Journal
OECOLOGIA
Volume 183, Issue 1, Pages 291-301Publisher
SPRINGER
DOI: 10.1007/s00442-016-3745-8
Keywords
Latitudinal gradients; Fecundity; Species range; Biogeography; Ammodramus caudacutus
Categories
Funding
- Competitive State Wildlife Grant via the United States Fish and Wildlife Service, Federal Aid in Sportfish and Wildlife Restoration to the states of Delaware, Maryland, Connecticut, and Maine [U2-5-R-1]
- United States Fish and Wildlife Service
- United States Department of Agriculture (National Institute of Food and Agriculture NH McIntire-Stennis Project) [225,575]
- New York Department of Environmental Conservation [AM08634]
- National Science Foundation [DEB-1340008]
- USDA National Institute of Food and Agriculture [ME0-H-6-00492-12]
- National Science Foundation
- National Park Service Gateway Learning Center Fellowship
- University of Maine
- University of New Hampshire
- University of Connecticut
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The range of a species is determined by the balance of its demographic rates across space. Population growth rates are widely hypothesized to be greatest at the geographic center of the species range, but indirect empirical support for this pattern using abundance as a proxy has been mixed, and demographic rates are rarely quantified on a large spatial scale. Therefore, the texture of how demographic rates of a species vary over its range remains an open question. We quantified seasonal fecundity of populations spanning the majority of the global range of a single species, the saltmarsh sparrow (Ammodramus caudacutus), which demonstrates a peak of abundance at the geographic center of its range. We used a novel, population projection method to estimate seasonal fecundity inclusive of seasonal and spatial variation in life history traits that contribute to seasonal fecundity. We replicated our study over 3 years, and compared seasonal fecundity to latitude and distance among plots. We observed large-scale patterns in some life history traits that contribute to seasonal fecundity, such as an increase in clutch size with latitude. However, we observed no relationship between latitude and seasonal fecundity. Instead, fecundity varied greatly among plots separated by as little as 1 km. Our results do not support the hypothesis that demographic rates are highest at the geographic and abundance center of a species range, but rather they suggest that local drivers strongly influence saltmarsh sparrow fecundity across their global range.
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