Responses of two species of heathland rodents to habitat manipulation: Vegetation density thresholds and the habitat accommodation model

The abundance of two native rodent species, Rattus lutreolus and Pseudomys gracilicaudatus, has been shown to correlate with vegetation density in coastal wet heath. Fox's habitat accommodation model relates relative abundances of such small mammal species to heathland vegetation regeneration following disturbance. Implicit in the model is recognition that it is successional changes in vegetation, not time per se, that drives the responses of small mammal species along a regeneration axis. Using a brush‐cutter we deliberately removed approximately 85% of vegetation around trapping stations and recorded significant reductions in the abundance of both P. gracilicaudatus (an earlier‐stage colonizing species) and R. lutreolus (a late seral‐stage species). A significant decrease in the abundance of only the latter had been demonstrated previously when 60–70% of the vegetation had been removed. Following the brush‐cutting both species re‐entered the mammalian secondary succession at different times, first P. gracilicaudatus followed by R. lutreolus after the vegetation cover thresholds of each species had been reached. The impact of this habitat manipulation experiment was to produce a retrogression of the small mammal succession, experimentally demonstrating causality between changes in vegetation density and subsequent small mammal habitat use.     

The geometry of habitat fragmentation: Effects of species distribution patterns on extinction risk due to habitat conversion

Land‐use changes, which cause loss, degradation, and fragmentation of natural habitats, are important anthropogenic drivers of biodiversity change. However, there is an ongoing debate about how fragmentation per se affects biodiversity in a given amount of habitat. Here, we illustrate why it is important to distinguish two different aspects of fragmentation to resolve this debate: (a) geometric fragmentation effects, which exclusively arise from the spatial distributions of species and habitat fragments, and (b) demographic fragmentation effects due to reduced fragment sizes, and/or changes in fragment isolation, edge effects, or species interactions. While most empirical studies are primarily interested in quantifying demographic fragmentation effects, geometric effects are typically invoked as post hoc explanations of biodiversity responses to fragmentation per se. Here, we present an approach to quantify geometric fragmentation effects on species survival and extinction probabilities. We illustrate this approach using spatial simulations where we systematically varied the initial abundances and distribution patterns (i.e., random, aggregated, or regular) of species as well as habitat amount and fragmentation per se. As expected, we found no geometric fragmentation effects when species were randomly distributed. However, when species were aggregated, we found positive effects of fragmentation per se on survival probability for a large range of scenarios. For regular species distributions, we found weakly negative geometric effects. These findings are independent of the ecological mechanisms which generate nonrandom species distributions. Our study helps to reconcile seemingly contradictory results of previous fragmentation studies. Since intraspecific aggregation is a ubiquitous pattern in nature, our findings imply widespread positive geometric fragmentation effects. This expectation is supported by many studies that find positive effects of fragmentation per se on species occurrences and diversity after controlling for habitat amount. We outline how to disentangle geometric and demographic fragmentation effects, which is critical for predicting the response of biodiversity to landscape change.     

基于目标物种栖息地适宜性和景观特征的保护地功能区划研究——以甘肃多儿国家级自然保护区为例

生境的破碎化是导致物种濒危的主要原因之一,功能区划是对保护地进行空间布局和提升保护成效的重要手段。通过对生境进行适宜性评价,进而指导合理区划,是提升保护地功能的重要措施。基于目前保护地功能区划中存在与目标物种适宜栖息地空间格局不一致、与周边联系紧密性不足、边缘效应明显等问题,以甘肃多儿国家级大熊猫(Ailuropoda melanoleuca)自然保护区为例,根据现有保护地区划景观特征,通过扩大研究尺度和开展栖息地适宜性评价,结合适宜栖息地异质性和功能区的景观特征,基于提升适宜栖息地完整性和连接度调整保护区功能区划,并通过比较区划前、后景观特征和栖息地适宜性的变化以及大熊猫的空间利用来评估本研究方法的有效性。研究表明：基于本方法的新区划核心区适宜栖息地增加了16.03%,被保护的优质栖息地增加,核心区内缘比由调整前的5.35和6.32下降至3.97,被保护的优质栖息地增加,边缘效应明显减小,提高了保护区适宜栖息地的完整性,加强了和周边优质栖息地的联系,有助于提升核心区的环境容纳量,增强抵御外来干扰的能力,改善大熊猫的生存状况,促进所在区域的种群交流。     

Effects of temperature and elevation on habitat use by a rare mountain butterfly: implications for species responses to climate change

