Reconciling global mammal prioritization schemes into a strategy

Abstract

The huge conservation interest that mammals attract and the large datasets that have been collected on them have propelled a diversity of global mammal prioritization schemes, but no comprehensive global mammal conservation strategy. We highlight some of the potential discrepancies between the schemes presented in this theme issue, including: conservation of species or areas, reactive and proactive conservation approaches, conservation knowledge and action, levels of aggregation of indicators of trend and scale issues. We propose that recently collected global mammal data and many of the mammal prioritization schemes now available could be incorporated into a comprehensive global strategy for the conservation of mammals. The task of developing such a strategy should be coordinated by a super-partes, authoritative institution (e.g. the International Union for Conservation of Nature, IUCN). The strategy would facilitate funding agencies, conservation organizations and national institutions to rapidly identify a number of short-term and long-term global conservation priorities, and act complementarily to achieve them.

1. Introduction

In 2002, the Baiji or Yangtze River Dolphin (Lipotes vexillifer) was last seen; comprehensive surveys in 2006 failed to find any evidence of the species' survival [1]. On 27 August 2009, the last known individual of the Christmas Island Pipistrelle (Pipistrellus murrayi) disappeared [2]. Similar stories could play out a 1000-fold among humanity's closest relatives, the Mammalia, with more than one in five species now facing a high probability of extinction [2]. Conservation resources are insufficient: not all the conservation actions needed can be taken [3], and clear conservation priorities must be set [4]. Duplicated efforts cannot be afforded if humanity is to staunch mammal loss [5,6], and global strategies are thus necessary to coordinate action. Clear precedents are available to guide the development of a global mammal conservation strategy. For example, the Global Strategy for Plant Conservation of the Convention on Biological Diversity [7] provides a coordinated framework for action by 193 countries towards safeguarding the world's plants. For birds, too, BirdLife International, a global civil society partnership of national bird conservation organizations from more than a 100 countries, has developed an explicit, coordinated strategy for bird conservation [8], while for amphibians, the Amphibian Specialist Group of the International Union for Conservation of Nature (IUCN) Species Survival Commission has prepared an Amphibian Conservation Action Plan [9]. Even though the effectiveness of these strategies in reducing threats to the respective taxonomic groups is yet to be fully realized, it may be argued that they have been instrumental in raising the attention of decision makers, facilitating fund raising and coordinating the conservation efforts of at least the major international conservation bodies.

The huge conservation interest that mammals attract [10] and the large datasets that have been collected on them (e.g. [11–13]) have propelled a diversity of global mammal prioritization schemes [14–16]. The papers presented in this issue build and expand on the existing schemes, adding dimensions and insights to an already complex and multi-faceted body of knowledge. None of these papers represents per se the strategy that would ensure the long-term persistence of the world's mammalian fauna. Any comprehensive strategy will necessarily have to include a diversity of schemes to tackle a variety of conservation challenges. Making sense of the different approaches to conservation prioritization requires an understanding of the potential role of each prioritization scheme (including, but not limited to, those presented in this theme issue) within a global strategy. In the Introduction to this theme issue, Rondinini et al. [5] explain why a global mammal conservation strategy is needed and discuss the key elements for its development. Here, we highlight some of the potential discrepancies between the schemes presented in this theme issue, and propose ways to resolve them towards a comprehensive global strategy for the conservation of mammals.

2. Strategies for species or for areas

One of the main apparent tensions in conservation (see also [14]) is that between the conservation of species and of areas. Some of the papers in this issue focus on species [10,17] and others on prioritizing areas [18–22], reflecting the state of the art of the current literature in conservation prioritization [5]. A methodology for reconciling the two approaches exists, and is based on the optimization of multiple species-specific conservation actions across space and time [23,24]. This methodology aids decision making regarding where and when to act in order to maximize (with the available resources) a quantitatively defined biodiversity benefit (e.g. in terms of habitat area, or number of individuals conserved for target species). The drawback is that it requires a large amount of data not only on the distribution of and threats to species, but also on the cost and effectiveness of alternative conservation actions specific to species and sites. Therefore, the value of this methodology for a global, fine-resolution strategy for the conservation of all mammals is currently limited by the availability of data (e.g. data on the distribution of direct killing from hunting and poaching), and it finds application only for the solution of more specific problems [25].

