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Prioritisation Assessments in Species Conservation

Prioritisation Assessments in Species Conservation

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Are some species more worthy of conservation than others?

Due to anthropogenic activities, the present rate of extinction rise is taking place at nearly 1000 times that of then natural background level of extinction observed from the fossil record. Conservation biology traditionally focuses on preventing extinctions, This magnitude of species decline far outweighs the amount of resources available to conservation in saving each one. As we become more aware of the growing list of species at imminent danger of extinction, the longstanding perspective in conservation that all species are equally worth saving, is being replaced by conservation triage, the need to allocate our scarce resources in the most efficient and effective way possible to secure those species that produce greatest conservation benefits. But can we really place a higher conservation value on one species over another? There is a growing body of prioritisation assessments that have applied the principles of triage to the allocation of conservation resources. The methods most often advocated in the literature consider the ecological function, phylogenetic distinctiveness, risk of extinction or cost of required conservation effort of a particular species. This essay will address each of these values in turn arguing that some species are indeed more worthy of conservation.

A variety of ecological studies have identified focal species that are much more important than others in maintaining ecological function in a communities or ecosystem. One of these is Paine’s 1969 seminal paper on starfish, which demonstrated that some species, which he termed ‘keystone’ species, through their biotic interactions, have stronger effects on the diversity and composition of a community than their abundance would suggest. Their removal from a system therefore has the potential to have large flow on effects, disrupting the ecosystem dynamic and influencing the abundances of other species. A good illustration of this is Berger et al’s 2001 study on the effects of the local extinction of 2 apex predators: Grizzly bears and wolves, in the southern Greater Yellowstone Ecosystem. This widespread removal of interactions with these keystone species resulted in the irruption of a once low-density moose population within this ecosystem and led to a significant rise in herbivory of riparian willow communities at sites lacking predation or hunting. This structural modification of willow communities had cascading effects, decreasing avian richness and diversity over the same region. This demonstrates the potential for the loss of keystones to disrupt ecosystem structure and function. Different to biotic interactions of keystone species, another type of focal species ‘ecological engineers’ have disproportionate effects through physical and chemical modification of the environment. These are species that directly or indirectly modulate the availability of resources to other species by causing…state changes in biotic or abiotic materials. While these activities do not involve direct trophic interactions between species, they modify, maintain and/or create habitats

which have large influences on other species. A useful example of this concept is seagrass. Seagrass beds modulate ocean currents, which may alter turbidity and sedimentation rates and hence food supplies for other organisms. The growth, survival and abundance of such organisms is therefore dependent on seagrass. Therefore, if our priority is to conserve ecological function in such systems, ‘keystone’ must be prioritised over species, which are more redundant in their function in such systems. A further point is that many keystone species and ecosystem engineers have significant effects on the maintenance of ecosystem services—hydrology, nutrient cycling and retention, erosion and sediment retention, for example—while at the same time creating habitat for other species that also influence biogeochemical processes via nutrient uptake, conversion,and release. These focal species are therefore of greater management concern and conservation benefit because of their value in providing these services. Their greater worth is evident, not only

Species may also have differential conservation value based on its level of uniqueness. According to this view, it is necessary not only to conserve as much species diversity as possible, but also to conserve sets of species that include as much ‘evolutionary history’ as possible. For advocates of species uniqueness as conservation prioritization criterion, the most frequently adopted measure of diversity is phylogenetic distinctiveness. For any particular clade within a phylogeny, this is the sum of the branch lengths of the subtree connecting all the taxa in the subset. Using this method, those old, monotypic taxa with few sister taxa posess the longest branches and are considered most valuable in conservation priorities. An example of such taxa are the two species of tuataras (Sphenodon) which are the only representatives of their order, which capture a high amount of unique genetic and feature diversity. This diversity is largely irreplaceable, when compared to the buttercup species clade in the Ranunculus genus which has hundreds of members that possess similar genes and features. It has been suggested that to maintain evolutionary processes, we should focus on the lineages with recent or ongoing speciation, instead of valuing relict species like tuataras that may be dead ends for evolution (Erwin 1991). These active lineages, or ‘‘evolutionary fronts’’, are capable of adapting and radiating as the environment changes. However, this view has been criticized, because it would imply prioritizing

