Patterns Of Habitat Loss Research Articles

Subspecies differentiation and range-wide genetic structure are driven by climate in the California gnatcatcher, a flagship species for coastal sage scrub conservation.

Understanding genetic structure and diversity within species can uncover associations with environmental and geographic attributes that highlight adaptive potential and inform conservation and management. The California gnatcatcher, Polioptila californica, is a small songbird found in desert and coastal scrub habitats from the southern end of Baja California Sur to Ventura County, California. Lack of congruence among morphological subspecies hypotheses and lack of measurable genetic structure found in a few genetic markers led to questions about the validity of subspecies within P. californica and the listing status of the coastal California gnatcatcher, P. c. californica. As a U.S. federally threatened subspecies, P. c. californica is recognized as a flagship for coastal sage scrub conservation throughout southern California. We used restriction site‐associated DNA sequencing to develop a genomic dataset for the California gnatcatcher. We sampled throughout the species' range, examined genetic structure, gene–environment associations, and demographic history, and tested for concordance between genetic structure and morphological subspecies groups. Our data support two distinct genetic groups with evidence of restricted movement and gene flow near the U.S.‐ Mexico international border. We found that climate‐associated outlier loci were more strongly differentiated than climate neutral loci, suggesting that local climate adaptation may have helped to drive differentiation after Holocene range expansions. Patterns of habitat loss and fragmentation are also concordant with genetic substructure throughout the southern California portion of the range. Finally, our genetic data supported the morphologically defined P. c. californica as a distinct group, but there was little evidence of genetic differentiation among other previously hypothesized subspecies in Baja California. Our data suggest that retaining and restoring connectivity, and protecting populations, particularly at the northern range edge, could help preserve existing adaptive potential to allow for future range expansion and long‐term persistence of the California gnatcatcher.

Rates and patterns of habitat loss across South Africa’s vegetation biomes

The loss of natural habitat resulting from human activities is the principal driver of biodiversity loss in terrestrial ecosystems globally. Metrics of habitat loss are monitored at national and global scales using various remote sensing based land-cover change products. The metrics go on to inform reporting processes, biodiversity assessments, land-use decision-making and strategic planning in the environmental and conservation sector. We present key metrics of habitat loss across South Africa at national and biome levels for the first time. We discuss the spatial patterns and trends, and the implications and limitations of the metrics. Approximately 22% of the natural habitat of South Africa has been lost since the arrival of European settlers. The extent and the rate of habitat loss are not uniform across South Africa. The relatively mesic Grassland, Fynbos and Indian Ocean Coastal Belt biomes have lost the most habitat, while the arid Nama-Karoo, Succulent Karoo and Desert have lost the least. Rates of loss increased across all biomes in recent years (2014–2018), indicating that the historical drivers of change (i.e. expansion of croplands, human settlements, plantation forestry and mining) are intensifying overall. We should caution that the losses we report are conservative, because the land-cover change products do not capture degradation within natural ecosystems. Preventing widespread biodiversity losses and securing the benefits we derive from biodiversity requires slowing and preventing further habitat degradation and loss by using existing land-use planning and regulatory tools to their full potential.
 Significance:
 
 The loss of natural habitat resulting from human activities is the principal driver of biodiversity loss in terrestrial ecosystems in South Africa.
 Monitoring trends and patterns of habitat loss at a national scale provides a basis for informed environmental decision-making and planning, thus equipping civil society and government to address habitat loss and protect biodiversity while also meeting key development and socio-economic needs.
 
 Open data set:
 https://doi.org/10.15493/SAEON.FYNBOS.10000011

Persistent geophysical effects of mining threaten ridgetop biota of Appalachian forests

Surface coal mining can permanently alter the rugged topography of Appalachia, which plays an important role in creating and maintaining the structure, composition, and diversity of this North American region's ecological communities. We used remote‐sensing datasets to characterize the past and future topographic impacts of surface coal mining on the mixed‐mesophytic forests of eastern Kentucky. To provide context, we examined the consequences of widespread topographic rearrangement for an imperiled ridgetop‐associated predator, the timber rattlesnake (Crotalus horridus). We found that surface mining disproportionately impacts ridgetop habitats, causing large reductions in suitable habitat for C horridus, and most likely other ridgetop‐dependent biota as well. Land permitted for surface mining is also concentrated in high topographic positions, and patterns of habitat loss are therefore likely to remain concentrated within these ecosystems. These permanent topographic shifts complicate restoration of pre‐existing microhabitats, create homogenized landscapes, threaten long‐term ecosystem health, and reduce the diversity of ecological communities.

