苜蓿草地生境丧失与破碎化对昆虫物种丧失与群落重建的影响

生境破碎化包括生境丧失与破碎化两个相对独立的过程,为探讨这两个过程各自对生物多样性的影响,本文利用苜蓿草地实验模型系统(EMS)构建了36个小区研究不同生境丧失与破碎化对昆虫群落及不同类群的影响,包括18个破碎化小区与18个连续小区,破碎化小区全部采用1 m×1 m(H=1)破碎,连续小区苜蓿连片(H=0),生境丧失采...     

Modelling the effect of habitat fragmentation on range expansion in a butterfly

There is an increasing need for conservation programmes to make quantitative predictions of biodiversity responses to changed environments. Such predictions will be particularly important to promote species recovery in fragmented landscapes, and to understand and facilitate distribution responses to climate change. Here, we model expansion rates of a test species (a rare butterfly, Hesperia comma) in five landscapes over 18 years (generations), using a metapopulation model (the incidence function model). Expansion rates increased with the area, quality and proximity of habitat patches available for colonization, with predicted expansion rates closely matching observed rates in test landscapes. Habitat fragmentation constrained expansion, but in a predictable way, suggesting that it will prove feasible both to understand variation in expansion rates and to develop conservation programmes to increase rates of range expansion in such species.     

Empirical methodology for predicting changes in species range extension and richness associated with climate warming

Species richness and extent of geographical range for North American freshwater amphipods and crayfish are strongly correlated with mean annual absolute, or range of, temperature, respectively. Such spatially based relationships are shown to be useful for predicting the biological consequences arising through scenarios of temporal climate warming.     

Experimental simulations about the effects of overexploitation and habitat fragmentation on populations facing environmental warming

Populations of many species are dramatically declining worldwide, but the causal mechanism remains debated among different human-related threats. Coping with this uncertainty is critical to several issues about the conservation and future of biodiversity, but remains challenging due to difficulties associated with the experimental manipulation and/or isolation of the effects of such threats under field conditions. Using controlled microcosm populations, we quantified the individual and combined effects of environmental warming, overexploitation and habitat fragmentation on population persistence. Individually, each of these threats produced similar and significant population declines, which were accelerated to different degrees depending upon particular interactions. The interaction between habitat fragmentation and harvesting generated an additive decline in population size. However, both of these threats reduced population resistance causing synergistic declines in populations also facing environmental warming. Declines in population size were up to 50 times faster when all threats acted together. These results indicate that species may be facing risks of extinction higher than those anticipated from single threat analyses and suggest that all threats should be mitigated simultaneously, if current biodiversity declines are to be reversed.     

The genetic signature of rapid range expansion by flying squirrels in response to contemporary climate warming

Climate is an important factor limiting species distributions. Historic climate‐change related range movements have modified the genetic diversity of species by the merging and splitting of gene pools and by the effects associated with recurrent founder events. These effects are often inferred, either from retrospective analyses of current genetic patterns or from simulations. Rarely has it been possible for the population genetic effects of range expansion to be examined with contemporaneous demographic data. We characterized the genetic signature of rapid range expansion by southern flying squirrels (Glaucomys volans) and compared these results to a stationary population of the closely related northern flying squirrel (Glaucomys sabrinus) in Ontario, Canada. Samples were taken during an approximately 200 km range expansion by G. volans (1994–2003) and genotyped at 6 (G. sabrinus) and 8 (G. volans) microsatellite loci. For G. volans, but not G. sabrinus, we found evidence of a latitudinal gradient in allele frequencies and a decrease in allelic richness along the axis of expansion. We found no evidence of isolation‐by‐distance in either species or of genetic bottlenecks in the area of G. volans expansion. These results suggest that serial founder events can cause an immediate reduction in genetic diversity following rapid range expansion with high levels of gene flow giving rise to heterogeneity within what would classically be termed panmixia. Given the pace of anthropogenic climate change, and the increasing incidence of range movements in response, this may be an important, immediate consequence of climate change.     

