title: Seasonal fecundity is not related to geographic position across a species' global range despite a central peak in abundance.
abstract: 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.
authors.affiliation: School of Biology and Ecology, Climate Change Institute, University of Maine, 200 Clapp Greenhouse, Orono, ME, 04469, USA. katharine.ruskin@maine.edu.
authors.forename: Katharine J
authors.initials: KJ
authors.lastname: Ruskin
authors.affiliation: Mid-Continent Ecology Division, U. S. Environmental Protection Agency, 6201 Congdon Boulevard, Duluth, MN, 55804, USA.
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Etterson
authors.affiliation: Maine Department of Inland Fisheries and Wildlife, Bird Group, 650 State Street, Bangor, ME, 04401, USA.
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Hodgman
authors.affiliation: Department of Ecology and Evolutionary Biology, Center for Conservation and Biodiversity, University of Connecticut, 75 North Eagleville Road, U-43, Storrs, CT, 06269, USA.
authors.forename: Alyssa C
authors.initials: AC
authors.lastname: Borowske
authors.affiliation: Department of Environmental and Forest Biology, State University of New York College of Environmental Science and Forestry, 1 Forestry Drive, Syracuse, NY, 13210, USA.
authors.forename: Jonathan B
authors.initials: JB
authors.lastname: Cohen
authors.affiliation: Department of Ecology and Evolutionary Biology, Center for Conservation and Biodiversity, University of Connecticut, 75 North Eagleville Road, U-43, Storrs, CT, 06269, USA.
authors.forename: Chris S
authors.initials: CS
authors.lastname: Elphick
authors.affiliation: Department of Ecology and Evolutionary Biology, Center for Conservation and Biodiversity, University of Connecticut, 75 North Eagleville Road, U-43, Storrs, CT, 06269, USA.
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Field
authors.affiliation: Department of Entomology and Wildlife Ecology, University of Delaware, 250 Townsend Hall, Newark, DE, 19716, USA.|U. S. Fish and Wildlife Service, Edwin B. Forsythe NWR, 800 Great Creek Road, Galloway, NJ, 08205, USA.
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Kern
authors.affiliation: U. S. Fish and Wildlife Service, Region 5 Division of Natural Resources, Stewart B. McKinney NWR, 733 Old Clinton Road, Westbrook, CT, 06498, USA.
authors.forename: Erin
authors.initials: E
authors.lastname: King
authors.affiliation: Department of Environmental and Forest Biology, State University of New York College of Environmental Science and Forestry, 1 Forestry Drive, Syracuse, NY, 13210, USA.
authors.forename: Alison R
authors.initials: AR
authors.lastname: Kocek
authors.affiliation: Department of Natural Resources and the Environment, University of New Hampshire, 46 College Road, Durham, NH, 03824, USA.
authors.forename: Adrienne I
authors.initials: AI
authors.lastname: Kovach
authors.affiliation: U. S. Fish and Wildlife Service, Rachel Carson National Wildlife Refuge, 321 Port Road, Wells, ME, 04090, USA.
authors.forename: Kathleen M
authors.initials: KM
authors.lastname: O'Brien
authors.affiliation: U. S. Fish and Wildlife Service, Parker River National Wildlife Refuge, 6 Plum Island Turnpike, Newburyport, MA, 01950, USA.
authors.forename: Nancy
authors.initials: N
authors.lastname: Pau
authors.affiliation: Department of Entomology and Wildlife Ecology, University of Delaware, 250 Townsend Hall, Newark, DE, 19716, USA.
authors.forename: W Gregory
authors.initials: WG
authors.lastname: Shriver
authors.affiliation: Department of Natural Resources and the Environment, University of New Hampshire, 46 College Road, Durham, NH, 03824, USA.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Walsh
authors.affiliation: School of Biology and Ecology, Climate Change Institute, University of Maine, 200 Clapp Greenhouse, Orono, ME, 04469, USA.
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Olsen
mesh_terms: D000818:Animals; D052284:Clutch Size; D003710:Demography; D005298:Fertility; D012621:Seasons; D020308:Songbirds
keywords: Ammodramus caudacutus; Biogeography; Fecundity; Latitudinal gradients; Species range