Seth B. Magle

A comparison of metrics predicting landscape connectivity for a highly interactive species along an urban gradient in Colorado, USA

Many organisms persist in fragmented habitat where movement between patches is essential for long-term demographic and genetic stability. In the absence of direct observation of movement, connectivity or isolation metrics are useful to characterize potential patch-level connectivity. However, multiple metrics exist at varying levels of complexity, and empirical data on species distribution are rarely used to compare performance of metrics. We compared 12 connectivity metrics of varying degrees of complexity to determine which metric best predicts the distribution of prairie dog colonies along an urban gradient of 385 isolated habitat patches in Denver, Colorado, USA. We found that a modified version of the incidence function model including area-weighting of patches and a cost-weighted distance surface best predicted occupancy, where we assumed roads were fairly impermeable to movement, and low-lying drainages provided dispersal corridors. We also found this result to be robust to a range of cost weight parameters. Our results suggest that metrics should incorporate both patch area and the composition of the surrounding matrix. These results provide guidance for improved landscape habitat modeling in fragmented landscapes and can help identify target habitat for conservation and management of prairie dogs in urban systems.

BEHAVIORAL RESPONSES TO REPEATED HUMAN INTRUSION BY BLACK-TAILED PRAIRIE DOGS (CYNOMYS LUDOVICIANUS)

Abstract This study addressed behavioral responses by black-tailed prairie dogs (Cynomys ludovicianus) to human intrusion in urban and rural environments in Boulder, Colorado. We expected that if prairie dogs habituate to repeated disturbances, they should allow a recurring human intruder to approach closer over time before sounding an alarm bark or initiating concealment. We also predicted that urban colonies could be approached more closely than rural colonies before displaying an avoidance response. Four colonies (2 rural and 2 urban) were approached >100 times over a 7-month period. Rather than exhibiting habituation, prairie dogs demonstrated increased responsiveness in concealment behavior, retreating to their burrows earlier, with recurring disturbances. Barking distances did not change consistently with repeated intrusion, but, over time, prairie dogs barked less frequently when performing their avoidance response, a result with implications for prairie dog management. Rural colonies had higher initial concealment distances, and these distances increased more rapidly with repeated intrusion than did concealment distances in urban colonies. Thus, rural prairie dogs may be more sensitive to human intrusion than urban prairie dogs.

Mark-Resight methodology for estimating population densities for prairie dogs

Abstract Accurate assessments of local population size of the black-tailed prairie dog (Cynomys ludovicianus) are essential because of their overall decline and importance to prairie ecosystems. We describe the use of mark–resight methodology to estimate black-tailed prairie dog population size and density. Study colonies include isolated urban habitat fragments in Denver, Colorado, USA, and unfragmented control colonies in the Pawnee National Grassland, USA. We compare results from various mark–resight estimators to those derived from linear transformations of visual counts of active prairie dogs. Our results suggest that mark–resight methods are feasible in both urban and rural systems, and reveal extremely high densities for isolated prairie dogs in urban sites. Our methodology can be used to obtain reliable, unbiased estimates of local population size and density.

Population genetic structure of black-tailed prairie dogs, a highly interactive species, in fragmented urban habitat

Abstract Fragmentation of wildlife populations can have detrimental effects, including genetic differentiation of populations, loss of genetic diversity, and inbreeding depression. We evaluated the genetic structure among isolated colonies of black-tailed prairie dogs (Cynomys ludovicianus) along an urban gradient in southern Denver, Colorado. Urban colonies are important ecologically and for educational purposes, and they serve as source populations for relocation efforts. Levels of genetic differentiation between colonies were high relative to colonies in natural habitat at comparable or greater distances. Prairie dog colonies depend on dispersal among colonies for long-term persistence, and we found evidence for reduced but measurable rates of movement of individual prairie dogs among urban fragments. We observed a trend for smaller and more isolated colonies to exhibit lower genetic diversity, but we did not detect inbreeding in any of the colonies sampled. Isolation-by-distance measures, including measures based on permeability of various features of urban habitat such as roads and development, did not explain genetic differences. Our system represents a possible end point in the genetic consequences of continued loss and isolation of prairie dog colonies as fragmentation increases in both urban and natural landscapes. Urban development could affect dispersal in unexpected and complex ways and requires further study, but prairie dog colonies and their associated wildlife communities in urban areas have the potential for long-term persistence if not extirpated by human activity.

Evaluating spatial overlap and relatedness of white-tailed deer in a chronic wasting disease management zone.

Wildlife disease transmission, at a local scale, can occur from interactions between infected and susceptible conspecifics or from a contaminated environment. Thus, the degree of spatial overlap and rate of contact among deer is likely to impact both direct and indirect transmission of infectious diseases such chronic wasting disease (CWD) or bovine tuberculosis. We identified a strong relationship between degree of spatial overlap (volume of intersection) and genetic relatedness for female white-tailed deer in Wisconsin’s area of highest CWD prevalence. We used volume of intersection as a surrogate for contact rates between deer and concluded that related deer are more likely to have contact, which may drive disease transmission dynamics. In addition, we found that age of deer influences overlap, with fawns exhibiting the highest degree of overlap with other deer. Our results further support the finding that female social groups have higher contact among related deer which can result in transmission of infectious diseases. We suggest that control of large social groups comprised of closely related deer may be an effective strategy in slowing the transmission of infectious pathogens, and CWD in particular.

