粪便学在有蹄类动物数量调查研究中的应用与展望

随着与分子生物学的结合,传统的粪便学不仅拓宽了在种群生态学、行为生态学及保护遗传学等研究时取样的范围,而且能提供更多的有效信息,使得传统的粪便计数方法得以在新的领域里发展。本文对传统粪便学在有蹄类动物数量研究中的应用加以总结,并结合国内外研究现状对分子粪便学在这一领域内的可靠性、局限性及应用前景做了概述。     

Indirect effects of domestic and wild herbivores on butterflies in an African savanna

Indirect interactions driven by livestock and wild herbivores are increasingly recognized as important aspects of community dynamics in savannas and rangelands. Large ungulate herbivores can both directly and indirectly impact the reproductive structures of plants, which in turn can affect the pollinators of those plants. We examined how wild herbivores and cattle each indirectly affect the abundance of a common pollinator butterfly taxon, Colotis spp., at a set of long‐term, large herbivore exclosure plots in a semiarid savanna in central Kenya. We also examined effects of herbivore exclusion on the main food plant of Colotis spp., which was also the most common flowering species in our plots: the shrub Cadaba farinosa. The study was conducted in four types of experimental plots: cattle‐only, wildlife‐only, cattle and wildlife (all large herbivores), and no large herbivores. Across all plots, Colotis spp. abundances were positively correlated with both Cadaba flower numbers (adult food resources) and total Cadaba canopy area (larval food resources). Structural equation modeling (SEM) revealed that floral resources drove the abundance of Colotis butterflies. Excluding browsing wildlife increased the abundances of both Cadaba flowers and Colotis butterflies. However, flower numbers and Colotis spp. abundances were greater in plots with cattle herbivory than in plots that excluded all large herbivores. Our results suggest that wild browsing herbivores can suppress pollinator species whereas well‐managed cattle use may benefit important pollinators and the plants that depend on them. This study documents a novel set of ecological interactions that demonstrate how both conservation and livelihood goals can be met in a working landscape with abundant wildlife and livestock.     

Impacts of large mammals on movements of the pouched mouse (Saccostomus mearnsi) in central Kenya

Populations of large wild mammals are declining worldwide, while the abundance of livestock is increasing. The absence of large mammals frequently leads to increases in the abundance of small mammals such as rodents, but little is known about how the loss of large mammals affects the behaviour of small mammals. To investigate this question, we analysed long‐term data collected at the Kenya Long‐term Exclosure Experiment, which excludes different combinations of large mammals from a savannah ecosystem in central Kenya. We investigated the effects of excluding large mammals, both wild and domestic, on the movements of the pouched mouse (Saccostomus mearnsi), the most common species of small mammal in this habitat. Mice moved ~20% more in the presence of wildlife, but their movements were not significantly affected by the presence of cattle. An index of intraspecific contacts between mice was higher at higher mouse densities, and these high densities were more likely when wildlife and cattle were absent. The results suggest that the absence of large mammals led to higher densities of small mammals, which resulted in a greater probability of intraspecific contacts, despite lower average movement distances.     

Long-term data reveal effects of climate,road access,and latitude on mountain goat horn size

Potential negative artificial selection on horn size is a concern for many harvested ungulates. The mountain goat (Oreamnos americanus) has distinct black horns, but targeting animals based on horn size in the field can be challenging. We analyzed over 23,000 horn records that included base circumference and total length, from which we also derived horn volume, from mountain goats harvested in Alaska, British Columbia, and the Northwest Territories from 1980 to 2016. We tested 3 potential drivers of horn size variation: geographical location, environmental conditions, and artificial selection. We found no support for a latitudinal effect with surprisingly little variation across the sampling distribution. The Pacific Decadal Oscillation had the largest effect outside age in the model, suggesting a role of climate in shaping variation. Mountain goats harvested closer to roads had larger horns, indicating that ease of access might allow hunters to be more selective, though the effect size was small. Our findings reinforce the value of accurate and complete record keeping on horn size, age, and sex of harvested animals, and highlight the importance of explicitly considering climate and accessibility when devising management strategies for the mountain goat.     

