The relative arrival time of species can affect their interactions and thus determine which species persist in a community. Although this phenomenon, called priority effect, is widespread in natural communities, it is unclear how it depends on the length of growing season. Using a seasonal stage-structured model, we show that differences in stages of interacting species could generate priority effects by altering the strength of stabilizing and equalizing coexistence mechanisms, changing outcomes between exclusion, coexistence and positive frequency dependence. However, these priority effects are strongest in systems with just one or a few generations per season and diminish in systems where many overlapping generations per season dilute the importance of stage-specific interactions. Our model reveals a novel link between the number of generations in a season and the consequences of priority effects, suggesting that consequences of phenological shifts driven by climate change should depend on specific life histories of organisms.
- Award ID(s):
- 1655626
- PAR ID:
- 10063722
- Date Published:
- Journal Name:
- Oecologia
- ISSN:
- 0029-8549
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract By causing phenological shifts that vary among species, climate change is altering time envelopes for species interactions, often with unexpected demographic consequences. Indirect interactions, like apparent competition and apparent facilitation, are especially likely to change in duration because they involve multiple interactors, increasing the likelihood of asynchronous phenological shifts by at least one interactor. Thus, we might observe ecological surprises if intermediaries of indirectly interacting species change their mediating behaviour.
We explored this possibility in a plant–pollinator community that is likely to experience asynchronous phenological shifts. We advanced and delayed the flowering phenology of two ubiquitous exotic plants of western Washington prairies,
Hypochaeris radicata andCytisus scoparius , relative to seven native perennial forb species whose phenologies remained unmanipulated. These species interact indirectly through shared pollinators, whose foraging behaviour influences plant reproductive success. We quantified impacts of experimental phenological shifts on seedset, pollinator visitation rates and visiting pollinator composition relative to an unmanipulated control. We first verified that unmanipulated indirect interactions between native and exotic plants were strong, ranging from facilitative to competitive.Seedset of native plants was strongly affected by changes in exotic flowering phenology, but the magnitude and direction of effects were not predicted by the nature of the original indirect interaction (facilitative vs. neutral vs. competitive) or the change in interaction duration. The relationship between pollinator visitation and seedset changed for most species, though changes in pollinator visitation rate and pollinator composition were not as widespread as effects on native seedset.
Synthesis . Changes in pollinator foraging behaviour in response to changes in available floral resources are probably responsible for the unexpected effects we observed. Asynchronous phenological shifts have the potential to produce large and unexpected effects on reproductive success via indirect interactions. -
Abstract Although there is mounting evidence indicating that the relative timing of predator and prey phenologies determines the outcome of trophic interactions, we still lack a comprehensive understanding of how the environmental context (e.g., abiotic conditions) influences this relationship. Environmental conditions not only frequently drive shifts in phenologies, but they can also affect the very same processes that mediate the effects of phenological shifts on species interactions. Therefore, identifying how environmental conditions shape the effects of phenological shifts is key to predicting community dynamics across a heterogeneous landscape and how they will change with ongoing climate change in the future. Here I tested how environmental conditions shape the effects of phenological shifts by experimentally manipulating temperature, nutrient availability, and relative phenologies in two predator–prey freshwater systems (mole salamander–bronze frog vs. dragonfly larvae–leopard frog). This allowed me to (1) isolate the effects of phenological shifts and different environmental conditions; (2) determine how they interact; and (3) evaluate how consistent these patterns are across different species and environments. I found that delaying prey arrival dramatically increased predation rates, but these effects were contingent on environmental conditions and the predator system. Although nutrient addition and warming both significantly enhanced the effect of arrival time, their effect was qualitatively different across systems: Nutrient addition enhanced the positive effect of early arrival in the dragonfly–leopard frog system, whereas warming enhanced the negative effect of arriving late in the salamander–bronze frog system. Predator responses varied qualitatively across predator–prey systems. Only in the system with a strong gape limitation were predators (salamanders) significantly affected by prey arrival time and this effect varied with environmental context. Correlations between predator and prey demographic rates suggest that this was driven by shifts in initial predator–prey size ratios and a positive feedback between size‐specific predation rates and predator growth rates. These results highlight the importance of accounting for temporal and spatial correlations of local environmental conditions and gape limitation when predicting the effects of phenological shifts and climate change on predator–prey systems.
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Abstract Climate change has changed the phenologies of species worldwide, but it remains unclear how these phenological changes will affect species interactions and the structure of natural communities. Using a novel approach to analyse long‐term data of 66 amphibian species pairs across eight communities, we demonstrate that phenological shifts can significantly alter the interaction potential of coexisting competitors. Importantly, these changes in interaction potential were mediated by non‐uniform, species‐specific shifts in entire phenological distributions and consequently could not be captured by metrics traditionally used to quantify phenological shifts. Ultimately, these non‐uniform shifts in phenological distributions increased the interaction potential for 25% of species pairs (and did not reduce interaction potential for any species pair), altering temporal community structure and potentially increasing interspecific competition. These results demonstrate the potential of phenological shifts to reshape temporal structure of natural communities, emphasising the importance of considering entire phenological distributions of natural populations.
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Abstract Species with different life histories and communities that vary in their seasonal constraints tend to shift their phenology (seasonal timing) differentially in response to climate warming.
We investigate how these variable phenological shifts aggregate to influence phenological overlap within communities. Phenological advancements of later season species and extended durations of early season species may increase phenological overlap, with implications for species' interactions such as resource competition.
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