Landscape modification resulting in habitat loss, fragmentation and intensification of land use is a serious threat to the earth’s biological diversity and the primary cause of the current extinction crisis. Recent research suggests the human-modified area of the landscape (that is not ‘traditional’ habitat for native species but potentially once was), or the ‘matrix’ (as it is hereafter called) has a major influence on wildlife persistence in modified landscapes. However, the matrix is a poorly studied and inadequately understood element of a modified landscape. There are at least two reasons for this. Firstly, the predominance of island biogeography and metapopulation theories in ecological thinking ensured that the matrix has historically been ignored in ecological research. Secondly, it is difficult to analyse matrix effects without confounding effects of habitat loss, habitat fragmentation and other aspects of landscape modification. As landscapes are modified attributes of the matrix co-vary with attributes of patches and landscapes, entangling their relative impacts on wildlife. Thus to investigate the independent influence of the matrix on mammals I selected 19 study landscapes by rigorous criteria to control for all potentially confounding patch and landscape attributes such as remnant forest patch size, shape, vegetation type, condition and position in the landscape, presence of any large (potential ‘source’) native forest patches within the landscape unit, as well as matrix land use composition and history. A study landscape was defined as the area within a 500 m radius of a remnant forest patch edge. Landscapes were selected along a gradient of rural-suburban residential development spanning the broadest achievable range of what I call ‘matrix development intensity’. This gradient was quantified by a novel weighted road-length metric that considered multiple road attributes to give significance to the ecological impact of different roads. Mammals and their habitat were sampled in three landscape elements within each landscape: remnant patch core, remnant patch edge and matrix to allow a landscape level inference. Mammals were sampled by a combination of Elliott traps, wire cage traps, hair funnels, scats and direct sightings. Thirty environmental variables were measured including habitat structure and disturbance and a full floristic survey was conducted. The matrix intensity gradient was characterised by increased anthropogenic disturbance such as increased housing density, closer proximity of sample sites to houses and higher human disturbance across the landscape mosaic, including in the core of remnant patches. However, matrix intensity was not the greatest source of overall variation in structural and floristic habitat attributes. Therefore the confounding of matrix effects with effects of remnant forest patch habitat attributes were successfully ruled out. Management actions of individual landholders can shape habitat attributes essential to mammals across the landscape mosaic. Mammal response to matrix intensity was species specific. Several native species declined in abundance, others were more resilient to moderate levels of matrix intensity, one species increased in abundance, and at least one species appeared unaffected by matrix intensity. Native species richness peaked at moderate levels, while exotic species richness and feral predators increased with matrix intensity and were negatively correlated with native species. Species response to matrix intensity appeared related to their use of edge or matrix habitat. However, an ability to use the matrix per se may not translate into an ability to persist in a landscape where development substantially reduces the habitat or movement value of the matrix. Seven a priori models of various remnant patch habitat, landscape and matrix influences on terrestrial mammal species richness were tested. Matrix attributes were the most important determinants of species richness. Matrix development intensity had a strong negative effect while matrix vegetation structural complexity had a strong positive effect on mammal species richness. Distance to the nearest remnant forest habitat was relatively unimportant. I hypothesised that thresholds of matrix intensity would exist where native species decline in abundance and exotic and native synanthropic species increase to dominate the mammal community. Thresholds were found for abundance of all native terrestrial species combined, macropod abundance and exotic rodent abundance. However, threshold models were only better than linear or cubic models for exotic rodent abundance. Matrix development intensity has a pervasive impact across the whole landscape mosaic that results in a complex range of environmental changes that individually and collectively impact the mammal community. Drawing on all results, I present a conceptual model of the overall impact of matrix development intensity on mammal community integrity. I conclude that a structurally complex matrix within a human-modified landscape can provide supplementary habitat resources and increase the probability of successful species movement across the landscape. Research needs to incorporate empirical data of specific matrix effects into models and theory of species distribution and abundance in human-modified landscapes. This can help guide application of management actions and landscape planning principles across different landscapes. Planning authorities and land managers need to explicitly acknowledge the importance of the matrix and the numerous factors that could be manipulated, such as retention or restoration of a structural vegetation layer that can assist mammal movement across the matrix, for greater landscape-wide conservation outcomes.
| Identifer | oai:union.ndltd.org:ADTP/286524 |
| Creators | Megan Brady |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
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