PARENT SESSION
Symposium 13: Prediction and prioritization of future invasive species
Organized by: RN Mack and M Lonsdale
Wednesday, August 10, 1:30 PM - 5:00 PM, Meeting Room 517 A, Level 5, Palais des congrès de Montréal

Invasive plants as missing life forms: New perspective on the Vacant Niche Hypothesis.

Mack, Richard,

ABSTRACT- Predicting the identity of future plant invaders and the communities they will invade are obviously inter-twinned issues, and both have proven difficult to resolve. Insights into the general characteristics of potential invaders arise through the venerable system of classifying communities' native species into life form spectra (sensu Raunkiaer), based on the height of each species' perennating bud. Communities with similar life form spectra, even widely separated and floristically unrelated communities, usually occur in similar macroclimates. In some intriguing cases, a community may not have a life form found in otherwise comparable communities with a similar macroclimate, i.e. the life form is absent. A putatively absent life form suggests an opportunity or niche for the entry of species that for whatever reason have not emerged from the native flora. This opportunity for alien plant entry and proliferation has been realized in many cases: e.g., a coastal marshland community without native trees that now supports an invasive tree (Sapium sebiferum), mud flat communities almost completely without native vascular plants but now dominated by invasive Spartina anglica. These examples provide support for the Vacant Niche Hypothesis, an early and often disputed hypothesis for the causes of invasions. Analyses of the life form spectra for many wetlands and temperate grasslands reveal that some lack native woody plants and may be then vulnerable to invasions by flood-tolerant or drought-tolerant alien woody species, respectively. Results assembled so far suggest that comparison of life form spectra in a more comprehensive manner world-wide could provide another component of our tool-kit for predicting invasive species and their new ranges.

Key words: life forms, Raunkiaer, invasion, empty niche