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Insect Assemblages in Grey Box Grassy Woodlands

Cheryl O'Dwyer
Melbourne School of Land and the Environment
University of Melbourne

Abstract for "Darwin 200: Evolution and Biodiversity" Conference

25-28 September 2009, Darwin, Australia

Insect assemblages within Grey Box Grassy Woodlands are not well studied, although it is assumed that higher quality sites - i.e., those that have multiple layers of vegetation structure and are large in extent - have greater species richness. This study aimed to investigate whether insect assemblages were affected by: habitat size (small, 2 ha; medium, 7.7 ha; and large, 21 ha); fragment condition (State 1, high quality, through to State 5, degraded); and plant diversity and/or habitat structure within fragments compared to a large reference block (300 ha) with multiple sites.  Over 17,000 insects were collected by sweep netting 36 sites four times per year over two years.   Sites with high quality vegetation (State 1) contained significantly more species (P = 0.003) and a greater abundance (P = 0.000) of insects compared to degraded sites (State 5), but differences between fragments of other vegetation quality States were not significant. This suggests that there is a gradient of diversity and abundance of insects from one vegetation state to the next.   Whilst there was no significant difference in insect abundance between fragments and the reference site (P = 0.14), there was a significant difference in species composition between fragments and the reference block (P = 0.05).  However, a pairwise comparison showed that small fragments that were of high quality did not differ from the reference block (P = 0.23). These results show that: (i) insect composition was more influenced by vegetation structure than by size; (ii) fragments and the reference block shared many species; and (iii) small high quality sites can be important refugia for insects.  Whilst there was no significant correlation between insect composition and plant diversity per se there was a significant correlation with plant structure (ie ground cover, litter, logs, height at 50cm, shrubs).  Morphospecies richness increased as the cover of native grasses and shrubs increased. 

Biobuzz issue NINE, AUGUST 2009