On Thursday September 14th Dr. David Flaspohler from Michigan Technological University will be presenting a seminar on his research at 11:40-12:40 in room 312A in Holdsworth Hall at UMass. Dr. Flaspohler is a conservation biologist interested in the influence of a variety of human activities on natural ecosystems, including trophic interactions and food-web dynamics in Hawaiian forests, which will be the topic of his presentation (abstract below). More information on Dr. Flaspohlers’ work can be found at http://www.mtu.edu/forest/about/faculty-staff/faculty/flaspohler/
Landscape-Level Experimental Decoupling of Competing Vertebrate Insectivores in Hawaiian Forest Islands
Ecologists have long sought to understand the role of predators as drivers of food-web structure, with particular modern emphasis on omnivorous predators in complex communities. Effective ecological experiments to resolve food web effects of mobile, large-bodied vertebrate predators are rare because of the large temporal and spatial dynamical scales over which these processes operate. Little is known about whether and how predators and ecosystem size – per se – interact to jointly influence food webs at landscape scales. In montane forests on the island of Hawaii, we manipulated the presence of invasive black rats (Rattus rattus) across 34 replicated, volcanically isolated forest fragments varying in size more than 100-fold, from 0.1 ha to greater than 10 ha. Within each forest fragment, or “kīpuka”, we excluded insectivorous birds with netted branches matched with open access paired branches in the forest canopies over two bird nesting seasons. Omnivorous rats and birds likely interact both directly via rat predation on nests and nestlings, and indirectly via competition for shared arthropod prey resources, such as spiders. Our overarching hypothesis was that rats alter bird behavior, demography, and the structure of arthropod food webs, but with greater severity in smaller forest fragments. Arthropod densities overall, and spider densities in particular, were positively, linearly related to log kīpuka area. After the first full year of experimental treatments, rats weakly and birds strongly reduced spider densities relative to respective treatments with predators excluded. Effects were contingent on kīpuka area, the height of samples in the forest canopy, and the distance from the edge of fragments. We observed no differences in diversity or demography of the forest bird community after just one year of rat exclusion. However, in the absence of rats, birds foraged at significantly lower heights in the forest canopy where they reduced arboreal spider densities to a greater degree than in the presence of rats. Our study integrates core principles of island biogeography, trophic omnivory, and food-web complexity toward a mechanistic understanding of food-web dynamics. Such syntheses are urgently needed for biodiversity conservation and restoration in the face of accelerating biological invasion by nonnative predators and the reduction of ecosystem size by habitat fragmentation.