Clement Reid - a Victorian Botanist ahead of his time

Diving straight into a a study on species migration, Pearson’s (2006) paper focuses on the uncertainty with which we can model species migration. I believe this will be a recurring theme when exploring the debate on climate change and species migration.

From examining fossil pollen data of postglacial migration of tree populations in North America, he concluded that migration rates were of the order of 100 m - 1000 m per year. These rates seem phenomenally fast and are often described as “Reid’s paradox” in recognition of Clement Reid, a Victorian botanist, who could not understand how such species could migrate so fast. A theory has been put forward where by this staggering rate of migration is explained by local dispersal from isolated populations that have managed to persist in microclimates where the regional climate has been ill-suited. The low density populations would not show up on the pollen record and hence might explain the massive rate of migration beyond the reconstructed climate ranges. This phenomenon is known as glacial refugia*.

This theory may pose problems looking towards the future. It is estimated that plant species will have to migrate at rates of over 1000 m per year in order to keep up with the current warming. Encouragement initially came from examining the historical records that hinted that such rates were possible, however McLachlan et al. (2005) believe that the migration rates were an order of magnitude slower (100 m per year) and the cause for optimism is unfounded.

Thomas et al. (2004) estimated species extinction from climate change for 1103 endemic species that cover approximately 20% of the earth. When using the maximum warming scenarios he estimated that the species, as he put it, “committed to extinction” were 21% - 23% if migration rates keep up with climate change and 38 - 52% if they do not. This is quite a frightening prospect.

New research is constantly adding to our knowledge and improving our understanding of the responses to climate change. It just goes to show that our predictions are filled with uncertainties and, frankly, guesswork. Future modeling needs to focus on local scale climates and possible refugia in areas that would be regionally unsuitable. This however is complex due to the difficulty in predicting local space climate change. Future dispersal models should not rely on unrealistic migration rates and instead should incorporate localized populations and genetic traits. Pearson’s (2006) findings gives us no cause for optimism when contemplating species response to climate change while arguing we need more research and information to reduce model uncertainty.

* There will be more detail of glacial refugia in subsequent posts.