In the past decade, a growing number of studies have modeled the effects of climate change on large numbers of species across diverse focal regions. Many common points emerge from these studies, but it can be difficult to understand the consequences for conservation when data for large numbers of species are summarized. Here we use an in-depth example, the multispecies modeling effort that has been conducted for the proteas of the Cape Floristic Region of South Africa, to illustrate lessons learned in this and other multispecies modeling efforts. Modeling shows that a substantial number of species may lose all suitable range and many may lose all representation in protected areas as a result of climate change, while a much larger number may experience major loss in the amount of their range that is protected. The spatial distribution of protected areas, particularly between lowlands and uplands, is an important determinant of the likely conservation consequences of climate change.
Climate change is likely to alter the species composition of protected areas, with important implications for conservation. For the last two decades it has been recognized that species might move into, or out of, parks and reserves as climate changes (Peters and Darling 1985). More recently, shifting range boundaries as a result of contemporary climate change have been observed for multiple species, underscoring the potential for climate change effects on species composition at fixed geographical points such as protected areas (Parmesan and Yohe 2003, Root et al. 2003).
Yet assessing the net effect of these movements has remained elusive—partly because observations of current range shifts are spotty, and partly because modeling of future range shifts for multiple species is data intensive and requires climate-change projections at a scale much finer than that offered by most global climate models. However, a variety of models of species responses to climate change are now available (figure 1, box 1), and multispecies modeling efforts are becoming more common (Bakkenes et al. 2002, Erasmus et al. 2002, Midgley et al. 2002, Peterson et al. 2002), including first attempts to assess the effects on species representation in protected areas (Araujo et al. 2004). These bioclimatic modeling studies have been important in highlighting the extinction risk associated with climate change (Thomas et al. 2004).
Each species responds to climate differently, so summary reports of multispecies modeling may be too brief to capture the full richness of either the methods or the results (Peterson et al. 2002). When multiple regions are combined (e.g., to estimate extinction risk; Thomas et al. 2004) or multiple species interactions are considered (e.g., to assess the effectiveness of protected areas; Araujo et al. 2004), it may be difficult for those not familiar with the regions or species to discern the underlying patterns of causation. One solution to this problem is to examine one region in depth and use it to illustrate general patterns that have been borne out in other regions.
Here we use a pioneering multispecies modeling effort that has been conducted for plants in the Cape Floristic Region of South Africa (figure 2) to illustrate how local biology, climate, and patterns of change combine to affect extinction risk and protected-area effectiveness. The Cape is a unique microcosm for such analysis, since it is both a bio-diversity hotspot and one of the world's six plant kingdoms (Simmons and Cowling 1996). The multispecies modeling effort for the Cape provides an excellent example of the potential effects of climate change on efforts to conserve species in protected areas, answering questions such as whether climate change will increase or decrease the number of species in protected areas, how these changes will unfold over time, and what species and areas will be most affected. In this article, we review the results of this modeling effort, with emphasis on similarities with and differences from findings from other regions, and on implications for protected areas and their ability to constrain species extinctions as climate changes.
The Cape as an example of multispecies modeling
The Cape studies are an example of bioclimatic (or “niche”) modeling, which has been conducted for many species in several regions of the world (table 1). The Cape studies assess the impact of climate change on more than 300 species in the protea family (Proteaceae; Midgley et al. 2003). The proteas—many of which are internationally important in the floral trade because of their large, colorful flowers and their attractive fruits and foliage—are excellent subjects for modeling biotic responses to future climate shifts because they are well studied and have life histories that make them directly sensitive to climate change (Midgley et al. 2001). All successful bioclimatic modeling efforts depend on information on the current distribution of the species of interest. In the Cape, the Protea Atlas Project, an extensive cataloguing effort, provides detailed information on current distribution of the proteas (Rebelo 2001). This information is used in bioclimatic models to establish how climate influences the current distribution of proteas and to model possible future changes (box 2).
The proteas studied are endemic to the Cape, another attribute important for multispecies modeling. Bioclimatic models perform reliably only when the climate and distribution information on which they depend is available for the entirety of a species' range, thus defining the complete “climate envelope”that the species currently finds suitable (Pearson and Dawson 2003). Using information from only a portion of a species' range may cause a bioclimatic model to ignore potentially broader tolerances represented by the species' range outside of the study area. For this reason, modeling should be restricted to species endemic to a study region, or should cover the full geographic range of the species in question.
The proteas are important conservation targets owing to their endemism and ecological significance. The family Proteaceae is one of the three floral elements that defines the fynbos, a vegetation type so diverse that it makes the region surrounding the Cape of Good Hope the world's smallest plant kingdom (Richardson et al. 2001). Proteas are the largest and showiest of the fynbos signature elements (Cowling 1992). The other defining fynbos elements are the ericas (Ericaceae), members of the heath family that have dwarf-shrub growth forms and small tubular or bell-shaped flowers, and the restios (Restionaceae), reed-like plants that resemble horse-tails. The fynbos has arisen in the mediterranean climate and rugged, mountainous terrain of the Cape, and some evidence suggests that some groups have diversified and speciated widely in the geologically short period since the Miocene (Richardson et al. 2001). Most soils of the Cape are nutrient poor, forcing adaptation and specialization in the plants that occur there, and the vegetation that has developed is prone to fierce fires that recur at intervals of 10 to 30 years (Cowling 1992). Strong winds whip the Cape region, creating unique conditions for fire and plant dispersal, factors that are central to the diversity of the region (Simmons and Cowling 1996).
Species are the unit of study in the Cape protea modeling because abundant evidence from the past indicates that species respond individually to change in climate, rather than as coherent communities. No-analog communities—associations of prehistoric plants or animals that are unlike any that currently exist—are a common feature of the paleoecological record. Modeling of the Cape has been conducted at the community (biome) level, and this modeling shows a southward collapse of the fynbos biome that contains the proteas. B