Effects of fragmentation on arthropod assemblages in heath and woodland
B.Sc. (Hons) 1997
1. The original vegetation of the Sydney region is highly fragmented as a
result of intense agricultural activity and urbanisation since 1788. We
investigated the effects of this fragmentation in the Sydney region on
arthropod assemblages in heath and woodland vegetation. Focusing on species
composition and functional roles, we compared the fauna of small urban
fragments with that of several spatially independent larger areas of
vegetation.
2. Pitfall and yellow pan traps were placed in 21 fragments of heath and
woodland classed as either 'small' ( 4 km2) or 'large' ( 80 km2) in the Sydney
region. Arthropods collected were sorted to family or genus and then to
morphospecies.
3. Heath and woodland habitats were found to contain different arthropod
assemblages and support different assemblages of ant functional groups. The
hypothesis that large and small habitat fragments contain different arthropod
assemblages was then tested for both vegetation types.
4. There was no relationship between species richness and fragment
area per se although the percentage of traps in which generalised myrmicines
were
present was negatively related to area.
5. Large and small habitat fragments contained different assemblages of
arthropods in both heath and woodland. Microhabitat characteristics were also
significantly different, with leaf litter, disturbance and ground cover
contributing most to the difference.
6. No single species accounted for more than 5% of the differences
between small or large fragments in either heath or woodland, suggesting that
'indicator species' would not be effective in the assessment of the state of
fragments. However, generalised myrmicines and opportunistic ant species
contributed to greater than 60% of the difference in ant functional groups in
woodland.
7. The fundamentally different fauna of small urban fragments may be a
result of any of a suite of pressures associated with fragmentation and
urbanisation, including increased anthropogenic disturbance, reduced area,
loss of hosts, invasion of new species and release from natural enemies. The
complex response of arthropods to fragmentation suggests that management goals
for smaller remnants should focus on the functional roles of invertebrates,
rather than on specific target taxa identified from surveys of larger,
undisturbed remnants