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Thursday, March 10, 2011

Study of spiders shows species may be able to adapt to global warming

From the Ecologist
Study of spiders shows species may be able to adapt to global warming
Species may be able to adapt to gradual increases in temperature preventing the collapse of biological communities in the face of global climate change

The predatory behaviour of spiders is unaffected by increased temperatures, according to research by Yale University, suggesting some species can adapt to global warming.

The Yale research examined a well-studied grassland food web, made up of a predatory spider, its grasshopper prey, and the plants grasshoppers fed on. The spider’s predatory behaviour is known to be temperature-sensitive, decreasing with increased temperatures. Researchers had expected higher temperatures to stop the spiders preying on grasshoppers, leading to more plants being eaten.

However, in the study, spider populations from warmer areas tolerated higher temperature ranges better than the populations from cooler areas and continued to control the grasshopper popualtion. This suggests they can adapt to local conditions and maintain their vital role in the community despite increased temperatures.

‘Species are almost certainly adapting to the climate change Earth has experienced during the past century,' study author Dr Brandon Barton told the Ecologist. 'My results show that species have the capacity to adapt to a range of temperatures, similar to those predicted by climate change models, and that a species’ role in the community can be conserved by this adaptation.’

Many similar experiments expose organisms to short-term, sudden increases in temperature, which does not allow for long-term gradual processes like climate change. Barton’s work overcomes these limitations by looking at populations along a natural temperature gradient to see if long-term changes in temperature would affect small-scale food webs. He sampled spiders at sites from a 500km, north-south axis, along the east coast of the United States, where temperature varied by 4.8C.

‘Ecologists must design experiments that explicitly test how gradual climate change will affect future systems, or else risk making unrealistic and misleading conclusions,’ Barton believes.

Dr Karsten Schönrogge, Principal Scientist at the Centre for Ecology & Hydrology, believes further research is required to improve our understanding of how species may adapt to climate change.

‘Rapid adaptation of species not just to temperatures, but any of the factors indicated to change under climate change [e.g. drought regimes, etc.] or other environmental change could potentially stabilise communities. If they [species] can adapt, understanding how quickly and how far would give us a much better understanding to predict possible impacts of climate change at community level,' he said.

Despite species ability to adapt, Barton remains unconvinced this can eliminate the negative impacts of climate change.‘Whether understated or exaggerated, all evidence suggests that the wide-reaching direct and indirect effects of climate change will have innumerable consequences on biological systems globally.’

Barton BT (2011) Local adaptation to temperature conserves top-down control in a grassland food web. Proc. R. Soc. B doi: 10.1098/rspb.2011.0030

A fundamental limitation in many climate change experiments is that tests represent relatively short-term ‘shock’ experiments and so do not incorporate the phenotypic plasticity or evolutionary change that may occur during the gradual process of climate change. However, capturing this aspect of climate change effects in an experimental design is a difficult challenge that few studies have accomplished. I examined the effect of temperature and predator climate history in food webs composed of herbaceous plants, generalist grasshopper herbivores and spider predators across a natural 4.8°C temperature gradient spanning 500 km in northeastern USA. In these grasslands, the effects of rising temperatures on the plant community are indirect and arise via altered predator–herbivore interactions. Experimental warming had no direct effect on grasshoppers, but reduced predation risk effects by causing spiders from all study sites to seek thermal refuge lower in the plant canopy. However, spider thermal tolerance corresponded to spider origin such that spiders from warmer study sites tolerated higher temperatures than spiders from cooler study sites. As a consequence, the magnitude of the indirect effect of spiders on plants did not differ along the temperature gradient, although a reciprocal transplant experiment revealed significantly different effects of spider origin on the magnitude of top-down control. These results suggest that variation in predator response to warming may maintain species interactions and associated food web processes when faced with long term, chronic climate warming.

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