Effects of urbanization on the behaviour of a keystone species

Habitat fragmentation and urbanization not only cause extirpation of species, but also alter the behaviour of species in human modified areas. We evaluated behavioural characteristics of the black-tailed prairie dog (Cynomys ludovicianus), a keystone species, in the urban landscape of Denver, CO, USA. Specifically, we investigated the proportion of vigilance, foraging, and social behaviour within a system of urban colonies that varied in area, degree of connectivity, and time since isolation. Overall, rates of vigilance were lower than are typically reported for black-tailed prairie dogs in grassland habitats. Colonies that were more isolated exhibited higher levels of vigilance, but colonies isolated for a longer period of time exhibited reduced vigilance. Thus, while urban stimuli may increase alertness in the most isolated colonies, we suggest that black-tailed prairie dogs might eventually adjust to these stimuli and relax their vigilance responses. Because behaviour varies based on age of fragments, we provide evidence that black-tailed prairie dog populations are responding to urbanization through behavioural changes that may be adaptive. The ability to understand how landscape-level factors influence black-tailed prairie dog behaviour provides important information about the response of keystone species to urban settings and can aid conservation and management efforts in fragmented systems.

Tree cavity availability across forest, park, and residential habitats in a highly urban area

Tree cavities are used by a wide variety of species for nesting, food storage, and cover. Most studies on cavity availability have been conducted in forests, and little is known about urban areas. With urbanization, species that excavate cavities may be less abundant, natural tree-decay processes are managed, and tree densities are reduced, all of which may influence tree-cavity availability. We investigated three questions: 1) What is the prevalence of tree cavities in different habitats in the Chicago area? 2) How do the characteristics of natural and woodpecker-excavated cavities and cavity-trees differ across habitats? 3) How does the urban landscape influence the prevalence of tree cavities? We tested the capacity for large urban parks and residential areas to provide tree cavities at levels similar to forested areas. We surveyed 1,545 trees in these three habitats for excavated and natural (caused by decay) cavities. Cavities were most available in forests, where the density of trees was highest. We found that a similar proportion of trees in forests and parks had excavated cavities, but excavated cavities were rare in residential areas. Trees containing cavities were larger than control trees and had more decay, and excavated cavities were in larger trees with more decay than natural cavity trees. Canopy cover was the main landscape variable influencing excavated cavity availability. Our results suggest that the prevalence of tree cavities may not be a limiting factor for urban wildlife, however that is contingent on the levels of use of natural cavities, which is currently unknown.

Mammal diversity and metacommunity dynamics in urban green spaces: implications for urban wildlife conservation

As urban growth expands and natural environments fragment, it is essential to understand the ecological roles fulfilled by urban green spaces. To evaluate how urban green spaces function as wildlife habitat, we estimated mammal diversity and metacommunity dynamics in city parks, cemeteries, golf courses, and natural areas throughout the greater Chicago, Illinois, USA region. We found similar α-diversity (with the exception of city parks), but remarkably dissimilar communities in different urban green spaces. Additionally, the type of urban green space greatly influenced species colonization and persistence rates. For example, coyotes (Canis latrans) had the highest, but white-tailed deer (Odocoileus virginianus) the lowest probability of persistence in golf courses compared to other green space types. Further, most species had a difficult time colonizing city parks even when sites were seemingly available. Our results indicate that urban green spaces contribute different, but collectively important, habitats for maintaining and conserving biodiversity in cities.

Habitat Dynamics of the Virginia Opossum in a Highly Urban Landscape

Abstract As urban habitats vary in composition and structure along the urban to rural gradient, different degrees of urbanization likely result in a diversity of landscape responses from wildlife. We investigated this relationship with the Virginia opossum (Didelphis virginiana), an urban adapted species that is both common and understudied in highly metropolitan landscapes. We investigated which landscape factors affect opossum occupancy, colonization, extinction, and detection by using a large system of motion-triggered camera traps in the Chicago metropolitan area over 10 seasons from spring 2010 to summer 2012. Opossum patch occupancy rates were highest near natural water sources regardless of urbanization, whereas occupancy rates in patches ≥1000 m from natural water sources decreased with increasing urbanization. Our results suggest opossums have relaxed habitat needs at intermediate levels of disturbance, as the ability to locate anthropogenic water sources may allow them to occupy previously uninhabitable patches.

Invasive European Buckthorn (Rhamnus cathartica L.) Association with Mammalian Species Distribution in Natural Areas of the Chicagoland Region, USA

ABSTRACT: Common buckthorn (Rhamnus cathartica L.) is an invasive Eurasian shrub that has successfully invaded many of the woodlands of the northeastern United States. While the ecology and invasive properties of this species are well documented, little research has focused on buckthorns effects on wildlife species. In this study, we surveyed 35 forest preserves and natural areas in the Chicago metropolitan region for the presence of buckthorn. Motion-triggered infrared cameras were used to detect mammal species in sites with and without buckthorn. Cameras were active for an average of four weeks for seven seasons during 2010 and 2011. White-tailed deer (Odocoileus virginianus Zimm.) were more likely to be present in sites without buckthorn, while coyotes (Canis latrans Say) and Virginia opossums (Didelphis virginiana Kerr) were more likely to be present in sites invaded with buckthorn. While there was no overall significant difference in raccoon (Procyon lotor L.) presence between the two site types, raccoons were more likely to be present in invaded sites during the spring season, a trend that was also observed for other mesocarnivores. Our results strongly suggest that the presence of invasive buckthorn impacts habitat use and the presence of wildlife species.