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Local- to continental-scale variation in the richness and composition of an aquatic food web

Buckley, Hannah L., Miller, Thomas E., Ellison, Aaron M., Gotelli, Nicholas J.
Global ecology and biogeography 2010 v.19 no.5 pp. 711-723
Sarracenia, aquatic food webs, arthropods, bacteria, chemistry, climate, environmental factors, host plants, host range, leaves, models, species diversity, British Columbia, Florida
We investigated patterns of species richness and composition of the aquatic food web found in the liquid-filled leaves of the North American purple pitcher plant, Sarracenia purpurea (Sarraceniaceae), from local to continental scales. We sampled 20 pitcher-plant communities at each of 39 sites spanning the geographic range of S. purpurea- from northern Florida to Newfoundland and westward to eastern British Columbia. Environmental predictors of variation in species composition and species richness were measured at two different spatial scales: among pitchers within sites and among sites. Hierarchical Bayesian models were used to examine correlates and similarities of species richness and abundance within and among sites. Ninety-two taxa of arthropods, protozoa and bacteria were identified in the 780 pitcher samples. The variation in the species composition of this multi-trophic level community across the broad geographic range of the host plant was lower than the variation among pitchers within host-plant populations. Variation among food webs in richness and composition was related to climate, pore-water chemistry, pitcher-plant morphology and leaf age. Variation in the abundance of the five most common invertebrates was also strongly related to pitcher morphology and site-specific climatic and other environmental variables. The surprising result that these communities are more variable within their host-plant populations than across North America suggests that the food web in S. purpurea leaves consists of two groups of species: (1) a core group of mostly obligate pitcher-plant residents that have evolved strong requirements for the host plant and that co-occur consistently across North America, and (2) a larger set of relatively uncommon, generalist taxa that co-occur patchily.