Regional diversity reverses the negative impacts of an alien predator on local species‐poor communities

Abstract

Species diversity is often an implicit source of biological insurance for communities against the impacts of novel perturbations, such as the introduction of an invasive species. High environmental heterogeneity (e.g., a mountainous gradient) is expected to beget greater regional species diversity and variation in functional traits related to environmental tolerances. Thus, heterogeneous metacommunities are expected to provide more tolerant colonists that buffer stressed local communities in the absence of dispersal limitation. We tested the hypothesis that importation of a regional zooplankton pool assembled from a diverse array of lakes and ponds lessens the impacts of a novel predator on local species-poor alpine communities by increasing response diversity (i.e., diversity of tolerances to environmental change) as mediated by variation in functional traits related to predator evasion. We also tested whether impacts varied with temperature, as warming may modify (e.g., dampen or amplify) invasion effects. An eight-week factorial experiment ([fishless vs. introduced Oncorhynchus mykiss (rainbow trout)] × [ambient temperature vs. heated] × [local vs. local + regional species pool]) was conducted using 32 1,000-L mesocosms. Associations between experimental treatments and species functional traits were tested by R-mode linked to Q-mode (RLQ) and fourth-corner analyses. Although the introduced predator suppressed local species richness and community biomass, colonization by several montane zooplankters reversed these negative effects, resulting in increased species diversity and production. Invasion resistance was unaffected by higher temperatures, which failed to elicit any significance impacts on the community. We discovered that the smaller body sizes of imported species drove functional overcompensation (i.e., increased production) in invaded communities. The observed ecological surprise showed how regionally sourced biodiversity from a highly heterogeneous landscape can offset, and even reverse, the local negative impacts of an invasive species. Further, prey body size was found to be a key species trait mediating the ecological impacts of the aquatic invasive predator. Our study highlights the novel application of a functional approach to understanding the impacts of biological invasions, using species traits that pertain directly to potential responses to exotic species.

A Functional Approach to Zooplankton Communities in Mountain Lakes Stocked With Non‐Native Sportfish Under a Changing Climate

“…All traits in our analysis were hypothesized to influence how species might respond to variation in the measured abiotic and biotic variables (i.e., response traits; Nock et al, ). For example, body size was included as smaller species are better suited metabolically to tolerate higher temperatures (Moore & Folt, ) while also being less conspicuous to visual predators (Brooks & Dodson, ; Loewen & Vinebrooke, ). Similarly, photoprotective pigmentation (carotenoids, melanin, or mycosporine‐like amino acids) was considered because of the risk of DNA‐damage by ultraviolet irradiance levels versus visual detection by fish predators, especially in clear, shallow lakes at higher elevations (Hansson, ).…”

Macroecological drivers of zooplankton communities across the mountains of western North America

“…Species' response traits should also be considered, as they mediate the effects of deterministic processes (e.g. Integration of critical environmental and spatial factors with trait-mediated species' responses is essential to filling scientific knowledge gaps concerning both natural community assembly and response to environmental changes (McGill et al 2006, De Bie et al 2012, Loewen and Vinebrooke 2016. Integration of critical environmental and spatial factors with trait-mediated species' responses is essential to filling scientific knowledge gaps concerning both natural community assembly and response to environmental changes (McGill et al 2006, De Bie et al 2012, Loewen and Vinebrooke 2016.…”

“…Based on metabolic theory as it applies to species diversity (Brown et al 2004), and the pronounced climatic gradients observed in mountain regions, we hypothesized that temperature along with precipitation would be the primary drivers of beta-diversity. Localized stocking of mountain lakes with sportfish (Crawford and Muir 2008) was also expected to help explain zooplankton variation owing to intensive size-selective predation (Loewen and Vinebrooke 2016). Localized stocking of mountain lakes with sportfish (Crawford and Muir 2008) was also expected to help explain zooplankton variation owing to intensive size-selective predation (Loewen and Vinebrooke 2016).…”

“…environmental filtering and non-random dispersal; Kramer et al 2008, Farjalla et al 2012. Integration of critical environmental and spatial factors with trait-mediated species' responses is essential to filling scientific knowledge gaps concerning both natural community assembly and response to environmental changes (McGill et al 2006, De Bie et al 2012, Loewen and Vinebrooke 2016.…”

“…In addition, we expected that spatially structured catchment features would account for a significant fraction of the residual variation in community composition not captured by climate, given the high degree of natural environmental heterogeneity characterizing our study region. Localized stocking of mountain lakes with sportfish (Crawford and Muir 2008) was also expected to help explain zooplankton variation owing to intensive size-selective predation (Loewen and Vinebrooke 2016). Further, since many mountain lakes are remote and insular because of large topographic barriers (Lyons and Vinebrooke 2016), we hypothesized that habitat connectivity would explain a substantial portion of beta-diversity attributable to species dispersal limitation.…”