Research themes

Ecology was once described to me by a mentor as “the most challenging of the sciences”, being the highest-order manifestation of scientific phenomena at all other levels of study – that how species interact with each other and their environment is the outcome of organismal differences, of physical, biochemical, and energetic constraints, of processes that unfold over space and time. Though this complexity offers endless opportunities for discovery at many intersections of science, it also poses a great challenge towards finding simple general rules that explain the distribution of biodiversity on Earth.
 
Research in my lab is motivated by deconstructing the complexity of our natural world, pairing experiments with population/metapopulation approaches, to weigh multiple drivers of ecological patterns against each other. Specific themes include:

Coexistence mechanisms across space and time

Competition and persistence in variable environments

What processes determine how many species co-occur on local scales at any given point in time? What proportion of co-occurring species coexist stably due to niche partitioning vs. transient persistence due to other mechanisms, and to what degree are niches partitioned within environments vs. between environments? It is these types of mechanisms that our lab seeks to disentangle using experiments designed to quantify the intensity of competitive interactions among species in different environments. We can then link competitive interactions to species’ functional traits and life history strategies (e.g., plasticity, maternal environmental effects, dormant seed banks) that confer persistence in temporally varying environments.

The spatial scale and distribution of ecological processes  

That ecological processes transition in importance with spatial scale is implicit in the design of all ecological research, and is fundamental to the concept of “local” and “regional” communities. ​Unlike local processes, however, regional processes are trickier to quantify. Our lab takes two approaches to doing so: First, we apply principles from island biogeography to test how species distributions are constrained by landscape features, and the scales at which those constraints manifest. For example, our current work shows that plant species distributions do not reflect dispersal limitation from far-away habitat patches, but rather, dispersal limitation from habitat patches that are not intersected by their dispersal vectors (e.g., deer). Second, we use manipulative experiments in the lab and field (e.g., seed additions) to test hypotheses that emerge from our observational work.

Evolution in ecological communities

Ecological communities are complex, yet tests of selection, local adaptation, and character displacement are generally performed in simplistic ecological contexts, such as in the absence competitors or in homogenous environments. Although parsing out and comparing sources of ecological complexity important for evolution is a big task, recent theoretical and empirical developments in ecology provide the quantitative tools to do so.

Our goal is to apply theory and empirical methods from community ecology to answer unresolved questions in evolutionary ecology, towards a general understanding of the mechanisms which generate (evolutionary) and maintain (ecological) biological diversity. Specific questions include: How do competitive differences evolve on microevolutionary timescales, and to what degree is their evolution driven by interactions with other species, divergent abiotic environments, or genetic drift? How does evolution unfold in diverse communities, and which competitors exert the strongest selection on focal species - the most common ones in the community, or the most related (ecologically similar) ones, or the community as a whole? What role does dispersal among localities play in determining which populations succeed or fail to establish and evolve in new sites?

Species invasions and biodiversity change

In California grasslands and many ecosystems across the world, habitat patches are fragmented not by road building or agriculture, but by the widespread invasion of annual grasses that form a dense impermeable matrix between habitat patches. As a consequence, the diversity and spatial distribution of native plant diversity we see today may be quite different from pre-invasion communities.
 
Although species invasions have been studied for decades, many pressing questions remain unanswered, specifically about their spatial and temporal impacts. Our lab is interested in: (1) understanding how invasive species impact the dynamics of native plant communities even if they are not directly interacting, by limiting dispersal among habitat patches, changing the size and shape of habitat patches, and concentrating herbivore pressure; (2) reconstructing diversity of plant communities pre-invasion, when and how invasions spread, and the spatial distribution of post-invasion species losses through time; (3) quantifying adaptation of invaders to refuge habitat conditions, which threaten to shrink remaining habitat patches.

Testing the functional trait underpinnings of coexistence

Seed bank (temporal coexistence mechanism) assay across species and environments

Plant composition surveys on serpentine "islands"

Lasthenia californica, an abundant early-flowering annual

Manipulating the spatial scale of dispersal using a seed vacuum

Field estimates of intensity of seed predation

Testing character displacement of root traits via clear pots