Multiscale seasonal factors drive the size of winter monarch colonies.

摘要: Monarch butterflies in eastern North America have declined by 84% on Mexican wintering grounds since the observed peak 1996. However, coarse-scale population indices from northern US breeding do not show a consistent downward trend. This discrepancy has led to speculation that autumn migration may be critical limiting period. We address this hypothesis examining role of multiscale processes impacting monarchs during autumn, assessed using arrival abundances at all known winter colony sites over 12-y period (2004–2015). quantified effects continental-scale (climate, landscape greenness, and disease) local-scale (colony habitat quality) drivers spatiotemporal trends sizes. also included summer migratory indices. Our results demonstrate higher abundance larger colonies as did greener autumns, proxy for increased nectar availability southern floral corridors. Colony sizes were positively correlated with amount local dense forest cover whether they located within Butterfly Biosphere Reserve, but influenced disease rates. Although we demographic link between fine-scale sizes, reveal conditions experienced during, culmination of, impact annual dynamics. Monarchs face growing threat if resources diminish under climate change. study tackles long-standing gap monarch’s cycle highlights importance evaluating understand mechanisms governing long-term trends.