DISPERSAL, POPULATION-GROWTH, AND THE ALLEE EFFECT - DYNAMICS OF THE HOUSE FINCH INVASION OF EASTERN NORTH-AMERICA

Since about 1940, when they were first released in the New York City a rea, house finches (Carpodacus mexicanus) have multiplied explosively and colonized much of eastern North America. We take advantage of the richly detailed documentation of this biological invasion to construct a mathematical model that predicts the rate of population spread on t he basis of readily measurable demographic parameters. We seek to impr ove on previous models by predicting a rate of spread that accelerates following an initial period of slower growth, a pattern of spread fol lowed by house finches as well as a variety of other invading species. We postulate that an Allee effect-disproportionately lowered fecundit y below a critical threshold density of abundance-is the mechanism lea ding to a slower rate of spread in the early stages of the invasion. O ur integrodifference equation model also emphasizes the link between l ong-distance dispersal and the rate of population spread.