How accurate are population models? Lessons from landscape‐scale tests in a fragmented system

There is a growing debate about the ability of Population Viability Analysis (PVA) to predict the risk of extinction. Previously, the debate has focused largely on models where spatial variation and species movement are ignored. We present a synthesis of the key results for an array of different species for which detailed tests of the accuracy of PVA models were completed. These models included spatial variation in habitat quality and the movement of individuals across a landscape. The models were good approximations for some species, but poor for others. Predictive ability was limited by complex processes typically overlooked in spatial population models, these being interactions between landscape structure and life history attributes. Accuracy of models could not be determined a priori, although model tests indicated how they might be improved. Importantly, model predictions were poor for some species that are among the best‐studied vertebrates in Australia. This indicated that although the availability of good life history data is a key part of PVA other factors also influence model accuracy. We were also able to draw broad conclusions about the sorts of populations and life history characteristics where model predictions are likely to be less accurate. Predictions of extinction risk are often essential for real‐world population management. Therefore, we believe that although PVA has been shown to be less than perfect, it remains a useful tool particularly in the absence of alternative approaches. Hence, tests of PVA models should be motivated by the cycle of testing and improvement.     

Do landscape barriers affect functional connectivity of populations of an endangered damselfly?

1. Landscape genetic approaches were used to assess functional connectivity of populations of the endangered damselfly Coenagrion mercuriale in a fragmented agricultural landscape in Switzerland. Spatial genetic clustering methods combined with interpolation by kriging and landscape genetic corridor analysis were applied to identify landscape elements that enhance or hinder dispersal and gene flow. 2. Spatial genetic clustering analysis divided the sampled populations into a northern and a southern genetic group. The boundary between the two groups coincided with a hill ridge intersecting the study area. Landscape corridor analysis identified five landscape elements that significantly affected gene flow. Elevation change, Euclidian distance, patches of forest and flowing waterbodies acted as barriers, whereas open agricultural land enhanced gene flow between populations of C. mercuriale. 3. This study showed that movement of C. mercuriale was not restricted to its preferred habitat (i.e. streams). Populations linked via continuous open agricultural land were functionally well connected if they were not more than about 1.5–2 km apart. In contrast, substantial elevation change and larger forest patches separated populations. These findings may serve as a basis to define conservation units and should be considered when planning connectivity measures, such as determining the locations of stepping stones, or the restoration of streams.     

Bird species richness in vegetation fences and in strips of residual rain forest vegetation at Los Tuxtlas, Mexico

Fragmentation of the lowland tropical rain forest has resulted in loss of animal and plant species and isolation of remaining populations that puts them at risk. At Los Tuxtlas, Mexico, lowland rain forests are particularly diverse in the avian fauna they contain and while most of the forests have been fragmented by human activity, many of the fragments still harbor diverse assemblages of bird species. In these landscapes, linear strips of residual rain forest vegetation along streams as well as linear strips of vegetation fences (live fences) crossing the pastures might provide some connectivity to bird populations existed in forest fragments. We investigated bird species richness and relative abundance in one 6-km long section of live fences (LF) bordering a dirt road and in two 6-km long sections of residual forest vegetation along a river (MR) and one permanent stream (BS). We used point count procedures which resulted in the count of 2984 birds representing 133 species. At the LF site we detected 74% of the species, 72% at the BS site and 57% at the MR site. Only 38% of the species were common among sites. Neotropical migratory birds accounted for 34–41% of the species counted at all sites. While edge and open habitat birds accounted for 6–10% of the species and for 50% of the records at the three vegetation strips, about 90% of the species were forest birds. Distance to forest fragments and degree of disturbance of the vegetation seemed to negatively influence bird species presence at the BS and MR strips. Rarefaction analysis indicated that the LF strip was richer in species than the other two sites, but the occurrence of the three vegetation strips in the landscape seem to favor the presence of many more species. We discuss the value of these vegetation strips to birds as stepping stones in the fragmented landscape.     

