Testing the validity of functional response models using molecular gut content analysis for prey choice in soil predators

Abstract

Analysis of predator–prey interactions is a core concept of animal ecology, explaining structure and dynamics of animal food webs. Measuring the functional response, i.e. the intake rate of a consumer as a function of prey density, is a powerful method to predict the strength of trophic links and assess motives of prey choice, particularly in arthropod communities. However, due to their reductionist set‐up, functional responses, which are based on laboratory feeding experiments, may not display field conditions, possibly leading to skewed results. Here, we tested the validity of functional responses of centipede predators and their prey by comparing them with empirical gut content data from field‐collected predators. Our predator–prey system included lithobiid and geophilomorph centipedes, abundant and widespread predators of forest soils and their soil‐dwelling prey. First, we calculated the body size‐dependent functional responses of centipedes using a published functional response model in which we included natural prey abundances and animal body masses. This allowed us to calculate relative proportions of specific prey taxa in the centipede diet. In a second step, we screened field‐collected centipedes for DNA of eight abundant soil‐living prey taxa and estimated their body size‐dependent proportion of feeding events. We subsequently compared empirical data for each of the eight prey taxa, on proportional feeding events with functional response‐derived data on prey proportions expected in the gut, showing that both approaches significantly correlate in five out of eight predator–prey links for lithobiid centipedes but only in one case for geophilomorph centipedes. Our findings suggest that purely allometric functional response models, which are based on predator–prey body size ratios are too simple to explain predator–prey interactions in a complex system such as soil. We therefore stress that specific prey traits, such as defence mechanisms, must be considered for accurate predictions.

Conversion of rainforest to oil palm and rubber plantations alters energy channels in soil food webs

“…Araneae and Chilopoda are generalist predators which commonly feed on Collembola (Eitzinger, Rall, Traugott, & Scheu, 2018;Rusek, 1998;Voigtländer, 2011). Unexpectedly and contrasting our first hypothesis, the biomarker FA composition of both Araneae and Chilopoda was different from that of Collembola, and comprised high proportions of plant and fungal biomarker FAs.…”

Assessing changes in arthropod predator–prey interactions through DNA‐based gut content analysis—variable environment, stable diet

“…This applies particularly to invertebrate food webs involving myriads of species, which in themselves are often difficult to identify visually. Moreover, molecular diet analysis allows tracking of predator–prey interactions in situations where soft prey remains in gut or faeces contain no identifiable morphological structures—or when a predator digests its prey extra‐orally, as is the case for centipedes or spiders (Eitzinger, Rall, Traugott, & Scheu, ; Wirta, Weingartner, Hambäck, & Roslin, ). Molecular tools have thus made it possible to track the multitude of invertebrate trophic interactions of predators by screening gut contents by DNA barcoding (Nielsen, Clare, Hayden, Brett, & Kratina, ; Traugott et al., ).…”

No guts, no glory: Gut content metabarcoding unveils the diet of a flower‐associated coastal sage scrub predator

“…, Eitzinger et al. ). This method provides a reliable means to examine the diets of small, cryptic arthropods that pre‐orally digest their food such as spiders and true bugs (Heteroptera).…”

“…Seri c Jelaska et al 2014, Rondoni et al 2015, Roubinet et al 2015, Schmidt et al 2016, Curtsdotter et al 2018, Eitzinger et al 2018. This method provides a reliable means to examine the diets of small, cryptic arthropods that pre-orally digest their food such as spiders and true bugs (Heteroptera).…”