Amount Of Habitat Loss Research Articles

Large-scale assessment of genetic diversity and population connectivity of Amazonian jaguars (Panthera onca) provides a baseline for their conservation and monitoring in fragmented landscapes

Jaguar population genetics has so far not been investigated on a broad scale in the Amazon rainforest, which constitutes the largest remaining block of continuous habitat for the species. Given its size, it serves not only as a stronghold but also as a reference for jaguar conservation genetics, against which fragmented landscapes can be compared. We assessed genetic diversity and population structure of Amazonian jaguars using 11 microsatellite loci and performed comparative analyses incorporating available data from two other South American biomes (Pantanal and Atlantic Forest) in which the species has faced different amounts of habitat loss and fragmentation. Using the largest genetic data set assembled to date for jaguars (n = 190), we observed that all diversity indices were consistently higher for the Amazonian population, with no genetic subdivision detected in that region, indicating large-scale connectivity across >3000 km. In contrast, we corroborate the inference of anthropic-driven genetic structure and bottlenecks for two Atlantic Forest populations. Our results indicate that the Amazon is a critically important stronghold for jaguars, comprising a highly diverse, panmictic population that allows a glimpse into the patterns of genetic connectivity that characterized this species prior to human intervention. In contrast, the Atlantic Forest populations jointly still retain considerable levels of genetic diversity, but this is currently partitioned among isolated fragments that are increasingly subjected to heavy anthropic disturbance. These results have important implications for jaguar conservation planning, highlighting the critical condition of Atlantic Forest populations and providing a genetic baseline to which they can be compared.

Focusing on rapid urbanization areas can control the rapid loss of migratory water bird habitats in China

Over 240 migratory water bird species depend on China's 18,000 km coastline as a vital stopover area. However, the rapid loss of natural wetlands has threatened this seasonal water bird migration over the last few decades. In the present study, to improve our understanding of the pattern and amount of habitat loss in key stopover areas (KSAs) and the spatial covariance between habitat loss and economic development, we conducted a spatially explicit evaluation of coastal habitat loss in KSAs and explored its relationship with social and economic dynamics along the China coast by integrating high-spatial resolution satellite imagery with an updated coastal water bird investigation data set. The remote sensing survey detected a habitat loss percentage of 19.4% in the KSAs during 2000 and 2010. Aquaculture, urbanization, and land reclamation were responsible for the most severe disturbances to coastal habitats. These results demonstrate that the losses of wetland habitats in the KSAs in Chinese coastal areas are more severe than those in other coastal areas even though more protective measures have been implemented in these areas. Risk-based analysis showed that the risk of habitat loss was greatest in undeveloped regions with rich natural wetland and large populations, thereby demonstrating the critical importance of shifting the focus of water bird conservation to these regions to ensure the conservation of migratory water birds in the East Asian–Australasian Flyway. These findings disagree with the hypothesis that more habitats are lost when the economy is more developed. Therefore, we suggest that focusing conservation decisions on areas undergoing urbanization might improve the effectiveness of conservation measures given the pressures due to various forms of wetland exploitation.

Quantifying habitat losses and gains made by U.S. Species Conservation Banks to improve compensation policies and avoid perverse outcomes

AbstractCompensation policies seek to counterbalance biodiversity losses caused by development; however, their effectiveness is rarely tested. We examined U.S. Species Conservation Banks (SCBs) in California, a compensation program initiated 30 years ago. We quantified the effect of 59 SCBs (15,350 ha) on habitat extent using statistical matching methods. SCBs averted a small, yet significant, amount of habitat loss (62 ha) between 2001 and 2011. However, unexpectedly, SCBs also averted significant habitat gains (1,424 ha). It is not possible to determine if losses averted by SCBs equaled losses caused by development for which credits were sold (because records of the latter do not exist), but estimated averted gains were 35 times greater than averted losses. To improve practice, SCBs must be designed to achieve outcomes that are additional and avoid crowding out other programs incentivizing statewide conservation goals.

The negative effects of habitat fragmentation operate at the scale of dispersal.

