Looks can be deceiving: ecologically similar exotics have different impacts on a native competitor

Area of Science:

• Ecology
• Invasion Biology
• Plant Community Dynamics

Background:

• Invasive species success is often linked to functional trait differences with native species.
• Few studies examine if functionally similar invaders have similar impacts on native communities.
• Understanding invasion dynamics requires considering diverse species interactions.

Purpose of the Study:

• To investigate the competitive impacts of two ecologically similar invasive grasses on a native forb, Waitzia acuminata.
• To assess how intraspecific and interspecific competition affect native and invasive species.
• To determine if similar functional traits in invaders lead to similar ecological impacts.

Main Methods:

• Conducted field and laboratory experiments assessing impacts of invasive grasses on W. acuminata.
• Measured various performance indicators for native and invasive species.
• Analyzed responses to intraspecific and interspecific competition, including frequency dependence.

Main Results:

• Two functionally similar invasive grasses exhibited divergent impacts: one facilitated, the other suppressed the native W. acuminata.
• Intraspecific competition was generally stronger than interspecific competition for the native forb.
• Invasive grasses showed weak evidence of competition, potentially benefiting from limited stabilization or interspecific interactions.

Conclusions:

• Divergent impacts of invasive species can occur even with similar functional traits.
• Native species can benefit from interactions with invasive 'benefactor' species, emphasizing the role of positive interactions.
• Accurate prediction of invasion dynamics necessitates considering neutral and positive interactions alongside competition.