Climate change leads to unequal shifts in the phenology of interacting species, such as consumers and their resources, leading to potential phenological mismatches. While studies have investigated how phenological mismatch affects wild populations, particularly the higher trophic level, we still lack studies and a framework for investigating how phenological mismatch affects ecosystems, particularly nutrient cycling. Given that different types of organisms are more likely to fall behind from a phenological perspective, we can make predictions about how communities and, as a consequence, ecosystems may be impacted. For example, if, as research suggests, secondary consumers are the most likely to be asynchronous with herbivores, then we might predict that herbivory may increase and lower trophic levels and productivity may decrease with climate change. Alternatively, more stable interactions, such as insect-flower associations, are less likely to become asynchronous and therefore are less likely to result in ecosystem-level changes with climate change. We conducted what we believe to be the only experiment designed to investigate how phenological changes influence ecosystem functioning. The experiment focused on a developing mismatch between a sedge and Pacific black brant in Alaska, USA, and its impacts on carbon and nitrogen cycling.
Results/Conclusions
We found that if migratory geese arrive later each year this change has positive effects on primary producers and the ecosystem. Late goose arrival increases plant biomass, sexual reproduction, and possibly genetic diversity, while decreasing forage quality. This, in turn, reduces soil N availability, and shifts the system from being a summer-season carbon source to a carbon sink. This example illustrates how a developing phenological mismatch can have cascading ecosystem consequences and even climate feedbacks. We suggest that, in general, late arrival by migratory herbivores, such as caribou, may have similar effects on productivity and ecosystem functioning. However, late arrival by higher trophic levels, such as insectivorous migratory species, may have the opposite effects. These effects are likely to be most evident in systems where (i) the phenologies of both species are influenced by climate change; (ii) the species have a strong interaction; and (iii) both species alter resource pools, so their asynchrony alters ecosystem functions, such as carbon uptake and nitrogen cycling. Phenological mismatch studies should no longer ignore ecosystem responses, and these types of studies should be no more difficult to design than any study measuring ecosystem responses.