Habitat loss is often considered the greatest near-term threat to biodiversity. Yet the impact of habitat fragmentation, or the change in habitat configuration for a given amount of habitat loss, has been intensely debated. We isolated effects of habitat loss from fragmentation on the demography, movement, and abundance of wild populations of a specialist herbivore, Chelinidea vittiger, by removing 2,088 patches across 15 landscapes. We compared fragmentation resulting from random loss, which is often considered in theory, to aggregated loss, which is often observed in the real world. When quantifying fragmentation caused by random vs. aggregated loss, aggregated loss led to less fragmented landscapes than random loss based on patch isolation, but more fragmented landscapes when based on isolation at a larger mesoscale scale defined by dispersal distances of C.vittiger. Overall, habitat loss decreased population size and demographic parameters, with thresholds occurring at approximately 70-80% patch loss. Synergistic effects also occurred, where an aggregated pattern of loss had negative effects at low, but not high, amounts of habitat loss. Effects on population size of C.vittiger were driven by reductions in movement and subsequent reproduction. The direction of habitat fragmentation effects from random and aggregated loss treatments, for a given habitat amount, was conflictingly positive or negative depending on the scale at which fragmentation was quantified. Fragmentation quantified at the scale of dispersal for this species best explained population size and highlighted that fragmentation had negative effects at a mesoscale. Our results emphasize the importance of quantifying habitat fragmentation at biologically appropriate scales.

Is habitat fragmentation good for biodiversity?

Habitat loss is a primary threat to biodiversity across the planet, yet contentious debate has ensued on the importance of habitat fragmentation ‘per se’ (i.e., altered spatial configuration of habitat for a given amount of habitat loss). Based on a review of landscape-scale investigations, Fahrig (2017; Ecological responses to habitat fragmentation per se. Annual Review of Ecology, Evolution, and Systematics 48:1-23) reports that biodiversity responses to habitat fragmentation ‘per se’ are more often positive rather than negative and concludes that the widespread belief in negative fragmentation effects is a ‘zombie idea’. We show that Fahrig's conclusions are drawn from a narrow and potentially biased subset of available evidence, which ignore much of the observational, experimental and theoretical evidence for negative effects of altered habitat configuration. We therefore argue that Fahrig's conclusions should be interpreted cautiously as they could be misconstrued by policy makers and managers, and we provide six arguments why they should not be applied in conservation decision-making. Reconciling the scientific disagreement, and informing conservation more effectively, will require research that goes beyond statistical and correlative approaches. This includes a more prudent use of data and conceptual models that appropriately partition direct vs indirect influences of habitat loss and altered spatial configuration, and more clearly discriminate the mechanisms underpinning any changes. Incorporating these issues will deliver greater mechanistic understanding and more predictive power to address the conservation issues arising from habitat loss and fragmentation.

Do Protected Areas Reduce Forest Fragmentation? A Microlandscapes Approach

Conservation policies influence both the amount of habitat loss and patterns of habitat fragmentation. This paper develops a “microlandscapes” approach that combines fragmentation measures with quasi-experimental evaluation methods in order to assess the effects of policy on habitat fragmentation. As an application, the paper estimates whether and to what extent wildlife sanctuaries and national parks in Thailand prevented forest loss and fragmentation. I find that both types of protected areas significantly increased forest cover, average forest patch size and maximum forest patch size. Comparisons between the two types indicate that wildlife sanctuaries were more effective than national parks in terms of protecting forest in the interior versus exterior areas of parks and preventing fragmentation conditional on the level of forest cover. The differences are consistent with predicted differences resulting from spatial patterns of enforcement that are uniform or core-focused in the wildlife sanctuaries versus boundary-focused or include agglomeration penalties in the national parks. Given the greater effectiveness of wildlife sanctuaries in preventing fragmentation and the suggestive link to enforcement types, these results reinforce existing theoretical work urging conservation managers to consider how the spatial distribution of enforcement may affect patterns of resource use.

The loss of forest birds habitats under different land use policies as projected by a coupled ecological-econometric model

Land use is driven by socio-economic factors that must be understood in order to mitigate habitat loss. Econometric land-use models describe how land use is affected by socio-economic factors, such as financial returns to different uses of land, and they can be linked to biological models to provide new insight for conservation. Our goal was to evaluate the effects of future land use change on the habitat of forest breeding bird species in northern Wisconsin. Specifically, we estimated the effects of land use change on the amount of habitat available and compared the effects of economic policy scenarios on bird habitat. To do this, we coupled a spatially-explicit econometric model of land use change on private lands with models of northern Wisconsin forest bird potential habitat, comparing a 50-yr baseline projection with a scenario providing incentives for forest growth and a high urban growth scenario. The baseline scenario suggests an average of 438,705ha of forest lost (10%), with 1.9% of that saved under the Forest Incentive scenario, and a 1.6% greater loss for the Urban Growth scenario. Under baseline projections boreal birds experienced the least amount of habitat loss (2–3%), and deciduous forest birds the most (6–8%). For some species, the projected loss of habitat exacerbates ongoing long-term declining population trend. Coupled economic-ecological models can be used to evaluate alternative incentive programs and to explore the complex interactions between policy, land use change, and broad spatial scale ecological processes that are highly relevant to conservation.