It will take time for sufficient global species- and area-specific data to become available on the intensity of threats and on the costs and benefits of conservation actions. In the meantime, a global mammal conservation strategy will need to rely on both site- and taxon-oriented prioritization schemes. On the one hand, site-oriented schemes may provide better tools for maximizing the return on investment of conservation money, by spreading the benefit across many species. On the other hand, taxon-oriented schemes have the potential to increase conservation success through the fine-tuning of actions at the local scale, particularly for species and populations restricted to small residual ranges. Traditionally, charismatic species have attracted disproportionate amounts of conservation money [14], but choosing which species should be the focus of these taxon-specific actions involves considering a diversity of issues such as extinction risk (current [2,11], intrinsic [26] and predicted future [15,22]), phylogenetic distinctiveness [17,27], the economic costs of conservation [26] and role within the ecosystem (see [14] for a more comprehensive review). A comprehensive global mammal conservation strategy should avoid the pitfalls of prioritization based on just one criterion, and systematically identify those taxa to be targeted with species-based conservation action.

3. Reactive and proactive conservation approaches

Increasingly sophisticated socio-economic and climatic scenarios [28–30] provide unprecedented opportunities for forecasting the potential future distribution (and decline) of species (e.g. [31]), including mammals [20,22]. Adding a time dimension to the conservation allocation problem requires planners to identify the appropriate time scale for conservation action, by deciding when to act proactively or reactively. In principle, conservation should be proactive, because it is easier and cheaper to conserve species when they are still abundant and non-threatened [3]. Furthermore, in theory at least, some of the species currently considered as threatened may cease being so in the future even in the absence of conservation action [32], and thus would not be high priorities for conservation investment. However, proactive conservation relies on uncertain predictions and assumptions about how many biological and socio-economic parameters unfold and interact (such as future patterns of land use, climate change and species responses to these changes). Methods to incorporate uncertainty in parameters and models are available [19,23], including ensemble modelling [20] and scenario modelling [33]. These methods can be used to identify solutions robust to uncertainty, but if these assumptions prove wrong, conservation efforts could be misallocated to areas and species that do not need them.

More importantly, for many of the world's species time is already running short. Among mammals, 594 species are already Endangered or Critically Endangered [10], and 166 of these are restricted to a single site [34,35]. The conservation of a very substantial fraction of mammalian diversity depends, therefore, on urgent—reactive—conservation action [4]. Real-life conservation practice needs, therefore, to include a mix of proactive and reactive conservation efforts, as complementary (rather than mutually exclusive) strategies. A comprehensive global mammal conservation strategy should incorporate methods for balancing the investment between the two, taking into account information on species' current [11], intrinsic [26] and predicted [22] extinction risk, and the probability of conservation success.

Forecasts of species decline introduce a new concept: the future responsibility for the conservation of species, which is particularly relevant at the country level. If scenario-based predictions are realistic, many countries will find themselves responsible for the conservation of species that have declined or disappeared elsewhere, even if the species in that particular country has been consistently stable or increasing (thus the country has not been responsible for the species decline) [22]. Anticipating these trends could potentially hugely increase the cost efficiency of a global conservation strategy.

4. Knowledge and action

An open question in conservation concerns the degree of confidence with which conservation action can proceed with imperfect data [36]. Previous analyses indicate that area-based conservation plans are robust to a certain amount of missing data. For example, Grantham et al. [37] and Gaston & Rodrigues [38] obtained good results from conservation planning based on survey data that were a very small subset of the full datasets available on the distribution of, respectively, proteas and birds in South Africa. In this issue, Rodrigues et al. [21] found that it is possible to represent mammalian phylogenetic diversity at the global scale in a near-optimal way in the absence of phylogenetic data (e.g. using species data, or taxonomy as a surrogate for phylogeny). These results suggest that conservation money is better directed to action rather than to further data collection [39].

Whereas it is generally agreed that the scarcity of data should not deter managers from taking conservation action, and that the largest share of money should be directed to action rather than data collection [40], the knowledge versus action debate assumes different meanings depending on the context and type of the conservation action. Indeed different actions require different quantity and quality of data. Management of animal populations, for example, requires measurement of at least the basic demographic and ecological parameters that define the populations and their potential responses to conservation action, whereas spatial distribution data may be sufficient for at least interim area-based interventions. But the dynamics of ecosystems and their components, for example, through climate change, suggest that area-based interventions will need long-term monitoring to ensure that they remain effective.

