Data from: Temperate grassland songbird species accumulate incrementally along a gradient of primary productivity

The more individuals hypothesis proposes that a higher availability of resources increases the total number of individuals that can be supported, and therefore the greater number of species that will be sampled. By contrast, the more specialization hypothesis proposes that increasing resource availability will permit specialists to exploit otherwise rare resources, thus increasing total diversity. We used 5 years of surveys of grassland songbird communities along an elevational gradient in British Columbia, Canada, to distinguish between these hypotheses.

Vegetation changed markedly in composition along the gradient and contrary to the expectations of the more specialization hypothesis, bird community composition was remarkably constant. However, both total abundance and species richness of birds increased with increasing water availability to plants. When we used rarefaction to correct species richness for differences in total abundance, much of the increase in bird diversity was lost, consistent with the expectations of the more individuals hypothesis.

Furthermore, high species richness was associated with reductions in territory size of common bird species, rather than the fine-scale spatial partitioning of the landscape. This suggests that bird diversity increases when greater resource availability allows higher densities rather than greater habitat specialization. These results help explain a pervasive global pattern in bird diversity on arid mountains, and suggest that in such landscapes conservation of grassland birds is strongly linked to climate and hydrology.

Usage notes bird_data These data describe the abundance of grassland songbirds identified during point count surveys in Lac du Bois Grasslands Protected Area near Kamloops British Columbia Canada between 2008 and 2012. envr_data These data describe the environmental data associate with bird point count locations performed in Lac du Bois Protected Area near Kamloops British Columbia Canada between 2008 - 2012.