The relationship between community diversity and exotic plants: cause or consequence of invasion? - Invasive Plants: Ecological and Agricultural Aspects - page 89

Figure 5. Influence of initial species richness on plot invasibility for Lonicera japonica and Rosa mul-
tiflora . Line represents logistic model predictions, points represent actual proportion of plots invaded
where N = 3. Logistic regression analysis: Lonicera -

χ

2 = 7.51, df = 1; P < 0.01; Rosa -

χ

2 = 4.62,

df = 1; P < 0.05

were heavily invaded, strongly suggesting that both invaders were displacing
resident species.
Both invasibility and impact processes interact to generate community
structure and dynamics associated with the invasion of these two species. The
overall negative association seen in the single-sample data is the net combina-
tion of both of these factors. Interestingly, these two processes are antagonis-
tic to each other, as selective invasibility would generate a positive association
while invader impacts would generate a negative association. Invader impacts
are clearly stronger in both of these cases, leading to the overall negative asso-
ciation even though invasibility partially obscures the impacts of invasion at
the community level.

Extensions of separating cause from consequence

There are some interesting extensions of our conceptual framework that sug-
gest invasion may alter community structure at a broader scale under certain
circumstances. In cases where invasibility and impacts of an invader are both