Potential consequences of climate warming for tropical plant species in high mountains of southern Ethiopia

Aim Species in the tropics respond to global warming by altitudinal distribution shifts. Consequences for biodiversity may be severe, resulting in lowland attrition, range‐shift gaps, range contractions and extinction risks. We aim to identify plant groups (growth forms, families, endemic status) with higher than average risks. Location South Ethiopian highlands. Methods Based on observational data from mainly unexplored and remote mountain regions, we applied a published model to project the consequences of an upward shift of thermal site conditions on the altitudinal distribution of 475 plant species. Annual average temperature increases of up to 5 °C were evaluated. Differences between groups of species were analysed by a permutation procedure and Generalized Linear Models. Results Because of a limited regional species pool, even mild warming is projected to create strong potential risks concerning lowland attrition, i.e. the net loss of species richness because of upward range shifts in the absence of new species arriving. Likewise, many species are expected to face range‐shift gaps, i.e. the absence of an overlap between future and current altitudinal ranges already under mild warming scenarios. Altitudinal contractions and mountain‐top extinctions will potentially become important when warming exceeds 3.5 °C. Mean area per species is projected to decline by 55% for the A2 emissions scenario (+4.2 °C until 2100) because of the physical shape of the mountains. Higher than average vulnerability is expected for endemic species as well as for herbs and ferns. Plant families that are especially threatened are identified. Main conclusions Lowland biotic attrition and range‐shift gaps as predicted by a simple model driven by shifts of isotherms will result in novel challenges for preserving mountain biodiversity in the inner tropics. Whereas contractions of occupied area are expected to threaten endemic and already endangered species in particular, we suggest that conservation priorities can be identified based on simple prognostic models even without precise regional warming scenarios.     

Deforestation and apparent extinctions of endemic forest beetles in Madagascar

Madagascar has lost about half of its forest cover since 1953 with much regional variation, for instance most of the coastal lowland forests have been cleared. We sampled the endemic forest-dwelling Helictopleurini dung beetles across Madagascar during 2002-2006. Our samples include 29 of the 51 previously known species for which locality information is available. The most significant factor explaining apparent extinctions (species not collected by us) is forest loss within the historical range of the focal species, suggesting that deforestation has already caused the extinction, or effective extinction, of a large number of insect species with small geographical ranges, typical for many endemic taxa in Madagascar. Currently, roughly 10% of the original forest cover remains. Species-area considerations suggest that this will allow roughly half of the species to persist. Our results are consistent with this prediction.     

Expanding northward: influence of climate change,forest connectivity,and population processes on a threatened species' range shift

Species' ranges are dynamic, shifting in response to a large number of interrelated ecological and anthropogenic processes. Climate change is thought to be one of the most influential drivers of range shifts, but the effects of other confounded ecological processes are often ignored even though these processes may modify expected range responses to climate change. To determine the relative effects of climate, forest availability, connectivity, and biotic processes such as immigration and establishment, we examine range changes occurring in a species of bird, the Hooded Warbler (Wilsonia citrina). We focus predominantly on the periphery of the species' northern range in Canada but we also examine data from the entire species' range. Nesting records in southern Ontario were obtained from two breeding bird Atlases of Ontario separated by a period of 20 years (1981–1985 and 2001–2005), and the rate of range expansion was estimated by comparing the number of occupied areas in each Atlas. Twelve hypotheses of the relationship between the rate of range expansion and factors known to influence range change were examined using model‐selection techniques and a mixed modeling approach (zero‐inflated Poisson's regression). Cooler temperatures were positively related to a lack of range expansion indicating that climate constrained the species' distribution. Establishment probability (based on the number of occupied, neighboring Atlas squares) and immigration from populations to the south (estimated using independent data from the North American Breeding Bird Survey) were also important predictors of range expansion. These biotic process variables can mask the effects of forest availability and connectivity on range expansion. Expansion due to climate change may be slower in fragmented systems, but the rate of expansion will be influenced largely by biotic processes such as proximity to neighboring populations.     

Impacts of landscape structure on butterfly range expansion

Since the 1940s, the distributions of several butterfly species have been expanding in northern Europe, probably in response to climate warming. We focus on the speckled wood butterfly Pararge aegeria in order to determine impacts of habitat availability on expansion rates. We analyse observed expansion rates since 1940 and also use a spatially explicit mechanistic model (MIGRATE) to simulate range expansion in two areas of the UK which differ in their distribution of breeding habitat (woodland). Observed and simulated expansion rates were in very close agreement but were 42%–45% slower in an area that had 24% less woodland. Unlike P. aegeria, the majority of butterfly species are not currently expanding, almost certainly because of lack of suitable habitat. Incorporating the spatial distribution of habitat into investigations of range changes is likely to be important in determining those species that can and cannot expand, and for predicting potential future range changes.     

