Another way in which humans have dealt with endangered wildlife populations has been through captive breeding and translocations. These techniques have been put forward in the past as methods to deal with future population pressures caused by climate change (Peters, 1992). However, although captive breeding and translocation are effective tools for conservation of some species, they may be appropriate for only a handful of species (see Box 5-8).
Box 5-8. Limitations of Captive Breeding and Translocation to Conserve Biological Diversity Threatened by Climate Change
In some cases, threatened populations of sensitive species could be augmented or reestablished through captive breeding for reintroduction, especially if the degree of climate change proves to be small or moderate. In combination with habitat restoration, such efforts may be successful in preventing the extinction of small numbers of key selected taxa. Similarly, translocation of wildlife between areas within their natural range also might mitigate the effects of small to moderate climate change. This strategy has been applied successfully to augment or restore depleted populations of various species (Boyer and Brown, 1988).
Captive breeding for reintroduction and translocation are likely to be less successful if climate change is more dramatic. Such change could result in large-scale modifications of environmental conditions, including loss or significant alteration of existing habitat over some or all of a species' range (Myers et al., 2000). Captive breeding and translocation therefore should not be perceived as panaceas for the loss of biological diversity that might accompany dramatic climate change, especially given the current state of the environment. Populations of many species already are perilously small; further loss of habitat and stress associated with severe climate change may push many taxa to extinction.
One limitation to captive breeding is the lack of space available to hold wildlife for breeding purposes. Zoos and offsite breeding facilities can be expected to accommodate no more than a small fraction of the number of species that might be threatened. Recent studies have indicated that no more than 16 snake species and 141 bird species could be accommodated and sustained in accredited North American zoos and aquariums in long-term management programs (Quinn and Quinn, 1993; Sheppard, 1995).
Captive breeding programs are expensive, and locating funding to support large numbers of programs could be difficult (Hutchins et al., 1996). For example, it costs US$22,000 to raise a single golden lion tamarin in the United States and reintroduce it to its native Brazil (Kleiman et al., 1991). Part of the cost associated with such programs includes the extensive scientific studies that must be conducted for the program to be successful. Reintroduction is technologically difficult and unlikely to be successful in the absence of knowledge about the species' basic biology and behavior (Hutchins et al., 1996). Rearing and release strategies must be tested experimentally, and released animals must be monitored to assess the efficacy of various methods (Beck et al., 1994). In the case of black-footed ferrets (Mustela nigripes) and golden lion tamarins, it took more than a decade to develop the knowledge base required for success.
If wildlife translocation involves moving species outside their natural ranges, other problems may ensue. Exotic species can have devastating effects on host ecosystems, including extinction of native fauna (McKnight, 1993). The unpredictable consequences of species introductions means that translocation is severely limited in its ability to conserve species that are threatened by climate change.
Finally, reintroduction and translocation programs cannot be successful if there is no appropriate habitat left for captive-bred or translocated animals to be released into (Hutchins et al., 1996). Not all of the habitat components that are necessary for a species to survive can be translocated. Entire suites of plant and invertebrate species may be critical elements for a species to succeed in a new environment, but no techniques exist for translocating intact biological communities. Although captive breeding and translocation have potential value for well-studied animals, these strategies appear to be impractical for the vast number of species threatened by rapid climate change.
Humans may need to adapt not only in terms of wildlife conservation but also to replace lost ecological services normally provided by wildlife. It may be necessary to develop adaptations to losses of natural pest control, pollination, and seed dispersal. Although replacing providers of these three services sometimes may be possible, the alternatives may be costly (Buchmann and Nabhan, 1996). Finding a replacement for other services, such as contributions to nutrient cycling and ecosystem stability/biodiversity, are much harder to imagine. In many cases, such as the values of wildlife associated with subsistence hunting and cultural and religious ceremonies, any attempt at replacement may represent a net loss.
In many agricultural/silvicultural systems, pesticides are used to prevent losses to pests (insects, pathogens, some vertebrates). In the past 50 years, pesticide use worldwide has increased more than 25-fold (Worldwatch Institute, 1999). The estimated cost of pesticide use in the United States in the mid-1990s was US$11.9 billion (equivalent to 4.5% of total U.S. farm production expenditures), and worldwide use was US$30.6 billion (Aspelin and Grube, 1999). Given that these values are for systems that still had some natural pest control, changes in wildlife distributions might necessitate changes in economic expenditures for pesticides.
However, pesticides often kill more than the target species, possibly eliminating natural predators that keep pest populations low. For example, increased pesticide use in Indonesia between 1980 and 1985 led to the destruction of the natural enemies of the brown planthopper. Subsequent increases in planthopper numbers caused reductions in rice yields estimated to cost US$1.5 billion (FAO figures cited in Pimentel et al., 1992).
Adaptation to loss of natural pollinators may be possible in some cases. Farmers sometimes lease bee colonies to pollinate their crops. Although this may be an option for the ~15% of crops fertilized by domestic honeybees, it may not be an option for crops typically fertilized by wild pollinators or for the 250,000 types of wild plants that are pollinated by 100,000 different invertebrate species (Buchmann and Nabhan, 1996).
Other reports in this collection