Research Interests

Plant Diversity and Climate Change

The projected loss and gain of suitability habitat of the New England Aster (Symphyotrichum novae-angliae) by 2070 under the IPCC's worst-case emission scenario (RCP 8.5). The model used to assess these changes is based on the species' present distribution and the associated climate and soil conditions. The model predicts a loss of over 60% of the species' current range, but a net gain of 10% with a major northward shift in range.

The projected loss and gain of suitability habitat of the New England Aster (Symphyotrichum novae-angliae) by 2070 under the IPCC's worst-case emission scenario (RCP 8.5). The model used to assess these changes is based on the species' present distribution and the associated climate and soil conditions. The model predicts a loss of over 60% of the species' current range, but a net gain of 10% with a major northward shift in range.

As a Fellow at the Harvard University Center for the Environment, my research focuses on understanding how future climate change will affect the biodiversity of the North American flora.  Do to this, I utilize environmental niche modeling on a large-scale to assess which plant species will be winners and losers under future climate change scenarios, and whether these species are concentrated in specific branches of the Tree of Life. Currently, we have data for nearly 12,000 plant species (58% of the total flora).

Phylogenetic distribution of decline in abundance over the past century (1900-2006) for the flora of Concord, MA. Decline abundance was concentrated in specific parts of the tree, highlighted above, and was also correlated with a lack of phenological sensitivity to climate change (Willis et al. 2008)

Phylogenetic distribution of decline in abundance over the past century (1900-2006) for the flora of Concord, MA. Decline abundance was concentrated in specific parts of the tree, highlighted above, and was also correlated with a lack of phenological sensitivity to climate change (Willis et al. 2008)

 

 

 

 

 

 

 

Phenology & Climate Change

Climate change has led to major changes in the phenology—the timing of seasonal activities, such as flowering—of some species but not others. The extent to which flowering time response to temperature is shared among closely related species might have important consequences for community-wide patterns of species loss under rapid climate change.

My colleagues and I use historic records to study how climate change has impacted the phenology of New England. This research takes on two involves two different, but complementary approaches.

Herbarium record of the common New England orchid, Pink lady’s-slipper (Cypripedium acaule).

Herbarium record of the common New England orchid, Pink lady’s-slipper (Cypripedium acaule).

The first approach has focused on mining the notebooks of botanists and naturalists from the last two centuries, including Henry David Thoreau, to study how flowering time and abundance have changed in the flora of Concord, MA. By comparing their detailed notes of when species flowered with current observations, we are able to assess how much species have responded to climate change over the last century, as well as, how well they have fared. This research lead to the finding that species that have not responded to climate change by adjusting their flowering time, have also experienced significant declines in abundance. 

The second approach focuses on mining the vast collections of the New England herbaria. Known as the New England Vascular Plant (NEVP) project, the aim of this project is to digitize and analyze the over 1.1.3 million herbarium specimens housed in 15 New England herbaria. These records represent snapshots of phenological events (e.g., flowering, fruiting, leaf-out) that can be linked to a specific date and location. In aggregate, these data can provide valuable insights into historic changes in phenology for a wide diversity of species from across the New England area. Furthermore, give the scale of the data that need to be processed, this project also lends itself nicely to utilization of citizen science crowdsourcing, an aspect we are developing with the lead creator, Dr. Edith Law, of the crowdsourcing platform Curio.

Speciation in the genus Cakile (Brassicaceae)

Cumulative post-zygotic reproductive isolation across 18 Cakile and Erucaria taxa in relationship to species' pairwise genetic distance.

Cumulative post-zygotic reproductive isolation across 18 Cakile and Erucaria taxa in relationship to species' pairwise genetic distance.

I am interested in the mechanisms that underlie the process of speciation. In particular, I am interested in the role of local adaptation in the evolution of reproductive isolation. The biological species concept (BSC) defines species by their reproductive integration, as well as, their reproductive isolation from other species. However, the mechanisms that result in reproductive isolation are many. Furthermore, the evolution of individual mechanisms can occur in multiple ways. The classic model of reproductive isolation is the Dobzhansky-Muller model. In this model, allopatric isolation of two populations inhibits gene flow allowing novel alleles to accrue in one or both populations that result in genic incompatibilities upon secondary contact. Similarly, populations in isolation may evolve other mechanisms of reproductive isolation such as differential habitat or mate preference. I am interested in how local adaptation influences the evolution of these mechanisms. While it is easy to imagine how local adaptation could influence habitat preference, it is not well understood how local adaptation influences the evolution of other mechanisms, in particular, the evolution Dobzhansky-Muller incompatibilities. For instance, local adaptation could accelerate the evolution of Dobzhansky-Muller incompatibilities if incompatible alleles were under selection in the different environments.

To address the role of adaptation in speciation, I study speciation in the genus Cakile (Brassicaceae). I am currently employing hybridization experiments, common garden experiments, and comparative methods to study the evolution of reproductive isolation and ecological diversification across the clade.