Two issues should be considered more closely to find a way through the ‘how much knowledge’ question. One is related to expanding the collection of data on taxa that have not received conservation attention so far [40]. While priority setting appears generally robust to missing data within a taxon, even a broad one like mammals, analyses of congruence between priorities for very different taxa have produced mixed results [41,42]. Thus it cannot be taken for granted that a global conservation strategy for mammals, for example, would be sufficient for the conservation of other unrelated taxa, including plants and invertebrates. A second issue, more directly relevant to the development of an effective conservation strategy for mammals, concerns the balance between monitoring and action. Clearly, for a conservation strategy to be economically efficient in the long term, the effectiveness of conservation action must be evaluated to enable adaptive management (the modification of management interventions in the light of new information) [43]. Therefore, part of the conservation funding should be devoted to long-term monitoring, which is necessary to build the evidence base for conservation. A potential solution of the monitoring side of the knowledge versus action debate should comprehensively consider the costs and benefits of monitoring and action in the long term. A comprehensive global mammal conservation strategy should evaluate the return on investment of the whole process (and its uncertainty), from priority setting to achieving conservation, in order to evaluate the relative contributions of acting and monitoring [44,45].

If it is clear that the best available information should be used in mammal conservation plans [21], this does not necessarily depend on accumulating more data, since much can be achieved by extracting the most information from existing data. The global habitat suitability models presented here [46] are one way forward, at the very least to guide priorities for future research. The use of these models in large-scale conservation plans has been advocated in the past [47] to overcome at least partially the limitations of data, and at a small fraction of the cost of collecting further data. While applications of these models have been at times criticized [48], there are indications of their usefulness in a variety of conservation analyses, including the identification of gap species and priority conservation areas [49–51]. These support cautious optimism about their use, provided that they are robustly validated with field data. Other ways of extracting further information from existing data include data augmentation procedures [52] that can replace missing data with estimates based on known values. These procedures need further testing, but may provide surrogates of baseline life-history data (e.g. weight, generation length and reproductive rate) useful for the assessment of species conservation status and relative vulnerability to different threats [15,53].

5. Level of aggregation in indicators of trends

Indicators of trends at the local and global levels are instrumental to measure the progress (if any) towards the success of a global conservation strategy [54], and this theme issue presents two approaches to developing indicators at different scales: one based on direct data collection in the field [55], the other based on synthesis of data derived from the literature and expert knowledge (Red List Index [10]). The two types of indicator clearly have different properties and scope, with the Red List Index having the potential to be much broader in terms of spatial and taxonomic coverage. As such, it can be used to detect trends in a diversity of habitat types across biogeographic regions worldwide. Also, the wider coverage of the Red List Index should warrant a much smaller uncertainty when compared with an index based on direct observation, which is necessarily limited in taxonomic and spatial coverage by constraints in political, human and financial resources. On the other hand, systematic and long-term field data collection can be much more sensitive to local change than any indicator aggregated at the species level, thereby potentially reducing the reaction time to threats. Given the high cost of field data collection, a comprehensive global mammal conservation strategy should optimize it through taxon- and/or site-based prioritization schemes that identify the top priority species and sites for conservation monitoring.

6. Scaling a global strategy

A critical part of a strategy for global mammal conservation is the integration between global priorities and ensuring that effective actions are formulated and applied locally. This poses two related sets of problems for managing data, adjusting priorities and establishing institutional linkages: scaling down global priorities, and scaling up local actions.

Scaling down within the context of a comprehensive strategy for mammal conservation will involve practical mechanisms for translating global priorities into actions, via agencies and non-governmental organizations working across national, ecoregional and other intermediate extents. This translation must acknowledge that global priorities need to be partly redefined at intermediate and local scales, given the richer and finer resolution data available for progressively smaller parts of the world. This implies an iterative and protracted process of adapting broader-scale to local priorities, as new data become available and as unforeseen constraints and limitations are encountered. Unresolved questions arise. What institutions will be needed to manage the unavoidably adaptive nature of this process? How can the institutions that are responsible for assembling the necessary fine-resolution data (e.g. the IUCN for species data) mobilize the resources needed to systematically update global datasets as new data become available? And what data will be necessary and sufficient to define global priorities and then guide or support regional and local action scheduling?

