Abstract Detail

Past Presidents' Symposium: Biodiversity: Past, Present, and Future

Fukami, Tadashi [1], Wilson, Erin E. [2], Knowlton, Jessie L. [3], Gruner, Daniel S. [4], Leopold, Devin R. [3], Flaspohler, David J. [5], Giardina, Christian P. [6].

Biodiversity in a fragmented landscape: linking forest productivity, introduced predators, and native arthropod and bird communities in lava-fragmented ecosystems in Hawaii.

Ecologists have long sought to understand the effect of predators on community structure, with growing attention to omnivorous predators. Ecologists have also attempted to elucidate the role of ecosystem size as another determinant of community structure, with an increasing focus on habitat complexity and productivity for mechanistic explanations. However, little is known about how predators and ecosystem size may jointly influence community structure. This synthesis is needed for biodiversity conservation and restoration in the face of biological invasion and habitat fragmentation. We are using forest fragments of varying size naturally created by lava flows on the Island of Hawaii to investigate interactive effects of non-native omnivorous rats and forest fragment size on arboreal arthropod communities. Active on trees, rats may affect arboreal arthropods by predation, but may also indirectly affect them by preying on eggs and nestlings of birds, which themselves consume arthropods, or by competing against birds for shared arthropod resources. The net effect of rats is hard to predict. However, because trees are shorter in smaller forest fragments and rats are more active in shorter forest canopy, we hypothesized that rats would affect both birds and arthropods more greatly in smaller fragments. To test this hypothesis, we are using 34 fragments—all dominated by a single canopy species, Metrosideros polymorpha—that range in size from 0.1 to 10 ha. In 16 of these fragments, called kipuka, we have been continually removing rats with snap traps since June 2011. In the other 18 kipuka, no rats are being removed. In addition, within each kipuka, we locally excluded birds by covering M. polymorpha branches in the canopy with a net, each matched with open-access branches, during the bird nesting season in 2012 and 2013. After the first year of the experimental treatments, we found that rat removal weakly and bird exclusion strongly increased densities of some arthropod taxa such as spiders. We also found that these effects depended on the size of kipuka, the height of samples in the forest canopy, and the distance from the edge of the kipuka. So far no difference has been observed between rat-removed and non-rat-removed kipuka in bird abundance or composition. However, in rat-removed kipuka, birds foraged at significantly lower heights in the canopy where they reduced arboreal spider densities to a greater degree than in the kipuka where no rats were removed. Overall, these results support our hypothesis, but mechanisms are complex

Broader Impacts:

Related Links:
Kipuka project
Tadashi Fukami

1 - Stanford University, Department of Biology, Stanford, CA, 94305, USA
2 - University of California, Riverside
3 - Stanford University
4 - University of Maryland
5 - Michigan Technological University
6 - US Forest Service Institute of Pacific Islands Forestry

Keywords:
ecology
island biogeography.

Presentation Type: Symposium or Colloquium Presentation
Session: SY12
Location: Grand Ballroom A/Riverside Hilton
Date: Wednesday, July 31st, 2013
Time: 4:45 PM
Number: SY12007
Abstract ID:247
Candidate for Awards:None