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

e assigned the same biodiversity score as those that are rare and narrowly distributed (New 1984, Driscoll 1994) and links with
other biological studies where species names are used can rarely be made except by later reference to preserved voucher
specimens. Imprecise taxonomic information severely limits connections with the whole range of existing biological and
ecological information about particular taxa (Churchill 1997).
Thus it is generally difficult to determine whether a particular grassland area contains a good representation of the invertebrate
fauna. The criterion of rarity is also difficult to assess given the general low level of invertebrate knowledge. It requires
examination over temporal and spatial scales largely beyond the reach of current resources. Endemism may be a better criterion
(Driscoll 1993), but again often requires more knowledge than is available (Melbourne 1993), except for a very limited range of
organisms, or at the biogeographical scale.
Landscape criteria and the biological attributes of species
Landscape criteria are intended to enable the integration of habitat patch attributes, dispersal characteristics and dispersal
opportunities of the organism with population biology, conservation genetics and the features of the surrounding landscape to
arrive at guidelines for conservation (Driscoll 1994). For example, small populations may frequently become extinct, but that is
not a problem if recolonisation from surrounding habitat is inevitable. However knowledge of the dynamics of invertebrate
metapopulations is very difficult to investigate in fragmented grassland remnants (Yen 1999). Consideration of these
complications led Driscoll (1994) to conclude that until such time as a wide range of invertebrates with variable dispersal
abilities and life strategies could be assessed, all native grassland remnants were potentially important for invertebrate
conservation, and conservation approaches should attempt to ensure maximal connectivity between the remnants.
Consideration of the biological significance of grassland invertebrate faunas must include identification of taxa restricted to
grasslands and determination of the presence of threatened species (Yen 1995). The most important criteria in determination of
species at risk are low vagility (Hill and Michaelis 1988, Farrow 1999), low reproductive rate, long development period and
degree of endemicity (Hill and Michaelis 1988). These criteria are clearly apparent for grassland invertebrate taxa known to be
endangered (see below).
Knowledge of the distribution of invertebrate species is often too limited to determine whether a species is restricted to
grasslands. Ants are amongst the better known groups and ants of native grasslands have been found to be largely a subset of
those of neaby woodlands (New 2000), again paralleling the vascular plants. Most grassland plants are also found in other
vegetation formations, particularly grassy woodlands, but if invertebrate foodplants or larval hosts are restricted to grasslands
then breeding populations of the invertebrate must also be restricted to grasslands. Some species may be restricted to grasslands
by multiple factors, e.g. microclimate and food plant distribution. The endangered Ptunurra Xenica Oriexenica ptunarra L.E.
Couchman (Lepidoptera: Satyrinae), a Tasmanian endemic, has Poa-feeding larvae and occurs in “open plains and poorly
drained areas bordering mountain lakes and swamps”, in open grassy woodlands and tussock grasslands, mainly in the Midlands
(Braby 2000 pp. 495-496). Two other Xenica species O. orichora (Meyrick) and O. latialis Waterhouse and Lyell are mainly
restricted to alpine grasslands in south-eastern Australia (Braby 2000). The thermal requirements of these species (including
open sunny areas for the adults to bask) are probably important in determining the habitat occupied. Similarly, grasshopper
diversity is impacted when trees reduce insolation in grasslands (Samways 2005).
Low vagility occurs when species are wingless or have reduced aptery, e.g. female grass anthelids, Pterolocera spp.,
(Lepidoptera: Anthelidae) are virtually wingless (Common 1990); the primitive, diverse, endemic Australian tribe Amycterini
(Coleoptera: Curculionidae) with some species in grasslands, are wholly flightless (Zimmerman 1993), and morabine
grasshoppers are very sluggish and sedentary. Poor dispersal abilities are particularly important in highly fragmented habitats
where remnant habitat patches are small and vulnerable to severe disturbances. Farrow (1999) noted that three of four
endangered ACT insects were flightless, but found that only seven species, about 2% of species sampled in canopies of ACT
grasslands, had flightless adults: one cicadellid, four Orthoptera and two micro-Hymenoptera spp. A higher proportion, of course
could be expected to occur in the ground- and soil-dwelling faunas.
Low reproductive rates probably occur in some large weevils and morabine grasshoppers. Species with long development
periods probably include the Golden Sun Moth Synemon plana Walker (Edwards 1994). Rhopaea sp. (Coleoptera:
Melolonthinae) may have a 2 or 3 year life cycle, making them more vulnerable to local extinction (Allsopp 2003). Local
endemicity is exhibited for example by sun moths (Castniidae), anthelids, Amycterinae and Morabinae. These factors are
considered in more detail below in relation to various grassland invertebrates identified as threatened or at risk in south-eastern
Australia.
Management effects
Various effects of grassland management on invertebrate species have been studied. Intensification of use generally results in
loss of specialist species and increases in the proportion and dominance of common generalist species and exotic species
(Tscharntke and Greiler 1995). Driscoll (1994) provided a brief review of grazing, pasture improvement, chemical use and fire.
Kirkpatrick et al. (1995 p. 87) claimed that herbicides “may badly affect native invertebrates”, but there appears to be little
published evidence. Farrow (1999 2006) evaluated the effects of grazing, fire and mowing on sites he sampled in the ACT, but
the small number of sites sampled provided largely inconclusive results. “There was no consistent evidence that burning had any
long-term impact on diversity” and “limited evidence from one site ... that regular mowing did not appear to limit biodiversity”
(Farrow 2006 p. 2). Natural variation due to drought had a more profound effect in reducing diversity than any of these
management measures (Farrow 2006).
Maintenance of microhabitat and habitat variability and plant diversity are basic requirements for invertebrate conservation.
Manipulation of patch dynamics, by promoting variation in plant diversity, plant age and successional stage can enhance species
richness (Tscharntke and Greiler 1995) but the increased diversity may comprise widespread, abundant species with little habitat
specificity. Farrow (1999 2006) found that the small, isolated urban grasslands with relatively uniform vegetation in the ACT
had markedly fewer species of canopy-living insects than the larger, better-connected, more vegetatively diverse, peri-urban
grasslands, but Farrow (2006 p. 11) concluded that the diversity was “not related to measurable or easily observable
environmental variables including vegetation diversity”.
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