Population biology of west coast Cakile maritima: effects of habitat and predation by Peromyscus maniculatus

Abstract

Survival patterns of Cakile maritima Scop. ssp. maritima seedlings in adjacent open-beach and foredune habitats differed, with significant cohort and seasonal effects only for open-beach plants. Open-beach plants were usually killed by fall storms. Some foredune plants (5.3%) survived into a second reproductive season, producing 85% of mature fruits in the foredune. Peromyscus maniculatus (Wagner) removed 95% of fruits matured by foredune plants. Sand burial of fruits increased their chances of escaping predation. Burial was 52-fold more likely for fruits on open-beach plants compared with foredune plants, resulting in lower seed predation on the open beach. Germination from P. maniculatus caches produced 63% of foredune plants, but they represented only 0.002% of all removed seeds. Cache plants had lowered survival relative to noncache plants, so that seed dispersal by P. maniculatus did not benefit C. maritima. Both foredune and open-beach populations were likely to decline if transition patterns among age-classes and fruit production rates observed in 1983 and 1984 remained constant. Because of high fruit production by overwintering plants, foredune plants produced more fruits than needed to maintain plant numbers, but predation by P. maniculatus reduced seed survival to less than 20% of the replacement rate for that habitat. Key words: Cakile maritima, Peromyscus maniculatus, plant–animal interactions, seed dispersal, seed bank, plant demography.