High Redundancy as well as Complementary Prey Choice Characterize Generalist Predator Food Webs in Agroecosystems

Abstract

Food web structure influences ecosystem functioning and the strength and stability of associated ecosystem services. With their broad diet, generalist predators represent key nodes in the structure of many food webs and they contribute substantially to ecosystem services such as biological pest control. However, until recently it has been difficult to empirically assess food web structure with generalist predators. We utilized DNA-based molecular gut-content analyses to assess the prey use of a set of generalist invertebrate predator species common in temperate agricultural fields. We investigated the degree of specialization of predator-prey food webs at two key stages of the cropping season and analysed the link temperature of different trophic links, to identify non-random predation. We found a low level of specialization in our food webs, and identified warm and cool links which may result from active prey choice or avoidance. We also found a within-season variation in interaction strength between predators and aphid pests which differed among predator species. Our results show a high time-specific functional redundancy of the predator community, but also suggest temporally complementary prey choice due to within-season succession of some predator species.

Molecular analysis indicates high levels of carabid weed seed consumption in cereal fields across Central Europe

“…Spontaneously high detections of aphids as food in individual fields would tend to support their potential as aphid biocontrol agents (Harwood and Obrycki 2005 ). Overall detection rates of lumbricid and collembolan alternative prey were higher than in Staudacher et al ( 2016 ) and lower than in Roubinet et al ( 2017 , 2018 ). However, in concurrence with our results, these studies revealed a preference for lumbricids over collembolans in P. cupreus and P. melanarius and the reverse preference in P. rufipes .…”

“…dipterans, thrips and intraguild prey, such as other carabid species or spiders. Low levels of predation on aphids, in comparison with other studies in European cereal fields (Staudacher et al 2016 ; Roubinet et al 2017 , 2018 ), may be ascribed to the fact that there were only few aphids present in the sampled fields. Spontaneously high detections of aphids as food in individual fields would tend to support their potential as aphid biocontrol agents (Harwood and Obrycki 2005 ).…”

“…Diagnostic multiplex PCR allows testing for a defined set of food taxa in parallel within one single reaction and is especially useful for screening large numbers of samples, as it is both time- and cost-effective (Sint 2012 ). Recently, such assays have been successfully applied to prey choice in invertebrate food webs including carabids in cereal fields (Roubinet et al 2017 , 2018 ; Staudacher et al 2018 ). In these studies, no feeding interactions were identified for about 45% of the arthropod predator individuals early in the season and 28% at the late period.…”

The return of the trophic chain: Fundamental vs. realized interactions in a simple arthropod food web

“…For example, seasonal changes in species composition cause temporal variation in the strength of interactions (Carnicer et al, ; Gabaldón et al, ; Wang et al, ), as well as changes in food web topology and structure (McLaughlin, Jonsson, & Emmerson, ). In agroecosystems, temporal variability in species interaction strength is detectable even within crop seasons, as recently shown by Roubinet et al () in a barley field. Therefore, because a species’ fundamental trophic niche (all of its potential interactions) is unlikely to be realized at a particular place or time, it is crucial to determine the resources which species in a community actually feed upon, and under what circumstances.…”

Species‐level predation network uncovers high prey specificity in a Neotropical army ant community

“…Generalism appears to be the norm in typical food webs, while specialism tends to be more common in mutualistic interaction networks (Ings et al, ). For instance, food webs of invertebrate predators in temperate agricultural fields were dominated by generalists ( H 2 ˈ : 0.22; Roubinet et al, ; see also van Veen, Müller, Pell, & Godfray, ). Compared to typical food webs, the army ant–prey network showed an exceptionally high degree of interaction specificity ( H 2 ˈ = 0.66).…”