Chemotherapy for ecosystems: Use of selective toxins to control invasive vertebrate pests
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A wide range of anthropogenic ecosystem disturbances accompanied the spread of European settlement across Australia after 1788. They included widespread land clearance, changed fire regimes, harvesting/persecution of native biota, hydrological change through damming and irrigation, and the introduction of new species (Lunney et al. 1997; Calver et al. 1998 and included references). In concert, these changes have contributed to the extinction of 17 mammalian species (Recher & Lim 1990), representing over 6% of the original mammalian fauna and about half of mammal extinctions worldwide in the last 200 years (Dickman et al. 1993). It seems unlikely that the situation has stabilized, because over 17% of extant Australian mammal species have suffered range reductions since colonization (Dickman et al. 1993). Garkaklis et al. (1998, 2000) highlighted that the extinct mammals included many burrowers and diggers, so a suite of species involved in soil turnover, nutrient cycling, and plant propagule dispersal have disappeared. The disruption of such critical ecosystem processes in the face of anthropogenic stressors is a critical tenet of ecosystem health theory and suggests a loss of health in the ecosystem as a whole (Costanza et al. 1998; Rapport 1998a,b).
Recent experimental evidence confirmed the significant role of the invasive predators the red fox (Vulpes vulpes) and feral house cat (Felis catus) in the decline of several extant mammals (e.g., Kinnear et al. 1998; Risbey et al. 1999; Risbey et al. 2000 and, by implication, in the extinction of related species. Control of invasive predators is now a major part of recovery plans for a range of Australian mammals (Maxwell et al. 1996), primarily by baiting with the toxin sodium monofluoroacetate (commonly referred to as compound 1080, pronounced 'ten-eighty') (see Twigg & King 1991 for a major review). However, wildlife advocates are often uneasy about poisoning campaigns, so delicate public relations issues are involved (Calver & King 1986; Temple 1990; Marks et al. 2000).
Cancers in human health are a tempting metaphor for the destruction wrought by invasive vertebrates to ecosystem health (Robert Colona, quoted in Stokstad 2000; Stone 2000. In the case of cancers, there is evidence that physiological or psychosocial distress may depress immune system function and contribute to the onset of disease. Malignant cells then proliferate and may disperse, disrupting normal functioning and causing death. Similarly, anthropogenic disturbances may predispose ecosystems to invasion by alien species, which displace indigenous species or modify ecosystem processes and disrupt ecosystem health. Furthermore, the metaphor can be extended to embrace treatments for cancer, with the use of toxins to eradicate or control invasive species seen as "chemotherapy for ecosystems." Several authors have explored the parallel between human health and ecosystem health (e.g., Ehrenfeld 1995; Rapport 1998a. Others have noted the power of such metaphors to encourage community involvement in environmental issues (O'Laughlin 1996; Calver 2000). In this paper, we extend the concept of the human health/ecosystem health metaphor as an educational tool, using the Australian case study of controlling destructive invasive predators by poison baiting. The destructive invasive species can be regarded as cancer cells in the ecosystem and the poison baiting as chemotherapy to eradicate or contain them. The metaphor may allay community disapproval of poisoning as a control method by relating it to a familiar form of medical treatment used to protect human health. We develop the metaphor by:
(1) overviewing the nature of human cancers and the applications, side effects, and limitations of human chemotherapy;
(2) overviewing characteristics of species introductions and the applications and limitations of chemical control of invasive species, with special reference to predator control in Western Australia as an example of "ecosystem chemotherapy";
(3) assessing the validity of the "ecosystem chemotherapy" metaphor by applying it to a range of ecosystems and commenting on its potential in community education.
The discussion reveals that the "chemotherapy for ecosystems" metaphor is robust in some cases and has potential as an educational tool. It is especially useful in highlighting the value of prevention, as opposed to cure, in the case of invasive species and emphasizing the importance of allowing local communities to make decisions about local ecosystem health.
|Publication Type:||Journal Article|
|Murdoch Affiliation:||School of Biological Sciences and Biotechnology|
|Copyright:||(c) Blackwell Science|
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