Delayed germination and dispersal in desert annuals: Escape in space and time

Abstract

A model is developed to consider the interplay between dispersibility and delayed germination in desert annuals. The model explores the effect of low levels of dispersal, considered realistic for annual plants, on optimal germination fraction. The model also demonstrates the effect of the amount and accuracy of "predictive" (responsive to the environment) dormancy on the optimal innate germination fraction (not responsive to environmental conditions).Optimal germination fraction is found to be very sensitive to changes in despersibility especially at the limited dispersibilities that are realistic for annual plants. As dispersibility increases, optimal germination fraction increases. If plants make two kinds of seeds with differing despersibility, reproduction is maximized if the low dispersal seeds have delayed germination and the high dispersal seeds have quick germination. If dormancy mechanisms permit seeds to germinate when environmental conditions allow successful maturation, and remain dormant when environmental conditions do not permit successful maturation, what fraction of seeds should remain dormant under predicted good conditions as a hedge against inaccurate prediction of the environment? If environmental cues that break dormancy are uncorrelated with environmental conditions that permit successful maturation, predictive dormancy has little or no effect on the optimal innate germination fraction. When predictive dormancy lowers the probability of germinating when environmental conditions preclude successful maturation, the optimal innate germination fraction increases with increasing germination control by predictive dormancy. With a moderate degree of germination control by predictive dormancy, the optimal innate dormancy is still sensitive to changes in dispersal in the low dispersal ranges characteristic of annual plants.Evidence is presented from plant species that have both dispersal and germination dimorphisms to support the predicted correlation of high germination fractions with high dispersal.

The Problem of Pattern and Scale in Ecology: The Robert H. MacArthur Award Lecture

“…6), tradeoffs become evident; dispersal and dormancy are alternative ways to reduce the experienced variability, and selection for one reduces the selective pressure on the other because it changes the scale at which the environment is observed. Such theoretical predictions are borne out by data for a range of plant species (Werner 1979, Venable andLawlor 1980).…”

The Consequences of Brood Size for Breeding Blue Tits. Iii. Measuring the Cost of Reproduction: Survival, Future Fecundity, and Differential Dispersal

“…1) The mean survival rates plotted in Figure Id are arithmetic means; plotting geometric mean values (Cohen, 1966;Hastings and Caswell, 1979;Venable and Lawlor, 1980;Boyce and Perrins, 1987;but see MacArthur [1972] and Bulmer [1985]) would produce a relationship with a different shape. Cooper and Kaplan (1982), among others, have argued that the geometric mean is the appropriate method ofaveraging population growth rates over time, but, even if the geometric mean is appropriate for averaging population growth rate, it will, in many cases, be inappropriate for averaging a single component offitness (Nur, unpubl.…”

The Evolutionary Significance of Seed Germinability in an Alpine Meadow on The Eastern Qinghai-Tibet Plateau

“…mangrove trees) often germinate inside the ripe fruit, while still on the mother plant (Figueroa and Armesto, 2001); however, seeds of many desert plants remain dormant and viable, while buried in the soil for years or decades after dispersal (Venable and Lawlor, 1980). It has been argued theoretically that low germinability would be associated with life history attributes such as seed size (Thompson and Grime, 1979;Venable and Lawlor, 1980;Grime et al, 1981;Venable and Brown, 1988;Rees, 1993Rees, , 1994Cater and Ungar, 2003), seed dispersal mode (Garwood, 1983), longevity of plant (Thompson, 1987), and life form (Figueroa and Armesto, 2001).…”