Abstract
Soil fauna play a key role in nutrient cycling and decomposition, and in recent years, researchers have become more and more interested in this compartment of terrestrial ecosystems. In addition, soil fauna can act as ecosystem engineers by creating, modifying, and maintaining the habitat for other organisms. Ecologists usually utilize live catches in pitfalls traps as a standard method to study the activity of epigeic fauna in addition to relative abundance. Counts in pitfall traps can be used as estimates of relative activity to compare among experimental treatments. This requires taking independent estimates of abundance (e.g., by sifting soil litter, mark–recapture), which can then be used as covariates in linear models to compare the levels of fauna activity (trap catches) among treatments. However, many studies show that the use of pitfall traps is not the most adequate method to estimate soil fauna relative abundances, and these concerns may be extensible to estimating activity. Here, we present two new types of traps devised to study activity in litter fauna, and which we call “cul-de-sac” and “basket traps”, respectively. We experimentally show that, at least for litter dwellers, these new traps are more appropriate to estimate fauna activity than pitfall traps because: (1) pitfall traps contain 3.5× more moisture than the surrounding environment, potentially attracting animals towards them when environmental conditions are relatively dry; (2) cul-de-sac and basket traps catch ca. 4× more of both meso- and macrofauna than pitfall traps, suggesting that pitfall traps are underestimating activity; and (3) pitfall traps show a bias towards collecting 1.5× higher amounts of predators, which suggests that predation rates are higher within pitfall traps. We end with a protocol and recommendations for how to use these new traps in ecological experiments and surveys aiming at estimating soil arthropod activity.
Highlights
Soil fauna provide numerous and significant ecosystem functions and services in terrestrial ecosystems. They play a key role in nutrient cycling and storage, soil organic formation, and turnover via litter transformation; second, they create, modify, and maintain the soil habitat by acting as ecosystem engineers [1,2,3]; and third, given their recognized role as pest control agents [4,5] and their contribution to soil function, the sampling and analysis of soil fauna is essential in agroecosystem
Pitfall trapping is the standard method for collecting ground-dwelling arthropods and soil fauna in studies of ecological and agricultural entomology [13]
Comparing trap efficiency among each other with post-hoc Tukey tests, we found that pitfalls caught only 43% of the amount of collembolans collected by basket traps (Z = −5.510, p < 0.001; Figure 4b) and only 45% of the amount of collembolans collected by cul-de-sac traps (Z = 5.21, p < 0.001)
Summary
Soil fauna provide numerous and significant ecosystem functions and services in terrestrial ecosystems. Pitfall trapping is the standard method for collecting ground-dwelling arthropods and soil fauna in studies of ecological and agricultural entomology [13]. The relationship between actual abundances and pitfall trap catches has been shown to be either absent, weak, or highly variable among taxa, habitat, and time of the season [15]. It is not clear if the measure is activity, relative abundance, or a mixture of both. Pitfall trap catches in these types of studies are clearly biased towards surface-active arthropods, especially macrofauna (>2 mm), such as Orthoptera, Diptera, and Coleoptera [15,16,17], and towards active hunting spiders and other epigeic predators [18,19,20]
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