Ecological implications
Our results suggest that adult insects will emerge earlier under climate
change scenarios due to warming temperatures, but the termination of
insect activity will be less sensitive to changing climates. This may
lead to an overall lengthening of insect duration in response to global
warming, particularly in areas with high precipitation. Longer insect
activity periods may buffer against phenological mismatch of insects
interacting with other trophic levels, as long as insect abundance is
sufficiently high. However, mounting evidence suggests widespread
terrestrial insect declines
(van Klink et al.,
2020; Wagner et al., 2021; Warren et al., 2021), which raises the
threat of reduced ecological services regardless of how much synchrony
occurs between interacting species.
One of the fundamental unanswered questions in understanding insect
response to global change is which species will thrive — the winners,
and which will be most negatively impacted — the losers. Phenology may
be a key indicator of winners versus losers given recent work
demonstrating that changes in insect population sizes correlate with
phenological lability. Some insects may be able to adjust and thrive in
warmer environments if additional land use changes are not occurring
(Michielini et al.,
2021). For example, multivoltine Lepidoptera with early adult emergence
in warm years showed increased within- and between-year population
growth in Britain
(Macgregor et al.,
2019). Elongated adult activity periods were also the best predictor of
increases in relative abundance of Massachusetts butterflies
(Michielini et al.,
2021).
Our results point to two life history traits that may predict winners
and losers in the face of future climate change. Detritivores and
insects with larval habitats in freshwater exhibit a stronger response
of activity period to temperature than do other insects, indicating
these species may be relatively better suited to persist in novel
climate scenarios. Conversely, species that have underground larval
habitats may be more at risk, as duration for these species remains
relatively fixed across temperature gradients. We note that these
conclusions must be interpreted with care, as our models are primarily
fit across a spatial gradient. Space-for-time models of ecological
change are controversial because ecological processes are often
nonstationary
(Damgaard, 2019).
Still, some empirical studies support these inferences. A recent
meta-analysis found broad declines in terrestrial insects but increases
in freshwater insect populations
(van Klink et al.,
2020). No net declines in detritivores were detected across five long
term ecological research sites
(Crossley et al.,
2020), although these results have been questioned
(Welti et al., 2020).