Soil disturbance by a native rodent drives microhabitat expansion of an alien plant.

The 'niche opportunity' hypothesis proposes that alien plant establishment is generally driven by the integrated effects of environmental conditions, changes in resource availability and reduced herbivory pressure, but there is yet little evidence supporting such a complex interaction in nature. We evaluated the interactive effects of soil disturbance by the native fossorial mammal Spalacopus cyanus, microhabitat (beneath shrubs and open areas), and introduced herbivores (rabbit, Oryctolagus cuniculus) on the establishment (seedling emergence, adult abundance, aboveground biomass, and reproductive effort) of the alien annual plant Fumaria capreolata in a coastal matorral of central Chile. In the absence of disturbance, seedling emergence and plant establishment of F. capreolata was largely restricted to understory microhabitats. Soil disturbance by S. cyanus significantly increased seedling emergence and establishment, both beneath shrubs and in open areas. There was no effect of herbivore exclusion on the abundance, biomass and reproductive effort of F. capreolata, although the biomass of other co-existing species was reduced. Overall, these results suggest that native fossorial mammals may favor the invasion of F. capreolata by allowing microhabitat expansion into open areas and by increasing its performance in those microhabitats already occupied. We show how the interplay between soil disturbance, microhabitat, and reduced herbivory may explain invasion patterns at the local scale in natural communities. [ABSTRACT FROM AUTHOR]