Phenological shifts in a community context perspective
Community context proved to be a major modifying factor on the immediate
and long-term consequences of phenological shifts in our study. Recent
work has suggested that employing community contexts that extend the
duration resources are available could be a useful management tool to
help safeguard against climate-driven phenological mismatches in species
interactions, such as plant-pollinator (Timberlake et al. 2019;
Olliff‐Yang et al. 2020). While increasing intraspecific
competition extended the duration of Drosophila ’s larval stage,
our study indicates that it is not likely to promote host-parasitoid
interaction persistence. Limited resources not only slowed host
development, but increased host mortality, reducing the recruitment
potential for the next generation of parasitoids. Other studies have
found that, in addition to declines in individual survival, host
populations experiencing strong competition may also be of lower value
for parasitoids, reducing population growth to rates that are unable to
support long term parasitoid persistence (Jones et al. 2009; Cunyet al. 2019). Furthermore, if parasitized hosts are more inclined
to density-dependent mortality, as has been observed in some (Ives &
Settle 1996), but not all host-parasitoid systems (Spataro & Bernstein
2004; White et al. 2007), this effect is likely to be amplified.
Overall, these results suggest that extending the temporal availability
of hosts, via competition, is unlikely to dampen the effects of
phenological shifts, and that shifts towards later emergence times of
parasitoids may reduce host-parasitoid persistence if parasitoids
struggle to establish on high-density (e.g., low quality) host
populations.
Most phenological studies have examined consequences of phenological
shifts between pairs of interacting species, rarely considering whether
outcomes of phenological shifts differ when more than two species are
involved. Recent theoretical (Nakazawa & Doi 2012; Revilla et
al. 2014; Takimoto & Sato 2020) and experimental (Timberlake et
al. 2019; Olliff‐Yang et al. 2020) studies have pointed out this
gap and suggest that the presence of alternative resources should weaken
the effects of phenological mismatches, especially if those resources
have complementary phenologies. By combining experimental and
theoretical approaches, our results helped fill these gaps and showed
that multispecies host communities were more likely to support the
persistence of parasitoid populations across a broader range of
phenological shifts, temperatures, and competition levels than pairwise
interactions. Moreover, we found that the presence of an alternative
host diminishes differences in average host survival and parasitism
rates across different biotic and abiotic factors. Like in other
studies, temporal complementarity between species (e.g., variation in
growth rates), and a diversity of responses to environmental changes
were major stabilizing mechanisms in our system (Zhang et al.2013; Craven et al. 2018; Sasaki et al. 2019), though this
is the first example using a host-parasitoid system. While most studies
recognize that functional redundancy and trait diversity at any given
time can positively affect community resilience to environmental
changes, it is rarely considered that these community parameters
continuously change during the development of individuals within the
community. Future studies should explicitly consider that the degree of
functional redundancy within a community will likely vary during the
development of individuals within communities. Regardless, our results
suggest that the presence of alternative host species serves as an
important buffer to phenological shifts in ecological communities, as it
can provide complementary phenologies, increases functional redundancy,
and can dampen community responses to variation in biotic and abiotic
environments (Yachi & Loreau 1999; Yang 2020).