Community invasion by complex life cycles

Abstract

A complex life cycle (CLC) is one in which a sharp ontogenetic change occurs that permits the organism to exist in two different habitats or ecological niches. A simulation model based on life table calculations was used to describe the ecological conditions under which a CLC can increase when rare in the presence of one and two competitors having simple life cycles (SLCs). The model simulated the population dynamics of three species, each having four age classes, with density-dependent mortality in the juvenile stages and density-dependent fecundity in the adult stages. Adult CLCs live in one habitat and compete with one of the SLCs; juvenile CLCs live in a second habitat and compete with the other SLC. The quality of both habitats varies randomly and independently. Habitat quality influences population dynamics by altering the survivorship and fecundity of the age classes in the habitat. Simulations examined the population responses as a function of life table parameters. The effects of the life table parameters on the timing of population regulation were quantified by Istock's (1967) e. The simulations showed that: (1) single CLC populations have higher carrying capacities than single SLCs, (2) the equilibria of single CLC populations depend on e and on whether e is varied by altering the effects of density on mortality or fecundity, (3) CLCs can always invade and dominate a community composed of a single SLC regardless of e or environmental stochasticity, (4) in the absence of immigration, CLCs can only infrequently invade communities composed of two SLCs initially at equilibrium and (5) when immigration occurs, CLCs can readily invade and dominate communities of two resident SLCs, but invasion depends on e and on the variance of environmental quality.