Coexistence in multi-trophic communities: The dual roles of environmental variability and local niche partitioning.
ABSTRACT- Well understood are the situations where environmental variability promotes coexistence when species interactions preclude local niche partitioning. Much less well understood are the situations where species interactions do allow niche partitioning, but environmental variation modifies the density (or frequency)-dependent feedback loops that characterize species interactions. Here, I present experimental evidence of temporal variation modifying competitive outcomes in an insect host-parasitoid community where local niche partitioning occurs via intraguild predation/parasitism (IGP). I show that when host productivity constrains the expression of trade-offs that allow niche partitioning, differential responses by parasitoid species to temporal variation can strengthen intra-specific competition relative to inter-specific competition. This interplay between temporal variation and IGP not only increases opportunities for coexistence, but also changes species abundances to a pattern that is qualitatively different from IGP. These results suggest a mechanism for why communities with IGP do not lose species diversity in highly productive environments. More generally, the study highlights a mechanism for diversity maintenance via joint action of environmental variability and local niche partitioning that may operate in a wide variety of multi-trophic communities.
Key words: coexistence, environmental variation, intraguild predation, host-parasitoid
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