Abstract
In plant–arthropod associations, the first herbivores to colonise a plant may directly or indirectly affect community assembly on that particular plant. Whether the order of arrival of different arthropod species further modulates community assembly and affects plant fitness remains unclear.Using wild Brassica oleracea plants in the field, we manipulated the order of arrival of early‐season herbivores that belong to different feeding guilds, namely the aphid Brevicoryne brassicae and caterpillars of Plutella xylostella. We investigated the effect of herbivore identity and order of arrival on community assembly on two B. oleracea plant populations during two growth seasons. For this perennial plant, we evaluated whether foliar herbivory also affected herbivore communities on the flowers and if these interactions affected plant seed production.Aphid infestation caused an increase in parasitoid abundance, but caterpillars modulated these effects, depending on the order of herbivore infestation and plant population. In the second growth season, when plants flowered, the order of infestation of leaves with aphids and caterpillars more strongly affected abundance of herbivores feeding on the flowers than those feeding on leaves. Infestation with caterpillars followed by aphids caused an increase in flower‐feeding herbivores compared to the reversed order of infestation in one plant population, whereas the opposite effects were observed for the other plant population. The impact on plant seed set in the first reproductive year was limited.Our work shows that the identity and arrival order of early season herbivores may have long‐term consequences for community composition on individual plants and that these patterns may vary among plant populations. We discuss how these community processes may affect plant fitness and speculate on the implications for evolution of plant defences.
Highlights
The historical contingency of how the presence of individual species affects community assembly is an important determinant of community structure in many terrestrial and aquatic ecosystems (Chase 2003, Trussell et al 2003, Křivan and Schmitz 2004, Schmitz et al 2004, Fukami 2015)
By using ordination analyses that provide much more detailed analyses of the community dynamics through time than species abundance or richness, we identified that earlyseason herbivory in the first year (2012) had an effect on arthropod community composition during the remainder of the season for both Winspit and Kimmeridge plants (PRC, Winspit plants: first axis explained 5.86%, Monte Carlo permutation test, pseudo-F60,11: 31.4; p = 0.002, Fig. 1a; and on Kimmeridge plants: first axis explained 4.46%, Monte Carlo permutation test, pseudo-F60,11: 23.5; p = 0.002; Fig. 1b)
Plant populations differed in the effects of early herbivory on the arthropod community throughout the season (PRC, first axis explained 1.37%, Monte Carlo permutation test, pseudo-F12,11: 15.7, p = 0.002), and the effects of plant population and early-season herbivore infestation showed a significant interaction (PRC, first axis explained 5.48%, Monte Carlo permutation test, pseudo-F60,11: 29.2, p = 0.002)
Summary
The historical contingency of how the presence of individual species affects community assembly is an important determinant of community structure in many terrestrial and aquatic ecosystems (Chase 2003, Trussell et al 2003, Křivan and Schmitz 2004, Schmitz et al 2004, Fukami 2015). Historical contingency may result from direct species interactions such as density dependent effects in trophic relationships, or from indirect species interactions (Werner and Peacor 2003). These indirect interactions frequently result from one organism altering the quality of a resource that it shares with other community members (Werner and Peacor 2003). In complex food webs it is crucial to consider historical contingency to understand community structure as well as the evolutionary regime under which selection on community members occurs (Urban and De Meester 2009, Fukami 2015)
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