The effect of exotic invasives on diversity. Loren Hintz Bio255 Oct. 21, 2004. outline. Handout and extra email articles Diversity ( number of species vs. higher taxa or distribution) Houlahan and Findlay 2004 Rosenzweig 2001a Discussion. Assigned Readings.
Oct. 21, 2004
Exotic species diversity was positively correlated with native species diversity (r =.405)even when controlled for other factors that predict diversity (area, nearby forest , nitrogen and magnesium; p=.041) but it showed no significant relationship (r =.005)with rare species diversity even when controlled for other factors (area, road density, % wetland as bog/fen; p=0.168)
There was no significant difference between % of native (8%)and exotic (5.5%)dominant species (chi square =0.70)Houlahan and Findlay results
Examined the effect of 4 exotic and 4 native dominant species on S and Sr
3 of the 4 dominant exotic species studied showed a negative effect on rare species (purple loosestrife ,LyS, canary grass, PhY, and glossy buckthorn, RhF); but only canary grass showed the effect after controlling for other factors (14% Sr decrease per dominance score step.) Only canary grass, PhY, showed an effect on general native species.
Only willow, SaP, of the 4 dominant native species studied showed negative effect on both rare and native species (13% Sr decrease per dominance score step after controlling for other factors)Results of comparison of invasive (dominant) exotic and native species
Many studies contradict the textbook claim that purple loosestrife competively excludes native species
In Ontario wetlands exotic species do not decrease plant diversity
Native and exotic species have similar dominance probabilities and effects
Managers need to focus on specific community dominants irrespective of origin
Pathogens, predators have more impact; exotic plants may impact nutrient cycling; fire regimesConclusions Houlahan and Findlay
Si = C Azi
Sax and Gaines loosestrife competively excludes native species