Spatially and temporally discrete episodes of plant recruitment occur when relaxation of the resources that limit establishment and growth coincides with propagules. Dynamic, environment-based models of community invasibility are gaining traction but explicit accommodation for the rapidity with which local conditions can change, and their concurrent effects on recruitment is often lacking. We use empirically derived data to model the interactive effects of disturbance patch size (DPS), grazing intensity (GI) and soil resource availability (SRA) on the invader success probability (ISP) of a grazing-tolerant grassland species. Importantly, we consider two life history stages because invader size can determine whether shifts in below- and aboveground resources increase or decrease ISP.
Results/Conclusions
Although idiosyncrasies emerge from invader-specific and composition-dependent responses to available resources, our models generally predict: 1) thresholds in ISP exist across DPS – their magnitude increases dramatically with SRA, 2) invader size strongly affects ISP in smaller-sized patches containing high SRA, 3) regardless of invader size, grazing effects on ISP are large in small DPSs in high SRA areas, and 4) without grazing, varying SRA within a given DPS can have opposing effects on ISP. These empirically-supported findings dismiss the notion that increased availability in a recruitment-limiting factor necessarily results in higher recruitment rates. Moreover, the emerging framework highlights the importance of investigating the type and intensity of disturbance across other ecological dimensions. Lastly, to elucidate the generality of the working model, we propose that levels of DPS, GI and SRA be integrated across communities of different composition, as these interactions ultimately determine the above- and belowground resources available to potential colonists.
