Dispersal and Fragmentation
Does Dispersal influence extinction risk? A long term experimental study
Maldwyn John Evans. PhD. Australian National University
Habitat loss and fragmentation is considered to be a great threat to biological diversity (Davies et al. 2000). In some circumstances, dispersal allows species to survive in fragmented landscapes by compensating local extinctions with colonisations (Ranius 2006) and allowing adequate gene flow between populations to avoid genetic impacts (Schmuki et al. 2006). The Wog Wog experiment was established in 1985 to quantify the effects of habitat fragmentation on biodiversity (Margules 1993) and has produced some important studies on the effect of habitat fragmentation on beetle species (Davies & Margules 2000; Davies, Margules & Lawrence 2000; Davies et al. 2004; Davies et al. 2001). New data emerging this year, from research led by Drs Davies and Melbourne at the University of Colorado, will identify species of beetle that have become extinct and those that have survived in the experimental fragments over 25 years. I aim to find out why. My project will use detailed species-level research to identify the factors influencing the extinction or persistence of species in fragmented landscapes. By researching the dispersal capacity of beetle species with known responses to fragmentation, I will determine the influence of dispersal on the risk of extinction after fragmentation, with implications for reserve design, including large-scale connectivity projects.
Davies, KF & Margules, CR 2000, 'The beetles at Wog Wog: a contribution of Coleoptera systematics to an ecological field experiment', Invertebrate Taxonomy, 14. 953-6.
Davies, KF, Margules, CR & Lawrence, JF 2000, 'Which traits of Species Predict Population Declines in Experimental Forest Fragments?', Ecology, 81. 5, 1450-61.
-- 2004, 'A synergistic effect puts rare, specialized species at greater risk of extinction', Ecology, 85. 1, 265-71.
Davies, KF, Melbourne, BA & Margules, CR 2001, 'Effects of within- and between-patch processes on community dynamics in a fragmentation experiment', Ecology, 82. 7, 1830-46.
Margules, CR 1993, 'The Wog Wog habitat fragmentation experiment', Environmental Conservation, 19. 316-25.
Ranius, T 2006, 'Measuring the dispersal of saproxylic insects: a key characteristic for their conservation', Population Ecology, 48. 177-88.
Schmuki, C, Vorburger, C, Runciman, D, Maceachern, S & Sunnucks, P 2006, 'When log-dwellers meet loggers: impacts of forest fragmentation on two endemic log-dwelling beetles in southeastern Australia', Molecular Ecology, 15. 1481-92.
Mallee biodiversity in fragmented landscapes
The South Australian Government is committed to the establishment of five biodiversity corridors linking public and private lands across the State by 2010 as Target 3.4 in South Australia’s Strategic Plan (DPC 2004). This target is linked to the NatureLinks initiative and Wilderness Society's WildCountry program, which has an ambition to ensure environmental connectivity and flows at a continental scale. Information about the extent of environmental connectivity will be vital in assessing the potential for species range shifts to occur in the face of human-induced climate change, which is projected to change patterns of biodiversity over time scales as short as decades. The NatureLinks - East meets West Corridor in particular aims to connect fragmented mallee communities on the Eyre Peninsula with the more continuous mallee to the north.
Before physical connections can be made, the potential role of remnant vegetation in making those connections needs to be understood. The tops of sand dunes have been left uncleared in many agricultural landscapes on the Eyre Peninsula. These remnants provide a good model system to investigate the role of “stepping-stone” habitat patches in promoting connectivity across the landscape. In our mallee fragmentation projects, we are examining the use of remnant, dune-top mallee by plants and ground-dwelling vertebrates. The projects will also examine the potential for roadside vegetation to provide connections between dunes.
