ORIGINAL PAPER Introduced species provide a novel temporal resource that facilitates native predator population growth Jennifer A. Dijkstra • Walter J. Lambert • Larry G. Harris Received: 8 February 2012 / Accepted: 16 September 2012 / Published online: 23 September 2012 Ó Springer Science+Business Media Dordrecht 2012 Abstract Non-native species are recognized as important components of change to food web structure. Non-native prey may increase native predator popula- tions 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 vex- illum) 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 provid- ing 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. Keywords Apparent competition  Food webs  Colonial ascidians  Non-native  Invasive  Native predator Introduction A positive correlation between non-native prey and native predator populations suggests that non-native prey provide an additional food source that may lead to elevated native consumer and to reduced native prey populations (Roemer et al. 2002; Inger et al. 2010). This pattern is referred to as apparent competition, where abundance or distribution of consumers is changed by a prey species hence altering the popula- tion dynamics of the other prey species (Holt and Kotler 1987). Direct competition between invasive and native species has received much attention (e.g., Hamilton et al. 1999; Grosholz 2002). Apparent competition between non-native prey and native J. A. Dijkstra (&)  L. G. Harris Department of Biological Sciences, University of New Hampshire, Durham, NH 03824, USA e-mail: dijkstra@wellsnerr.org Present Address: J. A. Dijkstra Center for Coastal and Ocean Mapping, University of New Hampshire, Durham, NH 03824, USA e-mail: jdijkstra@ccom.unh.edu W. J. Lambert Department of Biology, Framingham State University, Framingham, MA 01701, USA 123 Biol Invasions (2013) 15:911–919 DOI 10.1007/s10530-012-0339-1