Experimental range expansion of the common duckweed (Lemna spp.)

Species range dynamics under global change

Understanding the movement of species geographical ranges is a fundamental goal of ecology and is of urgent importance given rapid global change. The expansion of species ranges (due to climate-driven range shifts or the introduction of new species) can lead to unique evolutionary changes in range-edge populations, and these evolutionary changes may in turn shape the dynamics of range expansion through eco-evolutionary feedbacks. Understanding future changes to species distributions therefore requires predictive frameworks and experimental tests of the eco-evolutionary dynamics of range expansion (see Usui et al. 2023 Trends Ecol. Evol. and Miller et al. 2020 Ecol. for perspective pieces).

In my current work, I use an experimental evolution approach using duckweeds (freshwater angiosperms) as a model plant community to test theories on how rapid eco-evolutionary interactions alter the dynamics of range expansion (e.g., Usui & Angert 2024 Ecol. Lett.). I use both field experiments and high-throughput experimental landscapes in the lab and greenhouse, through which I can track the ecological and evolutionary dynamics of populations and species moving across space and in real-time.

Some of my current interests are: 1) how environmental variation in space and time influences the predictability of population spread; 2) how species interactions (from competition to mutualisms) and co-evolution alters the dynamics of range expanding communities; and 3) the role of epigenetic mechanisms in mediating adaptive plasticity and colonization for clonal and invasive duckweeds.

Experimental evolution of duckweed communities in the lab and greenhouse. Right: Duckweeds in Vancouver BC

Adaptation to warming within ecological communities

Predicting the demographic and evolutionary fate of populations and species in response to warming is a pressing challenge for ecologists and evolutionary biologists. While population responses to rising temperatures occur within a community context where interacting species have the potential to impact eco-evolutionary outcomes, we lack a mechanistic understanding of: (1) how and when species interactions will alter population and evolutionary responses to warming, and in turn; (2) how population and evolutionary responses to warming will shape species interactions and community re-assembly.

To this end, I seek to understand how eco-evolutionary feedbacks shape population and community responses to warming. Here, some of my current interests include: (1) how interspecific competition alters adaptive evolution and population persistence at warming range edges (Usui & Angert 2026 Science); (2) how resource-use traits underlying competition could change under temperature stress (Gillies et al. 2024 Funct. Ecol.); and (3) how mutualistic interactions between plants and their microbial partners evolve under warming and alter thermal performance.

Testing local adaptation to warming range edges in competitive plant communities (from Usui & Angert, Science 2026)

Evolution of species coexistence

The immense biodiversity that we see across space and time, and the mechanisms leading to its origins and maintenance, is a key question that unites ecology and evolutionary biology. While evolutionary theory states that species diversity is initiated by the genetic divergence of lineages through the evolution of reproductive isolation (i.e., speciation), ecological theory states that successful diversification may also hinge upon whether ecological differentiation could could permit diverging lineages to coexist through time. When and how mechanisms of demographic persistence and coexistence evolves over time (i.e., the tempo and mode of coexistence mechanisms) then, is critical to our understanding of the origins and maintenance of the contemporary assemblage of species observed today (see Germain et al. 2021 Trends Ecol. Evol. for a perspective piece led by Rachel Germain at UBC Vancouver).

In a huge common garden consisting of 1890 competition trials simulating secondary contact between 126 allopatric and genetically diverging populations of duckweed, we empirically parameterized the tempo and mode of coexistence evolution within species and at timescales critical to lineage divergence (Usui & Sakarchi et al. 2026). Some of my other current interests on the evolution of species coexistence include: 1) the evolution of coexistence in hybrid duckweed species; 2) how rapid changes in climate across space and time alter the evolution of coexistence mechanisms and parapatric range limits; and 3) how evolution in host-symbiont (i.e., plant-microbiome) communities alters resource competition and coexistence outcomes over time.

Common duckweed, Lemna minor. Photo by Emma Menchions