Resetting nature’s clock: shifting seasons and species relationships
Every year, many of us gaze in fascination at the movement of nature's clock, looking forward to seeing wild plants coming into bloom or the arrival of the first migrant birds. Less obvious, but just as dramatic, populations of phytoplankton bloom below the surface of lakes and oceans, while fish migrate to their spawning grounds. Over time, the dedicated observer may even come to anticipate the dates that their favourite natural events will occur on. However, the timing of these seasonal events is changing. Many familiar "signs of spring" are occurring earlier in the year than they used to. Often these changes have come about because seasonal biological events are sensitive to climatic conditions. For this very reason, they continue to be used by the Intergovernmental Panel on Climate Change (IPCC) as tangible indicators of global warming.
Shifts in the biological seasons are likely to have significant effects upon ecosystems, and the goods and services that they provide to society, now and in the future. Importantly, species have been changing their "seasonal" behaviour to different extents over time, and this could disrupt the seasonal relationships between plants and animals. To understand what the consequences of these changes are likely to be, it would be useful to know which species groups are most, and least, affected by climate change. This would allow us to identify species that are particularly effective climate change indicators, and to make some tentative projections of what the future might have in store.
In a recent study we addressed this important knowledge gap. We combined a wealth of biological records from the UK, for as many species as possible, and information on the climatic conditions that might be affecting their seasonal activities. These incredible datasets were gathered by voluntary citizen scientists and also by professional scientists based at research institutes and universities. Altogether, we gathered more than 370.000 records for over 800 aquatic and dry-land plant and animal species, collected over many years.
We then related the seasonal behaviour of plants and animals to local temperature and rainfall. Furthermore, we developed a new statistical method to evaluate how much and in which cases a given species may be influenced by the annual temperature or rainfall cycle. Importantly, we examined and compared how much the seasonal activities of different species groups, such as plants and herbivores, predators and prey, change with temperature and precipitation.
Using our novel approach, we were able to show that the seasonal activities of UK plant and animal species are less sensitive to rainfall than to temperature. Generally, many natural seasonal events occur earlier under warmer conditions. It was also clear that species are usually influenced by temperature changes only in certain periods of the year. A clear pattern was that this temperature sensitivity varied among species at different levels in the food web.
In simple terms, for any given amount of temperature change, predators and prey are likely to change their seasonal "behaviour" by different levels. In particular, we found that predatory species were not as much influenced by climate change as prey species. This was the first time that such a pattern had been observed among so many species and habitats and at a national scale. Changes in the relative seasonal timings of predators and their prey may alter food webs, with implications for UK biodiversity and ecosystem health. If, as predicted, climate warming continues into the future, then the disparity in responses of predators and prey is also likely to increase. Interactions between species are complex, with changes in one species likely to have knock-on effects for others, which may result in effects that cascade throughout ecosystems.
We must now make every effort to understand the extent to which these effects may be realised, and the extent to which ecosystems might be resilient to change. To do this, we must recognise the immense value of long-term ecological research, and continue to invest in this activity. Crucially, environmental change often acts through complex networks of species interactions and relationships, and so we must also take care to monitor at the whole-ecosystem scale. Without this long-term view, we will be unable to detect emerging threats or to learn from our successes and failures in local environmental management and mitigation.
Thackeray, S., Henrys, P., Hemming, D., Bell, J., Botham, M., Burthe, S., Helaouet, P., Johns, D., Jones, I., Leech, D., Mackay, E., Massimino, D., Atkinson, S., Bacon, P., Brereton, T., Carvalho, L., Clutton-Brock, T., Duck, C., Edwards, M., Elliott, J., Hall, S., Harrington, R., Pearce-Higgins, J., Hye, T., Kruuk, L., Pemberton, J., Sparks, T., Thompson, P., White, I., Winfield, I. and Wanless, S. (2016).Phenological sensitivity to climate across taxa and trophic levels. Nature, 535(7611), pp.241-245.
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