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.
Highlights
Compared to many other systems, agricultural systems are simple and generally well-known in terms of species composition and trophic complexity, at least aboveground
Given the biotic and abiotic changes occurring during the cropping season in agricultural systems, we expect a decrease in food web specialization as the season progresses which should reflect changes in the distribution of feeding interactions at the predator species-level, possibly driven by an overall increase in prey abundances (H1)
A large majority of the detected feeding interactions were present in both sampling periods (Fig. 1) the proportion of generalist predator individuals that were negative for all prey targeted by the MGCA decreased from Early (54.6% ± 4.3, average ± SEM) to Late period (27.8% ± 4.3) (ANOVA, df = 14, P < 0.001)
Summary
Compared to many other systems, agricultural systems are simple and generally well-known in terms of species composition and trophic complexity, at least aboveground. Species abundances in agroecosystems are influenced by significant within-seasonal changes and disturbances due to field management, which has potential implications for both prey availability and predators’ preferences for different prey This might in turn affect the food web structure, including its degree of specialization[20], and the role of generalist predators as regulators of pest populations. The Early period typically coincides with the aphid colonization phase and has low overall herbivore abundance and low structural complexity of the crop, and the Late period is usually characterized by peak aphid populations, high overall herbivore abundance and high structural complexity of the crop[25] At both time points we (i) estimate the level of specialization of predator-prey invertebrate food webs at the network as well as species level, and (ii) analyse the potential (non-) randomness of predator diets in relation to a null model. The distribution of feeding interactions is expected to be more random early in the cropping season as a result of predators being able to make fewer active choices when prey is scarce (H2), which should be supported by individual link temperatures significantly differing more from zero late compared to early in the cropping season
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
