Using simulation models, based on studies of threatened and endangered species, to assess dispersal through complex habitats
Ecologists and conservation biologists now widely appreciate the potential importance of dispersal for the persistence of species in fragmented landscapes. Based on this knowledge, IWS research ecologists took part in a multiple species study on U.S. Department of Defense (DoD) land at Fort Bragg, North Carolina. The study was part of an effort through the Strategic Environmental Research and Development Program (SERDP) to develop models for predicting habitat use by endangered and at-risk animal populations on DoD lands. Managing military land to protect habitats and promote dispersal between patches is important for meeting legislative requirements, as well as maintaining biological diversity by supporting sensitive species.
The approach of IWS research in Fort Bragg stemmed from the link between small scale movement behaviors and long distance dispersal. We measured movement behaviors through experimentation and direct observation, then used the data to inform computer simulations to predict dispersal routes.
We focused on three wetland species which dispersed through the landscape in very different ways.
Saint Francis satyr (Neonympha mitchelii franscii)
~ Small wetland butterfly that inhabits early-succession wetlands in Fort Bragg.
~ Listed as “endangered” under the Endangered Species Act
~ Persistence depends on adults colonizing newly formed or restored habitats
~ Primary movement through slow undulating flight
~ Adult lifespan and dispersal period ~ 3 days
Ornate chorus frog (Pseudacris ornata)
~ Small frog that breeds in ephemeral ponds, spends summers in surrounding uplands
~ Found throughout Southeast United States
~ Experiencing range-wide decline
~ Must disperse between breeding and upland habitats annually
~ Primary movement on ground
~ Live 1-2 years, dispersal period may be from 1-150 days (only during rainy nights)
~ Simulated dispersal period of 100 days
Eastern tiger salamander (Ambystoma tigrinum tigrinum)
~ Salamander that breeds in ephemeral ponds, spends summers in surrounding uplands
~ Found throughout United States; Ft. Bragg near southern limit of range
State threatened species
~ Must disperse between breeding and upland habitats
~ Primary movement on ground
~ Live 10-20 years, dispersal period unknown
We tested the predictive power of the movement simulations against observed dispersal rates among a subset of sites in which we marked and regularly surveyed for Saint Francis Satyrs. The simulation performed particularly well at predicting places to which the butterflies would disperse.
We also mapped landscape features across the study area using remote-sensing data and ground-based inventories. These empirical data allowed us to parameterize and validate dispersal simulations for each of our target species. The simulation models may then predict the relative importance of dispersal habitat use for each species across the study extent.
Simulating dispersal based on habitat-specific movement behaviors is an effective method for:
~ predicting connectivity and determining landscape features that promote or inhibit dispersal
~ identifying important dispersal corridors linking populations on Ft. Bragg and protected wetlands off base
~ evaluating how changes in the landscape will affect connectivity for rare, threatened, and endangered species
~ locating potential restoration sites
Overall, the patterns of dispersal habitat use are widely divergent across species. Therefore, no single strategy to promote habitat connectivity will be optimal for all species managed on a landscape. Methods are needed to integrate connectivity values over a suite of species.
This project has created new knowledge about habitat connectivity for the target species that can be used by DoD to manage their populations more effectively.
We would like to acknowledge the cooperation of the Ft. Bragg Endangered Species Branch