Darwin's finches and climate change: insights from a resilient system

Climate change is known to influence biodiversity worldwide, with changes in organismal traits observed in many populations and species. Such effects are not universal, however, with some traits showing remarkable stability through time. Time-series analyses that link environmental variables to trait values can generate useful insights into trait evolution and its ecological bases. We use 24 years of data for beak and body traits in two species of Darwin's finches in the Galápagos Islands, alongside data on temperature and precipitation, to answer three questions: (Q1) is climate change present in our study sites? (Q2) do time-series of beak and body traits show detectable trends that suggest climate change effects? and (Q3) to what extent does weather influence annual variation in beak and body traits? We found that temperature and precipitation have been increasing over the past two decades-although this trend is minor in comparison to year-to-year variation. We next found that time-series of beak and body traits showed no detectable signs of climate change impact, instead they behave either as random walks or stable trajectories. Finally, for both species, analyses for short-term responses show that precipitation has a lagged, negative correlation with beak and body traits (effect size: maximum -0.632, minimum -0.131). Increased precipitation followed smaller traits in subsequent years. Associations of finch traits with temperature were more variable. We discuss reasons why Darwin's finches react to short-term weather changes but not to long-term climatic trends, and how these results relate to other findings in other tropical systems.