closely related and typically opportunistic species that are capable of adapting to

changing conditions. Opponents of this view argue that species like tuataras are relicts that that have limited ability to generate novel diversity, and those conservation efforts should instead focus on those branches that have recently undergone radiations. However, it is a dangerous to assume that we can predict future evolutionary potential and no general relationships between phylogeny and diversity over geological time have yet been established. But the species in rapidly diversifying lineages must have close relatives, and thus represent little unique evolutionary history and little character diversity compared to those more isolated and distinct branches. Therefore, by protecting phylogenetic diversity we are securing evolutionary potential: To have a wide base of variation from which evolution can proceed. In recognition of this, the Zoological Society of London, for example, has recently launched a programme to raise awareness and develop conservation strategies for evolutionarily distinct and globally endangered (EDGE) taxa (a combination of threat status and evolutionary distinctiveness) [30].The main goal of this approach is that by preserving as much phylogenetic history as possible, it will be more likely that the evolutionary potential of our world’s biota is preserved too.- Vasquez

Despite the argument for phylogenetic distinctiveness, such species are unlikely to be given conservation, given current choices for rarity and endemism- Mace Presently the large majority of conservation resources are prioritised according to the species threat level determined by the International Union for Conservation of Nature and Natural Resources (IUCN) red-listing criteria, which use quantitative rules to assign a risk of extinction (IUCN 2003). This approach is supported by many countries where the protection of endangered species is a legislated requirement- Wilson. For example, in Australia, species that are endangered and critically endangered are given priority for conservation spending at the national level (Possingham et al. 2002). This approach to prioritisation assumes that a focus on threatened species will result in the least extinctions (Possingham et al. 2002; Bottrill et al. 2008). However, this view is highly flawed in that while an assessment of threat status reveals the urgency of conservation intervention—it does not provide information about the the likelihood the conservation effort will work, and the associated benefits if it does. Conservation biology needs to devote more attention to identify and conserve keystone species and relatively less attention to rarity.”- Jordan Ultimately protecting only the rarest species is a symptomatic treatment and largely ignores the immediate and ongoing cost of conserving the species, and how these funds may be better spent elsewhere_ Wilson

A species that offers better conservation outcomes for the same amount of resources, should be the priority. For all known actions there is an associated cost and impact on assets of concern and conservation in no exception. From an economic perspective, conservation is about getting the most effective conservation from the available resources and some species cost more to save then they’re really worth. For example conservation costs may include land purchase, the cost of management, opportunity costs, compensation to a landowner, social costs, establishing a conservation program, the costs of information acquisition and planning, captive breeding programs. In making a cost-effective conservation decision, all of these potential costs for protecting a species must be taken into consideration. It might be that for the price of securing the most endangered species which may have limited ecological benefits and not be very evolutionarily distinct; you could secure a number of threatened species of more value for comparatively cheaper conservation actions. A prime example is the recovery and release conservation program for the endangered California condor, Gymnogyps californianus which amounted to US$35, over 20 years. While this was a significant conservation achievement in increasing the number of individuals in the wild from zero to 68, it is not a particularly valuable species ecologically or phylogenetically. It is possible then that the funds allocated to the condor could have instead been better spent in conserving species of a lower cost, but greater value.-Wilson


In making conservation decisions, some species are more valuable and do warrant greater amount of conservation resources than other species. In terms of ecological functioning, the role of some species is irreplaceable and vital for many of the ecosystem services that human society is reliant on. Other species may not provide such ecological benefits, but are distinct in their evolutionary history and may act as a valuable source of evolutionary potential to maximise diversity. In terms of cost and threat, species that are important but are cheaper in the conservation resources required to secure them are also of more conservation value, as they offer more bang for the buck. None of these measures of prioritization can be ignored, if we are to allocate our scarce resources to achieve the greatest conservation benefits. Although many studies and the initiative EDGE have combined species prioritization criteria, none have combined all the aspects discussed here. While such a measure may not lead to optimal use of conservation resources because of the lack of data and misinformed values of society, it would increase the chances of making good and defensible decisions in conservation planning.

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