1 Plants often suffer substantial loss of seeds to consumers. However, beca
use the seed-to-seedling transition is frequently ignored, quantitative est
imates of the effects of seed consumers on plant population dynamics are ra
2 We examined how post-dispersal seed predation by rodents affected seedlin
g emergence and subsequent adult plant abundance of bush lupine (Lupinus ar
boreus), a large N-fixing shrub common to coastal dunes in California. We m
onitored patterns of seedling emergence and survival over 3 years for seeds
sown into exclosed and control plots.
3 We sowed additional cohorts of seeds in the second and third years and co
mpared interannual variation in emergence patterns.
4 Rodent exclusion substantially reduced seedling emergence, with an averag
e of 109 seedlings emerging over 3 years from 476 seeds sown in rodent excl
usion plots vs. 26 from control plots. The intensity of granivory, however,
varied between years, with rodent exclusion increasing emergence from seed
s sown in year one, but not in year two.
5 Winter seedling mortality, due to cutworm herbivory, was similarly high i
n rodent-free and control plots, and its net impact was to reduce the diffe
rence in seedling abundance. Thus. by mid-summer in each of the three years
, there were only marginally more seedlings in rodent-excluded vs. control
6 The cumulative effect of protecting seeds, was, however, large. After 3 y
ears, an average of four adult lupines were established in rodent-free plot
s, whereas only 0.5 were found in control plots and lupine biomass was more
than 5-fold higher in exclusion plots.
7 Taken together, the results indicate that rodents play a critical role by
limiting the abundance and biomass of a large N-fixing shrub in dunes.