Protecting threatened and rare species of fauna

Typically, in any ecological community, most of the species are relatively uncommon or rare and there are only a few that are abundant, and threatened species are normally amongst the least abundant. It is often the rare or uncommon species that government environmental regulators will indicate that require management and are of conservation interest. So what is ‘rare’ and ‘common’ in the context of an ecological community? Although rare means in low abundance, a review of the literature indicates that the notion of low abundance must be considered in a broad context. There is no absolute definition of rarity; rather it is at one end of the continuum from common to rare. Sampling effort and methodology in fauna surveys also often defines what is rare, as we seldom actually know the structure of a fauna community. Cunningham and Lindenmayer (2005) provided the following useful table to assist with defining what is common and rare.

Table 1. What is rare and common (taken from Cunningham and Lindenmayer, 2005, p. 1136)

Abundance of species within a community

Habitat specifcity

Geographic range

Description

 Common Common Widespread

Widespread, occurs in a wide range of habitats

Common Common Restricted/localized

Highly localised distribution but occurs across a range of habitats and is abundant in places where it occurs

Common Rare/specialised Widespread

Widespread, but occurs in few habitats and is common in places where it occurs

Rare Rare/specialised Restricted/localized

Highly localised distribution and occurs in a few habitats, but is common in places where it occurs

Rare Common Widespread

Widespread and occurs across a range of habitats but is scarce in places where it occurs

Rare Common Restricted/localized

Highly localised, occurs across a range of habitats but is scarce in places where it occurs

Rare Rare/specialised Widespread

Widespread but occurs in few habitats and is scarce in places where it occurs

Rare Rare/specialised Restricted/localized

Highly localised distribution, occurs in few habitats and is scarsce in places where it occurs

Another way of looking at rare is species that are under direct threat or are vulnerable to extinction. If this is what we mean, then we should be focussed on threatened and be less concerned about rare species in an environmental impact assessment (EIA). However, Possingham et al. (2002) suggested that threatened species lists are designed to provide a qualitative indication of the risk of extinction, specifically to assess potential adverse impacts, help inform conservation priorities and as a component of State of the Environment reports. They went on to argue that these lists are now being used for the following four purposes, but were never designed to be used in this way:

  • set priorities for resource allocation among species;
  • inform reserve system design;
  • constrain development and exploitation; and
  • to report on the state of the environment.

Possingham et al (2002) went on to indicate the following three issues with the use of these lists to constrain development or exploration:

  • small impacts can be curtailed by listed species, but developments with large impacts on one or more non-listed species proceed with no mitigation requirements;
  • the high profile application of threatened species lists to constrain development affects the listing process itself (i.e. economic and social criteria override the criterion of extinction risk); and
  • the listing may increase the threats to species.

The last of these being the most serious, as it can lead to land managers destroying important habitat, denying the presence of the species in the area and thus avoiding implementing mitigation programs, and denying access to the area for research purposes.

The creation of a ranked abundance curve or a species abundance curve from fauna trapping data is always a downward sloping curve, with an abundance of a few species and a lot of species that are infrequently caught (Figure 1). This is also known as a Whittaker plot.

Species abundance curve 1 scott

Figure 1. Ranked abundance curve from a Pilbara trapping program (click figure for high res)

If the ‘Y’ axis is log transformed, then the curve is transformed to a near linear line (Figure 2) and the slope of the line can be used to describe the structure of the community.

Species abundance curve 2 scott

Figure 2. Logged transformed ranked abundance curve from a Pilbara trapping program as shown in Figure 1 (click figure for high res)

In EIA, consultants typically focus on species listed as threatened under the EPBC Act or the Wildlife Conservation Act, whereas the WA EPA (2002) Position Statement No 3 indicates that it is important to clarify that the intrinsic value of a species should not be judged only by its rarity or how threatened it is, and these species should also be considered in the context of their geographical distribution or their contribution to the sustainability of the ecosystem. So in this context, which of the categories shown in Table 1 should be the focus of an EIA assessment?

When mitigating potential impacts, should we be particularly concerned about and throwing a lot of money at:

  • protecting a small number of spiders in a development site that are listed ‘threatened’ in a habitat in which they are abundant?
  • protecting a small number of mammals in a development site that are listed ‘threatened’ when they are geographically widely distributed?
  • protecting a small number of reptiles in a development site that are listed ‘threatened’ then they exist on the periphery of their geographic distribution?
  • protecting a small number of birds in a development site that are listed ‘threatened’ when all the indications are that they are about to go locally extinct in the area anyway?

Or are there more fruitful ways in which these funds could be spent for the betterment of Australia’s threatened fauna?

References

Cunningham, R., B. and D. B. Lindenmayer. 2005. Modeling count data of rare species: some statistical issues. Ecology 86:1135-1142.

Environmental Protection Authority. 2002. Terrestrial Biological Surveys as an Element of Biodiversity Protection: Position Statement No. 3. Environment Protection Authority, Perth.

Possingham, H. P., S. J. Andelman, M. A. Burgman, R. A. Medellin, L. L. Master, and D. A. Keith. 2002. Limits to the use of threatened species lists. Trends in Ecology and Evolution 17:503-507.

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