In the opposite direction, scaling up involves the coordination of currently independent local conservation actions, so that they can be assembled into conservation systems that address global priorities for mammals while accounting for emergent properties of conservation networks such as complementarity, connectivity and the synergistic effects of multiple actions. This coordination will have to come from government or non-government institutions with effective engagement locally (following, for example, the structure adopted by the BirdLife partnership for birds). These institutions will need resourcing, as will effective actions in countries that contain global priority areas for mammals but are not capable of addressing them financially or socially.

Conservation strategies should be scaled not only in geographical space, but also along a taxonomic dimension. For example, detailed (and often regional) action plans exist for several mammal groups [56]. At the opposite extreme, global strategies could be developed, for example, for all vertebrates or for the entire biodiversity. At any taxonomic level, the trade-off is between the consideration of taxon-specific elements (e.g. life history and threats) and the optimization of conservation resources (since planning separately for many taxa increases the chances of uncoordinated efforts). For example, a plan for the conservation of large carnivores would account for the socio-economic conflict owing to the predation on livestock, but may ignore the potential effects of actions directed to habitat management for carnivores on the populations of small mammals. On the other hand, mammals are a coherent taxon in many respects. For example, many mammals are threatened by habitat loss, but relatively few are threatened by pathogens and invasive species, which are important threats to amphibians [2]. Whatever taxonomic scope is chosen for a conservation strategy, the problem of harmonizing it with strategies at higher and lower taxonomic levels remains open.

7. The opportunity to reconcile prioritization schemes into a strategy

Conservationists are now in a unique position to develop a comprehensive global conservation strategy for mammals. Knowledge has progressed significantly in the last 5 years and some of the most comprehensive datasets on any taxonomic group are now available. Methods exist to tackle a variety of conservation issues at different scales, well beyond the selection presented here. However, we are still far from having a single comprehensive strategy for all mammals.

What is now needed is a clear unity of intent, overcoming academic competition and personal interests, diffidence and personalities to achieve the ultimate goal of conserving the world's mammalian fauna into the future. But it would be unfair to blame only academia and its rules of assessing and rewarding scientists. A larger consensus will need to be built for an explicit mission by a responsible international conservation body directing all conservationists towards the goal of mammal conservation and calling for the contributions and competencies needed to reach the goal. The task poses complex intellectual, political and logistical challenges to reconcile a huge diversity of ecological, social, economic and administrative scales and a great variety of conservation tools under the same strategic umbrella.

So far scientists have been good at designing global ‘vertical’ (i.e. sectoral) strategies, as shown also by the papers in this issue, but have not been able to integrate them into a ‘horizontal’ plan. Now it is time for the scientific community to develop a fully integrated global mammal conservation strategy. This should include a high-level, clear vision of mammal conservation priorities agreed upon by policy makers, similar to what has been achieved for plants [4], but also with a thorough examination of issues and solutions for implementation (e.g. [6]), which should provide a seamless transition from a world strategy to effective local action and be agreed upon by conservation agencies and organizations. An operational starting point could be to clearly identify the different criteria used to value species, and assess which conservation scheme(s) best protect those values. The task of developing such a strategy should be ideally coordinated by a super-partes, authoritative institution (e.g. the IUCN) capable of convening all the relevant actors to discuss the issue. A global mammal conservation strategy would facilitate funding agencies, conservation organizations and national institutions to rapidly identify a number of short-term and long-term global conservation priorities, and act complementarily to achieve them (e.g. some working on avoiding extinctions, others working on the last wilderness areas) and thereby optimizing their resources.

We can continue to push forward our pet methods, objectives and species, in attempt to get the most funds individually for our specific goals and publish in the top scientific journals. Or, we can cooperate to reconcile the different approaches, develop a unifying global strategy for the conservation of mammals, and speak with a single, thus more resonant, voice. The urgency of mammal conservation firmly calls for greater effort towards achieving the latter option, and this theme issue aims to be a small first step in this direction. The knowledge achieved with mammal research provides a good stage to decide how to combine values, data and methods into a comprehensive, and potentially exemplar, global mammal conservation strategy.