The dynamic climate adaptation of indicator warbler species complex in the Pacific Rainforest

Understanding the functional responses of ecosystems to climate change is critical to predict and conserve global biodiversity. The evolution of indicator species provides an efficient avenue towards the functional biome response to climate change. Leveraging decades of citizen science data coupled with high-resolution spatiotemporal climate data, I dissected the climate change response of hybridizing Setophaga warblers, indicator species breeding in the mysterious canopy of the Pacific Rainforest. Breeding habitat temperature and precipitation powerfully predicted the breeding occupancy of the northern (S. townsendi) and the southern species (S. occidentalis). Both species showed positive climatic responses in the recent decade when the recent breeding occupancy was greater than the expected contingency. This implies the potential climate adaptation or life history plasticity in the breeding warbler populations. However, the S. occidentalis showed a compromised climate response in 2000-10, when the predicted breeding occupancy was significantly lower than the expected contingency. The compromised response might be due to rampant decline of July precipitation in 2000-10, compared to previous decades. Although the July precipitation continued to decline in 2010-20, S. occidentalis showed signs of recovery, after generations of climate adaptation. I further evaluated their breeding niche competition, reflected by the overlap of breeding occupancy between species. I found that the competition potential was the lowest in 2000-10 when both species were at the trough of breeding occupancy, which recovered in 2010-20. This study shed light on eco-evo feedback in the indicating species complex and illuminated the functional response of the rainforest ecosystem to climate change.