Demographic analysis of invasible habitat fraction identifies context-dependent roles of resource availability and biotic resistance in determining invasion success

Theories of plant invasions predict that plant communities should be more easily invaded when resources increase and/or competition decreases. We tested this with an experimentally introduced plant population by manipulating precipitation and resident community biomass. We used a spatially-explicit demographic approach to develop a new population-level metric of invasibility that quantifies the invasible habitat fraction (IHF) across the landscape.

The existing community was essentially uninvasible (median IHF ≈ 0%), but experimental manipulations greatly increased the range of outcomes, with maximum observed IHF values over 50%. However, changes in invasibility were often context-dependent, resulting in some outcomes that aligned with existing theory, and others that were not readily predicted. Moreover, variation in invasibility was often driven by specific sets of invader demographic vital rates.

Removing competitors revealed the capacity for strong biotic resistance, but this ...