Seed dispersal syndromes in a fire adapted plant

Background/Question/Methods

Dispersal is a process whereby biological agents with the ability to establish move to escape parent-offspring conflict and exploit unused resources in space or time.  In Spermatophytes, seeds are effectively the sole means by which to achieve the end of dispersal.  Many plants have coevolved with animals as agents of dispersal, and different guilds of animals ostensibly have had differential fitness effects on plants, hence the coevolution of plants and animals are multifarious.  This is phenotypically manifested as "dispersal syndromes," which are correlated diaspore traits matched to the behavior, physiology, and morphology of different types of dispersers.  The aim of the study was to determine if seed dispersal syndromes exist in a widespread, dominant member of fire-prone ecosystems, manzanita (Arctostaphylos).

Results/Conclusions

Herein the poster, we present data that demonstrate seed dispersal by two guilds of dispersers: scatter-caching rodents and medium-to-large mammals (hereafter, respectively rodents and mammals).  Rodents disperse (cache) seeds at depths (median = 4.1 cm) that are not statistically different than seedlings emerge (median = 5.5 cm), whereas we found that no seedlings emerge after mammal dispersal.  A multivariate analysis of fruit traits (PCA) found two statistically different clusters that correspond to dry fruits with large nuts (rodents dispersed) and more fleshy fruits with many nutlets (mammal dispersed).  These data suggest that there are distinct dispersal syndromes within manzanitas.  Given the ecology of manzanitas (fire-stimulated seedbanks and heat-sensitive seeds), this lends further supports that two-phased seed dispersal has been important to the evolution of the most diverse woody plant in the biodiversity hotspot, California Floristic Province.