Wildlife Monographs最新文献

The effect of non-native herbivores on ecosystems and diversity has become a global concern in conservation. Management challenges associated with non-native free-roaming equids have existed for decades in a wide range of ecosystems yet have been difficult to resolve. Although much of the challenge is associated with non-biological considerations, empirical ecological research is crucial for guiding sound management decisions. We conducted a field study on the associations between feral burros (Equus asinus) and elements of the Sonoran Desert ecosystem in Arizona, USA, during 2017–2019. We identified areas with and without established burro herds, and collected data on vegetation, ungulate sign, small mammals, birds, and herpetofauna at multiple, randomly selected grids within these areas, while accounting for vegetation community and distance to water. We predicted that burros would be associated with differences in vegetation metrics such as lower ground cover, smaller perennial plant size, and lower plant density, foliage density, recruitment, and species richness among perennial native plants susceptible to burro foraging or trampling. We further predicted that these differences would be accompanied by lower density or relative abundance and lower species richness of small mammals, birds, and herpetofauna. Finally, because burro distribution has been documented to be associated with water in this arid landscape, we predicted that effects would be most pronounced near water. The results of our study did not consistently support our predictions, perhaps because of small sample sizes or, in several cases, inherent complexities associated with seasonal burro habitat use and plant phenology patterns. However, our study documented that the presence of this feral equid is associated with a number of key differences that may be ecologically important and have the potential to alter community structure in this sensitive arid ecosystem. In areas with established burro herds, we documented lower ground cover, plant density, foliage density, or smaller plant size in several species, and changes were often influenced by distance from water. For example, density of Engelmann's prickly pear cactus (Opuntia engelmannii) was 94% lower and Anderson wolfberry (Lycium andersonii) plants were 49% smaller in areas with established burro herds. In areas with burros, we also recorded lower density of white bursage (Ambrosia dumosa) in areas distant from water. Of notable concern was that our metric of recruitment indicated 63% lower recruitment in saguaro cactus (Carnegiea gigantea) and that foliage densities of yellow paloverde (Parkinsonia microphylla) and desert ironwood (Olneya tesota) were lower in areas with established burro herds. Data on some plant species did not support our predictions. For example, white bursage and Anderson wolfberry plants were found at similar densities in areas with and without esta

Although ecological impacts of overabundant white-tailed deer (Odocoileus virginianus) are well documented in eastern North America, few studies have evaluated the long-term effects of adaptive deer population suppression after a period of overabundance. We examined vegetation community changes over a period of 30 years (1992–2021) on the Long Point Peninsula, Ontario, Canada following a >85% reduction of a previously overabundant white-tailed deer population. We documented a significant increase in species diversity and shifts in the species composition of understory plants and woody vegetation. We then evaluated several hypotheses to explain these patterns. Our results provide support for the all-you-can-browse hypothesis, in which the abundance of woody stems above the browse layer did not increase within the first 3 years of sampling but, consistent within an expected period of recruitment, increased by >1,500% from 1995–2021. We also found support for both the lawn maintenance hypothesis, with a significant decline in the proportional abundance of non-preferred species relative to preferred species, and for the seed bank hypothesis, with native species accounting for nearly 80% of new species observed over the sampling period. We conclude that the effective, long-term management and continued suppression of an previously overabundant white-tailed deer population can lead to increased vegetation community heterogeneity and diversity, which is likely one of the most important steps for the regeneration of woody stems and native vegetation communities.

The influence of bottom-up food resources and top-down mortality risk underlies the demographic trajectory of wildlife populations. For species of conservation concern, understanding the factors driving population dynamics is crucial to effective management and, ultimately, conservation. In southeastern British Columbia, Canada, populations of the mostly omnivorous grizzly bear (Ursus arctos) are fragmented into a mosaic of small isolated or larger partially connected sub-populations. They obtain most of their energy from vegetative resources that are also influenced by human activities. Roads and associated motorized human access shape availability of food resources but also displace bears and facilitate human-caused mortality. Effective grizzly bear management requires an understanding of the relationship between habitat quality and mortality risk. We integrated analyses of bottom-up and top-down demographic parameters to understand and inform a comprehensive and efficient management paradigm across the region. Black huckleberry (Vaccinium membranaceum) is the key high-energy food for grizzly bears in much of southeastern British Columbia. Little is known about where and why huckleberries grow into patches that are useful for grizzly bears (i.e., densely clustered fruiting shrubs that provide efficient access to high energy food) and how forage supply and mortality risk influence population vital rates. By following 43 grizzly bears tracked with global positioning system (GPS) collars (57 bear years) in a 14,236-km² focal area spanning the Selkirk and Purcell mountain ranges, we developed a model to identify huckleberry patches from grizzly bear use data. Over 2 years we visited 512 sites used by bears, identifying more than 300 huckleberry patches. We used boosted regression tree modeling associating geophysical, ecological, soil, climate, and topographical variables with huckleberry patches. We integrated this modeled food layer depicting an important pre-hibernation resource, into broader bottom-up and top-down analyses. In addition to berries, we examined bottom-up variables indexing vegetative productivity that were previously found to be predictive of bear use (e.g., alpine, canopy cover, greenness, riparian). We also examined top-down variables including road presence, road density, distance-to-road, secure habitat (defined as 500 m away from a road open to vehicular access), highways, human development, and terrain ruggedness. We evaluated the relationship of these variables to female habitat selection, fitness, and population density, testing the predictability and interrelatedness of covariates relative to bottom-up and top-down influences. We estimated resource selection functions with 20,293 GPS telemetry locations collected over 10 years from 20 female grizzly bears. We modeled fitness using logistic regression of spatially explicit reproductive data derived from genetically identified family pedigrees c

