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Free keywords:
network; apparent competition; bottom-up; climate; top-down;
trophic cascade
Abstract:
Global environmental changes threaten biodiversity and the interactions between species, and food-web
approaches are being used increasingly to measure their community-wide impacts. Here we review how
parasitoid–host food webs affect biological control, and how their structure responds to environmental
change. We find that land-use intensification tends to produce webs with low complexity and uneven
interaction strengths. Dispersal, spatial arrangement of habitats, the species pool and community differences
across habitats have all been found to determine how webs respond to landscape structure, though
clear effects of landscape complexity on web structure remain elusive. The invasibility of web structures
and response of food webs to invasion have been the subject of theoretical and empirical work respectively,
and nutrient enrichment has been widely studied in the food-web literature, potentially driving
dynamic instability and altering biomass ratios of different trophic levels. Combined with food-web
changes observed under climate change, these responses of food webs could signal changes to biological
control, though there have been surprisingly few studies linking food-web structure to pest control, and
these have produced mixed results. However, there is strong potential for food-web approaches to add
value to biological control research, as parasitoid–host webs have been used to predict indirect effects
among hosts that share enemies, to study non-target effects of biological control agents and to quantify
the use of alternative prey resources by enemies. Future work is needed to link food-web interactions
with evolutionary responses to the environment and predator–prey interactions, while incorporating
recent advances in predator biodiversity research. This holistic understanding of agroecosystem
responses and functioning, made possible by food-web approaches, may hold the key to better management
of biological control in changing environments.
