Top scientists from Scotland and the United States have revealed precisely how weather conditions cause multiple populations of a species within a large geographical area to have simultaneous increases or decreases in their abundance.

The findings made by researchers at the University of Glasgow and Pennsylvania State University (USA) have been published this week in world's premier journal for biological and physical sciences, Nature. The paper explores the process known as 'spatial synchrony', showing how occasional severe weather conditions directly cause the rapid increase or decrease in abundance and mobility of an intestinal parasite. The parasite infects populations of an important game bird hunted on country estates causing them all to either decline or thrive simultaneously in breeding success. The research is the first to pinpoint the specific role of climate in causing such incidents of spatial synchrony in animals.

Dr Daniel Haydon, Lecturer in Environmental and Evolutionary Biology at the University of Glasgow explains:

'It is unusual to have long time-series of population change and even more so to have historical records of key variables that impact on population dynamics. In this case we were able to access records of grouse bag-counts, measures of parasite abundance, and the temperature and rainfall experienced by these spatially disparate populations. This allows us not only to establish that populations do exhibit spatial synchrony but enables us to elucidate the probable mechanism by which this synchrony is brought about - and it is this that makes the study very unique.'

The research warns of the rapid ecological consequences of extreme and short-term fluctuations in weather conditions. Peter J. Hudson, the Willaman Chair in Biology at Pennsylvania State University and the Director of The Centre for Infectious Disease Dynamics at Pennsylvania State University explains:

'One of the characteristics of global climate change is that we are getting increased variation in temperature extremes -- sometimes we get colder winters followed by warmer summers and then suddenly we get a warm winter.'

'The research indicates that brief episodes of extreme weather conditions may produce important ecological effects, and that these effects could be big, quick, and dynamic. This result is important not just for Red Grouse but for our understanding of how large-scale global climate events and environmental factors can affect many local ecological processes and local populations of many species in which spatial synchrony is known to occur, including insects, rodents, birds, fish, and mammals.'

The researchers coupled their detailed field studies and ecological knowledge with statistical analyses of data that they obtained from the owners of 100 individual estates in the UK, where populations of Red Grouse have been maintained as game birds for more than 100 years. The team used a statistical technique recently developed by Haydon - a powerful new form of time-series analysis - to analyse data on the numbers of Red Grouse that hunters annually harvested since as far back as 1840. The records provide a gauge of the abundance of each of the 100 independently managed populations for each year.

Using this technique, the research team was able to identify the specific years in which the grouse populations were all pushed into the same phase of increase or decrease in abundance.

The researchers also report that synchrony in these grouse populations does not happen gradually over many years; rather, they all suddenly increase or crash together in just two or three years.

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For further details contact Mike Findlay in the University Press Office on 0141 330-3535.

Full paper details can be found at: Nature Journal Homepage.

This research was supported by the European Union Marie Curie Individual Fellowship (IMC) and by the Game Conservancy Trust in England.

First published: 22 February 2005