Editor’s Choice – Selecting among conservation strategies in a changing world
April 2013 (Issue 50:2)
Mokany, K., Harwood, T. D., Ferrier, S.(2013) Comparing habitat configuration strategies for retaining biodiversity under climate change Journal of Applied Ecology 50:2, 519-527
When natural habitats are falling apart, conservationists and decision-makers are haunted by a simple question: what to protect? Or, more dramatically said: “what to let go?” (Marris 2007). This simple question most often receives a disappointing answer: “well, it depends”. Hopefully, we can say a bit more: we can say that the question must be rephrased according to whether the protection of “areas” or “species” is at stake. Accordingly, conservation biology has been shaped by the discussion of the efficiency of species-based strategies and area-based strategies. Specific guidelines are recurrently proposed to restore, maintain, and reinforce specific areas or species. But is this division between species and area-based conservation satisfactory? Let’s say we want to protect both. Can we do that?
In theory, yes. What one simply needs to know is which species and areas are already secured. From that, one can decide what species and areas should be added in the new and optimized conservation plan. Of course, how this addition must be made is already tricky because there are several ways to do that. For instance, one can decide to increase the “connectivity” between existing protected areas with the new ones, to increase the “representativeness” of the species pool to be protected by prioritizing the addition of new specific species, or by “aggregating” new areas to the old one. One can also adopt a more “balanced approach” by combining these different options. Although sometimes complicated, these problems can be solved using algorithm optimization on a computer. Interestingly, species-specific criteria can be added to this decision rule. For instance, the selection can be constrained by a certain level of favourable habitat for the focal species. In this respect, reserve design and corresponding systematic conservation planning algorithms has become a key tool to identify the best options.
In practice, however, things are different. First, areas are changing and species are moving: what is considered good today is probably misleading tomorrow. Conservation planning must account for changes in species ability to track climate changes (Oliver et al. 2012). Moreover, species are not alone: the dynamics of many species depend on the dynamics of other species. These practical realities have often been neglected and are increasingly added to existing algorithms. In fact, the crucial issue of optimal habitat configuration in a changing world is still a big challenge for applied ecology.
Mokany and colleagues propose in their study to conciliate theory with practice and to revisit the problem from a practical and yet solid angle. They start with a real and typical situation: the distribution of plant biodiversity over a large area. They propose to test several strategies of habitat configuration (connectivity, aggregation, representativeness and a balanced approach) instead of focusing on one or two strategies separately. They assume that areas are changing (following climate change) and that species are not randomly distributed but have limited dispersal abilities and are also constrained by community assembly rules.
The strength of their approach is not really to add even more possibilities or parameters to the traditional existing algorithms of conservation planning. This would have rendered an approach more complicated and more complex than what is usually done. The relevance of their approach is rather to keep the story simple and straightforward from an applied perspective. Their data, sample, model and tests are easy to follow and to generalize to other situations or taxonomic group or target (e.g. one can adapt their framework to investigate how functional diversity could be maintained).
Moreover, four clear messages are delivered: i) There is no magic numbers or solutions to a general question such as “what is the best habitat configuration to maximize biodiversity”. The best strategy depends on the objective. This was intuitively expected and in this study it is clearly demonstrated. ii) Corridors are not a panacea. Maximizing habitat connectivity is not always the best strategy. This was also understood but their comparison reinforces previous findings (Hodgson et al. 2009). iii) Representativeness must be designed wisely. This strategy will indeed often imply the addition of small and isolated fragments, not necessarily efficient in the long run. iv) A balanced approach where representativeness, aggregation and connectivity are considered together is often a good option.
This paper is an important contribution because these very clear recommendations are deduced from quantitative tests, a transparent model, and well-defined hypothesis. Overall, Mokany et al. show that reserve selection and conservation planning do not reduce to a computer game with abstract pieces of lands and species but is anchored in theoretical expectations, practical objectives and constraints.
Hodgson, J. A., Thomas, C. D., Wintle, B. A. and Moilanen, A. (2009), Climate change, connectivity and conservation decision making: back to basics. Journal of Applied Ecology, 46: 964–969.
Marris E. (2007) Conservation priorities: what to let go. Nature, 450 :152-155.
Oliver, T. H., Smithers, R. J., Bailey, S., Walmsley, C. A., Watts, K. (2012), A decision framework for considering climate change adaptation in biodiversity conservation planning. Journal of Applied Ecology, 49: 1247–1255.
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