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How have UK plants and animals responded to recent climate changes?

November 2016 – The largest ever study on seasonal responses of plants and animals to climate in the UK, published earlier this year, reveals that species are showing divergent responses to recent climatic changes, and these differences are unsettling the ecological balance between predators and prey.

Climate sensitivities

The timing of events in nature, such as emergence of snowdrops, waking of dormice, spawning of salmon and migration of swallows, are sensitive to climate.

With changing climate, divergent changes in these ‘phenological’ events can desynchronise the interactions between predators and their prey, threatening ecosystem functioning.

This was the focus of research led by Dr Stephen Thackeray at the Centre for Ecology and Hydrology, in collaboration with many UK universities, non-government organisations and research institutes, including Dr Debbie Hemming, Scientific Manager of the Vegetation-Climate Interactions group at the Met Office Hadley Centre. Key results from this study (Thackeray et al, 2016) have recently been published in the journal Nature.

Phenological observations

The study brought together over 370,000 phenological observations from the UK on 800 marine, freshwater and terrestrial species covering virtually the entire food web on land and in water. It then combined these with location-specific, daily temperature and rainfall data from the National Climate Information Centre to analyse climate sensitivities and responses of individual species and groups of species within different trophic levels (positions) in the food chain.

Results

Results show that individual species across the UK have varied widely in their sensitivities to changes in climate over the last 40 years.

Although species at different trophic levels do not differ in the times of year at which they were sensitive to climate, they do vary widely in how sensitive they are.

For example, the phenology of species high up in the food chain (the secondary consumers e.g. birds) was shown to be about half as sensitive to temperature compared to the phenology of species at the base of the chain (the primary producers and primary consumers e.g. plants).

Such differences arise because species respond to temperature at different times of year and have evolved different temperature-sensitivities to suit the vagaries of their life-cycles.

To illustrate this, consider a winter moth egg of 2 millimetres in diameter, which has been lying dormant for months on a 40-metre-tall oak tree (Visser, 2016). It manages to hatch within days of its host's bud burst in order to feast on the new growth.

Obviously, these two species have radically different life cycles and physiological mechanisms that control their phenological events, and they will use different climate cues to determine the timing of these events. So, although the two sets of cues will be correlated, the cue used by the consumer (the moth in this case) will always be, to some extent, an unreliable predictor of oak bud burst.

It therefore follows that this lack of reliability in the timing of available food resources encourages consumers to evolve a less temperature-sensitive phenology than that of the lower trophic level species they rely on.

By combining the species sensitivities with climate change scenarios, this study also shows that primary consumers are likely to shift the timing of their phenological events twice as much by the 2050s as species at other trophic levels. These primary consumer species therefore provide an ideal early indicator, or sentinel, for monitoring and developing responses to the evolving impacts of climate variability and change on nature.

Broadly speaking, the results of this study indicate that some predator and prey interactions are starting to become desynchronised, and this is likely to continue under future projected climate change. These changes could lead to disruptions in the breeding success and survival of certain species, and ultimately biodiversity.

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