Habitat requirements and habitat use of the red-crowned toadlet Pseudophryne Australis and the giant burrowing frog Heleioporus Australiacus in the Sydney basin
- Publication Type:
- Thesis
- Issue Date:
- 2006
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Habitat requirements and habitat use for Pseudophryne australis and Heleioporus
australiacus were investigated to aid management of these threatened frogs around Sydney,
Australia. Much of the work focussed on roads, commonly encountered features in the
habitat of both species.
The habitat requirements based on locality records of both frogs in the Sydney Basin were
investigated at four spatial scales. Both species are habitat specialists. They showed a strong
geological association with Hawkesbury Sandstone and occupy upper topographic areas
with ephemeral watercourses of gentle gradients. Both frogs occur predominantly in areas of
higher precipitation and milder temperature regimes compared to averages representative of
the region. Leaf litter is an important feature of P. australis breeding sites, whereas H
australiacus generally associate with crayfish burrows. Both species are dependent on
natural vegetation with a complex structure.
H australiacus have a relatively long larval period (3 - 12 months) and breed in ephemeral
pools, exposing their tadpoles to the risk of dying due to early pond drying. In the
laboratory, tadpoles responded to decreasing water levels by shortening their larval periods
and metamorphosing earlier than siblings held at constant water level. Despite this plastic
response, a number of pools in the field failed to produce metamorphs due to early drying,
an observation also made on P. australis. Regular monitoring of breeding sites revealed
increased reproductive success away from roads for both species probably because of
relatively longer hydroperiods.
Spatial distributions and associations with habitat features, and movement patterns of both
frogs were further investigated using mark-recapture methods. Both species showed strong
site fidelity. P. australis formed small aggregations and predominantly selected leaf litter
piles despite their relatively low availability. Leaf litter piles in creeks moved over time and
the animals moved with these piles. In contrast, H australiacus individuals formed no
aggregations and showed no preference for any available structural vegetation type.
Locations of individuals were independent of relative distances to creeks and artificial
drains, but males appeared to be more common near culverts. However, individuals were
randomly distributed in space and nearest-neighbour distances were high relative to
individual movement distances, suggesting minimal overlap between relatively large home
ranges.
Radio-telemetry demonstrated that some H australiacus individuals burrow in the road
environment. There they would be at risk of being dug up and possibly injured during road
works.
The results are discussed in relation to the spatial requirements of both species and the
protection of utilised habitat features. Management options are suggested to mitigate the
impacts of road works. Differences in spatial dynamics of both frogs with overlapping
habitats highlighted in this study require species-specific management approaches.
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