Abstract
The ecological impacts of invasive species can be severe, but are generally viewed as highly unpredictable. Recent methods combiningper capitafeeding rates, population abundances and environmental contexts have shown great utility in predicting invader impacts. Here, clearance rates of the invasive Pacific oyster,Crassostreagigas, and native mussel,Mytilusedulis, were investigated in a laboratory experiment where oscillatory water flow and algal food concentrations were manipulated. Invasive oysters had lower clearance rates than native mussels in all experimental groups and did not differ among flow velocities or food concentrations. Native mussel clearance rates were higher at 5 cm s-1compared to 0 and 15 cm s-1flow velocities and increased with increasing food concentration. The Relative Impact Potential (RIP) metric was used to assess (i) the influence of flow velocity and food concentration on potential impacts ofC.gigason plankton resources and, (ii) the impacts of coexisting reefs, containing both species, on resources compared to monospecific native mussel beds. Greatest Relative Impact Potential of invasive oysters was seen at the lowest flow velocity, but became reduced with increasing flow velocity and food concentration. Relative Impact Potentials of coexisting reefs were generally greater than monospecific native mussel beds, with greatest impacts predicted at lowest flow velocity. We suggest that the greatest ecological impacts and competition potential ofC.gigaswill occur in areas with low flow velocity, but that increased flow will mediate co-existence between the two species.
Highlights
The ecological impacts of invasive species can be severe (Simberloff et al 2013, Dick et al 2017b) and the rate of invasive species introductions shows no sign of decline (Seebens et al 2017, 2018)
The Relative Impact Potential (RIP), a metric proposed by Dick et al (2017b), has combined per capita resource use with population abundances to better predict the ecological impacts of invasive species
Clearance rate increased with food concentration (Table 3)
Summary
The ecological impacts of invasive species can be severe (Simberloff et al 2013, Dick et al 2017b) and the rate of invasive species introductions shows no sign of decline (Seebens et al 2017, 2018). The Relative Impact Potential (RIP), a metric proposed by Dick et al (2017b), has combined per capita resource use with population abundances to better predict the ecological impacts of invasive species. The RIP combines facets of the ‘Total Response’ and the ‘Parker-Lonsdale’ equations (see Dick et al 2017b and Parker et al 1999, respectively) into one metric that produces absolute values of species impact on a resource. These absolute values can be used to compare impact, for example, the baseline impacts of native consumers in relation to invasive species. The semantic distinction between the two terms should be clarified as no link between the two has been found (Ricciardi and Cohen 2007)
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