Meta-analysis suggests biotic resistance in freshwater environments is driven by consumption rather than competition

Native communities are thought to mediate the establishment and performance of invasive species through competitive and consumptive interactions, a concept referred to as "biotic resistance.'' We investigated the generality of this concept across ecosystems. Despite the conspicuousness of freshwater invasions, investigations of biotic resistance have focused mostly on terrestrial and, more recently, marine coastal communities. We collected in-situ studies that tested the impacts of native freshwater communities on invading primary producers and consumers. Meta-analysis demonstrated that evidence of competitive biotic resistance in freshwater habitats was not as strong as that in marine and terrestrial ecosystems. In freshwater ecosystems consumptive resistance was significantly stronger than competitive resistance and consumptive resistance appeared to be as strong in freshwater as in marine and terrestrial systems. The limited number of studies considering freshwater biotic resistance hindered our ability to understand the importance of factors including latitude, experimental duration, and method. However, the strength of biotic resistance varied among freshwater habitats; specifically, biotic resistance was strongest in lentic environments. Our analysis identifies mechanisms underlying biotic resistance in freshwater ecosystems that warrant further investigation given the potential ongoing and future impacts of invasive species in these systems.