Abstract
Pitfall traps are frequently used to capture ground-dwelling arthropods, particularly beetles, ants and spiders. The capture efficiency of a pitfall trapping system strongly depends on the number and opening size of traps, how traps are distributed over the sampling area (spatial arrangement) and the movement characteristics of arthropods. We use numerical simulations for a single species to analyse the trap count patterns that emerge from these variables. Arthropod movement of individuals is modelled as correlated random walks, with multiple traps placed over an area, and catches are simulated as individual interaction with traps. We consider four different types of spatial arrangements of traps across a homogeneous landscape: grid (i.e. rectangular array), transect, nested-cross and randomised. We contextualise our results by considering the locomotion of Pterostichus melanarius, a highly active carabid beetle often serving as a biocontrol agent for the suppression of pest insects and weeds. By simulating the trapping of randomly moving ground-dwelling arthropods, we show that there is an optimal inter-trap separation distance (trap spacing) that maximises captures, that can be expressed using exact formulae in terms of trap opening sizes, sampling area and trap number. Moreover, for the grid and nested-cross arrangements, larger trap spacing to maximise spatial coverage over the whole sampling area is suboptimal. Also, we find that over a large sampling area, there is a hierarchical order for spatial arrangements in relation to capture efficiency: grid, randomised, transect, followed by the nested-cross. However, over smaller sampling areas, this order is changed as the rate at which trap counts accumulate with trap number varies across arrangements—eventually saturating at different levels. In terms of movement effects, capture efficiency is maximised over a narrow diffusive range and does not depend strongly on the type of spatial arrangement—indicating an approximate optimal mode of arthropod activity, i.e. rate of spread. Our approach simultaneously considers several important experimental design aspects of pitfall trapping providing a basis to optimise and adapt sampling protocols to other types of traps to better reflect their various purposes, such as monitoring, conservation or pest management.
Original language | English |
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Pages (from-to) | 2827-2843 |
Number of pages | 16 |
Journal | Methods in Ecology and Evolution |
Volume | 14 |
Issue number | 11 |
Early online date | 26 Sept 2023 |
DOIs | |
Publication status | Published - Nov 2023 |
Bibliographical note
Funding Information:DAA is funded by the Gulf University for Science and Technology (GUST) internal seed fund, grant award no. 234597. SP was partially supported by EPSRC, UK through Project EP/T027371/1. DR is funded by the ASICS project (ANR‐20‐EBI5‐004, BiodivERsA, BiodivClim call 2019–2020), and the French Polar Institute (Project 136‐SUBANTECO).
Publisher Copyright:
© 2023 The Authors. Methods in Ecology and Evolution published by John Wiley & Sons Ltd on behalf of British Ecological Society.
Data Availability Statement
All illustrations and MATLAB simulation codes are publicly and freely available on GitHub at https://github.com/daa119/pitfall_trapping and Zenodo at https://doi.org/10.5281/ZENODO.8033956 (Ahmed, 2023).PEER REVIEW
The peer review history for this article is available at https://www.webofscience.com/api/gateway/wos/peer-review/10.1111/2041-210X.14174.
Keywords
- arthropod movement
- capture efficiency
- diffusion
- inter-trap spacing
- pitfall trapping
- random walk
- sampling strategy
- spatial arrangement