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Can simple correlation analyses detect "bottom-up" trophic cascades among rodents on the Sevilleta NWR?
Friggens, Michael*,1, 2, Parmenter, Robert 1, 2, Yates, Terry1, 2, Gosz, James1, 2, 1 Department of Biology, Albuquerque, New Mexico2 Sevilleta Long Term Ecological Research Project, Albuquerque, New Mexico
ABSTRACT- In habitats with relatively low primary productivity (i.e., deserts), there is evidence that predators are largely donor controlled, leading predominantly to a two-link, primary production-herbivore food chain wherein herbivore abundance is mediated by primary production of vegetation. This "bottom-up" trophic cascade hypothesis has recently been enlisted to explain Peromyscus rodent density increase and subsequent Hantavirus outbreak in the Southwestern US. There is some debate as to the utility of simple linear correlation in explaining trophic relationships or in detecting trophic cascade. In order to test for the presence of bottom-up, resource driven dynamics among 3 families and 20 rodent species occurring across varying ecosystems with similar climatic regimes, we employed simple Pearson correlation statistics, comparing rodent species density with seasonal precipitation and vegetation production (as measured from AVHRR NDVI) at varying lags in five habitats from 1989-2000, as part of the Sevilleta Long Term Ecological Research project. We did not detect overall patterns based on taxonomic affinity or site. But although results were highly variable among species and between habitats, 15 of 20 species exhibited positive correlation to seasonal PPT and subsequent vegetation production in at least one habitat. Our results suggest that while there are certainly more complex explanations for density dynamics observed at our sites, simple correlation statistics succeeded in highlighting positive relationships with available resources and the presence of bottom-up trophic cascades in many instances on the Sevilleta National Wildlife Refuge.
Key words: trophic, correlation, rodent, Sevilleta