Which Should Live?

Ecology is the branch of science that studies the distribution and abundance of living organisms, and the interactions between organisms and their environment. Any ecological group is always in a dynamic equilibrium. If you change one part, some other part will change in response to that change. Changes may come from man, climate, pollution or any other change. In this case conservationists have been so successful at protecting endangered birds in a Spanish nature reserve that the birds are now killing the reserve's ancient cork oak forest. This may mean some bird colonies will have to be moved to protect the trees, some of which date back to the seventeenth century. Move is one method. In other cases (for example New Jersey) bears and deers are periodically hunted and killed because the alternative is that they will starve because of a lack of natural predation and food supply as a result of burgeoning populations. In order for ecology to work, it must be balanced.

The trees are the last part of a huge cork oak forest which once covered south-western Spain, and provide food for deer, wild boar and small mammals. The endangered Iberian Lynx often also uses old cork oak trees as breeding dens.

With around 70 nests in any one tree, researchers found that the nesting birds produce so much poo it upsets the delicate balance of the soil which nurtures the oaks.

The birds' faeces lead to high concentrations of salts in the soil, to which cork oak trees are particularly sensitive - the salt makes it hard for the trees to absorb enough water. The researchers found that cork oaks which are home to birds like the white stork, the spoonbill and the grey heron are in much worse condition than trees with no nesting birds.

"If populations of these birds continue to rise, the effect will increase. The source will still be there," says Cristina Aponte from the Instituto de Recursos Naturales y Agrobiologia de Sevilla, and co-author of the study published in Biological Conservation.

This case of one conservation success leading to the decline of other endangered species isn't as rare as you might think. In Polish forests, cormorants and protected wading birds have harmed ancient trees, elephants destroy endangered plants and trees in parts of South Africa, and the rare chamois in the Pyrenees feeds on the equally endangered larkspur plant.

Problems such as the birds on Spanish cork trees can occur for the best of reasons. Others have happened due to deliberate man made intervention into local ecologies such as rabbits introduced into Australia.

Since their introduction from Europe in 1859, the effect of rabbits on the ecology of Australia has been devastating. Rabbits are suspected of being the most significant known factor in species loss in Australia. The loss of plant species is unknown at this time. Rabbits often kill young trees in orchards, forests and on properties by ringbarking them.

For managers of the Spanish reserve, there is clearly a trade-off between maintaining the area for nesting birds and preserving the ancient cork oak forests. One solution to the problem would be to relocate the colony to a region where the trees are not as valuable or rare.

For further information: http://planetearth.nerc.ac.uk/news/story.aspx?id=893