Ecosystem‐level effects of a globally spreading invertebrate invader are not moderated by a functionally similar native

Abstract

Biological invasions are a key element of human-induced global environmental change. However, lack of knowledge of the indirect consequences of invasions, combined with poor understanding of how their ecological effects depend upon competitive attributes of the receiving community, hinders our ability to manage and predict the effects of invasive species on ecosystems. We established an experiment using a combination of both additive and substitutive experimental designs to explore the effects of the globally spreading mysid shrimp Hemimysis anomala on the biological structure of outdoor pond mesocosms in the absence and presence of a functionally similar native competitor, Mysis salemaai. The naturally smaller H. anomala had considerably stronger effects on primary producers, multiple aspects of consumer assemblages and overall biological structure of the ponds in comparison with the functionally similar native. Moreover, the magnitude of these effects was generally independent of the presence of M. salemaai and even total mysid density. Hemimysis anomala reduced both the abundance and diversity of zooplankton assemblages significantly, triggering a strong trophic cascade on phytoplankton and a simultaneous increase of benthic invertebrate biomass. These findings indicate that invasion by H. anomala may exacerbate the effects of nutrient enrichment on lakes. Our results demonstrate that introduced species can, irrespective of the presence of functionally similar natives, induce complex changes to ecosystems that reach beyond direct consumptive effects. Moreover, the cascading indirect effects of invasion can exacerbate the impacts of other stressors. Disregarding the complexity of indirect effects therefore risks underestimating significantly the global ecological footprint of biological invasions.

Dietary niche constriction when invaders meet natives: evidence from freshwater decapods

“…They can change fundamental ecological processes from the level of the individual to the whole ecosystem (Peltzer et al . ; Penk, Irvine & Donohue ; Penk et al . ) and frequently alter the distribution of native species via a range of competitive interactions, predation pressure and/or habitat degradation (Mack et al .…”

“…; Jackson et al . ; Penk, Irvine & Donohue ). Furthermore, highly invasive species tend to be more voracious than their native counterparts (Haddaway et al .…”

“…Ricciardi 2006;Jackson & Grey 2013) is a key driver of global environmental change with major implications for biodiversity and ecosystem functioning (Chapin et al 2000;Gurevitch & Padilla 2004;Pejchar & Mooney Walsh, Carpenter & Vander Zanden 2016), particularly in aquatic ecosystems, which tend to be especially susceptible (Rahel & Olden 2008). They can change fundamental ecological processes from the level of the individual to the whole ecosystem (Peltzer et al 2010;Penk, Irvine & Donohue 2015;Penk et al 2016) and frequently alter the distribution of native species via a range of competitive interactions, predation pressure and/or habitat degradation (Mack et al 2000;Simon & Townsend 2003;Hooper et al 2005). Classic invasion theory (Elton 1958) predicts that a successful invader can establish itself in an unoccupied niche or displace similar native species by overlapping their niche and eventually out-competing them for limited resources.…”

“…Despite these apparently contradictory processes (Ara ujo, Bolnick & Layman 2011), the dietary niche breadth of invasive and native competitors has rarely been examined, even though it is likely a key factor in determining invasion success and predicting impacts of invaders on biodiversity (e.g. Jackson & Britton 2013;Penk, Irvine & Donohue 2015).…”

“…They frequently occupy similar functional roles as shredders driving detrital processing (Nystr€ om, Bronmark & Graneli 1996;Dudgeon 1999;Dobson et al 2002;Lancaster et al 2008) and, consequently, the introduced crayfish might be expected to be functionally redundant (sensu Naeem 1998). However, even morphologically similar species can vary significantly in their effects on ecosystems (O'Connor & Bruno 2007;Matthews et al 2011;Jackson et al 2014;Penk, Irvine & Donohue 2015). Furthermore, highly invasive species tend to be more voracious than their native counterparts (Haddaway et al 2012;Alexander et al 2014), implying that red swamp crayfish could cause considerable alteration to ecosystem structure and processes were they to replace native crabs.…”