The Allee effect as a threshold in invasions

The Allee effect, most broadly, is when population size influences fitness. Allee et al –It can be a positive or negative relationship. –There can be a threshold level in population size, below which the population declines

Cappuccino 2004

Levine, J.M., et al A meta-analysis of biotic resistance to exotic plant invasions. Ecology letters. From Brooke QuarantineEradicationContainment

Cappuccino 2004

Mechanisms Failure to find mates Inbreeding depression Predator satiation Allelopathy Different strengths of inter- and intraspecific competition Stochastic effects on population sizes

Van Dyke 2003

Liebhold and Bascompte, 2003

Conclusions Eradication does not need to be 100% Extinction is stochastic and probabilistic Timing of eradication efforts is important

How does population structure influence Allee effects on invasive populations. Metapopulation structure and migration –Migration between invasive populations can increase effective population size One migrant per generation negates negative effect of inbreeding depression –Rescue effect

Van Dyke 2003

Questions Is the Allee effect likely to be important or useful for studies of invasive species? Can studies of rare species preservation be useful in studies of invasive species spread? How does understanding population structure influence invasion dynamics? When is there a negative effect of large population size on individual fitness? Are there other thresholds for invasion success that are not related to population size?