Results
The emergence of adult insect activity is impacted by temperature,
precipitation, temperature seasonality, life history traits, and the
interactions among these variables (Table 1). Species that diapause as
an egg have later emergence dates (approximately 45.7 days) than species
that overwinter as adults (Table 1). A one standard deviation (s.d.)
increase in temperature (4.77 °C) led to earlier emergence of
approximately 12.8 days (95% Bayesian credible intervals (CI) 3.6 -
22.0), but the effects of temperature varied with respect to regional
precipitation and human population density values. Compared to areas
with high human population density, emergence values are earlier in cool
regions with low population density, but later in warm regions with low
population density (Figure 3A). Insects in warmer areas emerge earlier
than in cool areas, and these phenology shifts are more extreme in wet
areas compared to drier areas (Figure 3B). The interaction between
temperature and diapause stage, and the interaction between
precipitation and voltinism also impacted the emergence of adult insect
activity. The emergence of species that diapause as larva or pupa were
more sensitive to temperature than species that diapause as adults or
eggs (Figure 3C). Univoltine species had earlier emergence in areas with
more precipitation, while species that are not univoltine had later
emergence in areas with more precipitation (Figure 3D). There was a
phylogenetic signal of the random species-specific intercept and the
random species-specific slopes of temperature seasonality and
precipitation (Supporting Information Figure S2). The partial
R2 of our best emergence model was 0.75 (Supporting
Information Figure S3).
The top termination model consisted of a set of predictors that included
precipitation, temperature seasonality, life-history traits, and the
interaction between temperature seasonality and diapause stage (Table
1). A one s.d. increase in precipitation (324 mm) led to a delay in
termination of approximately 3 days (95% CI 1.1 - 4.8). Termination of
activity was earlier for species that are first observed in spring or
summer compared to species that are first observed as adults in fall
(Table 1). Additionally, insect species that diapause as larvae
terminate adult activity earlier than insects that diapause in other
life stages (-18.4, 95% CI -35.8 - -0.7; Table 1). The termination of
species that diapause as eggs were the most sensitive to temperature
seasonality (Figure 4). Species that spend their immature life stage
underground had earlier termination than species that spend their
immature life stage in freshwater or aboveground. Detritivores had later
terminations than herbivores or carnivores. Phylogenetic signal was
again apparent for the species-specific random intercept and
species-specific random slope of temperature seasonality and
precipitation (Supporting Information Figure S2). The partial
R2 of our best termination model was 0.58 (Supporting
Information Figure S3).
The top model of adult insect duration was predicted by climate, life
history traits, and the interaction between temperature and these other
variables. Areas with greater temperature seasonality had shorter
durations (Table 1). Additionally, areas with high precipitation had
longer durations in warm regions but shorter durations in cool regions
(Figure 5A). In contrast to species whose immature habitat is above
ground or in freshwater, species whose immature habitat is underground
were found to have consistent durations, regardless of whether they were
in a warm or cool region (Figure 5B). Diapause stage was again an
important trait, with insects that diapause as adults having the longest
durations. Conversely, the durations of species that diapause as larvae
were the shortest, 44.8 days shorter than species that diapause as
adults (95% CI 26.1 - 62.7; Table 1). The duration of detritivores was
strongly tied to regional temperature, with duration being much longer
in warm regions compared to cool regions (Figure 5C). In addition to
there being a phylogenetic signal in species-specific intercept and the
species-specific slope of temperature, variation in duration was also
partially explained by the phylogenetic signal in the species-specific
precipitation slope (Supporting Information Figure 2). The partial
R2 of our best duration model was 0.75 (Supporting
Information Figure 3). The number of observations used to estimate the
phenometrics was included as a predictor variable in the top duration
model, as well as in the top emergence and termination model.