Combining conservation status and species distribution models for planning assisted colonisation under climate change

Effects of climate change are particularly important in the Mediterranean Biodiversity hotspot where rising temperatures and drought are negatively affecting several plant taxa, including endemic species. Assisted colonisation (AC) represents a useful tool for reducing the effect of climate change on endemic plant species threatened by climate change. We combined species distribution models (SDMs) for 188 taxa endemic to Italy with the IUCN red listing range loss threshold under criterion A (30%) to define: (a) the number of AC (measured as 2×2 km grid cells that should be occupied by new populations, i.e. grid cells = new populations) required to fully compensate for predicted range loss and to halt the decline below the 30% of range loss; (b) the number of cells necessary to compensate for range loss was calculated as the number of currently occupied cells lost under future climate due to unsuitable conditions. We used two representative concentration pathways, +2.6 and + 8.5 W//m2, optimistic and pessimistic scenarios respectively. Availability of suitable areas for AC was also assessed within the current species distribution and within protected areas. Under the optimistic scenario, no taxa would lose more than 30% of their range and AC would not be required. Under the pessimistic scenario, roughly the 90% of taxa showed a cell loss higher than 30%. Eight taxa were predicted to lose >95% of their range. For these species, AC was required from 13 to 16 new populations (=13–16 grid cells) per taxon to cap the range loss at 30%. For currently VU or EN species, an average number of 32–35 AC attempts would be necessary to fully compensate their range loss under a pessimistic scenario. Suitable recipient sites within protected areas falling in their projected range were identified, allowing for short-distance AC. Combining species distribution models and red listing thresholds under Criterion A has enabled the strategic planning of multiple species assisted colonisation minimising the effort in terms of new populations to be created and maximising the conservation benefit in terms of range loss compensation.