Introduced species provide a novel temporal resource that facilitates native predator population growth

Non-native species are recognized as important components of change to food web structure. Non-native prey may increase native predator populations by providing an additional food source and simultaneously decrease native prey populations by outcompeting them for a limited resource. This pattern of apparent competition may be important for plants and sessile marine invertebrate suspension feeders as they often compete for space and their immobile state make them readily accessible to predators. Reported studies on apparent competition have rarely been examined in biological invasions and no study has linked seasonal patterns of native and non-native prey abundance to increasing native predator populations. Here, we evaluate the effects of non-native colonial ascidians (Diplosoma listerianum and Didemnum vexillum) on population growth of a native predator (bloodstar, Henricia sanguinolenta) and native sponges through long-term surveys of abundance, prey choice and growth experiments. We show non-native species facilitate native predator population growth by providing a novel temporal resource that prevents loss of predator biomass when its native prey species are rare. We expect that by incorporating native and non-native prey seasonal abundance patterns, ecologists will gain a more comprehensive understanding of the mechanisms underlying the effects of non-native prey species on native predator and prey population dynamics.