Factors influencing the spatial distribution and ecological interactions of a habitat specialist, the semi-aquatic water rat (Hydromys chrysogaster)

Abstract

Semi-aquatic mammals, such as the native Australian water rat (Hydromys chrysogaster), are habitat specialists, often requiring additional adaptations to their environment compared to generalists. While the water rat is widely distributed, it is a species about which we know little. To increase our fundamental ecological and evolutionary knowledge about this species, my research focused on four key areas. First, I examined variation of body and extremity size across its geographical distribution, and found size was curvilinearly related to latitude, consistent with the abundant centre hypothesis. This hypothesis could be expanded to include ambient temperature to help explain extremity size variation. Second, I compared use of environmental factors between two semi-aquatic mammals, the water rat and the platypus (Ornithorhynchus anatinus), using species distribution models at a regional scale. Both species exhibited a similar response to the variables, but differed in magnitude (water rats more generalist, platypus more specialised). The results also showed including biotic factors in species distribution models increased model prediction. Third, I examined habitat use by water rats and found that they exhibited scale-specific responses to their environment. Habitat characteristics used were associated with reduced predation risk across all scales; however, the relative importance of each was strongly modified by spatial scale. Fourth, I tested if chemical cues from the water rat influence the common yabby (Cherax destructor), their prey. Water rat cues increased the time yabbies spent in corners, and influenced walking behaviours, but the exact nature of this response was unclear, requiring further exploration. The results from this thesis further our knowledge of the water rat as a species, but also of how semi-aquatic mammals respond to environmental factors across spatial scales, and it allowed me to answer some fundamental ecological and evolutionary questions.