Global warming and habitat choice
The distance from London to Barcelona is 1138km (737miles). Various animals live in both locations but very few travel between the two. Researchers have chosen ectotherms (cold-blooded animals) such as British and Spanish butterflies as their well-studied, mobile and choosy subjects, if a little indecisive!
The fact that the warm, dry habitats of Catalonia (40.5 - 43°N) differ from the cooler, damper areas the insects use in Britain (50 - 60°C) is critical. The respective microclimates found in the two locations vary according to vegetation. They determine whether butterflies can shift to cooler closed habitats in hot years or vice versa in cold years.
Temperature is very important to ecology for many reasons. Species range far from original habitats, or simply a few centimetres in the case of microclimates. The effect of moving a species depends on its mobility and whether its other ecological requirements are met. One of the simpler aims was to find out if the butterflies preferred shadier habitats in warmer areas.
Butterfly monitoring schemes provided an abundance of data , on abundance in the different habitats of the 36 spp. studied. For 15 years, recorders had walked transects of 2-4km, using a 5m "corridor." There were 85 suitable transects in Britain and 81 in Spain.
The findings were prepared by AJ. Suggitt of York University and his collaborators from Britain and Catalonia. Publication was in today's Biology Letters of the Proc. Roy. Soc. B. They found that thermal habitat sensitivity was common to all the species, but quite small. The climate difference between Britain and Spain caused an average of 6 to 7% of individuals to move to a closed habitat (woodland or dense scrub).
Comma butterfly, a closed habitat (woodland) species, feeding on nettle, elm or willow. Its populations are growing throughout Britain - Comma butterfly image via Shutterstock
That means that 1.3% of individuals shift their habitat per degree Celsius, because of the 5°C difference between the two countries. Obviously, then, most butterflies with open habitats in Britain maintain that preference in Spain. Host plant, mating behaviour or nectar resources could all affect the butterflies' associations to vegetation much more. The conclusion must be that there is not enough adaptability in species to respond to climate change, despite that small plasticity recorded.
Two situations suggested themselves to the researchers. Species that live in grass could also remove to longer grass. North facing slopes could be chosen in preference to south facing habitats. These two changes would be much more significant in buffering animals from global warming compared to the miniscule shift found in warmer years in this study. From a conservation point of view, the research here points to very grave consequences for some species and positive moves that could be possible for those species that are able to adapt breeding, feeding and other aspects of their ecology.
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