Landscape connectivity losses due to sea level rise and land use change

A fundamental problem in landscape ecology is understanding the isolating effects of different patterns of habitat loss and fragmentation on species and ecosystems. In the 21st century, urban development and sea level rise (SLR) are predicted to affect large areas of the United States, further exacerbating already fragmented and densely populated landscapes. Increasing or restoring habitat connectivity may ameliorate these effects, but the broad-reaching efforts required to assess current and future changes to connectivity, especially in low-lying areas vulnerable to SLR, are still under development. To address these issues, we strategically identified a small group of regionally significant species that represent a range of characteristics and ecological requirements useful for examining landscape connectivity. We used expert opinion to parameterize divergent species responses (i.e. resistance) to landscape features and to assess permeability of the landscape. From this, we estimated contemporary and future low-resistance habitat cores in the year 2100. We modeled six species for habitat connectivity using a multiscaled circuit theory-based approach and analysed them collectively to indicate landscape connectivity across the Southeastern United States. Using this approach, we were able to forecast changing connectivity patterns based on predicted urbanization and SLR. Our results suggest that there will be a 41% reduction in the number of low-resistance cores and a 35% decrease in mean area of remaining cores. In addition, current areas of high landscape connectivity will become more fragmented as future connectivity values indicate a more homogenized landscape structure. In the future landscape, pathways for connectivity are likely to move inland and northward as sea level and urbanization pressures increase. Our results may inform more comprehensive planning initiatives regionally or nationally, while simultaneously providing a multiscaled context for localized planning efforts.

Optimal management of a multispecies shorebird flyway under sea-level rise.

Every year, millions of migratory shorebirds fly through the East Asian-Australasian Flyway between their arctic breeding grounds and Australasia. This flyway includes numerous coastal wetlands in Asia and the Pacific that are used as stopover sites where birds rest and feed. Loss of a few important stopover sites through sea-level rise (SLR) could cause sudden population declines. We formulated and solved mathematically the problem of how to identify the most important stopover sites to minimize losses of bird populations across flyways by conserving land that facilitates upshore shifts of tidal flats in response to SLR. To guide conservation investment that minimizes losses of migratory bird populations during migration, we developed a spatially explicit flyway model coupled with a maximum flow algorithm. Migratory routes of 10 shorebird taxa were modeled in a graph theoretic framework by representing clusters of important wetlands as nodes and the number of birds flying between 2 nodes as edges. We also evaluated several resource allocation algorithms that required only partial information on flyway connectivity (node strategy, based on the impacts of SLR at nodes; habitat strategy, based on habitat change at sites; population strategy, based on population change at sites; and random investment). The resource allocation algorithms based on flyway information performed on average 15% better than simpler allocations based on patterns of habitat loss or local bird counts. The Yellow Sea region stood out as the most important priority for effective conservation of migratory shorebirds, but investment in this area alone will not ensure the persistence of species across the flyway. The spatial distribution of conservation investments differed enormously according to the severity of SLR and whether information about flyway connectivity was used to guide the prioritizations. With the rapid ongoing loss of coastal wetlands globally, our method provides insight into efficient conservation planning for migratory species.

Temporal patterns of road network development in the Brazilian Amazon

The Brazilian Amazon is a globally important ecosystem that is undergoing rapid development and land-use change. Roads are a key spatial determinant of land-use conversion and strongly influence the rates and patterns of habitat loss and represent a key component of models that attempt to predict the spatio-temporal patterns of Amazonian land-use change and the consequences of such changes. However, the spatio-temporal patterns of road network development are poorly understood and seldom quantified. Here, we used manually digitised satellite imagery at multiple temporal and spatial scales across the Brazilian Amazon to quantify and model the rate at which road networks are proliferating. We found that the road network grew by almost 17,000 km per year between 2004 and 2007. There was large spatial variation in road network density, with some municipalities having road densities as high as 0.5 km/km2, and road network growth rates were highest in municipalities with an intermediate road network density. Simulations indicated that road network development within municipalities follows a logistic growth pattern through time, with most of the development occurring within a 39-year time period. This time period is similar to those of other boom and bust development dynamics observed in the Brazilian Amazon. Understanding the temporal patterns of road development will aid the development of better predictive land-use change models for the Amazon, given the key importance of roads as a predictor of deforestation in many existing models.

