PhD student, James Cook University
Using wildlife corridors to connect habitat fragments for small mammals in Peninsular Malaysia
The effects of habitat fragmentation on ecosystems are becoming more severe as more wildlife habitats are cleared to make way for anthropogenic developments. Fragmentation is most rapid in developing countries such as Malaysia where land use change and the expansion of road networks are increasing. In rainforests, even narrow clearings can impede movements, reducing access to resources and limiting gene flow. One popular way of reducing fragmentation impacts is the use of wildlife corridors such as underpasses to link disconnected habitats. In Peninsular Malaysia, the government plans to restore connectivity between forests by building underpasses across roads which bisect them. Studies of barrier effects in rainforests are few however, and the ability of underpasses to mitigate fragmentation effects is largely unknown. Using small mammals such as forest rats, squirrels and civets as model organisms, I will examine how corridors affect community structure, movement, habitat use, and what habitat and structural features encourage them to use corridors. Smaller mammals are considered poor colonists with limited dispersal abilities and are likely to benefit from increases in connectivity brought about by the construction of corridors. I will improve on previous studies by incorporating fragmented and intact forest controls in my comparisons, and expect habitats connected by effective underpasses to have communities and animal movements closer to intact forests than fragmented ones. Meeting these objectives will help evaluate the conservation needs of different species, establish research priorities and come up with appropriate action plans for their conservation.
Abstract: Habitat destruction and overhunting are two major drivers of mammal population declines and extinctions in tropical forests. The construction of roads can be a catalyst for these two threats. In Southeast Asia, the impacts of roads on mammals have not been well-documented at a regional scale. Before evidence-based conservation strategies can be developed to minimize the threat of roads to endangered mammals within this region, we first need to locate where and how roads are contributing to the conversion of their habitats and illegal hunting in each country. We interviewed 36 experts involved in mammal research from seven Southeast Asian countries to identify roads that are contributing the most, in their opinion, to habitat conversion and illegal hunting. Our experts highlighted 16 existing and eight planned roads - these potentially threaten 21% of the 117 endangered terrestrial mammals in those countries. Apart from gathering qualitative evidence from the literature to assess their claims, we demonstrate how species-distribution models, satellite imagery and animal-sign surveys can be used to provide quantitative evidence of roads causing impacts by (1) cutting through habitats where endangered mammals are likely to occur, (2) intensifying forest conversion, and (3) contributing to illegal hunting and wildlife trade. To our knowledge, ours is the first study to identify specific roads threatening endangered mammals in Southeast Asia. Further through highlighting the impacts of roads, we propose 10 measures to limit road impacts in the region.
Pub.: 19 Dec '14, Pinned: 18 Aug '17
Abstract: Linear infrastructure such as roads, highways, power lines and gas lines are omnipresent features of human activity and are rapidly expanding in the tropics. Tropical species are especially vulnerable to such infrastructure because they include many ecological specialists that avoid even narrow (<30-m wide) clearings and forest edges, as well as other species that are susceptible to road kill, predation or hunting by humans near roads. In addition, roads have a major role in opening up forested tropical regions to destructive colonization and exploitation. Here, we synthesize existing research on the impacts of roads and other linear clearings on tropical rainforests, and assert that such impacts are often qualitatively and quantitatively different in tropical forests than in other ecosystems. We also highlight practical measures to reduce the negative impacts of roads and other linear infrastructure on tropical species.
Pub.: 15 Sep '09, Pinned: 18 Aug '17
Abstract: A leading hypothesis to explain the dramatic decline of Steller sea lions (Eumetopias jubatus) in western Alaska during the latter part of the 20th century is a change in prey availability due to commercial fisheries. We tested this hypothesis by exploring the relationships between sea lion population trends, fishery catches, and the prey biomass accessible to sea lions around 33 rookeries between 2000 and 2008. We focused on three commercially important species that have dominated the sea lion diet during the population decline: walleye pollock, Pacific cod and Atka mackerel. We estimated available prey biomass by removing fishery catches from predicted prey biomass distributions in the Aleutian Islands, Bering Sea and Gulf of Alaska; and modelled the likelihood of sea lions foraging at different distances from rookeries (accessibility) using satellite telemetry locations of tracked animals. We combined this accessibility model with the prey distributions to estimate the prey biomass accessible to sea lions by rookery. For each rookery, we compared sea lion population change to accessible prey biomass. Of 304 comparisons, we found 3 statistically significant relationships, all suggesting that sea lion populations increased with increasing prey accessibility. Given that the majority of comparisons showed no significant effect, it seems unlikely that the availability of pollock, cod or Atka mackerel was limiting sea lion populations in the 2000s.
Pub.: 08 May '15, Pinned: 31 Jul '17
Abstract: Ecological systems are vulnerable to irreversible change when key system properties are pushed over thresholds, resulting in the loss of resilience and the precipitation of a regime shift. Perhaps the most important of such properties in human-modified landscapes is the total amount of remnant native vegetation. In a seminal study Andrén proposed the existence of a fragmentation threshold in the total amount of remnant vegetation, below which landscape-scale connectivity is eroded and local species richness and abundance become dependent on patch size. Despite the fact that species patch-area effects have been a mainstay of conservation science there has yet to be a robust empirical evaluation of this hypothesis. Here we present and test a new conceptual model describing the mechanisms and consequences of biodiversity change in fragmented landscapes, identifying the fragmentation threshold as a first step in a positive feedback mechanism that has the capacity to impair ecological resilience, and drive a regime shift in biodiversity. The model considers that local extinction risk is defined by patch size, and immigration rates by landscape vegetation cover, and that the recovery from local species losses depends upon the landscape species pool. Using a unique dataset on the distribution of non-volant small mammals across replicate landscapes in the Atlantic forest of Brazil, we found strong evidence for our model predictions--that patch-area effects are evident only at intermediate levels of total forest cover, where landscape diversity is still high and opportunities for enhancing biodiversity through local management are greatest. Furthermore, high levels of forest loss can push native biota through an extinction filter, and result in the abrupt, landscape-wide loss of forest-specialist taxa, ecological resilience and management effectiveness. The proposed model links hitherto distinct theoretical approaches within a single framework, providing a powerful tool for analysing the potential effectiveness of management interventions.
Pub.: 10 Nov '10, Pinned: 31 Jul '17
Abstract: Roads and highways contribute enormously to habitat fragmentation, because they can inhibit or even block animal movement across them, which may result in the ultimate division of the populations adjacent to the roads into smaller isolated subpopulations. The isolation reduces gene flow and increases risk of extinction due to a decrease in the genetic diversity of the isolated population. The aim of the present study is to determine whether highways can cause genetic subdivision of the bank vole Myodes glareolus (Schreber, 1780) and yellow-necked mouse Apodemus flavicollis (Melchior, 1834). The study was carried out at three sites in the Highway D1 (Prague-Brno) in the Czech Republic, where a previous study demonstrated a barrier effect of the highway avoiding the interchange of individuals of both species. The genetic structure was determined from the analysis of six DNA microsatellites loci in M. glareolus and five in A. flavicollis. We found only weak genetic differences between populations living at opposite sides of the highway in either of the species and a low degree of subdivision, but significant positive correlation between genetic and geographical distance, which suggests isolation by distance in both species.
Pub.: 01 Dec '09, Pinned: 31 Jul '17
Join Sparrho today to stay on top of science
Discover, organise and share research that matters to you