Population Biology of an Annual Plant in a Temporally Variable Habitat

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Abstract
(1) A population of the summer annual Erucastrum gallicum (Brassicaceae) colonizing an abandoned limestone quarry near Syracuse, New York, U.S.A., was monitored for five consecutive years and its demographic performance was interpreted in relation to rainfall patterns. (2) Survival and percentage reproduction of plants that emerged in the spring varied markedly depending upon rainfall. Deevey survivorship curves, Types I, II, and III were observed in cohorts from a year with abundant rainfall, a year with intermittent rainfall and drought, and a year with spring drought, respectively. Growth and the number of seeds produced by the population were also influenced by rainfall. (3) The number of seeds produced per plant ranged from 24 to 1675. The latter value is similar to or greater than that recorded in many other annual species. (4) Several lines of evidence suggest that less than half the viable seeds in the soil germinate in any one year and that a substantial proportion of seeds survive from one year to the next. (5) Unlike some annual plants, that persist in variable habitats by exhibiting phenotypic plasticity in growth coupled with high seedling survival, E. gallicum persists in the quarry through a suite of traits including high seed output by those plants that survive to reproduce, germination by a small proportion of the seeds in the seed bank in any one year, and viability of seeds that remain in the soil for at least 1 year.