Disproportional risk for habitat loss of high‐altitude endemic species under climate change

AbstractThe expected upward shift of trees due to climate warming is supposed to be a major threat to range‐restricted high‐altitude species by shrinking the area of their suitable habitats. Our projections show that areas of endemism of five taxonomic groups (vascular plants, snails, spiders, butterflies, and beetles) in the Austrian Alps will, on average, experience a 77% habitat loss even under the weakest climate change scenario (+1.8 °C by 2100). The amount of habitat loss is positively related with the pooled endemic species richness (species from all five taxonomic groups) and with the richness of endemic vascular plants, snails, and beetles. Owing to limited postglacial migration, hotspots of high‐altitude endemics are situated in rather low peripheral mountain chains of the Alps, which have not been glaciated during the Pleistocene. There, tree line expansion disproportionally reduces habitats of high‐altitude species. Such legacies of climate history, which may aggravate extinction risks under future climate change have to be expected for many temperate mountain ranges.

Habitat loss and connectivity of reserve networks in probability approaches to reserve design

AbstractQuantitative methods for the design of reserve networks often select over‐dispersed reserves, and consequently a number of species extinctions can be expected in such reserves, especially if unprotected surrounding habitat is lost. A novel approach that deals with this problem is presented by considering factors such as habitat quality and spatial configuration of reserves during the selection process. Species‐specific effects of habitat loss and fragmentation, together with habitat composition, are taken into account when computing species probabilities of local occurrence. Sites are then chosen to represent all species with a given target probability. The method is applied to a dataset of butterflies and moths from the Creuddyn Peninsula, North Wales, UK, which includes species with various responses to habitat quality and configuration. The results show that the resulting level of reserve clustering will depend on the number of species for which the spatial configuration plays an important role (at the scale under consideration), and on the pattern and amount of habitat loss that is expected to follow around the reserves. The method represents a step towards taking better into account species persistence when selecting reserve networks in a changing world.

POPULATIONS ON FRAGMENTED LANDSCAPES WITH SPATIALLY STRUCTURED HETEROGENEITIES: LANDSCAPE GENERATION AND LOCAL DISPERSAL

The goal of this investigation was to study the effects of spatially structured habitat heterogeneities on locally dispersing single-species populations. In this investigation, the environmental heterogeneities were not randomly distributed, but rather were clustered by specifying probabilities of small local configurations of the landscape, as in local structure or pair approximations. This allows the study of landscapes with the same amount of habitat loss but different levels of fragmentation or clustering. I describe a simple algorithm for generating such structured landscapes. Spatially explicit simulations of population models on these landscapes were performed using stochastic cellular automata and compared to predictions from mean-field and pair approximations, for which detailed derivations are presented. For populations with local dispersal, I show that the spatial correlations of habitat types completely determine equilibrium population density on suitable sites and that the amount of suitable habitat has no effect, precisely the opposite of what the mean-field approximation predicts. When habitat types are randomly distributed on the landscape, the two approximations do almost equally well, and thus the additional complexity of the pair approximation is not justified. However, when habitat types are not randomly distributed, the mean-field approximation gives qualitatively incorrect predictions for population response to varying habitat heterogeneity. Thus, pair approximations combine some of the best features of spatially explicit and implicit models and serve as a useful supplement to those methods for understanding spatially structured ecological systems, especially where environmental heterogeneities are spatially correlated.

INFLUENCE OF LANDSCAPE AND HABITAT CHARACTERISTICS ON OVENBIRD PAIRING SUCCESS

We investigated the influence of disturbance type (agriculture and silviculture) within forested landscapes, amount of forest cover within 1 km of the site, and local habitat characteristics on the pairing success of Ovenbirds (Seiurus aurocapillus) in central Pennsylvania during May and June 1998. Because areas with low pairing success often are inferred to have high nest predation, we also examined whether pairing and nesting success were correlated across sites. We determined the pairing status of 116 male Ovenbirds on 10 sites within contiguous mature forest. Percent of males that were paired on each site ranged from 54–92% (mean = 78%). Pairing success was negatively associated with forest cover within 1 km and positively associated with leaf litter depth. Percent bare ground also was positively correlated with forest cover within 1 km of the site. Estimates of pairing success were unrelated to Ovenbird nesting success at each site (based on 48 nests), which suggests that site-level differences in nest predation or reproductive potential are not necessarily associated with the ability of males to acquire mates. Our data suggest that pairing success of Ovenbirds in forested landscapes is not reduced by the amount of habitat loss within 1 km and is determined by local habitat rather than landscape characteristics.