MODELING THE EFFECTS OF HABITAT FRAGMENTATION ON SOURCE AND SINK DEMOGRAPHY OF NEOTROPICAL MIGRANT BIRDS

Many songbird populations in the midwestern United States are structur ed as a network of sources and sinks that are linked by dispersal. We used a modeling approach to examine explicitly how populations respond to incremented fragmentation of source habitat and how this response may vary depending upon two life-history attributes: fidelity to natal habitat type and reproductive strength of the source. Fragmentation o f soul ce habitat led to a predictable decline in population for both attributes examined but the manner in which populations declined varie d depending upon the reproductive strength of the source and the level of fidelity When the source was weak and produced few excess individu als, fragmentation of source habitats resulted in a predictable and pa rallel population decline of adults in both the source and the sink. I n this situation high fidelity to natal habitats was important for mai ntenance of population sire and structure. Low fidelity to weak source s resulted in population extinction; populations experienced a demogra phic cost by dispersing from high quality source habitat to lout quali ty sink habitat. In contrast, when the source was strong and produced many excess individuals, fragmentation of the source led to population declines In both the source and the sink, but this decline was more a brupt in sink habitats. When the source was strong and produced a larg e excess of individuals, nonfidelity to natal habitats had little effe ct on metapopulation size and structure.