Fragility of nocturnal interactions: Pollination intensity increases with distance to light pollution sources but decreases with increasing environmental suitability

Abstract

Light pollution represents a widespread long-established human-made disturbance and an important threat to nocturnal pollination. Distance from the niche centroid where optimal environmental conditions join may be related to species sensitivity to habitat change. We estimated the environmental suitability of the plant species Erythrostemon gilliesii and of its guild of hawkmoth pollinators. We considered the overlap of suitability maps of both partners as the environmental suitability of the interaction. We used a three-year record of ten E. gilliesii populations to calculate pollination intensity as the number of individuals that received pollen per population. In addition, for each population, we measured the distance to the high light pollution source around a buffer of 15 km radius. Finally, we predicted pollination intensity values for environmental suitability ranging from 0 to 1, and distance to high light pollution sources ranging from 0 to 56 Km. Pollination intensity decreased along an axis of increasing environmental suitability and increased with distance to sources of light pollution. The highest values of pollination intensity were observed at greatest distances to sources of light pollution and where environmental suitability of the interaction was lowest. The prediction model evidenced that, when environmental suitability was lowest, pollination intensity increased with distance to sources of high light pollution. However, when environmental suitability was intermediate or high, pollination intensity decreased away and until 28 km from the sources of high light pollution. Beyond 28 km from the sources of high light pollution, pollination intensity remained low and constant. Populations under conditions of low environmental suitability might be more likely to respond to disturbances that affect pollinators than populations under conditions of high environmental suitability.