Mark C. Andersen

REGRESSION-TREE MODELING OF DESERT TORTOISE HABITAT IN THE CENTRAL MOJAVE DESERT

This paper describes an interdisciplinary study of the habitat requirements of threatened desert tortoises (Gopherus agassizii) on eight 225-ha study plots in a 14 000 ha study area near the southern boundary of the U.S. Armys National Training Center at Fort Irwin in the central Mojave Desert of southern California. The objective of the study was to produce an empirical, statistical, GIS-based model of desert tortoise habitat use based on a combination of field data and data derived from various spatial databases, including satellite imagery. A total of 11 primary and secondary data layers constitute the spatial database used for this project. Vegetation and tortoise relative density data were obtained from field surveys. Regression-tree methods were used to develop the statistical model. The tree has 11 terminal nodes and a residual mean deviance of 1.985. Out of 73 potential predictors in the model specification, only eight were selected by the algorithm to be used in construction of the tree. The mod...

Potential Applications of Population Viability Analysis to Risk Assessment for Invasive Species

ABSTRACT Population viability analysis, the use of ecological models to assess a populations risk of extinction, plays an important role in contemporary conservation biology. The premise of this review is that models, concepts, and data analyses that yield results on extinction risk of threatened and endangered species can also tell us about establishment risks of potentially invasive species. I briefly review important results for simple unstructured models, demographic models, and spatial models, giving examples of the application of each type of model to invasive species, and general conclusions about the applicability of each type of model to risk analysis for invasive species. The examples illustrate a portion of the range of potential applications of such models to invasive species, and some of the types of predictions that they can provide. They also highlight some of the limitations of such models. Finally, I present several conjectures and open research questions concerning the application of population viability analyses to risk analysis and control of invasive species.

Demographic Models and Reserve Designs for the California Spotted Owl

The California Spotted Owl (Strix occidentalis occidentalis), like the more well-known Northern Spotted Owl (Strix occidentalis caurina), appears to be in decline over at least a part of its geographic range. Two different types of reserve design have been implemented to protect Spotted Owls. The Spotted Owl Habitat Area (SOHA) system uses a fairly large number of small reserves; each SOHA is capable of supporting 1-3 nesting owl pairs. The Habitat Conservation Area (HCA) plan proposes a smaller number of fairly large reserves, each including 10-20 active Spotted Owl nests. The HCA reserve design strategy has been incorporated into current conservation planning for the Northern Spotted Owl. The Technical Assessment Team of the California Spotted Owl Assessment project has recommended preserving existing SOHAs within a lightly harvested matrix as an interim policy for conservation of the California Spotted Owl. In this paper we present results from two demographic models of the California Spotted Owl. The first model is based on a simple formulation of a birth-death process; the second model is a somewhat more detailed simulation model. The models are intended to provide a comparison of the SOHA and HCA reserve-design strategies. We are particularly interested in the ability of the two reserve designs to withstand recurring environmental catastrophes in the form of forest fires. The HCA strategy always leads to longer persistence times than the SOHA strategy. The essential difference between the two strategies appears to lie in the shape of the function that gives the probability of colonization of an empty nest site. These results have several implications for the conservation of California Spotted Owls and for conservation biology in general. (1) Some variant of the HCA reserve design strategy may be preferable to the interim strategy being proposed for conservation of the California Spotted Owl. (2) Simple, parameter-sparse models like ours can yield results comparable to those of more complex and detailed models. (3) Models that include the effects of catastrophic environmental perturbations have great potential for application in conservation biology.

The roles of risk assessment in the control of invasive vertebrates

Vertebrate pest species are an economically and ecologically important subset of the broader environmental problem of invasive alien species. Risk assessment has been shown to be a useful paradigm for identifying and comparing potential solutions to environmental problems in a variety of contexts, including problems associated with invasive species. Here I briefly review the important components of the risk assessment paradigm, and discuss potential applications of risk assessment approaches to several aspects of the control of invasive vertebrate pest species, including import and export controls to prevent establishment, evaluation of control measures for established species, and assessment of the severity of potential non-target impacts of control measures. Risk assessment can contribute to the solution of vertebrate pest problems by connecting science to policy and management decisions, by identifying and alleviating values-based controversies, and by integrating public participation and stakeholder involvement into science-based decision-making.

