Modeling the Effects of Habitat Fragmentation on Source and Sink Demography of Neotropical Migrant Birds

Abstract

Many songbird populations in the midwestern United States are structured as a network of sources and sinks that are linked by dispersal. We used a modeling approach to examine explicitly how populations respond to incremental fragmentation of source habitat and how this response may vary depending upon two life-history attributes: fidelity to natal habitat ~ype and reproductive strength of the source. Fragmentation of source habitat led to a predictable decline in population for both attributes examined, but the manner in which populations declined varied depending upon the reproductive strength of the source and the level of fidelity. When the source was weak and produced few excess individuals, fragmentation of source habitats resuited in a predictable and parallel population decline of adults in both the source and the sink. In this situation high fidelity to natal habitats was important for maintenance of population size and structure. Low fidelity to weak sources resulted in population extinction; populations experienced a demographic cost by dispersing from high quality source habitat to low quality 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 abrupt in sink habitats. When the source was strong and produced a large excess of individuals, nonfidelity to natal habitats had little effect on metapopulation size and structure.Modelaci6n de los efectos de la fragmentaci6n del h~tbitat sobre la demografia de fuentes y sumideros en aves neomigratorias tropicales Resumen: Muchas poblaciones de aves cantoras en el medio-oeste de los Estados Unities estdn estructuradas come una red de fuentes ("sources") y sumideros ('sinks'), que se encuentran conectadas por medio de la dis-persi6n. En el presente estudio, usamos una aproximaci6n de modelaci6n para examinar explicitamente come las poblaciones responden al incremento en la fragmentaci6n a del hdbttat fuente y come ~sta respuesta puede variar dependiendo de dos atributos de la htstoria de vida: fidelidad al ripe de hcibitat native y fortaleza reproductiva. La fragmentaci6n del hdbitat fuente condujo a una declinact6n predectble en el tama~o poblacional para ambos atributos examinados, pero la manera en que las poblaciones decltnaron vart6 dependtendo de la fortaleza reproductiva de la fuente y el nivel de fideltdad. Cuando la fuente era ddbil, y producta un bajo nf~mero de individuos excedentes, la fragmentaci6n del hdbitat fuente result6 en una predecible y paralela producfa decltnaci6n poblacional de los adultos, tanto en la fuente come en el sumidero. En esta situaci6n, una alta fldeltdad a los hdbitats natives fue importante para mantener el tamaao y estructura poblactonaL La baja fidelidad a fuentes d(biles di6 come resultado la extinci6n poblacional, las 1397 poblaciones expertmentaron un alto costo demogrdflco al dtspersarse de los hdbitat fuente de gran caltdad a los h~bttat sumidero de baja caUdad. En ...

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