Modeling the distribution of the endangered Jemez Mountains salamander (Plethodon neomexicanus) in relation to geology, topography, and climate.

The Jemez Mountains salamander (Plethodon neomexicanus; hereafter JMS) is an endangered salamander restricted to the Jemez Mountains in north-central New Mexico, United States. This strictly terrestrial and lungless species requires moist surface conditions for activities such as mating and foraging. Threats to its current habitat include fire suppression and ensuing severe fires, changes in forest composition, habitat fragmentation, and climate change. Forest composition changes resulting from reduced fire frequency and increased tree density suggest that its current aboveground habitat does not mirror its historically successful habitat regime. However, because of its limited habitat area and underground behavior, we hypothesized that geology and topography might play a significant role in the current distribution of the salamander. We modeled the distribution of the JMS using a machine learning algorithm to assess how geology, topography, and climate variables influence its distribution. The best habitat suitability model indicates that geology type and maximum winter temperature (November to March) were most important in predicting the distribution of the salamander (23.5% and 50.3% permutation importance, respectively). Minimum winter temperature was also an important variable (21.4%), suggesting this also plays a role in salamander habitat. Our habitat suitability map reveals low uncertainty in model predictions, and we found slight discrepancies between the designated critical habitat and the most suitable areas for the JMS. Because geological features are important to its distribution, we recommend that geological and topographical data are considered, both during survey design and in the description of localities of JMS records once detected.

Ancient colonization predicts recent naturalization in Anolis lizards.

The distributions and characteristics of naturalized species may be explained by novel anthropogenous aspects of world biogeography such as the creation of favorable transport environments for propagules on ships. Conversely, the unprecedented connectivity of humans may simply accelerate omnipresent ecological and evolutionary forces, for example, ships may allow species that are generally good dispersers to disperse more quickly. As a null hypothesis, there may be no human component to species naturalization. The first hypothesis predicts that naturalized species will possess unusual characteristics specific to interactions with humans. The latter two hypotheses predict similarity between ancient colonizers and recently naturalized species. In this article, we present a test of the latter hypotheses and show how they may be reconciled with the former. We show that species of Anolis lizard that are ancient solitary colonizers share characteristics of size, shape, scalation, and phylogeny with naturalized species of Anolis. Characteristics of ancient solitary colonizers predict naturalization approximately as well as characteristics of naturalized species themselves. These results suggest the existence of a general colonizing type of Anolis, and that contemporary patterns of naturalization are at least partially explained by abilities that are unrelated to interactions with humans.

Experimental evidence for reduced rodent diversity causing increased hantavirus prevalence.

Emerging and re-emerging infectious diseases have become a major global environmental problem with important public health, economic, and political consequences. The etiologic agents of most emerging infectious diseases are zoonotic, and anthropogenic environmental changes that affect wildlife communities are increasingly implicated in disease emergence and spread. Although increased disease incidence has been correlated with biodiversity loss for several zoonoses, experimental tests in these systems are lacking. We manipulated small-mammal biodiversity by removing non-reservoir species in replicated field plots in Panama, where zoonotic hantaviruses are endemic. Both infection prevalence of hantaviruses in wild reservoir (rodent) populations and reservoir population density increased where small-mammal species diversity was reduced. Regardless of other variables that affect the prevalence of directly transmitted infections in natural communities, high biodiversity is important in reducing transmission of zoonotic pathogens among wildlife hosts. Our results have wide applications in both conservation biology and infectious disease management.

The effect of habitat fragmentation and species diversity loss on hantavirus prevalence in Panama.

Habitat fragmentation and diversity loss due to increased conversion of natural habitats to agricultural uses influence the distribution and abundance of wildlife species and thus may change the ecology of pathogen transmission. We used hantaviruses in Panama as a research model to determine whether anthropogenic environmental change is associated with changes in the dynamics of viral transmission. Specifically, we wanted to determine whether hantavirus infection was correlated with spatial attributes of the landscape at both large and small scales or whether these changes are mediated by changes in community composition. When analyzed at coarse spatial scales, hantavirus reservoirs were more commonly found in disturbed habitats and edge habitats than in forested areas. At local scales, reservoir species dominance was significantly correlated with the slope of the terrain. To evaluate the effect of small-mammal diversity loss on infection dynamics, we implemented an experiment with selective species removal at experimental sites. Seroprevalence of hantavirus was higher in the community of small mammals and increased through time in the experimental sites. The higher seroprevalence in experimental plots suggests that greater diversity likely reduces encounter rates between infected and susceptible hosts. Our studies suggest that habitat loss and fragmentation and species diversity loss are altering hantavirus infection dynamics in Panama. Our work represents a multidisciplinary approach toward disease research that includes biodiversity concerns such as environmental change and degradation, human settlement patterns, and the ecology of host and nonhost species, work that may be especially important in tropical countries.

Modeling hantavirus reservoir species dominance in high seroprevalence areas on the Azuero Peninsula of Panama.

Habitat fragmentation commonly influences distribution of zoonotic disease reservoirs. In Panama, populations of rodent hosts of hantaviruses are favored by small habitat fragments isolated by agricultural lands. We expected a similar relationship between landscape characteristics and host distribution at fine geographical scales in southern Panama. The relative abundance of Zygodontomys brevicauda, the primary host for "Calabazo" virus, and other rodents was assessed at 24 sites within the Azuero Peninsula. We used satellite imagery to produce several spatial variables that described landscape; however, only slope was consistently related to abundances of the two most dominant rodent species. Using regression, we constructed a spatial model of areas of Z. brevicauda dominance, which in turn relates to higher infection rates. The model predicts highest abundances of Z. brevicauda in flat areas, where humans also dominate. These predictions have important ecological and conservation implications that associate diversity loss, topography, and human land use.

GIS-based model of stable hydrogen isotope ratios in North American growing-season precipitation for use in animal movement studies.

Stable hydrogen isotope ratios of precipitation (deltaD(p)) show distinct geographic patterns across North America. Over the last decade, ecologists have utilized growing-season deltaD(p) patterns to study the movements of migratory animals. The accuracy and precision of such studies is, in part, contingent upon the accuracy and precision of growing-season deltaD(p) maps. Previous mapping efforts have employed simple kriging procedures to produce smooth contor maps of growing-season deltaD(p). We attempted to improve these maps by incorporating the effects of altitude on both deltaD(p) values and growing season length. This involved producing elevation-corrected monthly deltaD(p), temperature, and precipitation amount values for 1-km grid cells across the continental United States and Canada using recently developed interpolation procedures. We used a geographic information system (GIS) to calculate a weighted-average growing-season deltaD(p) value for each grid cell using deltaD(p) and precipitation amount values for all months in which the mean temperature was greater than 0 degrees C. We used seven independent data sets to compare the precision of the resulting altitude-corrected map with another that did not account for altitude. Overall, predicted deltaD(p) values from the altitude-corrected map more closely matched observed values, and correspondence was more pronounced at finer spatial scales. Digital versions of the GIS-based maps generated during this effort are available via the Internet at http://biology.unm.edu/wolf/precipitationD.htm. These deltaD(p) layers can be combined with other types of spatial information, such as species' geographic ranges and habitat associations, to further improve our understanding of animal movements.