PARENT SESSION
Oral Session #29: Invasions: Predicting and understanding invasibility. Presiding: K. Kearns.
Tuesday, August 7, 2001. 1:00 PM to 4:45 PM. Madison Ballroom C.

Dampening environmental stochasticity among immigrant plants: The role of cultivation.

MINTON, MARK¹, MACK, RICHARD¹, ¹

ABSTRACT- The vast majority of non-indigenous species are destroyed swiftly upon immigration; environmental stochasticity is a plausible cause. All populations are susceptible to the vagaries of environmental stochasticity; small populations are however acutely sensitive. Most immigrant populations are small, consisting of a few thousand individuals or less. We contend that deliberate or inadvertent cultivation dampens the extremes of environmental stochasticity, thereby enabling an immigrant population to increase in size. Once sufficiently large, the population is no longer as vulnerable to these stochastic forces and may even become naturalized. In a series of multi-year factorial experiments using one native and three agricultural species, we examined the effect of different levels of cultivation on the persistence of founder populations. The cultivation excluded seed predators and plant grazers, and provided varying levels of irrigation. The effect of founder population size and density was also incorporated into the experimental design. In addition, an autumn sowing of the four species in a caged/uncaged experiment examined the effect and cause of winter seed destruction. Excluding seed predators and grazers and providing irrigation resulted in at least a two-fold increase in the number of survivors in each population. There was also a corresponding increase in the R₀. Larger immigrant populations did not display the radical swings in population size seen among smaller populations.

KEY WORDS: invasions, naturalization, environmental stochasticity, cultivation