New research challenges assumptions about biodiversity-invasibility relationships in lakes
New research from MAISRC is challenging assumptions about the biotic resistance of native lake ecosystems to aquatic invasive species.
Scientists analyzed an unprecedently large dataset of aquatic vegetation surveys from 1,102 lakes that had been gathered over 13 years to conduct this research. The team evaluated evidence for four distinct mechanisms that are commonly understood to drive patterns of native and invasive species richness: biotic resistance, competitive exclusion, environmental filtering, and environmental heterogeneity.
The results were surprising: researchers found no evidence for local-scale biotic resistance to invasions, a major paradigm for invasions. “Everybody has an instinct that diverse plant communities are inherently more resilient to invasions, but they’ve got limits,” said Dr. Ranjan Muthukrishnan, lead researcher on the project.
The team did find evidence of competitive exclusion, meaning that native species richness decreases when invasive plants arrive. They also found that native species richness decreased at many locations where invasive species richness was higher, such as at deeper depths or higher-nutrient lakes. This suggests that invasive plants are more tolerant to a wider range of conditions, better exploit degraded systems such as lakes with excess nutrients, and are overall better able to adapt to less-than-ideal conditions than native plants. That broader tolerance may be an important aspect of how invasive species are able to spread. The invasive plants included in the study were purple loosestrife, Eurasian watermilfoil, reed canarygrass, curly-leaf pondweed, narrow-leaf cattail, and hybrid cattail.
“This research is helping us understand the fundamentals of how invasions work,” added Muthukrishnan. “Much of this work had previously been done on terrestrial ecosystems, and it was easy to assume it would be similar in aquatic plant communities. It’s not.”
Finding no overall evidence that sites with more diverse plant communities are less likely to be invaded underscores the importance of preventing the spread of aquatic invasive species to begin with. It also suggests that managing watersheds to support and improve water quality may be a more effective means of mitigating invasions and their impacts.
“If you want to be able to make fine grain decisions about how to allocate resources, you must first know what the problem is,” added Muthukrishnan.