Solving the pitfalls of pitfall trapping: a two‐circle method for density estimation of ground‐dwelling arthropods

Abstract

Summary1. Pitfall traps are widely used for investigating ground-dwelling arthropods, but have been heavily criticized due to their species-, habitat-and attractant-specific trapping radius which produces unreliable estimation of species diversity and density. 2. We developed a two-circle method (TCM) for simultaneously estimating densities of ground-dwelling arthropods and the effective trapping radius. Multiple pairs of traps are located different distances apart, and the intersection of trapping areas can be calculated using the inverse trigonometric function. The density and effective trapping radius can be estimated from a nonlinear regression of the change in the total number of individuals caught with the distance between the paired pitfall traps. 3. We compared the performance of TCM with the estimator based on the nested-cross array (NCA) for arranging pitfall traps, by comparing predicted densities from these two methods with the real density obtained from the suction sampling method (SSM). 4. Simulations with known arthropod densities and effective trapping radius suggested that TCM produced accurate density estimation, while NCA significantly underestimated the known density. Pitfall trapping of ground-dwelling arthropods on two habitats (crop field and desert steppe) confirmed this conclusion when comparing estimation from TCM and NCA with densities obtained from the SSM. 5. TCM is a promising technique for the density estimation of ground-dwelling arthropods, especially for traps with liquid attractant and areas with relatively homogenous habitat and away from habitat edges.

Pitfall trap sampling bias depends on body mass, temperature, and trap number: insights from an individual‐based model

“…The passive sampling of ground arthropods with pitfall traps, that is, small containers buried to the ground, was used in many biodiversity and conservation studies across the recent decades and is still being used today (Greenslade , Zhao et al. , Brown and Matthews ). The benefits of pitfall trap sampling are its time efficiency and the high probability to detect rare and nocturnal species that other methods might miss (Spence and Niemelä , Lang , Cardoso et al.…”

“…The number of pitfall traps and their spatial arrangement have been shown to strongly influence the reliability of sampled densities for estimations of real densities (Scheller , Parmenter and MacMahon , Perner , Zhao et al. ). Moreover, only limited knowledge exists about how the species‐specific sampling bias may impact community‐level metrics considering variation in community structure across ecosystems, such as the distribution of species body masses across the abundance ranks (Topping and Sunderland ).…”

“…This is particularly true for the large group of ground-dwelling arthropods (here referred to as ground arthropods) as they are highly responsive to environmental changes and influence a large number of ecosystem functions such as predation and decomposition (Finke and Snyder 2010, Chaplin-Kramer et al 2011, Prather et al 2013. The passive sampling of ground arthropods with pitfall traps, that is, small containers buried to the ground, was used in many biodiversity and conservation studies across the recent decades and is still being used today (Greenslade 1964, Zhao et al 2013, Brown and Matthews 2016. The benefits of pitfall trap sampling are its time efficiency and the high probability to detect rare and nocturnal species that other methods might miss (Spence and Niemel€ a 1994, Lang 2000, Cardoso et al 2008).…”

“…Variation in the ambient temperature can produce considerable bias in pitfall sampling because the locomotory activity of most ground arthropods varies with ambient temperature, and sampled densities are proportional to locomotory activity (Thomas et al 1998, Woodcock 2005. The number of pitfall traps and their spatial arrangement have been shown to strongly influence the reliability of sampled densities for estimations of real densities (Scheller 1984, Parmenter and MacMahon 1989, Perner 2003, Zhao et al 2013. Moreover, only limited knowledge exists about how the species-specific sampling bias may impact community-level metrics considering variation in community structure across ecosystems, such as the distribution of species body masses across the abundance ranks (Topping and Sunderland 1992).…”

Fauna of ground-dwelling arthropods in vineyards of Zadar County (Croatia)

“…however, monoculture leads to landscape simplification and can cause decreasing of predatory arthropod population. According to Zhao et al (2013) ground-dwelling arthropods have significant functions in an agroecosystem, such as pest control and food chain maintenance. Nicholls et al (2008) reported that there are many ways in which enhanced plant biodiversity can contribute to the design of pest-stable agroecosystem.…”