Justin Gerlach
Research & conservation Red Listing invertebrates Publications Phelsuma Press

Climate change and extinction

Climate change is emerging as a major threat to bidoviersity as well as to human livelihoods. I have undertaken research into the impacts of climate change on several species. The publications arising from the research are summarised here.

Short-term climate change and the extinction of the snail Rhachistia aldabrae (Gastropoda: Pulmonata). Biol Lett.

Abstract: The only known population of the Aldabra banded snail Rhachistia aldabrae declined through the late twentieth century, leading to its extinction in the late 1990s. This occurred within a stable habitat and its extinction is attributable to decreasing rainfall on Aldabra atoll, associated with regional changes in rainfall patterns in the late twentieth and early twenty-first century. It is proposed that the extinction of this species is a direct result of decreasing rainfall leading to increased mortality of juvenile snails.

The potential effects of climate change on the status of Seychelles frogs (Anura: Sooglossidae). Journal of Threatened Taxa 3(6).

Abstract: The status of the Seychelles frogs of the family Sooglossidae was investigated, using monitoring data from 1993–2010, climate data from 1998–2010 and studies of populations and local climate effects. Climate monitoring at each plot covered rainfall and temperature, with leaf wetness and soil moisture being monitored additionally at one site. Analysis of the data and ecological modelling of the distribution identify geographical patterns in climate which explain the present distribution of the different sooglossid species. In addition it identifies a drying trend in the first quarter of the year which corresponds to frog population declines in mid-altitude forests. This is interpreted as evidence of an ongoing deterioration in the suitability of habitats for the frogs, with declines recorded in areas of marginal suitability. By extension it is assumed that currently optimal frog habitat is also undergoing a decline in suitability, due to early year decreases in moisture. Projected changes in climate were used to predict changes in ranges of the sooglossids over the next 90 years. This predicts significant declines, with the possible extinction of the palm frog Sooglossus pipilodryas by 2100. Accordingly all four sooglossid species should be categorised as Endangered, rather than their current status of Vulnerable.

Will climate change affect terrapin (Pelusios subniger paritalis andP. castanoides intergularis) conservation in Seychelles? Phelsuma 17A

Abstract: We report a modeling study on habitat suitability and predicted distribution shifts of two speciesof Seychelles’s freshwater turtles (Pelusios castanoides and P. subniger) under a climatechange scenario. We utilized data from the entire species distribution for modeling habitat suitabilityof the two species under current and future climate conditions, by using the MAXENT algorithm.At the continental scale, it appeared that P castanoides will shift its range towards more coastalareas, whereas P. subniger will move towards more southern sites. In the Seychelles archipelagoscale, habitat suitability for P. castanoides will decrease significantly, mainly in the interior areasof Mahé Island. On the contrary, the climatic conditions are predicted to remain suitable for P.subniger, which will enjoy a significantly increased habitat suitability in Seychelles.

Climate change, species extinctions and ecosystem collapse. Phelsuma 17A

Abstract: Climate change models have predicted many environmental impacts, but there have beenrelatively few published studies of ecosystem or population changes. Three studies of ecosystemsand populations are reported here from the Seychelles islands. A study of a seagrass and lagoonecosystem on Silhouette island, shows that rising sea-levels are causing changes in current patternsover the reef. Local increases in current speed act as a stress on the seagrass, leading to death ofthe plants over much of the reef-flat and loss of its stabilising function. Silt iseroded off the reef-flat and into the lagoon, removing habitat for some lagoon-dwelling animals.Significant changes in fish populations have been recorded, including the possible extinction of thegoby Asterropteryx gubbina; this is the first report of possible species extinction for which sea-levelrise appears to be the primary cause. Sea-level rise is also causing increased marine incursion intoestuarine habitat, this has led to declines in populations of the dartfish Parioglossus multiradiatus,which should be considered to be Critically Endangered. Climate change impacts are also apparentin terrestrial systems: the destablisation of a hybrid zone, leading to the extinction of the snailPachnodus velutinus in 1994 followed a period of reduced rainfall. This is in accordance withpublished models that predict increased frequency of extreme weather patterns in the region. Thesestudies indicate that rapid population and ecosystem changes are occurring. Climate change may already be one of the primary drivers of extinction.