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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.
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Resource limitation alters effects of phenological shifts on inter-specific competition
Phenological shifts can alter the relative arrival time of competing species in natural communities, but predicting the consequences for species interactions and community dynamics is a major challenge. Here we show that differences in relative arrival time can lead to predictable priority effects that alter the outcome of competitive interactions. By experimentally manipulating the relative arrival time of two competing tadpole species across a resource gradient, we found that delaying relative arrival of a species reduced the interaction asymmetry between species and could even reverse competitive dominance. However, the strength of these priority effects was contingent on the abundance of the shared resource. Priority effects were generally weak when resources were limited, but increased at higher resource levels. Importantly, this context dependencycould be explained by a shift in per capita interaction strength driven by a shift in relative body sizes of competitors. These results shed new light into the mechanisms that drive variation in priority effects and help predict consequences of phenological shifts across different environments.
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- 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 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.more » « less
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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.We leverage extensive historic (1958–1960) and recent (2006–2015) weekly survey data for communities of grasshoppers along a montane elevation gradient to assess the impact of climate on shifts in the phenology and abundance distributions of species. We then examine how these responses are influenced by the seasonal timing of species and elevation, and how in aggregate they influence degrees of phenological overlap within communities.In warmer years, abundance distributions shift earlier in the season and become broader. Total abundance responds variably among species and we do not detect a significant response across species. Shifts in abundance distributions are not strongly shaped by species' seasonal timing or sites of variable elevations. The area of phenological overlap increases in warmer years due to shifts in the relative seasonal timing of compared species. Species that overwinter as nymphs increasingly overlap with later season species that advance their phenology. The days of phenological overlap also increase in warm years but the response varies across sites of variable elevation. Our phenological overlap metric based on comparing single events—the dates of peak abundance—does not shift significantly with warming.Phenological shifts are more complex than shifts in single dates such as first occurrence. As abundance distributions shift earlier and become broader in warm years, phenological overlap increases. Our analysis suggests that overall grasshopper abundance is relatively robust to climate and associated phenological shifts but we find that increased overlap can decrease abundance, potentially by strengthening species interactions such as resource competition.more » « less
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Species‐specific phenological responses to changing climate are reshuffling the timing of species interactions, however we do not fully understand the consequences of these changes for species' population dynamics and community composition. In this study, we experimentally manipulated the timing of germination for five annual plant species from southern California and used pairwise competition experiments and coexistence theory to quantify how phenological shifts may impact species interactions and coexistence. We found that phenological shifts may help promote coexistence when they confer an advantage for competitively inferior species, but in other cases promote dominance by competitively superior species. Earlier germination generally increased species' performance relative to competitors, but the relative changes in intra‐and inter‐specific interactions caused more complex effects on niche and fitness differences. Phenological differences tended to reduce stabilising niche differences for many species pairs and reduced overall coexistence probabilities. Synthesis. While phenological differences among species have typically been considered a form of niche partitioning, it seems increasingly likely that phenological offsets could destabilise species coexistence. The net effects of changing phenology on species coexistence will depend on the complex combinations of effects on intra‐ and inter‐specific interactions, which remain challenging to predict.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1007/s00442-018-4214-3
