Non-linear ecosystems : intertwined consumptive and non-consumptive pathways following increase in predator habitat

The extent to which the diversity in habitat of an ecological system, or habitat heterogeneity, affects communities is an important aspect of ecology. Although higher habitat diversity is generally linked to higher species richness, how the increase in specific groups affects trophic dynamics in a system remains elusive. Studying biotic habitat modification, the formation of habitats by species and the subsequent alterations in persistence of other local species, can shed light on this topic. As biotic habitat modification tends to increase abundance and/or richness of specific taxa, the impacts of the increase of these specific groups can be analyzed. Tank bromeliads are common epiphytic biotic habitat modifiers throughout the Neotropics, and are facultatively associated with a variety of predatory arthropods. Here, we examine the community consequences of bromeliad-mediated increase in predator habitat in Costa Rican orange trees. As the effects of predation can attenuated by a variety of ecological processes, such as facilitative interactions, we examined two different aspects of community modification. First, in a manipulative experiment, we tested the hypothesis that bromeliads mediate trophic cascades in their support tree communities. In that view, we manipulated bromeliad densities on trees, and measured impacts on arboreal and bromeliad invertebrate communities, and leaf damage. Second, in an observational survey, we examined if the presence of bromeliads in a tree modified the behaviour of arboreal invertebrates, and interspecific interactions. We found that habitat modification by bromeliads was highly contingent on season and time of the day, and influenced arboreal invertebrate communities in various ways. Predators were more numerous with higher bromeliad densities, but effects on herbivores differed. Bromeliads did not modify cascading dynamics, and only weakly affected community structure, suggesting that invertebrate communities in orange trees can be functionally resilient. Even if bromeliads largely harboured predators, several groups of herbivores were commonly encountered in the epiphytes, plausibly attenuating cascading effects. The bromeliad-associated ants that dominated our system were strongly associated with honeydew-producing homopterans, suggesting less reliance on predation. These results suggest that the impacts of increased habitat heterogeneity on trophic dynamics can be attenuated by functional resilience and facilitative dynamics.Science, Faculty ofZoology, Department ofGraduat

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