Complex effects of elevated temperatures on consequences of
phenological shifts
Our results show that the effects of phenological shifts varied with
warming, but to what extent and why differed between hosts and
parasitoids. While growth rates of both host species increased with
warming, the declines in parasitism rates and increased host survival
across phenological shifts did not scale with differences in growth
rates. Thus, other factors, besides variation in growth rates among
temperatures, community contexts, and species contribute to differences
in effects of phenological shifts across treatments. Our dynamic model
revealed that host-parasitoid interactions were less likely to persist
in predicted global warming temperatures and identified that some host
and parasitoid species were completely unable to support interactions
under warming, even when parasitoid survival, host fecundity, and
phenological relationships were ideal (Fig. 3; Fig S7, Fig. S9, Fig.
S10). This highlights that physiological changes in elevated
temperatures, beyond shifts in development rates, can considerably
modify the effect of phenological shifts on species interactions. For
example, regardless of the developmental relationship, warming may
compromise immune systems or the ability to heal from injuries (i.e.,
oviposition punctures) (Catalán et al. 2012; Abram et al.2019), though other studies have found that hosts are more able to
successfully defend themselves against immature parasitoids in warmer
temperatures (Thomas & Blanford 2003; Wojda 2017). In addition,
parasitoids usually show lower thermal tolerances relative to their
hosts
(Karban
1998; Fellowes et al. 1999; Zamani et al. 2007; Agostaet al. 2018; Thierry et al. 2019), both of which support
our current findings. These discoveries have important implications for
persistence of key trophic interactions and top-down control, as such
interruptions to top down processes has been identified as key
consequences of climate change in terrestrial and aquatic systems
(Shurin et al. 2012; Velthuis et al. 2017; Derocleset al. 2018).