Evol Ecol Res 2: 387-407 (2000)     Full PDF if your library subscribes.

Dormancy strategies in a random environment: Comparing structured and unstructured models

Michael R. Easterling1,2 and Stephen P. Ellner1

1Biomathematics Graduate Program, Department of Statistics, CB 8203, North Carolina State University, Raleigh, NC 27695-8203 and 2Pharmacokinetics Branch, US Environmental Protection Agency, MD-74, Research Triangle Park, NC 27711, USA

Address all correspondence to Michael R. Easterling, Pharmacokinetics Branch, US Environmental Protection Agency, MD-74, Research Triangle Park, NC 27711, USA.
e-mail: easterling.michael@epa.gov


Hatching strategies are studied in a model of population dynamics in a random environment. The strategies are the fraction of dormant eggs that hatch each year. A projection matrix with random elements describes the population dynamics. The model extends the density-independent model of Dan Cohen and the density-dependent model of Stephen Ellner by adding structure to the egg bank, such that a fraction of the dormant eggs are buried and unavailable for hatching each year. Differences between the structured and unstructured models are analysed by deriving a small variance approximation for the population’s long-term growth rate and relating the growth rate to the egg bank structure and the environmental parameters. Tuljapurkar and Istock (1993) claimed that structured and unstructured models give very different predictions, especially when dormancy is high. We show that Tuljapurkar and Istock’s conclusions are the result of the particular dormancy type in their model, in which the maximum duration of dormancy is 2 years, rather than the addition of population structure. Using parameters estimated from field and experimental studies of the freshwater copepod Diaptomus sanguineus in Bullhead Pond, RI, the density-dependent model correctly predicts that the population should maintain a long-term pool of diapausing eggs, whereas the density-independent model makes the incorrect prediction that all eggs should hatch at their first opportunity. If the per capita burial and emergence rates are low, as may be the case for many plant populations, the ESS optimal hatching strategy is nearly that of an unstructured model with the mortality of non-hatchers increased by the burial rate.

Keywords: copepod, dormancy strategies, evolutionarily stable strategy, moment closure, structured population model.

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