Davis M.A., Grime J.P., Thompson K. (2000). Journal of Ecology.

Fluctuating resources in plant communities: a general theory of invasibility.

Reviewed 09/15/11

This paper details a conceptual theory of the invasibility of  plant communities. This theory is usually referred to as the Fluctuating Resource Availability hypothesis by the authors, I will simply refer to it as FRA. Invasion is thought to occur when the characteristics of the potential invader are adequate, their is a rise in the number of invading propagules, and the environment is particularly prone to the invasion. The theory supports that the invasibility of a community is directly linked to episodic rises in the local availability of unused resources. This can occur by two primary mechanisms; use by residents decreases for whatever reason, or resource supply increases. The fluctuation of the resource highs is key to the theory, and it must coincide with a high count of invading propagules to yield an invasion.
The authors present evidence from a variety of other studies on how previous sub-mechanisms both fall under the category of their hypothesis for invasion and provides support for it. Disturbance, whether local or regional, can lead to outright increase in resources in the local environment or it can decrease the use ability of residents and/or increase resident mortality; all of which can lead to a higher degree of resource availability. Eutrophication and floods are also examples of increases in resources for plant communities, as well as smaller events that lead to a rise in available sunlight for the invaders.
It is also suggested that the disequilibrium in optimal invasion conditions can lead to a diequilibrium in the interspecific competition rates between residents and invaders, which can in turn lead to coexistence of the two species. To me this leads to an idea that their may be some optimal range of high to low resource availability (in time or quantity) that can lead to coexistence, and that this ratio could potentially be modeled. It also seems to fit with theories about roadside invasions, which is a habitat that experiences frequent disturbance; possibly too much for native species to coexist with invaders.
While propagule intensity was posited by the authors as crucial to their theory, they provided little discussion on the variable. I also had some issues with the seven "predictions' they detailed in the final sections of their paper. It seemed as if predictions 2-5 were just examples of their theory and not really predictions in and of themselves.
Prediction 6 also registered as problematic to me. "There will be no necessary relationship between the species diversity of a plant community and its susceptibility to invasion."They argue that species diversity is not a consistent predictor of invasibility, but it is possible that relative high diversity may still negate a communities' invasibility, via the mechanism that by probability alone, at least a few species in a more highly diversified community will be able to pick up the slack and use more resources as they become available. I am not convinced that the mechanisms behind this particular prediction have been fully explored in their paper.