera) on seasonal snow patches in Japan

• Nozomu Takeuchi
• Krzysztof Zawierucha

Coastal wetlands can be saved from sea level rise by recreating past tidal regimes

• Mahmood Sadat-Noori
• Caleb Rankin
• William Glamore

Identifying unknown Indian wolves by their distinctive howls: its potential as a non-invasive survey method

• Sougata Sadhukhan
• Holly Root-Gutteridge
• Bilal Habib

Optimal fishing effort benefits fisheries and conservation

• Emma V. Sheehan
• Martin J. Attrill

The spreading of the invasive sacred ibis in Italy

• Marco Cucco
• Gianfranco Alessandria
• Irene Pellegrino

Exceptional fossil assemblages confirm the existence of complex Early Triassic ecosystems during the early Spathian

• Christopher P. A. Smith
• Thomas Laville
• Arnaud Brayard

Allelopathic effect of Artemisia argyi on the germination and growth of various weeds

Organophosphate poisoning of Hyacinth Macaws in the Southern Pantanal, Brazil

• Eliane C. Vicente
• Neiva M. R. Guedes

The critical role of natural history museums in advancing eDNA for biodiversity studies: a case study with Amazonian fishes

• C. David de Santana
• Lynne R. Parenti

Novel approach to enhance coastal habitat and biotope mapping with drone aerial imagery analysis

• João Gama Monteiro
• Jesús L. Jiménez
• João Canning-Clode

High resolution biologging of breaching by the world’s second largest shark species

• Jessica L. Rudd
• Owen M. Exeter
• Lucy A. Hawkes

The largest hoplophonine and a complex new hypothesis of nimravid evolution

• Paul Zachary Barrett

Dangerous demographics in post-bleach corals reveal boom-bust versus protracted declines

• Juliano Morais
• Renato A. Morais
• David R. Bellwood

Welwitschia : Phylogeography of a living fossil, diversified within a desert refuge

• Norbert Jürgens
• Imke Oncken
• Barbara Rudolph

Response of bacterial and fungal communities to high petroleum pollution in different soils

• Polina Galitskaya
• Liliya Biktasheva
• Svetlana Selivanovskaya

Integrating multiple chemical tracers to elucidate the diet and habitat of Cookiecutter Sharks

• Aaron B. Carlisle
• Elizabeth Andruszkiewicz Allan
• John O’Sullivan

Environmental stressors, complex interactions and marine benthic communities’ responses

• Charlotte Carrier-Belleau
• David Drolet
• Philippe Archambault

eDNA metabarcoding for biodiversity assessment, generalist predators as sampling assistants

• Louise Nørgaard
• Carsten Riis Olesen
• Laura Iacolina

Distance sampling surveys reveal 17 million vertebrates directly killed by the 2020’s wildfires in the Pantanal, Brazil

• Walfrido Moraes Tomas
• Christian Niel Berlinck
• Ronaldo Morato

Description of five new species of the Madagascan flagship plant genus Ravenala (Strelitziaceae)

• Thomas Haevermans
• Annette Hladik
• Patrick Blanc

A symbiotic aphid selfishly manipulates attending ants via dopamine in honeydew

• Tatsumi Kudo
• Hitoshi Aonuma
• Eisuke Hasegawa

Ixodiphagus hookeri wasps (Hymenoptera: Encyrtidae) in two sympatric tick species Ixodes ricinus and Haemaphysalis concinna (Ixodida: Ixodidae) in the Slovak Karst (Slovakia): ecological and biological considerations

• Alicja Buczek
• Weronika Buczek
• Michał Stanko

Genomic signatures of the evolution of defence against its natural enemies in the poisonous and medicinal plant Datura stramonium (Solanaceae)

• I. M. De-la-Cruz
• J. Núñez-Farfán

Timely poacher detection and localization using sentinel animal movement

• Henrik J. de Knegt
• Jasper A. J. Eikelboom
• Herbert H. T. Prins

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