Plant Community Assembly in Invaded Recipient Californian Grasslands and Putative Donor Grasslands in Spain

The introduction of exotic species to new regions offers opportunities to test fundamental questions in ecology, such as the context-dependency of community structure and assembly. Annual grasslands provide a model system of a major unidirectional introduction of plant species from EuropetoNorthAmerica. WecomparedthecommunitystructureofgrasslandsintwoMediterranean regions by surveying plots in Spain and in California with similar environmental and management conditions. AllspeciesfoundinSpanishgrasslandswerenativetoSpain,andoverhalfofthem(74of 139species)areknowntohavecolonizedCalifornia. Incontrast,inCalifornia,overhalfofthespecies (52 of 95 species) were exotic species, all of them native to Spain. Nineteen species were found in multiple plots in both regions (i.e., shared species). The abundance of shared species in California was either similar to (13 species) or greater than (6 species) in Spain. In California, plants considered pests were more likely than non-pest species to have higher abundance. Co-occurring shared species tended to maintain their relative abundance in native and introduced communities, which indicates that pools of exotic species might assemble similarly at home and away. These findings provide interestinginsightsintocommunityassemblyinnovelecosystems. Theyalsohighlightanexampleof startling global and local floristic homogenizationPeer reviewe