Biotic homogenization within and across eight widely distributed grasslands following invasion by Bromus inermis

Abstract

Invasive species can alter the structure and function of the communities they invade, as well as lead to biotic homogenization across their invasive range, thus affecting large‐scale diversity patterns. The mechanisms by which invasive species can lead to biotic homogenization are poorly understood. We argue that invasive species acting as strong, deterministic, and consistent filters within and across invaded communities are likely to cause biotic homogenization at multiple spatial scales. We studied Bromus inermis Leyss. invasion into eight grasslands covering most of the grassland and parkland natural regions of Alberta (western Canada). Specifically, we tested whether B. inermis (1) has a strong impact on species richness and composition, (2) consistently alters resources (nutrients, light, and soil moisture), imposing the same ecological filter to species establishment and persistence across sites, and hence (3) whether it leads to biotic homogenization within and across sites. We recorded plant cover and resources across native‐to‐invaded transition areas combining space‐for‐time substitutions with time‐series data analyses. Bromus inermis invasion was associated with rapid biotic homogenization of communities, within and among the eight grasslands. The sharp changes in species relative abundances following invasion was the initial driver of biotic homogenization, and species loss was delayed. Supporting the idea that biotic homogenization can occur when an invasive species presents a broad and consistent filter, resources modified by B. inermis invasion (particularly light and certain nutrients) were altered rather consistently within and across sites. The 50% reduction in light was likely the initial driver of biotic homogenization, and the increase in nutrient availability probably facilitates the displacement of species from the invaded areas and could lead to the establishment of self‐reinforcing dynamics. Overall, our results support the idea that invaders acting as strong, deterministic, and consistent ecological filters are likely to cause biotic homogenization of the communities they invade.

Seasonal impoundment alters patterns of tidal wetland plant diversity across spatial scales

“…Although the overall diversity of dominant plants did not differ between impounded and tidal brackish wetlands, the species identity and functional attributes of dominant plants did differ. As species presence, relative abundance, and functional traits can alter ecosystem function (Lefcheck et al 2015, Stotz et al 2019), management‐induced changes in dominant plant composition likely affect important ecosystem processes, including carbon cycling (Kroeger et al 2017), climate change resilience (Stagg et al 2016), and long‐term restoration potential (Wolff et al 2019). As the functional traits of rhizomatous perennial graminoids found in tidal brackish wetlands and non‐rhizomatous annual graminoids or perennial forbs found in impounded brackish wetlands are not equivalent, changes in dominant species could lead to important, but understudied, shifts in ecosystem function (Hooper et al 2005).…”

Exotic species drive patterns of plant species diversity in 93 restored tallgrass prairies

“…We did find evidence that within‐site beta diversity was higher in native‐dominated than exotic‐dominated restorations, consistent with the sampling of sites from Minnesota to Texas by Martin and Wilsey (2015). This may be driven in our sites by the abundance of Bromus inermis , which has been shown to reduce diversity in northern prairies by homogenizing plant communities within and across grasslands (Stotz et al 2019). These results are inconsistent with a deterministic model of assembly, wherein beta diversity is predicted to increase over time through environmental sorting.…”

Northern temperate pastures exhibit divergent plant community responses to management and disturbance legacies identified through a producer survey

“…Healthy tame pastures had lower floristic diversity, in part because weedy forbs may have been outcompeted by forage grasses or were reduced by efforts to renovate pastures through fertilization and herbicides (Bork et al, 2007). In contrast, few native perennial forbs and grasses persisted in cultivated tame grasslands, where species like Bromus inermis create unsuitable environments for native plants, ultimately decreasing species richness and promoting homogeneity (Fink & Wilson, 2011; Stotz et al, 2019). Reduced diversity is an indicator of impaired ecosystem function but is not currently considered in grassland health assessments (Symstad & Jonas, 2011).…”