Breakpoint phenological responses in high-Arctic arthropods

Many arthropod species show earlier seasonal activity trends with warming,
but these responses cannot continue indefinitely. Beyond a threshold,
phenological responses may no longer keep pace with climate change. While
many studies estimate linear phenological responses to climate, few test
for breakpoint responses. Here, across a 28-year time series, we examined
linear and breakpoint responses to temperature and snowmelt across 15
arthropod taxa in seven plots from high-Arctic Greenland, a region
experiencing pronounced warming. Our meta-analysis revealed support for a
breakpoint response in two of six phenological driver and event
combinations. This breakpoint response was found in the onset and peak of
activity to the timing of snowmelt, where activity advanced with snowmelt
until a threshold, after which the relationship levelled off. While we
also found a breakpoint response in peak phenology to temperature, this
disappeared when controlling for snowmelt in the model, underscoring the
importance of considering multiple environmental cues to prevent incorrect
inferences about plasticity limits. Most responses did not show evidence
of a breakpoint in phenological response, and instead showed consistent
phenological sensitivity to environmental cues across our study period.
Our findings point to a need for a wider assessment of the prevalence of
breakpoint phenological responses to climate change.