Predator abundance attenuates positive density-dependent breeding spatial dispersion in a semi-colonial bird

Abstract

The spatial organisation of breeding populations can influence fitness and population dynamics, yet the spatial expression of density dependence may vary with ecological context. We investigated whether predator abundance alters this expression in the northern lapwing (Vanellus vanellus), a loosely social ground-nesting wader. Using long-term breeding-bird monitoring data from agricultural landscapes, we quantified spatial organisation using a Normalised Spatial Dispersion Index (NSDI) and modelled its relationships with lapwing density, hooded crow (Corvus cornix) abundance, habitat composition, and winter climate using generalised additive mixed models. Spatial organisation showed density dependence, but this relationship weakened progressively with increasing crow abundance. At low crow abundance, increasing lapwing density was associated with greater spatial dispersion, whereas the relationship approached zero at high crow abundance. Although it became slightly negative at the upper end of the crow-abundance gradient, uncertainty provided no clear evidence of a reversal to density-dependent aggregation. Broad-scale habitat composition and winter precipitation were not supported as predictors, whereas warmer winter temperatures were associated with greater aggregation. Our results show that predator context can attenuate the spatial expression of density dependence, suggesting that spatial organisation may be an overlooked component of variation in density-dependent population processes.