One size does not fit all: context specificity drives invasion in grassland plants

Abstract

There has been little consensus of the relative importance of three determinants of invasion – invader traits, propagule pressure, and community susceptibility to invasion determined by resource availability (invasibility) – given the logistical difficulties of disentangling their interactions. I tested whether combinations of factors driving invasion (invasion pathways) of ten grassland invaders were similar among species or context-specific. I tested this by quantifying traits with a greenhouse study, followed by a factorial field experiment [with different scenarios of propagule pressure (seed count) and invasibility (nutrients, disturbance, biotic resistance)]. My work supported context-specificity. None of the invaders had ubiquitous success among experimental treatments. Each tested factor was important, with some being more commonly important than others (e.g., propagule pressure). I find invasion pathways were highly differentiated by species identity. These findings may help to explain the current lack of consensus in the literature with deriving generalizable predictions of grassland plant invasions.