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DO HABITAT POTENTIAL, POPULATION DENSITY, AND FIRES INFLUENCE SCRUB‐JAY SOURCE–SINK DYNAMICS?
Author(s) -
Breininger David R.,
Oddy Donna M.
Publication year - 2004
Publication title -
ecological applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.864
H-Index - 213
eISSN - 1939-5582
pISSN - 1051-0761
DOI - 10.1890/03-5002
Subject(s) - shrub , biological dispersal , habitat , ecology , geography , population density , population , ridge , vital rates , sink (geography) , population growth , demography , biology , cartography , sociology
The concept of source and sinks can guide conservation, but empirical studies are needed to demonstrate that this concept applies to the real world. We investigated whether the source–sink concept could help to clarify the influence of habitat potential (scrub ridge characteristics), population density, and fires (shrub heights) on Florida Scrub‐Jay ( Aphelocoma coerulescens ) demography and dispersal. We mapped territories and measured survival, recruitment, emigration, immigration, and shrub heights annually for 12 years. We classified territories as oak if they overlapped well‐drained ridges, oak–palmetto if they overlapped poorly drained ridges >0.4 ha, and palmetto–oak if they only overlapped poorly drained ridges <0.4 ha. Territory size differed little among these categories but was negatively correlated with the annual number of breeding pairs, which ranged from 12 to 27. Scrub ridge characteristics influenced the locations of sinks and potential sources, whereas population density and fires caused temporal variation in demographic success. Oak territories were usually sources because they were net exporters of individuals and because recruitment exceeded mortality. Oak–palmetto territories sometimes functioned as sources but were often pseudo‐sinks because density dependence caused mortality to exceed recruitment. Palmetto–oak territories were true sinks because they were net importers of individuals and mortality exceeded recruitment regardless of population density. All scrub was short (<1.2 m) or medium height (1.2–1.7 m), but the spatial arrangement of these height classes changed regularly because fires occurred every 2–7 years. We observed a quadratic relationship between demographic success and the area of medium‐height scrub within territories. Territories that had 0.9–1.2 ha of medium‐height scrub had the highest demographic success. Applying source–sink concepts at the territory scale was useful to quantify habitat variation at a spatial scale relevant to population processes, reserve design, and habitat management. Our approach can be applied by using territory maps or geographic information systems to partition heterogeneous landscapes into territories and then by classifying territories into potential sources and sinks using scrub ridge characteristics and shrub heights.