Biodiversity in Australia's National Reserve System - Part ... - BushBlitz

The findings of the studies of species being found in large or small numbers of reserves
provide simple results. Species present in larger numbers of reserves in the NRS are those
that are mobile and/or have large ranges. Hence, they are present in or able to easily move
through large areas of land and be present in many reserves. Birds and bats are very good
examples, having larger numbers of species in many reserves because they move over large
areas. On the other hand, the invertebrates provide the major numbers or species present in
very few reserves. Many species have very small ranges and the non-flying terrestrial
species are relatively immobile. Hence, they are not likely to cover large areas and so can
not be present within larger numbers of reserves. Many land snails have very small
distributional ranges, having evolved in specific rocky ranges and so will never be
represented in many reserves. However, they can be highly reserved if their limited area of
habitat is protected.
One of the encouraging results of this study was that nearly all species of all 11 studied
groups are found in more than one protected area and that, where a species is found in only a
very few protected areas, these are generally areas greater than 1000 ha in size. Larger areas
are less prone to edge effects and will usually contain a greater diversity of sites and larger
populations, making these populations more robust to stochastic events and have larger
genetic pools for evolutionary development. One thousand hectares was chosen as the cutoff
size for a larger reserve based on its use for the same purpose by Rodrigues et al 2004.
They used this as a minimum effective size for a reserve for a number of taxa. It is not
specifically clear that 1000 ha is a suitable size to maintain any specific population over the
long-term, but such an area seems likely to provide a significant area of habitat for smaller,
relatively immobile species, allowing them to maintain relatively large numbers of
individuals. Smaller areas have been found to maintain populations within fragmented
landscapes with Drinnan (2005) finding 3.5 ha to be a useful reserve size threshold and, more
importantly, patches greater than 50 ha were able to maintain forest interior species and
species that were sensitive to human disturbances. Tocher et al (1997) also found no obvious
loss of frogs in fragments much smaller than 1000 ha. This suggests that 1000 ha is likely to
provide a substantial area of habitat in which to conserve populations of any of the terrestrial
invertebrates and the smaller terrestrial vertebrates. They are not necessarily sufficiently
large for species that fly or the more mobile vertebrates. Furthermore, we point out that
fragmentation of the remaining native vegetation through land clearing remains a serious
threat as it will isolate even larger areas of retained land and can render 1000 ha or larger
reserves of little value for all but the smallest species over the very long term.
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