Dune top Remnants
Adam Schutz completed his honours project at Flinders University, examining reptiles in dune-top remnants within a few kilometres of Hambidge Conservation Park. The project was funded by DEH SA. (Schutz and Driscoll 2008, Austral Ecology 33: 641-652)
Abstract: Species need to disperse at a broad range of spatial scales, the recognition of which has spawned programs such as Wildlands and WildCountry that aim to restore large-scale connectivity. To achieve connectivity, a first step is to understand how wildlife uses existing remnants. In this study we examine the effect of remnant isolation and condition on the reptile fauna of fragmented mallee habitats in southern Australia. In three replicate landscapes we use pitfall traps to survey reptiles in five landscape elements; Conservation Park, Connected, Disconnected and Isolated fragments, and the agricultural matrix. Reptile species richness, abundance, abundance of snakes, skinks and the ten most common species had no significant association with landscape elements, excluding the matrix. This was despite a substantial reduction in plant species richness in the fragments, particularly of shrubs. Only seven individual reptiles were captured in the matrix, most on one site with deep sandy soils. The farmland on clay soils appeared to be relatively impermeable for reptiles, although four species could traverse 100m of cleared sand dune. The lack of an isolation effect, combined with weak evidence for dispersal between remnants suggests that populations in remnants are persistent, or that occasional dispersal by common reptiles maintains populations. In contrast with common species, fewer rare species were captured in remnants compared with the Conservation Park, implying that some species may be entirely excluded from the remnants. Our study suggests that the spatial configuration and condition of the fragments sustain populations of many common reptile species. Remnants will therefore be invaluable as attempts are made to restore landscape-scale permeability. However, additional conservation effort should be made to restore plant species that have been lost from the agricultural landscape and to better define the suite of reptile species that may not be able to use the remnants at all.
Dune tops and roadsides at large distances from conservation parks
Joel Williams' honours project at Flinders University was supervised by Don Driscoll (ANU), Michael Bull (Flinders Univ), and Louisa Halliday (DEH SA).
- To determine which reptile species can or cannot use dune-top remnants at distances of up to 10km from large mallee remnants.
- To determine if roadside vegetation between dune tops may act as connecting habitat for dune-dwelling species of reptiles and plants.
- To describe the impact of dune-top condition on the animal and plant species present.
The replicated design includes sites in swales and dunes in conservation parks, in swales on roadsides, on adjacent dunes connected to the swales and on dunes that are not connected to roadside vegetation.
This project fills in important knowledge gaps about the value of linear remnants for achieving the goals of Naturelinks (SA Dpt Environment and Heritage), taking the WildCountry approach.
Reptiles in replanted mallee.
Sacha Jellinek (email@example.com), University of Melbourne.
Is Habitat Restoration Working? The extent that animals use revegetated remnants and corridors in fragmented landscapes
Sacha's project is supervised by Dr Kirsten Parris and Dr Brendan Wintle (University of Melbourne) and Dr Don Driscoll (ANU).
A large-scale loss of biodiversity is currently occurring throughout Our existing system of reserves is likely to be too small and too vulnerable to large-scale disturbances, such as fire and climate change, to solve the problem of floral and faunal loss. In order to maintain biodiversity, researchers believe extensive revegetation of the landscape is necessary. Although some of this revegetation and habitat restoration has already taken place, there is a lack of knowledge on how effective these areas have been in providing habitat for animal species. There is also a lack of knowledge on the role of linkages (such as wildlife corridors) in sustaining biodiversity. Without this information there may be substantial expenditure of resources without the expected reduction in risk of species extinctions. These natural resource problems, such as habitat loss, habitat fragmentation and habitat degradation, and the resulting loss of ecosystem function and biodiversity are underpinned by interlinking factors of ecological, social and economic systems. Biodiversity loss cannot be solved by focusing on only one of these factors, but requires the integration of people and the environment in socio-ecological systems (SES). The aim of my PhD project is to determine the influence of revegetation programs on biodiversity. This will be undertaken by determining the ecological processes occurring in remnant areas, revegetated areas and cleared land; by assessing landholder attitudes and practices to revegetation; and determine the connections between the two systems. My project will provide valuable information on the effectiveness of restored areas for biodiversity and add to the existing knowledge on the best way to strategically design restoration projects.