Reduced intraspecific competition in introduced plant populations suggests a role for self-limitation in invasion success

Ecological diversity depends on mechanisms that promote species
coexistence, yet some non-native plants form monospecific stands,
suggesting an ability to escape self-limiting processes that constrain
native flora. Whereas invasion success is often attributed to enhanced
interspecific competition, it may also result from reduced intraspecific
competition within introduced populations. Using a controlled greenhouse
experiment, I compared competitive outcomes among single native and
introduced populations of five plant species (Gleditsia triacanthos, Pinus
sylvestris, Paulownia tomentosa, Solidago canadensis, Viola sororia).
Individuals were grown in within-range (native × native, introduced ×
introduced) and across-range (native × introduced) pairings to test
whether introduced populations exhibit weaker intraspecific competition.
Introduced populations generally showed reduced self-limitation compared
with native conspecifics, consistent with relaxed intraspecific density
dependence. Because only one population per range was tested, these
findings reflect population-level contrasts rather than species- or
range-wide generalizations. Even so, the results indicate that modest
reductions in self-limitation at the population level can substantially
enhance the potential for invasive dominance, highlighting relaxed
intraspecific competition as an underrecognized pathway to invasion
success.