Literature review: Impact of Chilean needle grass ... - Weeds Australia

abiotic influences affecting lower trophic levels”. However there has been very little comparable research into spider
communities in any habitats in Australia (Churchill 1997), they interact with invasive plants only indirectly (Mgobozi et al.
2008) and their specialisation by prey type also appears to be relatively low, limiting their usefulness.
Correlations between the richness of taxa may be coincidental, a response to common environmental factors (e.g. climate) or to
different factors that are spatially covariant, or the result of biological interactions between taxa (e.g. Hymenoptera parasitoids
and their hosts) (Wolters et al. 2006). Unfortunately many studies have used groups for which there is no a priori reason to
believe have good indicator value (Wolters et al. 2006).
Driscoll (1994) recommended beetles, ants and grasshoppers as suitable indicator groups for south-eastern Australian grasslands,
based on the relatively large size of the constituent species, their functional significance, variablity in dispersal abilities and,
possibly most importantly, the availability of taxonomic knowledge and expertise. But what studies of these groups might
‘indicate’ is unclear. New (2000) suggested that ants might be good indicators of habitat complexity, but lack of primary
phytophagy in the group suggests they would show little response to simple floristic change. Gibson and New (2007) suveyed
beetles and ants in a Victorian grassland, but found that nearly all were widespread regionally, and provided no correlative
measures for environmental change. Farrow (1999) argued that the use of phytophagous Chrysomelidae and Curculionidae – the
most diverse Coleoptera families he detected in ACT grasslands – as indicators was compromised by poor understanding of their
life histories and larval and adult host plants. Grasshoppers were considered also to be not particularly useful because of their
highly clumped distributions due to particular oviposition requirements, their need for solar insolation and inter-annual
dependence on rainfall (Farrow 1999).
New (2000) assessed previous studies of ant diversity in temperate Australian grasslands and evaluated the suitability of ants as
indicators of habitat conditions. Surveys that detected most of the surface active resident species commonly detected 20-30
morphospecies. He considered ants to be poor indicators in Victorian grasslands because the species present are relatively habitat
tolerant and the habitat is relatively heterogeneous at the fine scale. Ant diversity of grasslands dominated by native or exotic
grasses were similar, and species composition of the grasses was probably less influential than structural diversity in the
vegetation and overall habitat complexity. Miller and New (1997) evaluated pitfall trapping of ants as an indicator of grassland
disturbance as manifested by the invasion of the exotic grass Holcus lanatus L., in Austrodanthonia grasslands at Mount Piper,
Victoria. They detected 36 morphospecies by fortnightly pitfall trapping over seven months and concluded that the rankings of
generic diversity at each site “usually coincided” with ranking of sites on a scale from “most natural” to “most degraded”. The
grassland ant fauna appeared to be easier to define in terms of sampling effort than the much more diverse fauna of woodlands,
but the grasslands sampled nevertheless indicated a mosaic of ant assemblages that differred between sites with apparent
vegetational homogeneity. Native and exotic dominated sites had a similar number of species, while rare species and many more
common species were not habitat specific. Only the subordinate Camponotus group appeared to be a good indicator of ‘natural’
sites (New 2000). Hinkley and New (1997) found that short term sampling using pitfall traps was inadeqate to assess ant species
diversity and that sampling across seasons and extensive sampling in summer were required to enable reasonably complete
inventories. Single trapping events (of c. 14 days) collected no more than half the species found by repeated trapping over
fortnightly intervals for 7 months.
Despite Evans’ (1966 p. 9) comment that the Australian cicadelloid (Hemiptera: Cicadellidae, Eurymelidae and Membracidae)
fauna of “grasses, and of annuals and perennials generally, is very sparse”, Farrow (1999) found that the diversity and
distribution 32 species of Cicadellidae obtained in sampling at 11 grasslands in the ACT, provided a good approximation of the
total number of canopy insect species at individual sites. He recommended the family as a relatively homogeneous grass-feeding
group suitable for use as an indicator. However Yen at al. (1994a) found only five Cicadellidae spp. in Victorian basalt plains
grasslands. It is not clear whether this contrast in regional diversity is real or a sampling artefact (Farrow 1999).
Ease of sampling, taxonomic accesibility, ecological (trophic and microhabitat) diversity and functional importance are generally
agreed to be the most important criteria for indicator groups (Melbourne 1983, New 1984, Churchill 1997). Melbourne (1993)
found that the diversity of genera of Formicidae and to a questionable degree Carabidae (Coleoptera) provided sufficient
taxonomic resolution to assess differences in the species diversity of these groups in ACT grasslands, and that plant community
was a reasonably good predictor of diversity of these taxa. However it is likely that no single invertebrate group could be be used
as an adequate estimater for all the others (Melbourne 1993). Farrow (1999) for example found that ACT grassland sites ranked
for biodiversity using the Collembola data of Greenslade (1994) did not correspond with his own rankings based on canopydwelling
insects. A recent meta-analysis of over 200 studies found that no vertebrate, invertebrate or vascular plant taxon has
been found to be a good predictor for the richness of other taxa; indeed supposed indicator taxa have often proved to be
disappointingly inadeqate for the task, although invertebrates at the