The consistency and stability of abundance–occupancy relationships in large-scale population dynamics
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- 1Abundance–occupancy relationships comprise some of the most general and well-explored patterns in macro-ecology. The theory governing these relationships predicts that species will exhibit a positive interspecific and intraspecific relationship between regional occupancy and local abundance. Abundance–occupancy relationships have important implications in using distributional surveys, such as atlases, to understand and document large-scale population dynamics and the consequences of environmental change. A basic need for interpreting such data bases is a better understanding of whether changes in regional occupancy reflect changes in local abundance across species of varying life-history characteristics.
- 2Our objective was to test the predictions of the abundance–occupancy rule using two independent data sets, the New York State Breeding Bird Atlas and the North American Breeding Bird Survey. The New York State Breeding Bird Atlas consists of 5332 25-km2 survey blocks and is one of the first atlases in the USA to be completed for two time periods (1980–85 and 2000–05). The North American Breeding Survey is a large-scale annual survey intended to document the relative abundance and population change of songbirds throughout the USA.
- 3We found that regional occupancy was positively correlated with relative abundance across 98 (β = 0·60 ± 0·11 SE, P < 0·001, R2 = 0·60) and 85 species (β = 0·67 ± 0·06 SE, P < 0·001, R2 = 0·57) in two separate time periods. This relationship proved stable over time and was notably consistent between breeding habitat groups and migratory guilds.
- 4Between 1980 and 2005, changes in regional occupancy were highly correlated with long-term abundance trend estimates for 75 species (β = 5·73 ± 0·24 SE, P < 0·001, R2 = 0·88). Over a 20-year period, woodland and resident birds showed an increase in occupancy while grassland species showed the greatest decline; these patterns were mirrored by changes in local abundance.
- 5Although exceptions existed, we found most changes in occupancy parallel changes in local abundance. These findings support the basic predictions of the abundance–occupancy rule and demonstrate its consistency and stability in species and groups of varying life-history characteristics.