Addressing risks to biodiversity arising from a changing climate: The need for ecosystem restoration in the Tana River Basin, Kenya

and reptiles are only able to disperse at 0.1 km/yr on average. The inclusion of a realistic dis- persal scenario is a key benefit of the Wallace Initiative and this can be seen as a proxy for cli- mate-smart conservation management, where protected areas are linked by corridors and species can disperse. Full dispersal, which has frequently been previously used in species distri- bution modelling, has been deemed to be unrealistic, due to factors such as barriers to species movement, a lack of instantly available suitable habitats and the dynamics of range shifts that have previously been observed [13, 55]. For this research, the difference between projected changes in species richness when species are able to shift their range compared to when they are unable to move beyond their current geographic range has been examined for mammals and birds as a sensitivity analysis to examine the potential importance of facilitating move- ment. Based on the realistic dispersal rates described above, birds and mammals may be able to move rapidly enough to remain in equilibrium with the climate. Based on the low dispersal rates found in the published literature, it has been assumed that plants, amphibians and rep- tiles are unlikely to be able to move at a sufficient speed to track their preferred climate. There- fore, this analysis has not been included for these taxonomic groups. Results Proportions of species at risk from climate changes Results show that climate change poses a significant threat to the biodiversity of the basin. In

most cases, a significant proportion of current modelled species richness could be lost (Fig 2). For all five taxa, the proportion at risk increases steadily with higher levels of warming. With 2˚C warming, a basin-average of 38% of birds and 31% of mammals could see a loss of their suitable climates. With 4.5˚C warming, 65% of birds and 54% of mammals could be lost from the basin. For plants, 56% of modelled species could be at risk with 4.5˚C of warming. Simi- larly, around 50% of reptiles and amphibians could be lost from the area under the business as usual scenario. Climatic refugia Climate refugia were identified for all five taxa within the Tana River Basin. When warming is limited to 1.5˚C, the greatest proportion of the basin is projected to be refugia for all taxa, rang- ing from 88% of the basin for reptiles to 31% for birds (Fig 3). Limiting global temperature rise is shown to be particularly beneficial for plants, which means that animals may be benefitted indirectly as they depend on plants for survival (as they provide habitat and food sources). 82% of the basin is projected to be refugia for plants with 1.5˚C but only 23% if warming reaches 2˚C. This is reduced to 3% with 4.5˚C warming. When warming is limited to 2˚C, around 81% of the basin (76,600 km2) is projected to con- tain refugia for at least one taxonomic group, including 18% within PAs, although some of this land has already been converted to agriculture (Fig 4). 76% of the basin is considered refugia for reptiles, 54% for amphibians, 38% for mammals, 23% for plants and 15% for birds. Only

areas in the west of the basin are not projected to be refugia for amphibians (S1 Fig) and rep- tiles (S5 Fig). For birds, mammals and plants (S2–S4 Figs), refugia are concentrated around the mountains in the north, along the main river in the east of the basin and the Tana Delta in the southeast. The Hanshak-Nyongoro Community Conservancy, Ishaqbini Hirola Commu- nity Conservancy, Lower Tana Delta Conservation Trust and Ndera Community Conservancy in the south of the basin are projected to contain refugia by most models. Significantly, there are cells within the basin where all 21 GCMs project refugia for all four animal taxa with 2˚C warming. These areas where the models are in agreement may prove important areas to focus PLOS ONE Risks to Kenya’s biodiversity from climate change PLOS ONE | https://doi.org/10.1371/journal.pone.0254879 July 21, 2021 6 / 25