Simulation results: changes in host-parasitoid persistence
with phenological shifts, warming, and community context
The persistence of host-parasitoid interactions was less probable if
parasitoids were perfectly synchronized with their hosts or if the
shifts in relative emergence times became too delayed (e.g., delay
6-days) (Fig. 3). However, the effects of phenological delays on
host-parasitoid persistence varied significantly with warming; that is,
the probability of parasitoid persistence was significantly greater at
the 4-day delay window in ambient temperatures (OR = 2093.8, P
< 0.001), while a delay of 2-days resulted in the highest
chance of persistence under warming (OR = 0.49, P = 0.0013). We also
found that under simulated warming, the chances of parasitoid
persistence were limited to a single delay window (2-day), while two
windows of delay (2- and 4-day) indicated parasitoid persistence in
24°C, supporting predictions that accelerated development rates narrow
the window of vulnerability in host-parasitoid interactions.
Importantly, warming reduced the probability of host-parasitoid
persistence, irrespective of phenological relationships (OR = 83.5, P
< 0.001).
Our simulations indicated that high levels of resource competition among
hosts did not increase the number of relative emergence times that
supported parasitoid persistence in either ambient or elevated
temperatures. Instead, the chances of parasitoids persisting for
extended generations was significantly greater when competition levels
were low, and this was consistent across all phenological delays, except
0-day (OR = 1.8, P = 0.19). Importantly, the presence of alternative
host species (i.e., the sulfurigaster-birchii combination)
significantly increased the probability of parasitoids persisting when
averaged across all phenological shifts and temperatures (Fig. 3). This
suggests, that while our single generation experiment identified
intermediate levels of survival and parasitism rates when alternative
host species were present, those differences in survival and parasitism
rates had meaningful, positive effects on host-parasitoid coexistence
across multiple generations.