Seasonal fecundity is not related to geographic position across a species’ global range despite a central peak in abundance

Authors

Katharine J. Ruskin, University of Maine
Matthew A. Etterson, U. S. Environmental Protection Agency
Thomas P. Hodgman, Maine Department of Inland Fisheries and Wildlife
Alyssa C. Borowske, University of Connecticut
Jonathan B. Cohen, State University of New York College of Environmental Science and Forestry
Chris S. Elphick, University of Connecticut
Christopher R. Field, University of Connecticut
Rebecca A. Kern, University of Delaware, U. S. Fish and Wildlife Service
Erin King, U. S. Fish and Wildlife Service
Alison R. Kocek, State University of New York College of Environmental Science and Forestry
Adrienne I. Kovach, University of New Hampshire
Kathleen M. O’Brien, U. S. Fish and Wildlife Service
Nancy Pau, U. S. Fish and Wildlife Service
W. Gregory Shriver, University of Delaware
Jennifer Walsh, University of New Hampshire
Brian J. Olsen, University of Maine

Document Type

Article

Date of this Version

10-7-2016

Citation

Oecologia (2017) 183:291–301 DOI 10.1007/s00442-016-3745-8

Comments

This document is a U.S. government work and is not subject to copyright in the United States.

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.