Vegetation treatments have been widely implemented in efforts to enhance conditions for wildlife populations. Yet the effectiveness of such efforts often lack rigorous evaluations to determine whether these practices are effective for targeted species. This is particularly important when manipulating wildlife habitats in ecosystems that are faced with multiple stressors. The sagebrush (Artemisia spp.) ecosystem has been altered extensively over the last century leading to declines of many associated species. Wyoming big sagebrush (A. tridentata wyomingensis) is the most widely distributed subspecies, providing important habitats for sagebrush-obligate and associated wildlife. Sagebrush often has been treated with chemicals, mechanical treatments, and prescribed burning to increase herbaceous forage species released from competition with sagebrush overstory. Despite many studies documenting negative effects of sagebrush control on greater sage-grouse (Centrocercus urophasianus) habitat, treatments are still proposed as a means of improving habitat for sage-grouse and other sagebrush-dependent species. Furthermore, most studies have focused on vegetation response and none have rigorously evaluated the direct influence of these treatments on sage-grouse. We initiated a 9-year (2011–2019) experimental study in central Wyoming, USA, to better understand how greater sage-grouse respond to sagebrush reduction treatments in Wyoming big sagebrush communities. We evaluated the influence of 2 common sagebrush treatments on greater sage-grouse demography and resource selection. We implemented mowing and tebuthiuron application in winter and spring 2014 and evaluated the pre- (2011–2013) and post-treatment (2014–2019) responses of sage-grouse relative to these management actions. We evaluated responses to treatments using demographic and behavioral data collected from 620 radio-marked female greater sage-grouse. Our specific objectives were to evaluate how treatments influenced 1) sage-grouse reproductive success and female survival; 2) sage-grouse nesting, brood-rearing, and female resource selection; 3) vegetation responses; and 4) forbs and invertebrates. Our results generally suggested neutral demographic responses and slight avoidance by greater sage-grouse in response to Wyoming big sagebrush treated by mowing and tebuthiuron. Neither mowing nor tebuthiuron treatments influenced nest survival, brood survival, or female survival. Selection for nest and brood-rearing sites did not differ before and after treatments. Females selected habitats near treatments before and after they were implemented; however, the strength of selection was lower after treatments compared with pre-treatment periods, which may be explained by a lack of response in vegetation and invertebrates following treatments. Perennial grass cover and height varied temporally yet did not vary systematically between treatment and control plots. Forb cover and species

Species conservation requires an understanding of the factors and interactions affecting species distribution and behavior, habitat availability and use, and corresponding vital rates at multiple temporal and spatial scales. Opportunities to investigate these relationships across broad geographic regions are rare. We combined long-term waterfowl population surveys, and studies of habitat use and breeding success, to develop models that identify and incorporate these interactions for upland-nesting waterfowl in the Prairie Pothole Region (PPR) of Canada. Specifically, we used data from the annual Waterfowl Breeding Population and Habitat Survey (1961–2009) at the survey segment level and associated habitat covariates to model and map the long-term average duck density across the Canadian PPR. We analyzed nest location and fate data from approximately 25,000 duck nests found during 3 multi-year nesting studies (1994–2011) to model factors associated with nest survival and habitat selection through the nesting season for the 5 most common upland nesting duck species: mallard (Anas platyrhynchos), gadwall (Mareca strepera), blue-winged teal (Spatula discors), northern shoveler (Spatula clypeata), and northern pintail (Anas acuta). Duck density was highly variable across the Canadian PPR, reflecting positive responses to local wetland area and count, and amounts of cropland and grassland, a regional positive response to latitude, and a negative response to local amounts of tree cover. Nest survival was affected by temporal and spatial variables at multiple scales. Specifically, nest survival demonstrated interactive effects among species, nest initiation date, and nesting cover type and was influenced by relative annual wetness, population density, and surrounding landscape composition at landscape scales, and broad geographic gradients (east-west and north-south). Likewise, species-specific probability of nest habitat selection was influenced by timing of nest initiation, population density, relative annual wetness, herbaceous cover, and tree cover in the surrounding landscape, and location within the Canadian PPR. We combined these models, with estimates of breeding effort (nesting, renesting, and nest attempts) from existing literature, in a stochastic conservation planning model that estimates nest distribution and success given spatiotemporal variation in duck density, habitat availability, and influential covariates. We demonstrate the use of this model by examining various conservation planning scenarios. These models allow estimation of local, landscape, and regional influence of conservation investments and other landscape changes on the productivity of breeding duck populations across the PPR of Canada. These models lay the groundwork for the incorporation of conservation delivery costs for full return-on-investment analyses and scenario analyses of climate, habitat, and land use change in regional and c