Home range and habitat use by Geoffroy's cat (Oncifelis geoffroyi) in a wet grassland in Argentina

Geoffroy's cat Oncifelis geoffroyi is a little-known South American small felid. We report data on the spatial ecology of four adults (two males and two females) that were radiotracked in an area of wet grassland of the Argentine Pampas from February 2000 to April 2001. The mean home range size varied from 248 ha [90% minimum convex polygon (MCP)] to 342 ha (100% MCP), with male home ranges c . 2.5 larger than those of females. Home range overlap averaged 44.7%, and was more extensive between males than between females but it decreased markedly when outliers were excluded. Forest patches were used more than expected by their availability within home ranges. These patches hosted many large defecation sites, possibly acting as 'communication centres' where information was exchanged among individuals in the form of scent marks. Despite the lack of a clear preference for tall grasslands, this was the most frequently used habitat. We argue that natural grasslands in the Pampas ecoregion are important for O. geoffroyi and that their alteration can affect the conservation status of this cat. The comparison of our data with those reported previously suggests that Geoffroy's cat can show a certain degree of flexibility in its spatial behaviour.     

Breeding behaviour, home range and habitat selection in Rock Firefinches Lagonosticta sanguinodorsalis in the wet and dry season in central Nigeria

Knowledge of a species’ movement behaviour and habitat choice is a prerequisite for assessing its ecological requirements to plan successful conservation strategies. Little is known about these factors in the Rock Firefinch, a recently described species which is probably endemic to the Jos Plateau in central Nigeria. We investigated home range size, habitat use and breeding behaviour of the Rock Firefinch in Amurum forest reserve in central Nigeria during the wet (August–October) and the dry season (November–December) using radiotracking. Birds showed high site fidelity. They mainly moved alone or in pairs but did not have exclusive home ranges. Home range size tended to be larger during the dry season due to long movements to water sources. Birds generally preferred inselberg habitat and avoided farmland. During the dry season they additionally utilized gallery forests where water was readily available, and as a result of having to cross scrub savannah to get to water, scrub savannah was also more heavily used during the dry season. Birds bred between the late rainy (September–October) and the early dry season (November). Nest‐sites were associated with rocky boulders. Both sexes contributed to incubation. Daily egg survival rate calculated using the Mayfield method was 0.89 (0.83–0.95 95% confidence interval); no nests failed during the chick stage, but sample size was only four nests. Of all 14 nests found, 50% were depredated and only 29% of breeding attempts succeeded in producing Rock Firefinch chicks. A second breeding attempt was recorded when the first one failed. Chick production just about compensated adult mortality (measured in a separate study at the site) such that the population is probably stable at present. However, given the large uncertainty in our underlying assumptions, more data are needed to confirm this. We suggest that the presence of inselberg habitat in close proximity to water sources is the essential and limiting resource for this species.     

小三江平原湿地东方白鹳(Ciconia boyciana)生境丧失的生态后果

采用生境套娃方法反映水禽——东方白鹳生境需求的层级系统基础上,利用GIS技术建立定量化分析模型,深入探讨了小三江平原生境丧失对东方白鹳生境空间分布的影响。结果显示:与初始状态1954年相比,东方白鹳繁殖生境丧失了81.9%,平均斑块面积缩小了88%;同时,生境面积的丧失是伴随生境破碎化过程发生的。1983之后生境破碎化明显加剧,到2005年生境连通度显著降低,生境处于高度破碎化状态。研究表明,生境丧失对东方白鹳繁殖生境的影响不仅取决于关键生境要素的变化,生境空间异质性改变更为重要。     

Rapid climate change-related growth decline at the southern range edge of Fagus sylvatica

Studies on Fagus sylvatica show that growth in populations toward the southern limit of this species' distribution is limited strongly by drought. Warming temperatures in the Mediterranean region are expected to exacerbate drought where they are not accompanied by increases in precipitation. We studied levels of annual growth in mature F. sylvatica trees over the last half‐century in the Montseny Mountains in Catalonia (northeast Spain). Our results show significantly lower growth of mature trees at the lower limit of this species' distribution when compared with trees at higher altitudes. Growth at the lower Fagus limit is characterized by a rapid recent decline starting in approximately 1975. By 2003, growth of mature trees had fallen by 49% when compared with predecline levels. This is not an age‐related phenomenon, nor is it seen in comparable populations at higher altitudes. Analysis of climate‐growth relationships suggests that the observed decline in growth is a result of warming temperatures and that, as precipitation in the region has not increased, precipitation is now insufficient to ameliorate the negative effects of increased temperatures on tree growth. As the climate‐response of the studied forest is comparable with that of F. sylvatica forests in other southern European regions, it is possible that this growth decline is a more widespread phenomenon. Warming temperatures may lead to a rapid decline in the growth of range‐edge populations and a consequent retreat of the species distribution in southern Europe. Assessment of long‐term growth trends across the southern range edge of F. sylvatica therefore merits further attention.