Scale-dependent habitat relationships of a semi-aquatic mammal in a highly regulated, freshwater ecosystem

Context:
Understanding what factors influence species occupancy in human-modified landscapes is a central theme in ecology. This is particularly vital for freshwater semi-aquatic organisms that occupy both terrestrial and aquatic environments that have often undergone severe habitat alteration from flow modification, water abstraction, and human encroachment. A greater understanding of their habitat and hydrological requirements is needed to predict how further changes to freshwater systems will impact their persistence.

Objectives:
We identified scale-dependent habitat and hydrological relationships in a semi-aquatic mammal from a highly modified and regulated, inland freshwater ecosystem in south-eastern Australia.

Methods:
We used motion-sensing cameras to collect abundance data on rakali (Hydromys chrysogaster) from 62 sites encompassing multiple aquatic habitat types. Negative binomial N-mixture models were used to determine which habitat and hydrological variables influenced rakali abundance at a site and landscape level. Landsat-derived inundation and vegetation landscape metrics were analysed at two spatial and three temporal scales.

Results:
We found habitat relationships differed depending on spatial scale. Site habitat characteristics such as dissolved oxygen and bank slope influenced rakali abundance. Landscape-scale variables at finer spatial scales (representative of total home range size), and broader temporal scales (30 years) provided the best models of rakali habitat requirements. The importance of water permanence depended on habitat type, with permanent lotic habitats supporting the largest rakali populations, suggesting this is critical refuge habitat to conserve in dry years.

Conclusions:
We highlight the importance of measuring features at multiple spatial scales and describe factors that may impact the persistence of freshwater semi-aquatic mammals. Our findings have broad implications for managing wetlands by using environmental water to improve habitat requirements, water permanence and persistence of semi-aquatic mammals in human-modified landscapes.