Sympatric species respond differently to environmental change

The timing of breeding is an important aspect of a species’ realised niche, a method of avoiding competition and a key determinant of breeding success. The flexibility of these strategies may structure community assemblages, particularly in highly seasonal environments such as the Polar Regions. Flexibility in timing likely determines the adaptability of species to rapid, anthropogenic ecological change. Variance in a species’ phenology over time and across locations is an important source of information, but phenology is only rarely recorded at appropriate spatial scales due to the difficulty of monitoring. Using a network of time-lapse photographic cameras to monitor a large number of colonies of three Pygoscelid species of penguins, we show that two species (Adélie and Chinstrap) breed earlier in warmer years, both at the individual colony and species levels. Both temperature-sensitive species have shown a population decline over the roughly 10 years of our study in the Antarctic Peninsula, while Gentoo penguins (temperature insensitive) have stable or increasing populations, particularly at the Southern edge of their range. Latitude was an important determinant of the start of breeding across the same region and temperature-related breeding in Adélie and Gentoo, but not Chinstrap penguins (which have a narrower range than the other two). The sensitivity to temperature in Adélie and Chinstrap penguins is greater than previously reported. The phenological responses to temperature differed according to latitude, showing greater sensitivity to temperature at warmer, lower latitudes. Our results demonstrate that the flexibility of reproductive strategies within as well as between closely related species needs to be considered as a landscape of outcomes with some adaptation to local conditions. This study offers a starting point to understanding whether polar animals can adapt to rapid change or whether elasticity is indicative of increasing stress given the two species showing the most adaptation to changing temperatures are declining in the study area.