RESUMO
Migratory populations often stop over for short periods of time at predictable sites along their migration routes. These staging areas can be heavily used and are potentially critical to the survival of the migrants. This paper presents a method for estimating the number of individuals using such an area and their average residence time. The estimator is based on daily population estimates and records of repeat sightings of identifiable individuals. Its application is illustrated with observations on a population of migrating birds, some of which could be identified from bands that were readable from a distance.
Assuntos
Biometria , Densidade Demográfica , Animais , Aves , Ecossistema , Voo Animal , Modelos Estatísticos , Fatores de TempoRESUMO
Pielou's (1972) measures of niche width and overlap are related to ecological components of diversity. This relation is exploited to derive modified niche metrics with improved characteristics.
RESUMO
Zonation patterns of salt marsh vegetation were examined at latitudes ranging from 44°40'N at Halifax, Nova Scotia, to 58°50'N at Churchill, Manitoba. It was found that in all areas examined the landward boundaries of the species' zones were more nearly coincident (i.e., more clustered) than their seaward boundaries. A conspicuous latitudinal trend was found: the clustering of both landward and seaward boundaries increased with increasing latitude. Evidence that between-species competition influences the locations of zone boundaries was also obtained. Possible implications of the results in terms of a relationship between intrapopulation polymorphism and latitude are discussed.
