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Competition of tree species is focus of Mexican research trip

Published: 18 June 2004

Four undergraduates from the University of Southampton are travelling to Mexico this summer to investigate the ecological mechanisms that come into play when different tree species compete with one another for limited natural resources.

Environmental Science student Marta Correia, and Biology students Sarah Ellis, Christina de Poitiers and Oliver May will begin a three-month stay in South America at the end of June. During this time, they will conduct their own individual projects as part of a larger University of Southampton study on Co-existence and relative abundance in forest trees which began in 1998.

The research team will be based in the Pacific coastal region of Jalsico state, south-west of Guadalajara in two adjacent forested reserves: the Chamela Biological Station and the Cumbres de Cuixmala Reserve. The reserves are mainly tropical deciduous forest, with some tropical semi-deciduous forest and contain a rich diversity of plant species. Whilst some project work is being undertaken in the UK, Mexico offers a greater sample size for the research. Over 200 woody species have been identified growing in Chamela's 1600 hectares.

Talking about the research trip, Dr Colleen Kelly of the University's Division of Biodiversity and Ecology who is heading up the study explains: "The more similar species are in nature, the more they need the same resources and the more they compete when they come in contact with one another. When competition is too strong - when there are lots of individuals of one or both species clamouring for resources - the better competitor will eventually win out and exclude the other species."

Some tree species are able to get around this fundamental ecological process because they flourish in different soil or light conditions and so do not compete with one another strongly. They may also co-exist because over time they 'trade off' the production of successful offspring, a process called 'recruitment'. For example, in British woodland, although ash and sycamore need much the same sorts of conditions, in some years ash seedlings do better and in other years sycamore seedlings are more successful, so that both species can be found thriving in the same wood.

The projects will examine different aspects of the ecology and competition between six species of the genus Bursera in the area, including their numbers and distribution, growth rates, and the effects of parasites and insects on growth and survival. Initially the team as a whole will collect research data, with conclusions written up individually.

Marta Correia will document population fluctuations over time in three tree species of Bursera. She will measure trunk diameter of 100-300 individual trees of each species and construct histograms of tree sizes. Any unusual deviations from the expected regularity of tree size can then be analysed for fluctuations in 'recruitment' for both rare and common species.

Competition between seedlings of rare and common species will be compared in Sarah Ellis's project. Rarer species are predicted to be the better competitors and Sarah will establish if this is so both by measuring their growth rates.

Herbivory, the consumption of plants by animals, is the focus of Oliver May's project. After exposing individual seedlings of the six Bursera species either to a herbivore known to attack them under natural conditions or to similar damage that he inflicts himself, Oliver will observe the impact on individual seedling growth and survival.

Christina de Poitiers will be looking at whether year-to-year differences in seedling success depends on year-to-year variation in herbivores, and whether that in turn depends on the parasitoid wasps that attack and leave their eggs to develop within the herbivores. Christina will be keeping alive herbivores until the parasitoid eggs they carry hatch and emerge from the body of their hosts.

It is hoped that findings from these four projects and the overall study will allow for better management for diversity in the future.

Notes for editors

The University of Southampton is a leading UK teaching and research institution with a global reputation for leading-edge research and scholarship. The University has over 19,200 students and 4800 staff and plays an important role in the City of Southampton. Its annual turnover is in the region of £250 million.

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