California Gnatcatcher and Cactus Wren

California gnatcatcher and cactus wren: spatially explicit population models for two target species of the Natural Community Conservation Planning effort in Southern California

funded by Los Angeles County Museum of Natural History, and Southern California Edison

Summary

        This project aims at developing habitat-based metapopulation models for the California gnatcatcher Polioptila californica and the cactus wren Campylorhynchus brunneicapillus in central and coastal regions of Orange County, California. The California gnatcatcher (a federally-listed threatened species) and cactus wren are two of the three "target species" in the State of California's Natural Community Conservation Planning (NCCP) program. The target species are considered as surrogates for the conservation of coastal sage scrub, a plant community that has decreased substantially from its historic coverage as a result of urban and agricultural development, and has become fragmented.

        In this project RAMAS GIS was applied to the habitat and demographic data on the two target species. The application started with a statistical analyses of observation locations, and GIS maps for elevation, slope, and vegetation (exported from ARC/Info) to characterize the habitat of the two birds. The habitat maps were validated by predicting the habitat suitability values for one half of observation locations, with the model estimated from the other half, and by predicting the habitat suitability values for location of singles, with the model estimated from location of pairs.

        The habitat maps were then analyzed to determine the spatial structure of the metapopulation model. These data were combined with demographic parameters estimated from field work conducted by Atwood et al. (1995) to produce spatially-explicit, stage-structured, stochastic metapopulation models for the two species. Simulations and sensitivity analyses with these models pointed out to the relative importance of density dependence and temporal variation in vital rates (including the frequency and the magnitude of catastrophic declines in vital rates as was observed in the winter of 1994-95).

        The results of the project were presented at a talk at the ESA/SCB meeting in Providence, RI, in August 1996, and were published in the following paper:

Akçakaya, H.R. and J.L. Atwood. 1997. A habitat-based metapopulation model of the California Gnatcatcher. Conservation Biology 11:422-434.

Also see: List of AB Publications

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