WINTER SURVIVAL OF NORTHERN PINTAILS IN THE MIDDLE RIO GRANDE VALLEY, NEW MEXICO

Abstract In response to continued low population numbers of Northern Pintail (Anas acuta) in North America and to increase knowledge of the geographic variation in pintail survival rates, we estimated 126-day (27 October–2 March) survival for male and female pintails wintering in the Middle Rio Grande Valley, New Mexico, during 2001–2002 (SY1) and 2002–2003 (SY2). Sixty-nine adult male and female pintails were marked with radio-transmitters and tracked throughout the study period. Weekly relocation data in relation to study year, sex, time (week), body condition at capture, and hunting seasons were modeled using the known-fate procedure in Program MARK. Year, sex, time, and body condition covariates did not improve model performance in estimating survival, so we used the most parsimonious model to produce an overall winter survival estimate of 0.597 ± 0.077 (95% C.I. = 0.442–0.735). Weekly survival estimates did not differ between hunting and nonhunting seasons. Male and female point estimates did not differ (χ12 = 0.209, P = 0.65). Our adult female survival estimate of 0.639 ± 0.117 (95% C.I. = 0.396–0.827) was 5.5%–28.6% lower than published estimates for adult female pintails in 5 other geographic regions. No winter survival estimates for males in other geographic regions were available for direct comparison with our study. Although relatively small sample sizes may have contributed to the lack of statistical differences in weekly survival between years, sexes, and hunting seasons, as well as to the lack of influence of body condition, relatively abundant water and food resources and absence of hunting in a refuge setting contributed to consistent survival probabilities. Because our low survival estimates, relative to other geographic regions, cannot be attributed to hunting, we postulate that natural causes of mortality play a larger role in pintail survival in our study region than in other wintering regions.

HABITAT CHARACTERISTICS OF ASHMUNELLA (GASTROPODA: PULMONATA: POLYGYRIDAE) AT WHITE SANDS MISSILE RANGE AND FORT BLISS, NEW MEXICO

Abstract We studied the habitat characteristics of 7 species of montane land snails in the genus Ashmunella in southern New Mexico from July 1999 to September 2000. We compared 9 numeric variables and 4 categorical variables by species. Geographic differences in microhabitat variables exist among these species; however, these differences tend to be obscured when comparing species, because some species are ecological generalists that occupy a wide range of habitat types. Although this study determined that different populations occupy ecologically distinct habitats in a broad range of environmental conditions, it remains unclear whether these factors influence the morphological characters on which past workers assigned species status. Management plans for the conservation of these species should take careful note of demonstrated habitat differences among and within the species.

Evaluating Biodiversity Metric Response to Forecasted Land Use Change in the Northern Rio Grande Basin

The effects of future land use change on arid and semi-arid watersheds in the American Southwest have important management implications. Seamless, national-scale land-use-change scenarios for developed land were acquired from the US Environmental Protection Agency Integrated Climate and Land Use Scenarios (lCLUS) project and extracted to fit the Northern Rio Grande River Basin, New Mexico relative to projections of housing density for the period from 2000 through 2100. Habitat models developed from the Southwest Regional Gap Analysis Project were invoked to examine changes in wildlife habitat and biodiversity metrics using five ICLUS scenarios. The scenarios represent a US Census base-case and four modifications that were consistent with the different assumptions underlying the A1, A2, B1, and B2 Intergovernmental Panel on Climate Change global greenhouse gas emission storylines. Habitat models for terrestrial vertebrate species were used to derive metrics reflecting ecosystem services or biodiversity aspects valued by humans that could be quantified and mapped. Example metrics included total terrestrial vertebrate species richness, bird species richness, threatened and endangered species, and harvestable species (e.g., waterfowl, big game). Overall, the defined scenarios indicated that the housing density and extent of developed lands will increase throughout the century with a resultant decrease in area for all species richness categories. The A2 Scenario, in general, showed greatest effect on area by species richness category. The integration of the land use scenarios with biodiversity metrics derived from deductive habitat models may prove to be an important tool for decision makers involved in impact assessments and adaptive planning processes.

The Future of the Environmental Movement@@@Environmentalism for a New Millennium: The Challenge of Coevolution

Although closely associated with the 1960s, the environmental movement has a long history in the United States. In this book, Leslie Paul Thiele describes this history, particularly environmentalism as a social movement, tracing it from its beginnings in the mid-1800s to its broad role in the culture today. With a dispassionate eye, the author presents the key stages in environmentalisms development and the concerns which have driven it. The volume touches on issues in philosophy, political science, and sociology, and can serve as a general introduction to the field or as a textbook for courses in environmental ethics, environmental politics, or American social history.