Assessing the influence of environmental heterogeneity on bird spacing patterns: a case study with two raptors
Article first published online: 22 DEC 2005
Volume 29, Issue 2, pages 240–250, April 2006
How to Cite
Cornulier, T. and Bretagnolle, V. (2006), Assessing the influence of environmental heterogeneity on bird spacing patterns: a case study with two raptors. Ecography, 29: 240–250. doi: 10.1111/j.2006.0906-7590.04287.x
- Issue published online: 22 DEC 2005
- Article first published online: 22 DEC 2005
- Manuscript Accepted 3 October 2005
Testing for aggregation or regularity in point patterns is difficult in the presence of spatial variation in abundance due to environmental heterogeneity. Using a recently developed method generalizing Ripley's K function for non homogeneous point patterns, we test the aggregation of the nests in two species of birds (little owl and Montagu's harrier) exhibiting heterogeneous distributions in response to landscape structure. We compare the results obtained under different null models accounting for environmental heterogeneity at large and/or small spatial scales.
Whereas both species were initially found to form clusters at some scale, taking spatial heterogeneity into account revealed that 1) territorial little owls showed no clustering of territories when habitat availability was considered; 2) semi-colonial harriers still formed significant clusters, but part of the aggregation in this species could be explained by landscape structure alone. Our results highlight that it is feasible and highly recommended to account for non-stationarity when testing for aggregation. Further, provided that sufficient knowledge of the study system is available, this approach helps to identify behavioural and environmental components of spatial variation in abundance. Additionally, we demonstrate that accounting for large or small-scale heterogeneity affects the perception of spacing behaviours differently, so that both need to be considered.