Plant-animal pollination systems. 2. Fewer pollinator than plant species

Abstract

A differential equation model was used to study the effects of pollinator individual-constancy foraging behavior on a plant-pollinator system. Individuals of a single pollinator species or population (e.g. bees from a hive) visited two plant species, but any individual was relatively constant to one of the plant taxa. The model presented reduces to the one-plant:one-pollinator model of Wells (1983) when only one plant species is present. (1) Criteria suggested by the one-plant: one-pollinator model which predict the pollinator species and the plant species that will be generalists, also predict which pollinator species and which plant species are likely to form a stable system equilibrium involving more plant species than animal pollinator species in the two-plant:one-pollinator model. (2) Minimal level of constancy expected for individual foragers of a ubiquitous generalist pollinator species is the largest {di/bi} the pollinator is likely to encounter; where di = instantaneous survival rate, and bi = instantaneous reproductive rate of plant species i. (3) The observed level of forager individual constancy to a plant species i, ψi, is ψi = α + (1 − α)λi where λi = frequency of plant species i, and (1 − α) = probability of randomly choosing the plant species to next visit. (4) A plant species population has the potential of increasing when its relative frequency, λi, is λi ≥ (di/bi − α)/(1 − α). Note bi > di. (5) Individual constancy reduced the probability of plant minority taxon extinction, and increased the likelihood of a stable equilibrium involving more plant species than pollinator species.