Abstract
Trapping is a common sampling technique used to estimate fundamental population metrics of animal species such as abundance, survival and distribution. However, capture success for any trapping method can be heavily influenced by individuals’ behavioural plasticity, which in turn affects the accuracy of any population estimates derived from the data. Funnel trapping is one of the most common methods for sampling aquatic vertebrates, although, apart from fish studies, almost nothing is known about the effects of behavioural plasticity on trapping success. We used a full factorial experiment to investigate the effects that two common environmental parameters (predator presence and vegetation density) have on the trapping success of tadpoles. We estimated that the odds of tadpoles being captured in traps was 4.3 times higher when predators were absent compared to present and 2.1 times higher when vegetation density was high compared to low, using odds ratios based on fitted model means. The odds of tadpoles being detected in traps were also 2.9 times higher in predator-free environments. These results indicate that common environmental factors can trigger behavioural plasticity in tadpoles that biases trapping success. We issue a warning to researchers and surveyors that trapping biases may be commonplace when conducting surveys such as these, and urge caution in interpreting data without consideration of important environmental factors present in the study system. Left unconsidered, trapping biases in capture success have the potential to lead to incorrect interpretations of data sets, and misdirection of limited resources for managing species.
Highlights
Estimates of abundance and distribution for populations and species are fundamental metrics for understanding and managing wildlife [1]
The largest main effect on the tadpole capture rate was that of predator presence
Our results demonstrate that two common environmental factors that vary substantially over small spatial and temporal scales significantly affect the capture success of a widespread, standardised trapping technique for tadpoles
Summary
Estimates of abundance and distribution for populations and species are fundamental metrics for understanding and managing wildlife [1]. Any technique-related bias in the sampling of individuals has the potential to affect the accuracy of population estimates. Identifying factors that affect the success of a sampling technique is important to minimise bias that results from non-random and non-independent sampling in order to make accurate inferences about population dynamics. Passive trapping is a common sampling technique for capturing animals, for species that are cryptic or difficult to survey by other means [3,4,5]. Capture success can be influenced by behaviour, which in turn affects detectability and capture rate Such changes in behaviour are problematic for trapping techniques if the altered behaviour influences capture success. Capture rates and detection probability can change within a population due to behavioural shifts over small spatial or temporal scales despite the use of a standardised trapping technique. Despite the potential for biased estimates, passive trapping devices continue to be widely used because they are simple and inexpensive, and can be replicated [6, 7]
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