Agriculture Reference
In-Depth Information
ecological literature. Associations between diversity and exotic plant cover
have been used as evidence for both the regulation of neighborhood invasibil-
ity by diversity and the impacts of exotic plants on resident species. These two
pathways of interaction must be separated conceptually to assess the relation-
ship between exotic plant invasion and community diversity. These contrasting
mechanisms can be formalized into two hypotheses, the
invasibility hypothe-
sis
and the
impact hypothesis
(Fig. 2). The hypotheses differ in the role of
diversity - as a regulator of exotic plant invasion or as a response to invasion.
These two mechanisms also function at significantly different ecological
stages, one at the establishment phase of the invader, the other once an inva-
sion has successfully occurred and the species begins to spread within a site.
In the invasibility hypothesis, the diversity of the neighborhood serves as an
ecological filter that determines the invasion success of an exotic species.
While there is no
a priori
reason to expect a single direction for the outcome
of this interaction, most studies have focused on the inhibition of invasion by
diversity. This reflects the overwhelming focus on competitive or other nega-
Figure 2. Schematic model of the two major hypotheses explaining the relationship between commu-
nity diversity and exotic plant invasion. The invasibility hypothesis states that community diversity
regulates the invasion of exotic species into a community, generating a relationship between diversi-
ty and exotic plant invasion. The impact hypothesis states that following invasion by exotic species,
interaction between the resident community and the invader lead to changes in community diversity.
As there is no
a priori
assumption of directionality for this relationship, both positive and negative
diversity/invasion relationships are shown.
Search WWH ::
Custom Search