There have been claims that our understanding of some issues in ecology and evolution could be biased because more empirical work is conducted in temperate than in tropical regions. For example, in ecology and evolution, some topics receive more attention than others, if for no other reason than the geographic distribution of researchers. To determine if our perspective on issues in ecology and evolution could be biased due to where empirical research is conducted, what taxonomic groups are studied, or which studies get cited more frequently, we conducted a structured sampling by 4-year intervals of empirical studies using the ISI Web of Science database spanning the years 1991 to 2017. We chose nine topics of broad relevance to both temperate and tropical systems: climate tolerance, density dependence, interspecific competition, local adaptation, mimicry, parental care, predator-prey interactions, sexual selection, and speciation. To determine if there is a temperate bias in empirical research with respect to our nine topics, we analyzed data on numbers of papers classified by topic and taxon with a two-way contingency test. To determine if temperate papers get cited more frequently than tropical papers, we used two sets of general linear models to analyze data on citation rates.
Results/Conclusions
We identified 1,800 papers suitable for our analyses from a structured sample of ~60,000 peer-reviewed empirical studies. We found significantly greater numbers of empirical studies conducted in temperate systems than in tropical systems. Tropical studies were nearly absent from some topics. There were also strong taxonomic biases across topics and geographic regions. Of 349 papers focused on plants across the nine topics, only 12% were in the tropics. In contrast, although there were only 29 papers on arachnids, nearly half of them (41%) were on tropical systems. Interestingly, there was no evidence for citation bias toward temperate or tropical studies, but some taxonomic groups garnered significantly higher rates of citation than other taxa. At the extremes, papers focused on amphibians (highest citation rate: least squares mean = 52.0 ± 6.6 s.e.) were cited at over twice the rate as papers focused on crustaceans (lowest citation rate: least squares mean = 20.4 ± 7.3). While we documented clear biases towards number of studies in temperate regions, the difficult, but essential task ahead is to better understand how these biases influence the state of our knowledge in ecology and evolution.