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|Title:||Differential avian extinction from Barro Colorado Island, Panama: Nest predation and population genetic factors|
|Author(s):||Sieving, Kathryn Ermine|
|Doctoral Committee Chair(s):||Karr, J.|
|Department / Program:||Biology|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||On Barro Colorado Island (BCI), a 1500 ha forest preserve in Gatun Lake (part of the Panama Canal) that has been isolated form mainland forest for 75 years, eight species of birds in the terrestrial insectivore guild have gone extinct, one is declining, and 3 persist. I evaluated two alternative hypotheses to explain differential BCI extinctions among these bird species.
Interspecific variation in nest design and placement may underly differential extinction from BCI. Selecting 5 species from the terrestrial insectivore guild, 2 that are extinct and 3 that persist on BCI, I constructed 200 hand-made nests, 40 each of the 5 types. The nests, containing 2 Coturnix quail eggs, were placed on 2 island and 2 mainland sites in 3 experiments. BCI nest losses were higher than mainland. The two nests of BCI-extinct species suffered lower overall predation than the three nests of BCI-persistent species. However, the ratios of island to mainland predation were disproportionately higher for BCI-extinct nest types.
Species which inbreed at a low rate will be less susceptible to inbreeding depression than highly outbred species when habitat isolation severely reduces breeding population size. To test this (second) hypothesis, I evaluated the prediction that relatively inbred species should be persistent on the Gatun Lake islands, whereas relatively outbred species should be extinct. I used DNA fingerprinting to measure local genetic similarity (i.e. level of inbreeding) for 7 species sampled on mainland sites, 3 of which are extinct from BCI. One species of wren that is extinct on BCI had significantly higher similarity than the other 6 species. Hypothesized advantages of mild inbreeding prior to genetic isolation are not supported by the data. Apparently, mechanisms exist whereby outbred species may persist in conditions of intense inbreeding, and inbreeding depression does not appear to be a major cause of avian extinctions from BCI. Results suggest that over evolutionary time species-specific rates of nest loss may determine clutch replacement capability, thereby causing variation in tolerance of inflated insular nest losses, either from nest predation or genetic inviability.
|Rights Information:||Copyright 1991 Sieving, Kathryn Ermine|
|Date Available in IDEALS:||2011-05-07|
|Identifier in Online Catalog:||AAI9136734|