Flowering phenology for seven California annual species under two rainfall treatments

Premise: Shifts in the timing of life history events, or phenology, have
been recorded across many taxa and biomes in response to global change.
These phenological changes are often studied in a single species context,
but considering the community context is essential for anticipating the
cascading effects on biotic interactions that are likely to occur.
Focusing on an annual grassland plant community, we examined how
experimental changes in precipitation affect flowering phenology in a
community context and explore the implications of these shifts for
competitive interactions and species coexistence. Methods: We
experimentally manipulated rainfall with rainout shelters and recorded
detailed flowering phenology data for seven annual species including two
grasses and five forbs. We assessed how their first and peak flowering
days were affected by changes in rainfall and explored how flowering
overlap between competing species changed. Results: Changes in rainfall
shifted flowering phenology of some species, but sensitivity differed
among neighboring species. Four of the seven species studied started
and/or peaked flowering earlier in response to reduced water availability.
The idiosyncratic shifts in flowering phenology have the potential to
alter existing temporal dynamics that may be maintaining coexistence, such
as temporal separation of resource-use among neighbors. Conclusions: Our
results show how species-specific phenological consequences of global
change can impact community dynamics and competition between neighboring
plants and warrant future research.