The relationship between community diversity and exotic plants: cause or consequence of invasion? - Invasive Plants: Ecological and Agricultural Aspects - page 90

Figure 6. Impacts of invasion on species richness for Lonicera japonica and Rosa multiflora .
Regression analysis: Lonicera - F 1,218 = 34.88; P = 0.0001; R 2 = 0.14; Rosa - F 1,186 = 13.53;
P = 0.0001; R 2 = 0.07. Analyses were conducted only on invaded plots only to avoid confounding
effects of richness on invasibilty.
in the same direction (e.g., low diversity areas are more invaded and invasion
leads to species displacement), we would expect to see increased variance in
neighborhood diversity across the site. Similarly, in cases where these two
processes function antagonistically towards each other (e.g., high diversity
areas are more likely to be invaded and there is subsequent species displace-
ment), we would predict an overall decrease in the variance of neighborhood
diversity as invasion intensity increases.
Of the three species within the BSS data that show significant species dis-
placement and a positive association between invasion and species richness
( Elytrigia repens , Lonicera japonica and Rosa multiflora ), only E. repens (a
grass) had decreased variance with invasion intensity as predicted. Thus,
invaded systems may become more homogeneous during the course of inva-
sion. The variation seen among invaders may represent the intensity of inter-
action between the invader and resident community and the time scale over
which these interactions occur. The two species that did not exhibit a relation-
ship dominate systems for much longer and may generate a response as the
invasion proceeds. This relationship should be explored in other systems to see
whether it is a common consequence of plant invasions.