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Feeding and foraging ecology of the Australian water rat, Hydromys chrysogaster , in a riparian ecosystem

Feeding and foraging ecology of the Australian water rat, Hydromys chrysogaster , in a riparian ecosystem. Kristin Connell (University of Sydney) Supervisor: Dr Clare McArthur Co-supervisors: Prof Chris Dickman & Dr Tom Grant. General background. Largest rodent in Australia

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Feeding and foraging ecology of the Australian water rat, Hydromys chrysogaster , in a riparian ecosystem

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  1. Feeding and foraging ecology of the Australian water rat, Hydromys chrysogaster, in a riparian ecosystem Kristin Connell (University of Sydney)Supervisor: Dr Clare McArthur Co-supervisors: Prof Chris Dickman & Dr Tom Grant

  2. General background • Largest rodent in Australia • Only semi-aquatic mammal besides the platypus • Highly specialised for aquatic environment: • Webbed feet • Altered molars • Dense, water repellent hair

  3. Listed as secure Declined nationally between 10 to 50% since European settlement Hunted for fur Extermination program Widespread distribution within Australia, but populations patchily distributed Historical and current distribution

  4. Life history • Females of this species mature relatively late • Length of gestation, litter size, age at weaning and age at maturity suggest a low reproductive output • Primarily K-strategist

  5. Habitat modification Natural habitat degradation • Fragmentation of landscape • Altered levels of nutrients and chemical in water • Invasion by feral predators • Competition with introduced species • Altered microclimates Study site which has suffered from land clearing and erosion

  6. Purpose of study • Investigate the diet and foraging behaviour • Determine the limiting factors affecting the distribution of H. chrysogaster • Museum specimens and field research

  7. Museum based work Museum samples used to investigate: • Bergmann's Rule • Biogeographic variation in diet

  8. Warm-blooded animals from colder climates/ higher altitudes larger than counterparts in warmer/lower altitudes Pattern exists in 50% of carnivores Determine if this exists for H. chrysogaster 1. Bergmann’s Rule and body size in H. chrysogaster

  9. Skull length Skull width Snout length Snout width Chest girth Eye size Body length Tail length Ear size Pes length Morphological characterstics

  10. Investigate broad scale dietary patterns across Australia: Food items consumed Particle size for each organ Size of digestive organs in relation to body weight and size Size of prey in relation to individual Gut content and morphology in relation to geography Relationship between morphology and diet 2. Biogeographic variation of food habits of H. chrysogaster in Australia

  11. Field based research Wollondilly River at Arthursleigh, NSW H. chrysogaster burrow along the Wollondilly River

  12. Field based research con’t • Effects of the introduced red fox (Vulpes vulpes) on the foraging behaviour of Hydromys chrysogaster • Food selectivity of H. chrysogaster in a riparian environment • Habitat factors influencing distribution of and abundance of H. chrysogaster • Patch selectivity in foraging behaviour in H. chrysogaster: guiding parameters in patch choice

  13. 3 Effects of the introduced red fox (Vulpes vulpes) on the foraging behaviour of H. chrysogaster

  14. Does the presence of introduced red fox (V. vulpes) affect terrestrial foraging behaviour? Does interspecific competition occur between H. chrysogaster and V. Vulpes? Interactions between H. chrysogaster and V. vulpes

  15. Methods Three trials: • Transects of track plates before and after fox removal • Transects with alternating scented and unscented plates every 20m • Instantaneous alternatives, 2 plates at each station

  16. 4. Food selectivity of H. chrysogaster in a riparian environment • Which food items are selected based on food availability? • Do seasonal differences exist in the use of the aquatic feeding mode? • Are there altitudinal differences in the feeding mode?

  17. Are there changes in prey size preference in different stages of foraging? • What are the advantages of aquatic foraging in terms of food availability? • What are the impacts of water quality on the diet of H. chrysogaster?

  18. 5. Habitat factors influencing distribution of and abundance of H. chrysogaster • How do animals feed and forage within varying water depths and widths? • Is there a direct relationship between river width and depth and food availability? Site along the Wollondilly River where H. chrysogaster are present

  19. What terrestrial habitat characteristics influence the presence/absence of H. chrysogaster? • What factors influence the size and use of home ranges?

  20. 6. Patch selectivity in foraging behaviour in H. chrysogaster: guiding parameters in patch choice • Do animals discriminate between small and large prey in patches with equal numbers of prey items? • Do animals discriminate between small and large prey in patches with equal biomass of prey? • Do animals discriminate between patches that are shallow and deep which contain the same volume of prey?

  21. Thank you

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