Shifts in phenological mean and synchrony interact to shape competitive outcomes

Abstract

Climate change–induced phenological shifts are ubiquitous and have the potential to disrupt natural communities by changing the timing of species interactions. Shifts in first and/or mean phenological date are well documented, but recent studies indicate that shifts in synchrony (individual variation around these metrics) can be just as common. However, we know little about how both types of phenological shifts interact to affect species interactions and communities. Here, we experimentally manipulated the hatching phenologies of two competing species of larval amphibians to address this conceptual gap. Specifically, we manipulated the relative mean hatching time (early, same, or late relative to competitor) and population synchrony (high, medium, or low levels of variation around the mean) in a full 3 × 3 factorial design to measure independent and interactive effects of phenological mean and population phenological synchrony on competitive outcomes. Our results indicate that phenological synchrony within a population strongly influences intraspecific competition by changing the density of individuals and relative strength of early‐ vs. late‐arriving individuals. Individuals from high‐synchrony populations competed symmetrically, whereas individuals from low‐synchrony populations competed asymmetrically. At the community scale, shifts in population phenological synchrony interact with shifts in phenological mean to affect key demographic rates (survival, biomass export, per capita mass, and emergence timing) strongly. Furthermore, changes in mean timing of species interactions altered phenological synchrony within a population at the next life stage, and phenological synchrony at one life stage altered the mean timing of the next life stage. Thus, shifts in phenological synchrony within populations cannot only alter species interactions, but species interactions in turn can also drive shifts in phenology.

Phenological synchrony shapes pathology in host–parasite systems

“…Thus, even small shifts in the phenology could drive a profound alteration in the corresponding interaction strengths. As a consequence, systems with highly synchronized phenological patterns should be more sensitive to shifting phenologies relative to communities that tend to promote lower synchronization [50,51].…”

Stage-mediated priority effects and season lengths shape long-term competition dynamics

“…Relative arrival time changes those interacting traits (e.g. behavior, defense mechanism or size; Van Buskirk 1992; Lawler and Morin 1993;Hoverman and Relyea 2008;Yang and Rudolf 2010;Rasmussen et al 2014;Poulos and McCormick 2014;Rudolf 2018;Carter andRudolf 2019, Sniegula et al 2019), subsequently changing species interactions. The outcome of interactions therefore depends on relative changes in per-capita effects driven by changes in relative timing (phenology) of interactions, and is more likely to result in seasonal variation in community composition with variable phenology.…”

Warming erodes individual‐level variability in life history responses to predation risk in larvae of the mayfly Cloeon dipterum

“…The ongoing climate change is going to affect biotic interactions and population dynamics in multiple ways (Boukal et al., 2019). Here, we have demonstrated that warming may indirectly erode variation in individual life histories and the degree of synchronisation in species phenology that underpins long‐term stability of populations and communities mediated by interspecific interactions (Bjørnstad, Nelson, & Tobin, 2016; Carter & Rudolf, 2019). In our experiment, predation risk promoted cohort splitting and otherwise had only limited impact on individuals in C. dipterum larvae but warming broke down this response and led to tighter synchronisation of individual development.…”

“…Here, we have demonstrated that warming may indirectly erode variation in individual life histories and the degree of synchronisation in species phenology that underpins long-term stability of populations and communities mediated by interspecific interactions (Bjørnstad, Nelson, & Tobin, 2016;Carter & Rudolf, 2019). In .…”

“…Desynchronisation of development within populations driven by bet‐hedging LH strategies such as cohort splitting can increase fitness in unpredictable environments (Shima, Noonburg, Swearer, Alonzo, & Osenberg, 2018; Tarazona, García‐Roger, & Carmona, 2017) and alter the effects of biotic interactions across their weak and strong pressures (Carter & Rudolf, 2019). Altered survival, biomass, fecundity, and emergence timing may in turn affect the phenology in the next generation (Carter & Rudolf, 2019). Our results imply that warming can make cohort splitting unfeasible.…”