PARENT SESSION
Oral Session #70: Invasive Species: Aquatic.
Presiding: S. Juliano
Wednesday, August 7. 1:00 PM to 4:45 PM. Grand Ballroom East, Radisson.
Allee effects and the success of colonizing species: Bythotrephes longimanus in North America.
Drake, John*,1, Lodge, David1, Yan, Norman2, 1 University of Notre Dame, Notre Dame, IN2 York University, Toronto, Ontario, Canada
ABSTRACT- Developing quantitative risk assessment methods for invasive species is an important research frontier. This study addresses the importance of Allee effects in the establishment success of the spiny water flea, Bythotrephes longimanus, and underscores the importance of nonlinear population dynamics in biological invasions. The spiny water flea is a highly invasive, palearctic predatory cladoceran that invaded the Laurentian Great Lakes in the 1980s and subsequently invaded many inland lakes. Although a substantial supply of viable propagules exists, many lakes continue to lack this species, consistent with the observation that the base rate of successful establishment for introduced populations is low (probably <10%). One hypothesis proposed to explain this low base rate is that Allee effects prohibit the persistence of small or sparse introduced populations. We hypothesize that some populations of spiny water flea, despite summertime parthenogenetic growth, are unable to achieve densities required for production of over-wintering, sexually produced resting eggs, producing such an effect. To test this hypothesis, we developed a model of mate limitation for seasonally parthenogenetic species that predicts a critical density of males required for population persistence. We parameterized this model with data from summertime censuses of females for several lakes over multiple years to predict this critical density. A comparison of the critical density with the observed density of males in introduced populations showed that the Allee effect should be expected in natural populations and thus could account for the low base rate of establishment. This result suggests that models that do not consider Allee effects are likely to substantially overestimate the probability of establishment and that Allee effects (and other nonlinear phenomena) should be an integral part of risk assessments of biological invasions.
KEY WORDS: Allee effect, invasion, colonization, Bythotrephes longimanus