Abstract 1. The present study used the mountain specialist butterfly Parnassius apollo as a model system to investigate how climate change may alter habitat requirements for species at their warm range margins. 2. Larval habitat use was recorded in six P. apollo populations over a 700 m elevation gradient in the Sierra de Guadarrama (central Spain). Larvae used four potential host species (Sedum spp.) growing in open areas amongst shrubs. 3. Parnassius apollo host‐plant and habitat use changed as elevation increased: the primary host shifted from Sedum amplexicaule to Sedum brevifolium, and larvae selected more open microhabitats (increased bare ground and dead vegetation, reduced vegetation height and shrub cover), suggesting that hotter microhabitats are used in cooler environments. 4. Larval microhabitat selection was significantly related to ambient temperature. At temperatures lower than 27 °C, larvae occupied open microhabitats that were warmer than ambient temperature, versus more shaded microhabitats that were cooler than ambient conditions when temperature was higher than 27 °C. 5. Elevational changes in phenology influenced the temperatures experienced by larvae, and could affect local host‐plant favourability. 6. Habitat heterogeneity appears to play an important role in P. apollo larval thermoregulation, and may become increasingly important in buffering populations of this and other insect species against climatic variation.     

The mid‐domain effect and habitat complexity applied to elevational gradients: Moss species richness in a temperate semihumid monsoon climate mountain of China

The utility of elevational gradients as tools to test either ecological hypotheses and delineate elevation‐associated environmental factors that explain the species diversity patterns is critical for moss species conservation. We examined the elevational patterns of species richness and evaluated the effects of spatial and environmental factors on moss species predicted a priori by alternative hypotheses, including mid‐domain effect (MDE), habitat complexity, energy, and environment proposed to explain the variation of diversity. Last, we assessed the contribution of elevation toward explaining the heterogeneity among sampling sites. We observed the hump‐shaped distribution pattern of species richness along elevational gradient. The MDE and the habitat complexity hypothesis were supported with MDE being the primary driver for richness patterns, whereas little support was found for the energy and the environmental factors.     

Nature protection areas of Europe are insufficient to preserve the threatened beetle Rosalia alpina (Coleoptera: Cerambycidae): evidence from species distribution models and conservation gap analysis

1. Natura 2000 network (N2000) and national protected areas (NPAs) are recognised as the most important core ‘units’ for biological conservation in Europe. 2. Species distribution models (SDMs) were developed to detect the potential distribution of the rare and threatened cerambycid beetle Rosalia alpina L. in Europe, and the amount of suitable habitat within the N2000 network [special areas of conservation (SACs) and special protection areas (SPAs)], NPAs (e.g. national parks, regional parks, state reserves, natural monuments and protected landscapes) and the overall European protected area network (EPAN) (N2000 + NPAs) was quantified. 3. According to this analysis, the suitable habitat for R. alpina in Europe amounts to c. 754 171 km² and stretches across substantially uninterrupted areas from Portugal to Romania (west to east) and from Greece to Germany (south to north). The overlay between the existing system of conservation areas in Europe (N2000 and NPAs) and the binary map for R. alpina showed that only c. 42% of potential habitat is protected. SACs and SPAs protect c. 25% and 21% of potential habitat, respectively. However, because the two site types often spatially overlap, when taken together the entire N2000 network protects c. 31% of potential habitat. Instead, NPAs offer a degree of protection of c. 29%. Overall, almost 60% of the area potentially suitable for the species is unprotected by the EPAN, an aspect that should be considered carefully when planning the conservation of this beetle at a large scale. 4. These results may also help to focus field surveys in selected areas where greater chances of success are encountered to save resources and increase survey effectiveness.     

Likelihood of changes in forest species suitability,distribution, and diversity under future climate: The case of Southern Europe

Forest conservation strategies and plans can be unsuccessful if the new habitat conditions determined by climate change are not considered. Our work aims at investigating the likelihood of future suitability, distribution and diversity for some common European forest species under the projected changes in climate, focusing on Southern Europe. We combine an Ensemble Platform for Species Distribution Models (SDMs) to five Global Circulation Models (GCMs) driven by two Representative Concentration Pathways (RCPs), to produce maps of future climate‐driven habitat suitability for ten categories of forest species and two time horizons. For each forest category and time horizon, ten maps of future distribution (5 GCMs by 2 RCPs) are thus combined in a single suitability map supplied with information about the “likelihood” adopting the IPCC terminology based on consensus among projections. Then, the statistical significance of spatially aggregated changes in forest composition at local and regional level is analyzed. Finally, we discuss the importance, among SDMs, that environmental predictors seem to have in influencing forest distribution. Future impacts of climate change appear to be diversified across forest categories. A strong change in forest regional distribution and local diversity is projected to take place, as some forest categories will find more suitable conditions in previously unsuitable locations, while for other categories the same new conditions will become less suited. A decrease in species diversity is projected in most of the area, with Alpine region showing the potentiality to become a refuge for species migration.     

