Temporal variation in fitness components and population dynamics of large herbivores

In large-herbivore populations, environmental variation and density depende nce co-occur and have similar effects on various fitness components. Our re view aims to quantify the temporal variability of fitness components and ex amine how that variability affects changes in population growth rates. Rega rdless of the source of variation, adult female survival shows little year- to-year variation [coefficient of variation (CV <10%)], fecundity of prime- aged females and yearling survival rates show moderate year-to-year variati on (CV <20%), and juvenile survival and fecundity of young females show str ong variation (CV >30%). Old females show senescence in both survival and r eproduction, These patterns of variation are independent of differences in body mass, taxonomic group, and ecological conditions. Differences in level s of maternal care may fine-tune the temporal variation of early survival. The immature stage, despite a low relative impact on population growth rate compared with the adult stage, may be the critical component of population dynamics of large herbivores. Observed differences in temporal variation m ay be more important than estimated relative sensitivity or elasticity in d etermining the relative demographic impact of various fitness components.