In nature, animals are part of multitrophic food webs where the spatial distribution and behavior of resources, competitors, and enemies may vary widely among systems. In response, animals may employ different strategies to exploit resources: either a locally restricted resource use, with a full exploitation of local resources of various qualities, or a search of wide areas and specialization on high quality resources. Only one strategy may be employed because of a basic life history trade off: either invest in eggs (full local exploitation) or in longevity (searching). Different solutions to this trade off are found in gregarious and solitary parasitoids, respectively. Gregarious parasitoids, those that lay clutches of eggs into hosts, are usually more fecund than their solitary congenerics, and should therefore have less time/energy to search. Earlier theory has shown that the interactions with competitively superior solitary parasitoids are a major obstacle to the evolution of gregariousness. However, the spatial properties of the habitat and the abovementioned trade-off have hitherto not been included in the theory. Using an intriguing empirical example of spatial interactions in a plant-herbivore-parasitoid system as a starting point, we ask what spatial properties of the environment and functional responses in the interactions between trophic levels may favor or disfavor the evolution of the gregarious life history pattern in parasitoids, and derive predictions from theory. We discuss the likelihood of different scenarios in a multitrophic co-evolutionary context, thereby addressing infochemical use by searching parasitoids and aggregative and defensive behavior in herbivorous hosts.
Species 1: Hymenoptera Braconidae Cotesia glomerata (parasitoid, parasitic wasp)
Species 2: Hymenoptera Braconidae Cotesia rubecula (parasitoid, parasitic wasp)
Species 3: Lepidoptera Pieridae Pieris spp (cabbage white butterflies)
Keywords: density dependence, foraging
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