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LIFE HISTORY AND SEED DISPERSAL OF THE SHORT‐LIVED CHAPARRAL SHRUB DENDROMECON RIGIDA (PAPAVERACEAE)
Author(s) -
Bullock Stephen H.
Publication year - 1989
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.1002/j.1537-2197.1989.tb15132.x
Subject(s) - biology , biological dispersal , seed dispersal , longevity , ecology , population , shrub , chaparral , propagule , seed dispersal syndrome , reproduction , fecundity , intraspecific competition , demography , sociology , genetics
The natural history of the short‐lived, fire‐following shrub Dendromecon rigida Benth. was studied with emphasis on reproductive output and the consequences of seed dispersal, by intensive study of one population and comparisons with several others. In 16 populations throughout California, mean seed weight ranged from 10 to 16 mg, and was not correlated with rainfall, elevation or latitude. Seed number per fruit ranged from 3 to 11. Adult populations ranged in size up to several million, but each was probably even‐aged, established after recent disturbance. Seed‐dispersing ants were found at all localities. Reproduction began one year after establishment. Precocious reproduction did not increase mortality; rather, longer‐lived plants were more fecund at all ages. The percentage of the population reproducing and fruit number in the most fecund plants were directly related to rainfall in the preceding six months, regardless of plant age. Reproduction also differed according to topographic position. Mean life expectancy of one‐year‐old plants was about six years, and only 5% survived to age 10 years. Intraspecific density effects were not apparent. Seed longevity probably exceeds adult longevity by a factor of five or ten. The fruits are explosive and secondary dispersal is by gravity and ants. The ants are attracted to a caruncle which represents 14% of the propagule's caloric content. In the intensive study area ants removed more seeds from more sites than did vertebrate seed predators. Pogonomyrmex subnitidus developed large nests on open sites on ridges, and thus provided uphill (even interdrainage) dispersal; it discarded seeds on the soil surface, free to roll but open to predation. Camponotus species had fewer foragers but many small nests in well‐covered sites, and discarded the seeds in underground refuse galleries. Dispersal thus affects exposure to predation, the microsite of germination, conspecific aggregation, and position in the mosaic patterns of topography and fire.