|
Résumé :
|
Faunal and floral atlases can provide invaluable information on species distributions and relative abundance, and have played a key role in detecting and diagnosing population changes. Most atlases rely on simple but effective field methods that can be employed by large numbers of volunteer surveyors so as to make the best use of their finite effort. For ornithological atlases, such methods have been modified to better quantify relative abundance in the breeding season. Here, we evaluate how effort should be invested in space (number of samples) and time (time per sample) in order to optimise species lists and relative abundance estimation for birds in Britain and Ireland in winter. Species accumulation curves show only slight differences in the ability to derive complete species lists whether effort is invested in time or in space. However, relative abundance precision is markedly improved if effort is invested in space at the expense of time. These results give clear guidance on the general way in which methods should be devised (i.e. more samples, each for less time), but analyses relating the shape of species accumulation curves to habitat diversity suggest the precise trade-off between surveying in space and time varies between landscapes. Designers of atlases must therefore optimise their study design for the landscape of the particular region in question.
|