Christopher Johnstone

Project Title

The Impact of Habitat Fragmentation on Measurable Indicators of Physiological Stress in the Small Australian Marsupial Antechinus agilis

Abstract

Habitat fragmentation is considered a major threat to biodiversity worldwide, yet the future of many vertebrate species now depends entirely on their ability to persist in restricted ‘islands’ of habitat in an altered matrix. As the world’s natural habitat continues to be cleared and fragmented through anthropogenic action, it is of increasing conservation importance that we understand the mechanisms underlying the decline and loss of species that occurs after fragmentation.

In vertebrates, overt threats to survivorship or reproduction elicit a stress response, leading to changes in behaviour (e.g. sheltering, escape) and physiology (e.g. increase in heart rate, mobilisation of energy substrate stores) that improve an individual’s immediate chances of surviving and producing young. However, prolonged or frequent acute stress responses can lead to a pathological state of physiological exhaustion termed chronic stress. Chronic physiological stress has been reported to correlate with reductions in reproductive output, immunocompetence, and rate of growth, and an increase in molecular aging  (i.e. oxidative stress and telomere shortening).

I am currently examining whether indicators of chronic physiological stress vary among populations of the forest-interior adapted dasyurid, the agile antechinus (Antechinus agilis), living in fragmented and (paired) unfragmented study sites. The research aims to determine whether habitat fragmentation may lead to an increase in the stressfulness of the environment to the point that chronic physiological stress might potentially become a factor influencing reproduction, survivorship and ultimately persistence at the site. Concurrently, the study will quantify variables in the environment at landscape, land management and floristic levels in order to investigate specific relationships between patterns of physiological stress and the environment. In order to explore specific inter-correlations, the study has been framed in terms of a number of detailed questions.

1. Is physiological stress higher for populations of A. agilis living in fragmented habitat when compared to continuous habitat of a similar kind?
2. Is physiological stress higher in populations of A. agilis inhabiting forest fragment edges when compared to interiors?
3. Do populations of A. agilis living in a fragmented habitat show morphometric or parasite measurements that would suggest a poorer overall condition when compared to populations in continuous habitat of a similar kind?
4. Is physiological stress in A. agilis correlated with landscape, land management, or vegetation variables, such as isolation distance, grazing history, the level of fox or cat control, size of fragment, edge-area ratio, or floristic characteristics?
5. Is there an association between physiological stress levels of A. agilis and fecundity up to the pouch young stage?

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