Vegetation changes associated with a population irruption by Roosevelt elk

Interactions between large herbivores and their food supply are central to the study of population dynamics. We assessed temporal and spatial patterns in meadow plant biomass over a 23‐year period for meadow complexes that were spatially linked to three distinct populations of Roosevelt elk (Cervus elaphus roosevelti) in northwestern California. Our objectives were to determine whether the plant community exhibited a tolerant or resistant response when elk population growth became irruptive. Plant biomass for the three meadow complexes inhabited by the elk populations was measured using Normalized Difference Vegetation Index (NDVI), which was derived from Landsat 5 Thematic Mapper imagery. Elk populations exhibited different patterns of growth through the time series, whereby one population underwent a complete four‐stage irruptive growth pattern while the other two did not. Temporal changes in NDVI for the meadow complex used by the irruptive population suggested a decline in forage biomass during the end of the dry season and a temporal decline in spatial variation of NDVI at the peak of plant biomass in May. Conversely, no such patterns were detected in the meadow complexes inhabited by the nonirruptive populations. Our findings suggest that the meadow complex used by the irruptive elk population may have undergone changes in plant community composition favoring plants that were resistant to elk grazing.     

Barren‐ground caribou (Rangifer tarandus groenlandicus) behaviour after recent fire events; integrating caribou telemetry data with Landsat fire detection techniques

Fire regimes are changing throughout the North American boreal forest in complex ways. Fire is also a major factor governing access to high‐quality forage such as terricholous lichens for barren‐ground caribou (Rangifer tarandus groenlandicus). Additionally, fire alters forest structure which can affect barren‐ground caribou's ability to navigate in a landscape. Here, we characterize how the size and severity of fires are changing across five barren‐ground caribou herd ranges in the Northwest Territories and Nunavut, Canada. Additionally, we demonstrate how time since fire, fire severity, and season result in complex changes in caribou behavioural metrics estimated using telemetry data. Fire disturbances were identified using novel gap‐free Landsat surface reflectance composites from 1985 to 2011 across all herd ranges. Burn severity was estimated using the differenced normalized burn ratio. Annual area burned and burn severity were assessed through time for each herd and related to two behavioural metrics: velocity and relative turning angle. Neither annual area burned nor burn severity displayed any temporal trend within the study period. However, certain herds, such as the Ahiak/Beverly, have more exposure to fire than other herds (i.e. Cape Bathurst had a maximum forested area burned of less than 4 km²). Time since fire and burn severity both significantly affected velocity and relative turning angles. During fall, winter, and spring, fire virtually eliminated foraging‐focused behaviour for all 26 years of analysis while more severe fires resulted in a marked increase in movement‐focused behaviour compared to unburnt patches. Between seasons, caribou used burned areas as early as 1‐year postfire, demonstrating complex, nonlinear reactions to time since fire, fire severity, and season. In all cases, increases in movement‐focused behaviour were detected postfire. We conclude that changes in caribou behaviour immediately postfire are primarily driven by changes in forest structure rather than changes in terricholous lichen availability.     

Resource availability and plant diversity explain patterns of invasion of an exotic grass

Aims In this study, we examine two common invasion biology hypotheses—biotic resistance and fluctuating resource availability—to explain the patterns of invasion of an invasive grass, Microstegium vimineum.Methods We used 13-year-old deer exclosures in Great Smoky Mountains National Park, USA, to examine how chronic disturbance by deer browsing affects available resources, plant diversity, and invasion in an understory plant community. Using two replicate 1 m 2 plots in each deer browsed and unbrowsed area, we recorded each plant species present, the abundance per species, and the fractional percent cover of vegetation by the cover classes: herbaceous, woody, and graminoid. For each sample plot, we also estimated overstory canopy cover, soil moisture, total soil carbon and nitrogen, and soil pH as a measure of abiotic differences between plots.Important findings We found that plant community composition between chronically browsed and unbrowsed plots differed markedly. Plant diversity was 40% lower in browsed than in unbrowsed plots. At our sites, diversity explained 48% and woody plant cover 35% of the variation in M. vimineum abundance. In addition, we found 3.3 times less M. vimineum in the unbrowsed plots due to higher woody plant cover and plant diversity than in the browsed plots. A parsimonious explanation of these results indicate that disturbances such as herbivory may elicit multiple conditions, namely releasing available resources such as open space, light, and decreasing plant diversity, which may facilitate the proliferation of an invasive species. Finally, by testing two different hypotheses, this study addresses more recent calls to incorporate multiple hypotheses into research attempting to explain plant invasion.