Rapid species displacement during the invasion of Florida by the tropical house gecko Hemidactylus mabouia
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- Short, K.H. & Petren, K. Biol Invasions (2012) 14: 1177. doi:10.1007/s10530-011-0147-z
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There is considerable interest in understanding how invasive species disperse across landscapes, and how they affect resident species. However, quantifying these processes using mark recapture or manipulative experiments can be time consuming and costly. A different approach is to study density changes across a broader landscape, and take advantage of naturally existing replicate locations that are imperfect, but plentiful. We documented sites of recent colonization and measured density changes in the invasive gecko Hemidactylus mabouia and the prior resident gecko Hemidactylus garnotii in Florida. We surveyed geckos at 398 locations from 19 regional sites distributed across central and southern Florida. We documented changes in abundance through repeated censuses of 56 locations in areas of sympatry between 2001 and 2009. Complete displacement occurred in <7 years at several locations, and overall there was a >10% increase in H. mabouia per year. There was evidence that H. mabouia reaches a higher carrying capacity than H. garnotii, which likely contributes to its competitive dominance. Changes in relative abundance within patches were consistent with a density dependent mechanism of displacement, suggesting the decline of H. garnotii is functionally linked to increases in H. mabouia abundance, which allows us to rule out coincidental factors not directly associated with H. mabouia. However, simulations showed that even highly asymmetric differences in carrying capacity and competitive ability were not sufficient to account for the rapid displacement we observed. We conclude that mechanisms other than resource competition must be at work to drive species displacement in this system.