Freshwater ecosystems are being invaded at exponential rates. Aquatic invasions can degrade habitats, disrupt water supply systems, damage fisheries, and threaten native species. Presently, resource managers lack reliable methods to anticipate and prioritize aquatic invasion threats. My research seeks to develop a predictive understanding of aquatic invasions, using a combination of experimental approaches, empirical modelling, and field studies. I have been fortunate to work with excellent students who have made important contributions toward this goal. I encourage prospective students to contact me about working in my lab (see our EDI statement). I supervise MSc and PhD candidates through McGill's Biology graduate program. Each year, we recruit new students to study the impacts of invasive species on freshwater ecosystems. Our students typically pursue one or more of the following research objectives:

Identify predictors of invasion success.
Some interesting research questions include: Can the invasion success of a species be predicted from its biological traits? In what ways do human disturbance and propagule pressure influence the vulnerability of aquatic habitats to invasion? How do species interactions affect invasion success? For example, we are exploring how phylogenetic relationships and evolutionary experience influence the interactions between introduced species and the communities they encounter (Anton et al. 2020). From a meta-analysis on terrestrial plant invasions, we discovered that the effect of native herbivores on introduced plants is six times stronger on plants that are novel genera to the region, suggesting that the evolutionary naiveté of introduced species to resident enemies determines their invasion success (Ricciardi & Ward 2006).

Test invasion theories using aquatic communities.
Aquatic communities are valuable systems for testing the generality of invasion models. For example, Elton's hypothesis that species-poor communities are more vulnerable to invasion than species-rich communities could be tested in freshwater or marine ecosystems. Using field experiments and meta-analysis, we are investigating Simberloff & Von Holle's alternative hypothesis that introduced species may facilitate one another to cause an accelerated accumulation of invaders and their synergistic impacts - an "invasional meltdown".  Data from the Great Lakes (Ricciardi 2001) suggest that facilitative interactions between invaders are more common than antagonistic interactions, allowing the possibility that the invasion rate and impacts are influenced by the invasion history of the system. 

Develop predictive models of impact for aquatic invasions, particularly under climate change.
We are interested in predicting which invasions will fundamentally alter fish and invertebrate communities - e.g. why some invaders cause cascading impacts through food webs and whether these impacts are predictable.  My lab is determining how the impact of an invader is dependent on the composition of the invaded community and with other environmental conditions.  For example, a synthesis of cases studies has revealed that introduced species that represent novel (ecologically distinct) life forms to the invaded system pose the greatest threat to native biodiversity (Ricciardi & Atkinson 2004). We are also studying impacts caused by interactions between aquatic invasions and other environmental stressors, such as climate change and river impoundment. We have been working with colleagues to synthesize theories of impact in order to ultimately develop a general theoretical framework. Our major focus in the coming years is to investigate how climate change affects the impact of aquatic invasions.

Understand the role of invasion in biodiversity loss.
Freshwater animals are disappearing faster than land animals (Ricciardi & Rasmussen 1999). Invasions are recognized as a major cause of extinction, but to what extent are invasions contributing to declines in freshwater biodiversity in North America and across the globe? What kinds of invaders are most likely to promote species loss? And more problematically, how do invasions interact with other environmental stressors to cause extinctions? Another question that we are exploring is how non-native species compare with native species with respect to their potential to undergo pest outbreaks, or to suppress native populations. We have shown that non-native predators cause greater damage to native populations than do native predators (Paolucci et al. 2013), and are far more likely to contribute to global extinctions (Blackburn et al. 2019). We are now exploring the synergistic effects of invasion and climate warming on native biodiversity.

Develop risk assessment models for invasive species.
We are developing risk assessment tools for predicting the impacts of invasive species on native biodiversity.  For example, the world's richest diversity of freshwater mussels is found in North America, where they are highly endangered. One threat to their survival is the zebra mussel, which can destroy native mussel populations through intense biofouling (the photo shows a severely fouled mussel from the St. Lawrence River; it is carrying more than twice its own weight in zebra mussels attached to its shell). Field evidence suggests that habitat variables such as water chemistry determine whether native mussels can persist in systems invaded by zebra mussels (Jokela & Ricciardi 2008). We are building statistical models to identify which native populations are vulnerable to extinction and which habitats are suitable refugia for them. In recent years, we have tested novel methods of forecasting the impacts of predators based on their functional responses (e.g. Iacarella et al. 2018; Dickey et al. 2020; Grimm et al. 2020).

Our research has been supported by the following agencies: