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

Abstract

The relative arrival time of species often affects species interactions within a community, contributing to priority effects. Recent studies on phenological shifts under climate change have generated renewed interest on priority effects, but their role in shaping long-term dynamics of seasonal communities is poorly resolved. Here we use a general stage-structure competition model to determine how different types of priority effects influence long-term coexistence of species in seasonal systems. We show that while shifts in mean and variance of relative arrival time can alter persistence and coexistence conditions of species, these effects depend on season length and type of priority effect. In "slow" systems with one or a few cohorts per season, changes in mean and seasonal variation of relative arrival time strongly altered species persistence through trait-mediated priority effects. In contrast, competition outcome in "fast" systems is largely determined by numeric priority effects due to interaction between many overlapping generations. These results suggest that empirically observed priority effects may arise from fundamentally different mechanisms, and that fast-generating systems may be less impacted by seasonal variation in phenology. Our model provides important insight into how natural communities respond to increasing variation in phenology over seasons under climate change.

Priority effects determine how dispersal affects biodiversity in seasonal metacommunities

“…This discrepancy arises because we incorporated seasonality and realistic spatial and temporal variations of arrival order in our model. These variations lead to a constant reshuffling of competitive hierarchies across time and space that reduces or prevents local and regional extinction, as predicted by previous theoretical results in non-spatial models (Rudolf 2019; Zou and Rudolf 2020). When aggregated on a spatial or temporal scale, this reshuffling of competitive hierarchies can also lead to intransitive competition, which is predicted to stabilize multispecies systems (Allesina and Levine 2011; Levine et al 2017).…”

“…Priority effects can be generated by at least two fundamentally different mechanisms, broadly categorized as “numeric” or “trait-mediated” (Rudolf 2019; Zou and Rudolf 2020). Numeric priority effects arise from the positive frequency dependence of the species with higher abundance (Ke and Letten 2018).…”

“…In nature, this occurs through altered traits that could affect species interactions, such as size and behavior, or modified environment from the difference in arrival times (Poulos and McCormick 2014; Rasmussen et al 2014; Rudolf 2018; Blackford et al 2020). These changes in interacting traits often result in a change of species’ competitive interactions that correlate with their relative arrival times (Rudolf 2019; Zou and Rudolf 2020). Therefore, if trait-mediated priority effects occur, the competitive outcome of early and late arrivers are not only determined by their numeric difference but also their relative arrival times.…”

Untangling the complexity of priority effects in multispecies communities

“…Of these six scenarios, (iii), (v) and (vi) all represent priority effects. The common omission of cases (v) and (vi) in theoretical studies is a consequence of assuming that model parameters are fixed and history independent (Rudolf, 2019; Zou & Rudolf, 2020). In reality, interaction strengths can be history dependent (Carter & Rudolf, 2019; Poulos & McCormick, 2014; Rasmussen et al, 2014; Sniegula et al, 2019; Vannette & Fukami, 2017).…”

Untangling the complexity of priority effects in multispecies communities

“…Of these six scenarios, (III), (V) and (VI) all represent history-dependent priority e ects. The common omission of cases (V) and (VI) in theoretical studies is a consequence of assuming that model parameters are fixed (Rudolf, 2019;Zou & Rudolf, 2020). In reality, interaction strengths can be history-dependent (Rasmussen et al, 2014;Poulos & McCormick, 2014;Vannette & Fukami, 2017;Carter & Rudolf, 2019;Sniegula et al, 2019), increasing the scope of priority e ects.…”