Consequences of insular population structure: Distribution and extinction of spruce grouse populations

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Abstract
The population structure of the spruce grouse (C. canadensis) was studied in the Adirondack Mountains of New York, USA. Isolated habitat patches (25) exist and are occupied by spruce grouse, with 7 suitable but unoccupied patches existing at the periphery of the range. The regional distribution and abundance of spruce grouse is correlated with the amount of lowland coniferous forest habitat. Unoccupied patches were significantly smaller and significantly farther from occupied patches than were other occupied patches. For all patches, as distance from the nearest occupied patch increased, the percent of occupied patches decreased linearly. Birth and death rates were incorporated for spruce grouse into the MacArthur-Wilson survivorship model which closely predicted the proportion of occupied patches for an average population density (2.8 .female. spruce grouse/100 ha). For the same demographic parameters, extinction times were calculated which indicate that the 15 habitat patches of a carrying capacity of .ltoreq. 3 female spruce grouse (.ltoreq. 100 ha) would have an average extinction time of less than 6 yr. This in part accounts for the high proportion of these patches which are unoccupied. Extinctions and recolonizations of patches were observed during the study. The patterns of patch occupancy can partially be predicted based on their size, spatial arrangement and the demographic characteristics of the spruce grouse.