Relationships between flowering phenology and community composition in an experimental restoration of northwest prairies

Phenology, the timing of biological life cycles, is a key indicator of
global climatic change, with numerous studies showing that species'
phenologies are shifting in response to climate change. Despite general
trends (e.g., warming causing earlier arrival of spring events such as
leaf-out and flowering onset), studies repeatedly reveal that phenological
changes tend to be species-specific and thus may alter species
interactions. Less studied is the potential feedback between biotic
interactions and phenology and the impacts on species’ fitness. To
understand the consequences of shifting phenology for species and
communities, we need to quantify how phenology and competition interact to
affect species’ fitness. Here, we studied the potentially interacting
effects of species’ phenology and competition on plant fecundity (as a
proxy for fitness). We sowed seeds of various species combinations to test
how variation in competitor species richness, identities, and densities
affect the phenology and fecundity of an annual wildflower, Clarkia
purpurea, using an unconventional experimental design to encourage public
engagement with the experiment. We found that C. purpurea’s flowering
phenology varied with competitor identity and competitor species richness,
that fecundity was negatively correlated with competitor density but not
species richness, and that the strength of competition tended to vary by
competitor identity but appeared unrelated to the relative phenology of
the competitor. These findings offer unique evidence that competitive
interactions may impact plant phenology and fecundity in complex ways and
could influence species’ persistence and coexistence conditions in our
changing global environment.