Community ecology of invasions: direct and indirect effects of multiple invasive species on aquatic communities

Abstract

Abstract. With many ecosystems now supporting multiple nonnative species from different trophic levels, it can be challenging to disentangle the net effects of invaders within a community context. Here, we combined wetland surveys with a mesocosm experiment to examine the individual and combined effects of nonnative fish predators and nonnative bullfrogs on aquatic communities. Among 139 wetlands, nonnative fish (bass, sunfish, and mosquitofish) negatively influenced the probability of occupancy of Pacific treefrogs (Pseudacris regilla), but neither invader correlated strongly with occupancy by California newts (Taricha torosa), western toads (Anaxyrus boreas), or California red-legged frogs (Rana draytonii ). In mesocosms, mosquitofish dramatically reduced the abundance of zooplankton and palatable amphibian larvae (P. regilla and T. torosa), leading to increases in nutrient concentrations and phytoplankton (through loss of zooplankton), and rapid growth of unpalatable toad larvae (through competitive release). Bullfrog larvae reduced the growth of native anurans but had no effect on survival. Despite strong effects on natives, invaders did not negatively influence one another, and their combined effects were additive. Our results highlight how the net effects of multiple nonnative species depend on the trophic level of each invader, the form and magnitude of invader interactions, and the traits of native community members.

The Impacts of Recently Established Fish Populations on Zooplankton Communities in a Desert Spring, and Potential Conflicts in Setting Conservation Goals

“…Our results mimic the findings of earlier workers showing negative effects of mosquitofish presence on invertebrates (both zooplankton and macroinvertebrates [26,27,[44][45][46]), often including the near-complete elimination of cladocerans [26,27,44,45]. Our results are also consistent with previous studies that have shown that rotifers escaping fish predation as a result of comparatively very small body size [46] (also see [27]).…”

Integrating occupancy models and structural equation models to understand species occurrence

“…Of the native species, two are federally protected and are of broad conservation concern ( A. californiense and R. draytonii ), and A. boreas has declined in specific regions (Lannoo 2005). Some populations of these species are currently threatened by invasive species including nonnative fishes and bullfrogs, which potentially act as predators and competitors for native amphibians (Fisher and Shaffer 1996, Lawler et al 1999, Preston et al 2012). Further, widespread cattle grazing in this region has the potential to affect the population dynamics of amphibians at breeding sites directly via trampling, and indirectly by removing vegetation and increasing the concentration of nitrogenous compounds in wetlands (Robins and Vollmar 2002, Roche et al 2012).…”

Invasion Complexities: The Diverse Impacts of Nonnative Species on Amphibians

“…Preston et al (2012) showed the ways in which multiple invaders can directly and indirectly affect such communities. Across 139 wetlands, they determined that introduced fishes and bullfrogs (L. catesbeianus) decrease the probability of occupancy of native Pacific Tree Frogs (Pseudacris regilla) using occupancy models and experimental venues.…”