Phenological inertia versus lability of ant responses to experimental climatic warming
Shifts toward earlier phenology (the timing of life cycle events) are a hallmark of species’ responses to global climate change. While the majority of species examined to date tend to exhibit shifts toward earlier phenology, there is considerable variation in both the magnitude, and to a lesser degree, the direction of phenological change. Variability in species’ historical selective environments and other species-level traits may resolve some of this observed variability in the magnitude and direction of phenological change. We examine phenological responses of several ant species to experimental climate change in our two large-scale experimental warming arrays (heated from ambient to 5.5 °C above ambient air temperature), positioned at the northern and southern boundaries of temperate hardwood forests in eastern North America. We then link these phenological responses both to changes in ant worker density to better understand the performance and fitness consequences of phenological shifts, and to species’ traits to better resolve variability in phenological shifts.
After three years of experimental climatic warming, we found considerable variation in the magnitude and direction of phenological change as a function of the degree of warming for the ant species inhabiting our experimental chambers. Tropical-lineage, warm-adapted species such as Crematogaster lineolata exhibited strong phenological lability, with shifts toward earlier phenology under experimental warming, altering the timing of peak abundance from early September under ambient conditions to early April under the warmest conditions. Some temperate-lineage, cool-adapted species such as Prenolepis imparis exhibited strong phenological inertia in response to warming, yet experienced large increases in ant worker density with increases in the degree of experimental warming. Other temperate-lineage species displayed more idiosyncratic phenological responses. Our results suggest that while phenological responses to climate change may differ between species, species-level traits, including the historical selective environment (tropical versus temperate origin), can better inform forecasts of phenological responses to climate change.