Ecological Modelling 220 (2009) 867–878 Contents lists available at ScienceDirect Ecological Modelling journal homepage: www.elsevier.com/locate/ecolmodel Simulating population variation and movement within fragmented landscapes: An application to the gopher tortoise (Gopherus polyphemus) Todd BenDor a,∗ , James Westervelt b , J.P. Aurambout c , William Meyer b a Department of City and Regional Planning, University of North Carolina at Chapel-Hill, Chapel Hill, NC 27599, USA b U.S. Army Engineer Research and Development Center, Construction Engineering Research Laboratory (CERL), Champaign, IL 61826, USA c Australian Department of Primary Industries, Parkville, Victoria 3554, Australia article info Article history: Received 27 February 2008 Received in revised form 17 December 2008 Accepted 5 January 2009 Keywords: Habitat fragmentation Spatial dynamic model Gopher tortoise (Gopherus polyphemus) Conservation biology Landscape ecology Land-use change abstract As the human activity footprint grows, land-use decisions play an increasing role in determining the future of plant and animal species. Studies have shown that urban and agricultural development cannot only harm species populations directly through habitat destruction, but also by destroying the corridors that connect habitat patches and populations within a metapopulation. Without these pathways, populations can encounter inbreeding depression and degeneration, which can increase death rates and lower rates of reproduction. This article describes the development and application of the FRAGGLE model, a spatial system dynamics model designed to calculate connectivity indices among populations. FRAGGLE can help planners and managers identify the relative contribution of populations associated with habitat patches to future populations in those patches, taking into account the importance of interstitial land to migration success. The model is applied to the gopher tortoise (Gopherus polyphemus), a threatened species whose southeastern U.S. distribution has diminished significantly within its native range due to agricultural and urban development over the last several decades. This model is parameterized with life history and movement traits of the gopher tortoise in order to simulate population demographics and spatial distribution within an area in west-central Georgia that supports a significant tortoise population. The implications of this simulation modeling effort are demonstrated using simple landscape representations and a hypothetical on land-use management scenario. Our findings show that development resulting in even limited habitat losses (10%) may lead to significant increases in fragmentation as measured by a loss in the rate of dispersions (31%) among area subpopulations. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Habitat loss and associated habitat fragmentation is a growing problem worldwide and is considered to be one of the greatest threats to biodiversity as well as a primary cause of the current high rate of species extinction (Wu et al., 2003). Habitat fragmen- tation is defined as the process through which a natural habitat becomes divided into isolated small patches of complex geometri- cal form, within a sea of generally inhospitable land uses (Bunnell, 1999; McComb, 1999). Fragmentation negatively affects many species, since smaller habitat patches support disproportionately smaller populations that are more prone to local extinction than larger ones (Hanski, 1997; McComb, 1999; Berec, 2002). By increasing patch isola- ∗ Corresponding author. Department of City and Regional Planning, CB# 3140, UNC-Chapel Hill, New East Building, Chapel Hill, NC 27599-3140, USA. Tel.: +1 919 962 4760; fax: +1 919 962 5206. E-mail address: bendor@unc.edu (T. BenDor). tion, fragmentation effectively decreases the gene pool of local populations, thereby favoring inbreeding depression and making the population more prone to demographic stochasticity (Berec, 2002). It also modifies the quality of the remaining habitat by increasing edges and reducing core habitat, which can further increase biodiversity loss among core-dwelling species. FRAGGLE is designed to generate connectivity indices among populations within a metapopulation to help understand the relative mixing of the populations. However, the consequences of fragmentation depend on the par- ticular species considered, and both positive and negative effects have been reported (Kremsater and Bunnell, 1999). Fragmenta- tion tends to negatively impact species that prefer interior habitat, while benefiting edge-adapted species (Fahrig, 1999; With, 1999). The extent to which fragmentation impedes movements within a metapopulation (set of local populations connected by migrating individuals) has also been linked to the vagility and life history characteristics of each species (McComb, 1999). Although fragmen- tation is strongly connected to habitat loss, in this article we focus on the connectivity issues that result from fragmentation. 0304-3800/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.ecolmodel.2009.01.005