Multi-scale patterns of habitat use by reptiles in regenerating dryland landscapes

Abstract

Native and regrowth vegetation is cleared to create landscapes that are suitable for agricultural production. Biodiversity is greatly reduced in cleared areas, and ecosystem functions can be lost. However, biodiversity and ecosystem function can be, at least partially, reinstated by active and passive restoration. Restoration success depends on land use history, the soil and vegetation type, and the location and climate. Extensive restoration opportunities exist in dryland landscapes that have been cleared for grazing or pasture before being abandoned. In drylands, reptiles assist in maintaining ecosystem function by occupying key trophic positions that facilitate energy flow from invertebrates to larger predators. However, there is only a limited understanding of the capacity for reptiles to persist in cleared and regenerating dryland landscapes, and the drivers of such persistence or loss. Consequently, decisions about the loss, retention or restoration of vegetation in these areas are made without a good understanding of the costs and benefits for key fauna. The aim of this thesis was to identify and understand the distributions and habitat use patterns of reptile communities and species in cleared and regenerating dryland landscapes. In this thesis, I apply a novel approach to the study of landscape ecology and restoration by incorporating the metabolic and thermal physiology of reptiles into the investigation of landscape-level patterns of distribution and habitat use. This thesis tests the applicability of theories about vegetation age and habitat value, the conceptualisation of landscapes, local- and landscape-level influences on fauna, and using resource availability to define habitat, to reptiles in regenerating dryland landscapes. These theories were tested in a highly modified semi-arid woodland region of southern Queensland, Australia, using two methods: i) surveys of reptile communities and species, and ii) intensively monitoring the movements and habitat use patterns of a focal species, the woma python Aspidites ramsayi. Regrowth vegetation is an important component of regenerating landscapes; however, the habitat value of regrowth in dryland landscapes is not well understood. This thesis establishes that young (10-23 year old) regrowth woodlands have high value as habitat for reptiles, with communities in intact and regrowth woodlands being equivalent. In addition, the focal species of this thesis, the woma python, used regrowth woodland ecosystems more often than intact woodlands. These findings contradict the general view, reflected in vegetation protection legislation, that regrowth vegetation is substandard habitat for fauna.Landscapes can be conceptualised using discrete and continuous representations of landscape features, with fauna varying in the strength of their response to different landscape models. To better understand the drivers of reptile distributions in regenerating landscapes, I compared the distribution of reptiles in these landscapes with binary, mosaic, and continuous models of habitat context. Reptile distributions varied in their compatibility with binary, mosaic and continuous conceptualisations of habitat context, with no single conceptualisation dominating. In addition, habitat context had little impact on reptiles in regenerating dryland landscapes, whereas site-level attributes, such as vegetation type, complexity and fallen stem density, were highly influential in driving distribution patterns. These findings confirm that the availability of structural features that create shelter sites, rather than habitat context, plays a key role in driving both species- and community-level patterns of habitat suitability for reptiles inhabiting drylands. Daily and seasonal temperatures fluctuate widely in sub-tropical and temperate drylands. Therefore, I predicted that the availability of shelter sites that are good thermal buffers would have a strong influence on the habitat use patterns of reptiles inhabiting these areas. To test this theory, I continuously monitored the temperature and habitat use patterns of twelve woma pythons in a regenerating dryland landscape over 21 months. Landscape-level habitat use patterns of this dryland specialist were strongly driven by the availability of underground shelters, with thermal analyses revealing that underground burrows were the only shelters capable of buffering womas from sub-zero (presumably lethal) winter temperatures. These findings suggest that the identification and protection of thermally suitable shelter structures may be more important to the conservation of threatened reptile species inhabiting disturbed and regenerating dryland landscapes than the regeneration of vegetation. The thesis outcomes have important implications for the management of cleared and regenerating dryland landscapes. Firstly, reptile communities in regrowth and intact woodlands were equivalent after just 10-23 years of passive restoration. Consequently, biodiversity in cleared landscapes will benefit from the protection of both young and old regrowth areas, either via legislation and/or landholder incentive schemes. Secondly, the availability of suitable shelter resources has a large impact on the distributions and habitat use patterns of reptiles in dryland ecosystems. Therefore, a focus on increasing the availability of shelter sites, and minimising threats to underground shelters, are effective restoration and conservation methods for enhancing reptile presence and persistence in disturbed dryland landscapes. Such measures to improve habitat quality will have a large and positive impact on ecosystem functioning in cleared and regenerating dryland landscapes.n