Islands within islands: The effects of habitat fragmentation, novel community interactions, and climate on Hawaiian Drosophila populations.
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2015-12
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Abstract
Habitat fragmentation, invasive species, and shifting climate regimes are major threats to island ecosystems. Hawaii's ecosystems have been largely transformed since human colonization, with fragmented upland forests remaining important refugia for native organisms. Hawaiian Drosophila represent a large radiation of nearly 1000 endemic species, including a number of endangered and declining species. These endemic flies are important indicator species for ecosystem change, tending to be sensitive niche specialists. I examined a network of 28 lava-fragmented forests ("kipuka") on Mauna Loa to determine the effect of fragment size, presence of invasive rats, and seasonal changes in microclimate on the abundances of native Drosophila tanythrix, D. silvestris, D. sproati, and D. murphyi, and the exotic D. suzukii. All flies responded positively to increasing kipuka area. Rat exclusion had a significant and mostly positive impact on both native and exotic Drosophila abundances, but the effect varied with individual species, suggesting that rats may amplify the impact of predators on Drosophila or predate them directly, but also affect other nodes in the community. Increasing kipuka isolation from surrounding forest tended to benefit Drosophila, perhaps due to release from competitors. Exotic flies represent the vast majority of Drosophilids observed in small kipuka, and significantly outnumbered natives in all kipuka before crashing in the winter. In contrast, native flies were more abundant in winter, and rare picture-wing species were found almost exclusively in kipuka larger than 2.5 hectares. Overall, it appears that habitat fragmentation and invasive species disrupt Hawaiian Drosophila communities; the rarest species require large kipuka and the absence of rats. D. suzukii may be replacing native Drosophila in smaller kipuka, but appear maladapted to Hawaii's cold winters at higher elevations. This dynamic could tip in favor of D. suzukii as temperature isoclines climb upslope with global climate change.
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Ecology, Entomology, Conservation biology, Drosophila suzukii, Habitat fragmentation, Hawaii, Hawaiian Drosophila, Invasive species, Island biogeography theory
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156 pages
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