The roles of landscape context, niche breadth, and range boundaries in predicting species responses to habitat alteration

Extant species in human‐dominated landscapes differ in their sensitivity to habitat loss and fragmentation, although extinctions induced by environmental alteration reduce variation and result in a surviving subset of species with some degree of ‘resistance’. Here, we test the degree to which variable responses to habitat alteration are (1) essentially an inherent property of a taxon subject to constraints imposed by its geographical range, as suggested by Swihart et al. (2003), (2) a function of the landscape in which a species occurs, or (3) a function of spatial trends occurring on large scales. We used data collected on 33 vertebrate species during 2001–04 across the upper Wabash River basin, Indiana, in 35 square ‘landscapes’, each 23 km² in size. Six species of forest rodent, six species of grassland rodents, seven species of bats, eight species of aquatic turtles, and six species of amphibians were sampled at 504, 212, 590, 228, and 625 patches, respectively. The fraction of patches of primary habitat (e.g. forests for tree squirrels, wetlands for aquatic turtles) occupied by a target species was used as a response variable. On a basin‐wide scale, 47% of variation in proportional occupancy among species could be explained by taxon‐specific variables; occupancy rates were related positively to niche breadth and negatively to the proximity of a geographical range boundary. After controlling for species effects, landscape‐level occupancy rates varied significantly for 16 of 33 species, with variation partitioned among landscape variables alone (mean = 11% of variation), spatial trend variables alone (26%), and both variable sets jointly (8%). Among landscape variables, percentage forest cover positively affected occupancy rates of three bat species and a tree squirrel. Variation in occupancy rates among landscapes was consistent with large‐scale spatial trends for 13 species. Our findings demonstrate the general importance of niche breadth as a predictor of species responses to habitat alteration and highlight the importance of viewing the effects of habitat loss and fragmentation at multiple spatial scales.     

Bird richness and composition along an agricultural gradient in New Guinea: The influence of land use,habitat heterogeneity and proximity to intact forest

Abstract We examined variation in bird species richness, abundance and guild composition along an agricultural gradient in New Guinea, and looked for any additive influence of habitat heterogeneity on these variables. The study was based on a grid of survey plots, six plots wide and 24 plots long with the long axis running from a settlement 2.4 km through active and abandoned agricultural plots towards a large area of forest. Each circular survey plot (25 m radius) was assigned to a broad habitat type, ten habitat measures taken, and birds counted for 1 h in each plot. Principal component analysis (PCA) habitat axis 1 described an axis of decreasing forest alteration (larger trees, greater tree densities, fuller canopy) that was positively correlated with distance from the settlement. Bird richness and abundance were highest at intermediate disturbance levels (plots with mid‐range axis 1 scores). Proportions of insectivores and frugivores increased with decreasing forest alteration, while proportions of nectarivores decreased. We calculated three measures of habitat heterogeneity by comparing each plot's PCA score to those of eight neighbouring plots (50–110 m away). These measures reflected how different the plot was to its neighbours, how variable the habitat was around the plot, and the degree to which the plot bordered less disturbed forest. We related these measures to plot bird variable scores independently, and to residuals following regressions of bird scores against PCA scores. Heterogeneity measures had no significant influence on abundance or richness measures, but there were greater proportions of frugivores in plots showing a given degree of habitat alteration if they bordered more pristine habitat. While we readily identified differences in bird communities along the agricultural gradient, the influences of habitat heterogeneity were not striking for birds at this fine scale.     

Utilizing a multifaceted approach to assess the current distribution and conservation status of an uncommon species: the golden mouse (Ochrotomys nuttalli) in Florida

Aim

Our goal was to assess the conservation status of the understudied and naturally uncommon habitat specialist, the golden mouse (Ochrotomys nuttalli), at the edge of its range where its historically fragmented habitat has been subjected to severe loss.

Location

Peninsular Florida, north of approximately 27° latitude, USA.

Methods

We used data gathered from museum collections, regional biologists, geographic information systems (GIS) layers, field surveys and DNA sequencing to determine the habitats that best explain the distribution of the species, examine changes in the geographic extent of both the species and its habitats, and compare genetic differentiation between populations occupying disjunct regions. The results from these multiple analyses were combined to assess the conservation status of the species.

Results

Golden mouse occurrence records align well with the distribution of hardwood habitats in Florida. These habitats occur naturally as ‘islands’, but have become increasingly fragmented by anthropogenic land use. Despite habitat loss, the location of the southern range periphery has remained relatively unchanged in location over the past century. Genetic analysis reveals a history of limited dispersal of females among habitat ‘islands’ that likely predates anthropogenic landscape fragmentation. This pattern suggests that isolated populations that are extirpated will have little to no chance of successful recolonization.

Main conclusions

The combined results from multiple analyses produced a more complete picture of the threats faced by this previously data‐deficient species than any single analysis would have. Although the species' southern range limit cannot be shown to have retracted in the face of human expansion, habitat fragmentation clearly has put the species at increased risk. Conservation and management of hardwood habitats are critical to the persistence of the golden mouse at the edge of its range.