Mapping to inform conservation: A case study of changes in semi-natural habitats and their connectivity over 70 years

Intensification of human activities has caused drastic losses in semi-natural habitats, resulting as well in declining connectivity between remaining fragments. Successful future restoration should therefore increase both habitat area and connectivity. The first steps in a framework for doing so are addressed here, which involve the mapping of past habitat change. We present a method which is unique in: the large area covered (2500km2), the high resolution of the data (25×25m), the long period assessed (70years), and a system for translation of land use maps into Broad Habitat Types using soil surveys.We digitised land use maps from the 1930s for the county of Dorset in southern England. The resulting map was compared to the UK Land Cover Map of 2000. For our example area, land use shifted dramatically to more intensive agriculture: 97% of all semi-natural grasslands were converted into agriculturally-improved grassland or arable land as were large proportions of the heathlands and rough grasslands (−57%). The other important driver of change was afforestation (+25%). The larger habitat areas became fragmented, with average fragment size of different habitats falling by 31–94%. Furthermore, the connectivity between fragments dropped drastically, by up to 98%.Analyses such as those presented here not only quantify the scale and pattern of habitat loss, but are important to inform land-use planning to restore biodiversity by both increasing the available habitat and facilitating dispersal among habitat fragments. We discuss the possible steps for such a framework.

National housing and impervious surface scenarios for integrated climate impact assessments

Understanding the impacts of climate change on people and the environment requires an understanding of the dynamics of both climate and land use/land cover changes. A range of future climate scenarios is available for the conterminous United States that have been developed based on widely used international greenhouse gas emissions storylines. Climate scenarios derived from these emissions storylines have not been matched with logically consistent land use/cover maps for the United States. This gap is a critical barrier to conducting effective integrated assessments. This study develops novel national scenarios of housing density and impervious surface cover that are logically consistent with emissions storylines. Analysis of these scenarios suggests that combinations of climate and land use/cover can be important in determining environmental conditions regulated under the Clean Air and Clean Water Acts. We found significant differences in patterns of habitat loss and the distribution of potentially impaired watersheds among scenarios, indicating that compact development patterns can reduce habitat loss and the number of impaired watersheds. These scenarios are also associated with lower global greenhouse gas emissions and, consequently, the potential to reduce both the drivers of anthropogenic climate change and the impacts of changing conditions. The residential housing and impervious surface datasets provide a substantial first step toward comprehensive national land use/land cover scenarios, which have broad applicability for integrated assessments as these data and tools are publicly available.

Landscape legacies: Koala habitat change in Noosa Shire, South-east Queensland

Present day Australian landscapes are legacies of our colonial history, while future landscapes will be legacies of ecological processes and human impacts occurring today. This paper investigates the legacies of European settlement of Noosa Shire, South-east Queensland, with particular emphasis on the economic and political drivers and the resultant loss and fragmentation of Koala Phascolarctos cinereus habitat. Patterns of habitat loss between 1860 and 1970 were quantified at a coarse level from historical and land tenure records, while changes over the past 30 years were mapped at a finer spatial resolution from aerial photography and satellite imagery. Periods of high economic growth and to lesser extents depression are linked to increased vegetation clearing. Fifty per cent of P. cinereus habitat has been lost since 1860, with habitat class 2A (30-<50 per cent of preferred habitat trees) and 2C (10-<30 per cent of preferred habitat trees) suffering the highest proportion of loss. The period of greatest habitat loss was between 1890 and 1910, linked to the development of the dairy industry in the western half of Noosa Shire. A second significant phase of loss occurred since 1970, linked to the planting of exotic pine plantations, urbanisation and rural subdivision, with 35 per cent of remaining habitat being cleared, mainly in the southern part of the Shire. The cumulative loss of habitat has been accompanied by increasing levels of habitat fragmentation indicated by reduced patch size and increased patch linearity. Further analysis of the temporal aspects of habitat change is required in order to test the hypothesis that there is a relaxation period between the timing of habitat loss and current pattern of habitat occupancy of P. cinereus populations.