Strategic Planning for Species Conservation: A Handbook - IUCN

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Strategic Planning for Species Conservation (c) compare the level of each possible agent of decline with that in areas, or at times, where the species is/was not in decline; for example determine whether harvest levels have increased over time, or whether local population extinctions have occurred in areas where habitat destruction has occurred. Use these comparisons to identify one or more likely agents of decline; (d) test the hypothesis that the agent(s) of decline have been correctly identified by experiment: in most cases the experimental “treatment” can be a management intervention designed to combat the threat, and so confirmation of the cause of decline can be combined with active efforts to conserve the species. Although Caughley and Gunn’s (1996) method may appear labour-intensive, this level of scientific rigor is entirely appropriate for such a critical component of SCS planning. Moreover, their approach need not be arduous if (as is often the case) there is clear evidence for decline being associated with some straightforward factor such as overharvest or habitat destruction (e.g., see Box 5.3). If the causes of a species’ decline are less straightforward – for example if they involve interactions between more than one factor – then the extra effort made to identify the causes will be worthwhile, since management interventions directed only at the most obvious factor may fail to halt or reverse declines. Often threats may be so confounded that the identification of the key factor in population decline is very difficult. For example, in highly fragmented environments, a species may be more subject to predation by other natural predators, may be more prone to be hunted by humans (because humans have easier access to small patches of their habitat), may be more apt to raid crops and hence be killed by humans, and may be more likely to suffer effects of malnutrition due to reduced food availability or compressed animal density. Each of these threats might be dealt with in a somewhat different way (e.g., predator reduction, poaching patrols, crop field deterrents, and artificial feeding, respectively), especially if what appears to be the ultimate threat (habitat fragmentation) is not readily rectified. Rigorous studies to disentangle these confounded effects are unlikely to exist for most species. In the absence of hard data, a listing and discussion of all the possibly important threats may spur future studies and provide more avenues for potentially effective conservation than a best guess about a single dominant threat. Population responses to conservation efforts will in the end give the best indication of what the threats were. For example, if improving anti-poaching measures is associated with an increase in population size, then over-hunting can be assumed to have been a key threat. The first two steps of Caughley and Gunn’s (1996) “recipe” – studying the species’ natural history and identifying possible causes of decline – are likely to have been conducted prior to the development of a SCS, at least for some species in each taxon. Key aspects of the species’ natural history will have been summarised earlier in the Status Review. The “threats” section should thus list evidence for and against particular factors representing threats to species persistence, based on the correlational methods outlined in Caughley and Gunn’s (1996) step (c), or, where available, on experimental evidence from their step (d). Box 5.3 provides some examples of threat analyses based on these sorts of evidence; note that the analysis process is not always arduous. The examples are chosen to show how threat analyses can sometimes be conducted for groups of species as well as for single species. When a list of multiple threats is generated during the threat analysis process, it may be helpful to categorise these into most serious, less serious and so on, so as to ensure that resources and efforts are focused on those Objectives and Actions that will have the greatest effect in saving the species. 35
Box 5.3 Examples of threat analyses for various species Example 1: Causes of Asian elephant (Elephas maximus) decline in Sumatra 36 5. Status Review Problem: Field surveys revealed that, of 12 sites in Sumatra’s Lampung Province which formerly supported elephant populations, only three contained elephants in 2002. Threat analysis: Field surveys and analyses of remote sensing data showed that, at the nine sites which no longer supported elephants, native habitat had been converted to agriculture, whereas the three occupied areas still contained relatively intact forest. No experimental test was needed to confirm habitat loss as the ultimate cause of elephant decline. At some of the sites, the last elephants had been live-captured by wildlife authorities to alleviate human–elephant conflict; hence conflict was a proximate threat, ultimately caused by loss of habitat which placed elephants in closer contact with people and their crops (Hedges et al. 2005). Example 2: Causes of black rhino (Diceros bicornis) decline in the Luangwa Valley, Zambia Problem: Black rhinos in the Luangwa Valley declined to extinction between 1979 and 1985. Threat analysis: Comparisons of rhino sighting rates in different sectors of the park revealed that rates of rhino decline were highest where anti-poaching patrols were least intensive. The hypothesis that poaching was causing the decline was supported by retrieval of rhino carcasses with their horns removed. Quasi-experimental evidence to confirm the importance of poaching as the key cause of rhino decline came from a comparison of population trends in different rhino populations, which showed that rhino populations were growing in areas receiving substantial investment in anti-poaching (Leader-Williams and Albon 1988). Example 3: Causes of decline of resident wildebeest (Connochaetes taurinus) in the Masai Mara ecosystem, Kenya Photo 5.3 Wildebeest (Connochaetes taurinus) migration in the Masai Mara © Karin Svadlenak-Gomez Problem: Resident wildebeest declined by 81% between 1977 and 1997. Threat analysis: Ottichilo et al. (2001) used spatial and temporal analyses to compare changes in wildebeest density with rainfall, the conversion of habitat to cultivation, and the density of livestock. Their results showed that loss of wildebeest was associated with conversion of wet season grazing and calving areas from savannah to cultivation. No experimental test of this hypothesis could be conducted since restoration of habitat was not possible. Example 4: Causes of decline of island foxes (Urocyon littoralis) on Santa Cruz Island, California Problem: This island-endemic subspecies declined by 90% between 1993 and 1999. Threat analysis: Potential causes of decline were predation by exotic golden eagles (Aquila chrysaetos; Roemer et al. 2001), and infection by an exotic pathogen (heartworm; Crooks, Scott, and Van Vuren 2001). Sightings of golden eagles increased markedly around the time that the fox decline began, and 19 of 21 carcasses of radio-collared foxes appeared to have been consumed by eagles; in contrast, eagle sightings remained extremely infrequent on other islands where foxes did not decline (Roemer et al. 2001). Evidence of apparent heartworm exposure was found among foxes on Santa Cruz Island, but was also found on another island where foxes did not decline (it was
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