Higher temporal variability of forest breeding bird communities in fragmented landscapes

Abstract

Understanding the relationship between animal community dynamics and landscape structure has become a priority for biodiversity conservation. In particular, predicting the effects of habitat destruction that confine species to networks of small patches is an important prerequisite to conservation plan development. Theoretical models that predict the occurrence of species in fragmented landscapes, and relationships between stability and diversity do exist. However, reliable empirical investigations of the dynamics of biodiversity have been prevented by differences in species detection probabilities among landscapes. Using long-term data sampled at a large spatial scale in conjunction with a capture-recapture approach, we developed estimates of parameters of community changes over a 22-year period for forest breeding birds in selected areas of the eastern United States. We show that forest fragmentation was associated not only with a reduced number of forest bird species, but also with increased temporal variability in the number of species. This higher temporal variability was associated with higher local extinction and turnover rates. These results have major conservation implications. Moreover, the approach used provides a practical tool for the study of the dynamics of biodiversity.

Figure 1

Relation between the mean species richness over the study period and the average forest patch size of a scene centered on each BBS route in 1974 (average forest patch size was log-transformed). Graphs were drawn for area-sensitive and non-area-sensitive species for the states of Maryland (A), New York (B), and Pennsylvania (C). Mean species richness was computed for survey routes for which more than 15 estimates of species richness were available over the 22-year period considered (1975–1996).

Figure 2

Relation between the CV of species richness and the average forest patch size of a scene centered on each BBS route in 1974 (average forest patch size was log-transformed). Graphs were drawn for area-sensitive and non-area-sensitive species for the states of Maryland (A), New York (B), and Pennsylvania (C). CVs were computed for survey routes for which a minimum of 15 estimates of species richness was available over the 22-year period considered (1975–1996).