Key findings: The TVA approach incorporating SDMs showed that fewer species might be vulnerable to climate change compared to using a simple TVA, and resulted in more species with no consensus. The SDM approach incorporating TVAs showed that the projected changes in range under climate change were highly variable. For most species, the recommended management options are to facilitate species dispersal, and to identify sites of suitable climate persisting within the species current ranges.
Once the two approaches to assess the vulnerability of species and PAs to climate change had been implemented, Durham University explored the potential for combining the SDM and TVA approaches to produce integrated assessments of the potential threat of climate change to species of conservation concern in West African PAs.
TVAs use species trait data to inform the exposure, sensitivity and likely adaptability of species to changes in climate. SDMs, by relating the occurrence of a species to climate, can be used to assess the sensitivity of a species to projected changes in climate, with climate exposure being informed by projections of changes in climate. However, SDMs do not consider the ability of a species to respond to changes in areas of suitable climate as a result of their biological traits.
SDM and TVA methodologies were combined in two ways:
1. Climate suitability projections were used for individual species under scenarios of future climate to replace the simpler climate exposure measures more usually included in TVAs. The likely vulnerability of species to climate change was then estimated by combining these exposure projections with sensitivity and adaptability information from TVA analyses, resulting in an integration of SDM and TVA approaches termed 'modified TVA'.
2. Relevant trait data were incorporated into SDMs, both as a dynamic element within models of species responses to climate change and, for traits that could not be incorporated within dynamic distribution model, using dichotomous trait-based queries. This resulted in a mixed approach to the combination of traits and spatial modelling, termed 'modified SDM'.
It was found that the degree to which these two methods differ is greatly affected by how species that have no consensus in their future climate impact (i.e., no consistent trend in their response to predicted changes) are treated.
Compared to the climate change vulnerability assessment of Carr et al. (2014), the 'modified TVA' approach, which incorporates spatially-explicit modelled climate suitability, indicates fewer amphibian species vulnerable to climate change per site and, instead, many more species with little consensus in the degree to which they may be vulnerable to future climate change. The overall climate vulnerability of birds using the 'modified TVA' approach suggests fewer climate vulnerable species than does the original analysis in the southern parts of the region, with around 70 species projected to experience declining climate suitability in PAs in the South, compared to projection of over 100 species in the original TVA analyses. The 'modified TVA' approach also indicated a large number of bird species for which no climate change vulnerability consensus could be reached. The number of mammal species considered vulnerable by Carr et al. (2014) is broadly similar in its patterning to the number arising from the 'modified TVA' but, again, the total number of species identified as vulnerable in the individual PAs are smaller than in the original estimation. The 'modified TVA' approach also highlights less certainty (a lack of consensus) in parts of SE Nigeria and coastal areas of Ghana, Cote D'Ivoire and Liberia.
The 'modified SDM' approach showed that the projected changes in range under future climate change are very variable, after considering traits such as dispersal ability, generation length, and age to first breeding in addition to climatic suitability. This approach allowed site-level climate vulnerability to be evaluated and the formulation of management recommendations for individual species based on their potential to respond to projected climate change. For most species of West Africa, the principal management options will be (i) to facilitate the natural dispersal of species from their current range to areas of suitable climate in future, and (ii) to identify sites of suitable climate persisting within the species current ranges that can be prioritised for conservation management.
Number of mammal species previously classified as climate change vulnerable by Carr et al. (2014) that are assessed as climate change vulnerable by 2040-2069 using the modified-TVA analyses: (a) number of species experiencing decreasing climate suitability in each PA, (b) number of species with no consensus of future climate impact and (c) number of species for which climate suitability is increasing in PAs.
