Abstract
Confirmation bias, i.e., the tendency of humans to seek out evidence in a manner that confirms their hypotheses, is almost overlooked in ecological studies. For decades, insect herbivory was commonly accepted to be highest in tropical regions. By comparing the data collected blindly (when the observer was not aware of the research hypothesis being tested) with the results of non-blind studies (when the observer knew what results could be expected), we tested the hypothesis that the records made in the tropics could have overestimated community-wide losses of plant foliage to insects due to the confirmation bias. The average loss of leaf area of woody plants to defoliating insects in Brazil, when measured by a blind method (1.11%), was significantly lower than the loss measured in non-blind studies, both original (5.14%) and published (6.37%). We attribute the overestimation of the community-wide losses of plant foliage to insects in non-blind studies to the unconsciously preconceived selection of study species with higher-than-average levels of herbivory. Based on our findings, we urge for caution in obtaining community-wide characteristics from the results of multiple single-species studies. Our data suggest that we may need to revise the paradigm of the highest level of background insect herbivory in the tropical regions. More generally, we argue that more attention should be paid by ecologists to the problem of biases occurring at the pre-publication phases of the scientific research and, consequently, to the development and the wide application of methods that avoid biases occurring due to unconscious psychological processes.
Highlights
The relationships between plants and herbivores are among the most intensively studied biotic interactions (Tylianakis et al, 2008; Jamieson et al, 2012), and the amount of plant biomass consumed by herbivores is the key characteristic of the intensity of these interactions
The proportion of leaf area lost to all feeding guilds did not differ from the proportion of leaf area lost to externally feeding defoliators alone (Kruskal–Wallis test: χ 2 = 0.07, df = 1, P = 0.80), justifying the combination of these data for the search of publication bias and demonstrating that miners and gallers usually contribute only a minor fraction to the total plant damage by herbivorous insects
Data obtained from blindly taken photographs demonstrated that woody plants in Brazil lose, on average, 1.11% of their leaf area to defoliating insects
Summary
The relationships between plants and herbivores are among the most intensively studied biotic interactions (Tylianakis et al, 2008; Jamieson et al, 2012), and the amount of plant biomass consumed by herbivores is the key characteristic of the intensity of these interactions. It is commonly accepted that herbivores consume, on average, 18 percent of the biomass produced annually in terrestrial ecosystems (Cyr & Pace, 1993), and this value is widely cited as the proof of the substantial impact of herbivores on plants (e.g., Polis, 1999). Or implicitly, the numerical values reflecting the pressure which herbivorous insects impose on plants are among the cornerstones of numerous hypotheses/theories related to insect-plant relationships, such as the ‘green world’ hypothesis (Hairston, Smith & Slobodkin, 1960; Polis, 1999) the exploitation ecosystem hypothesis (Oksanen et al, 1981; Polis, 1999), the Janzen–Connell hypothesis (Janzen, 1970), the optimal defence theory (Rhoades, 1979), the growth–differentiation balance hypothesis (Herms & Mattson, 1992) and many others, as well as of theories explaining evolution of plant traits (Coley & Aide, 1991) and formation of biogeographical patterns (Moles et al, 2011)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
