Thursday, August 7, 2008: 9:00 AM
202 E, Midwest Airlines Center
Katie Schneider, Graduate Program in Behavior, Ecology, Evolution, and Systematics, University of Maryland, College Park, MD and William F. Fagan, Department of Biology, University of Maryland, College Park, MD
Background/Question/Methods Resource availability, especially in the form of spatial subsidies, can greatly influence biodiversity patterns and community dynamics. Ecosystem-level experimental manipulations have proved critical to ecological understanding of the importance of spatial subsidies, especially in aquatic systems like lakes, ponds, and tree-holes. Although few terrestrial systems are appropriate for these kinds of studies, caves are a key exception because their self-contained structure makes them amenable to ecosystem-level experimentation. We took advantage of this unique opportunity in caves to experimentally examine the link between resource availability and biodiversity in these (sub)terrestrial habitats. After performing baseline censuses of invertebrates, all organic material (1450 kg wet weight) was removed from 12 caves (depth 20′ - 80′), and exclusion boxes were constructed to prohibit natural resources from entering. Next, each cave was stocked with standardized quantities of the two major natural subsidies to the cave environment: leaves (in the form of leaf packs) and carcasses (commercially supplied rodents). For 2 years, Schneider rappelled monthly into each cave and measured the colonization and utilization of these resources.
Results/Conclusions Although a substantial assortment of skeletal remains were collected, most of the organics removed consisted of plant material. Within the caves, the arthropod community differed depending on the type of subsidy introduced (leaf pack or rat carcass). On average, caves receiving rat treatments had significantly higher species richness and total abundance than caves subsidized with leaf packs. Total arthropod abundance differed between treatments over the duration of the experiment and over the temporal “life” of the individual resources, which were restocked upon exhaustion. Leaf packs decayed very slowly, whereas rats quickly decomposed and needed to be restocked on average every 128 days. The invertebrate community utilizing the rats changed over the course of the decomposition. The leaf packs, on the other hand, harbored a relatively constant community over time. In total, 99 morphospecies were observed. Overall, members of the Orthoptera, Acari, and Collembola were observed most commonly. Detritivorous collembolans and diplopods were the most commonly observed arthropods on the leaf packs; however, predaceous (and obligate) cave carabids were not only observed, but also discovered reproducing underneath a leaf pack. Dipteran larvae were most abundant in the rat treatments, however collembolans were more frequently observed over time. Results of this experiment illustrate the important impacts that spatial subsidies can have on food web structure, community dynamics, and successional patterns in a detritus-based system that is completely dependent on allochthonous inputs.
