Potential interactions between native and alien plants and bees in invaded ecosystems. (Interactions among native species are not shown for clarity.) Note that native specialist bees (those which forage on one or a few host plants) and specialised plants (that can only be pollinated by one or a few pollinators) do not benefit from alien invasion, whereas alien generalist bees and generalised plants benefit the most. Interactions among alien bees and plants may result in the formation of invasion complexes. Black lines indicate direct impacts of plants on bees (by providing a forage resource) and broken grey lines indicate direct impacts of bees on pants (through pollination service). The broken black lines represent resource competition among native and alien species.