Conservation strategies to mitigate impacts from climate change in Amazonia

Protected area systems and conservation corridors can help mitigate the impacts of climate change on Amazonian biodiversity. We propose conservation design criteria that will help species survive in situ or adjust range distributions in response to increased drought. The first priority is to protect the western Amazon, identified as the 'Core Amazon', due to stable rainfall regimes and macro-ecological phenomena that have led to the evolution of high levels of biodiversity. Ecotones can buffer the impact from climate change because populations are genetically adapted to climate extremes, particularly seasonality, because high levels of habitat diversity are associated with edaphic variability. Future climatic tension zones should be surveyed for geomorphological features that capture rain or conserve soil moisture to identify potential refugia for humid forest species. Conservation corridors should span environmental gradients to ensure that species can shift range distributions. Riparian corridors provide protection to both terrestrial and aquatic ecosystems. Multiple potential altitudinal corridors exist in the Andes, but natural and anthropogenic bottlenecks will constrain the ability of species to shift their ranges and adapt to climate change. Planned infrastructure investments are a serious threat to the potential to consolidate corridors over the short and medium term.     

First Report of Chytridiomycosis in a Dying Toad (Anura: Bufonidae) from Cuba: A New Conservation Challenge for the Island

Infection by the chytrid fungus Batrachochytrium dendrobatidis was detected in a male Bufo longinasus dunni, a small toad endemic to central Cuba. The individual was severely infected and in decaying condition. Sections of the skin were examined through standard histological procedures. Several stages of the fungus were confirmed and are illustrated in this contribution. Implications for amphibian conservation in Cuba are discussed.     

黑龙江省完达山地区马鹿生境破碎化及其影响因子

应用景观生态学原理和地理信息系统技术,分析黑龙江省完达山地区马鹿生境相关因子重要性、对景观连接度进行模糊相对赋值,建立了景观连接度评价模型及景观斑块指数,研究了黑龙江省完达山地区关于马鹿生境的景观连接度水平、生境的适宜性以及景观的空间结构。结果表明:(1)在155.6km2的面积中,适宜地区的总面积仅为14.81km2,占研究地区的9.52%;次适宜地区的总面积为9.57km2,占研究地区的6.15%;一般适宜地区的总面积为130.05km2,占研究地区的83.58%;不适宜地区的总面积为1.17km2,占研究地区的0.75%;(2)研究地区马鹿各类适宜地区呈多个斑块且相互隔离,在空间分布上处于破碎状态,而且不适宜地区斑块(人为活动景观)的面积比例虽小,在生态系统中形态上的破碎化程度较小,但对马鹿的生境的生态功能的丧失起到重要作用。     

The composition of the carabid fauna on poor sandy road-side verges in relation to comparable open areas

In The Netherlands, the majority of heathlands and dry, unproductive grasslands have been brought into cultivation or afforested since the end of the 19th century. As a result, the original landscape has become highly fragmented. Nowadays, the heath habitat occurs in more or less isolated patches only. Many of these fragments show a small spatial variation in conditions. Ground-dwelling arthropods, with a low dispersal power and a specific preference for poor, sandy, open habitats, could disappear from such small fragments under the influence of temporarally unfavourable conditions. As recolonization from other fragments is often very difficult because of hostile surrounding areas, isolated small fragments that have lost their populations will remain unoccupied. The absence of some carabid species in such small, isolated fragments is thought to be the result of this situation. By introducing heathy corridors between such fragments, animals might be enabled to pass a hostile environment. This study shows that heathy road-side verges can possibly function as such a corridor. On the studied road-side verges, carabid species of poor sandy, open habitats were present, including the more rare species. Some species even found a better habitat at road-side verges than in adjacent poor sandy open areas. For other species the road-side verge seemed to be a more marginal habitat in which they occur only because of the presence of a suitable adjacent area. The distance to such an area, as well as the width of the poor sandy, open strip on the road-side verge seem to be important conditions for the occurrence of the latter species. In order to increase the survival chance in such a corridor, it is suggested that some wider strips or patches be created at the road-side verges, suitable for reproduction. In this way, road-side verges might contribute to a metapopulation structure by which species are better protected against regional extinction.Communication No. 470 of the Biological Station of the Agricultural University Wageningen, Kampsweg 27, 9418 P.D. Wijster, The Netherlands.     

Designing a “tailor-made” ecological network using geographical information systems

During the last few years, geographical information systems (GIS) have spread as powerful tools for landscape analysis. The main purpose of this work was to use GIS to display an ecological network made up of core areas, key areas and ecological corridors. As an example of the application of this method we refer to the population of deer (Cervus elaphus) and roe deer (Capreolus capreolus) in an alpine area in northwestern Italy. The method provided an overall view of the ecological network of the area, highlighting how linear infrastructures can affect animal populations and consequently, their survival probability.     

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.