Proceedings
4th Microcomputer Applications in 
Fish & Wildlife Conference
October 24-27, 1999
Stateline, Nevada

PVA's for Populations with Movements Constrained by Landscape Pattern: the Case of the Southwestern Willow Flycatcher

Roland H. Lamberson*, Department of Mathematics, Humboldt State University, Arcata, CA

Barry Noon, Dept. of Fishery and Wildlife Biology, Colorado State University, Ft. Collins, CO

To develop a population viability analysis for the southwestern willow flycatcher, we are exploring multiple models, looking for concordance in model output among competing approaches. A common thread linking the different models is an initial focus on habitat - its amount, quality, and spatial distribution. The tight relationship between the distribution of flycatchers and riparian habitat strongly suggests that movement may be constrained to these linear habitat patches. Such patches can be viewed as fixed nodes of a graph with multiple patterns of connectivity reflecting different "allowable" pathways of movement. Varying assumptions about the degree to which riparian habitat constrains movement uniquely defines different metapopulation boundaries. Our results demonstrate how different assumptions about the "correct" patterns of connectivity affect estimates of persistence and optimal reserve design. Finally, we compare inferences from various connectivity models to traditional demographic-based models, and to incidence functions models parameterized by extensive survey data.

Nadav Nur*, Gary Page, William J. Sydeman, and Lynne E. Stenzel, Point Reyes Bird Observatory, Stinson Beach, CA 94970

In recent years, Population Viability Analyses (PVAs) are being relied upon more and more to guide the development of species-specific conservation and wildlife management programs, e.g., by the US Fish & Wildlife Service (USFWS) and by IUCN. Such real-life applications are to be encouraged and yet those who construct and apply such models face a formidable challenge: All population-dynamic models are limited by the accuracy of the demographic parameter values used in the simulations, information that is often incomplete or unavailable. Here we present examples of two bird species, designated as Threatened or potentially threatened, for which we have developed metapopulation-based PVAs. The goal of this paper is to demonstrate how useful results may be obtained from PVAs in the face of uncertainty of parameter values. In the case of the Snowy Plover, a shorebird, whose Pacific coast population is designated as Threatened by the US Dept of Interior, good demographic data were available for most parameters for one or more subpopulations. Here data indicated that dispersal among subpopulations (along the Pacific coast) was relatively high and so results were not sensitive to the precise magnitude of dispersal. Instead, the difficulty is that reproductive success is unknown for most subpopulations and this parameter is likely the key to long-term viability of Pacific coast Snowy Plovers. For the second species, the Ashy Storm-Petrel, a seabird found off the coast of central and southern California, we developed a PVA that considered the entire species and specifically the largest colony (that breeding on the South Farallon Islands). Our objective here was to evaluate the status of the species, currently listed as Near Threatened by IUCN, to determine whether it merited stronger protection by the USFWS and IUCN. Here, results were sensitive to the precise magnitude (and direction) of dispersal among colonies. Despite uncertainty about the likely rate of population decline in the future, it is clear that (1) the population is likely to continue to decline, and (2) considering the small number of individuals for this species (fewer than 7000 breeding individuals) and the localized nature of the breeding colonies, the species should be classified as Threatened according to IUCN guidelines.

H. Resit Akçakaya, Applied Biomathematics, 100 North Country Road, Setauket, NY 11733, Tel: 516-751-4350, resit@ramas.com

Assessing the anthropogenic impact on endangered species often involves predicting the effects of a particular change in the land-use patterns. This is often done by modeling the metapopulation dynamics of the species in the landscape. However, the landscape and, as a result, the spatial structure of the metapopulation often do not remain unchanged, thus the assessment of viability must incorporate the dynamic nature of the landscape. The transitional dynamics of the landscape can be incorporated into assessment of viability and threat by combining methods of landscape prediction with those of metapopulation simulation. The link between the landscape model and metapopulation model can be provided by statistical models of habitat suitability for the species in focus. There are several other issues to consider when linking a landscape model that predicts changes in habitat with a metapopulation model that predicts changes in abundance based on the spatial structure of the habitat. These include the spatial and temporal scales of the two types of models involved, the flow of information between the models, and incorporation of stochasticity.

Virginia Dale*, Linda Mann, and Tom Ashwood, Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6036

Regional population dynamics occur in species that exist as a set of subpopulations distributed across space and time that interact with each other via dispersal and migration. The endangered Karner blue butterfly, Lycaeides melissa samuelis, is distributed patchily in open forests ranging from Vermont to Wisconsin. These patchily distributed and ephemeral habitats suggest that conservation actions for the species need to consider spatial arrangement of the butterfly and its habitat. Regional population models offer a means to organize the spatial and temporal information and to project spatial patterns of the subpopulations. Therefore, a regional population model was developed for the Karner blue butterfly and applied to Fort McCoy, a military installation in west central Wisconsin where the butterfly is locally abundant. Analysis of the model results indicates that improvements are needed in estimates of the population parameters for adult dispersal and for bivoltine survivorship from eggs to larvae in order to more fully understand the effects of dispersal and survivorship on populations of the butterfly. Clearly these parameters are critical aspects of the butterfly’s biology. The model results also identify locations of subpopulations of the butterfly at Fort McCoy that require particular conservation focus. Thus the Karner blue butterfly model illustrates two benefits of using regional population models in efforts to enhance conservation. They can identify parameters for which uncertainties need to be reduced and features of the specific subpopulations that require management attention.

NOTE: * indicates presenter