My research is on the ecology and evolution of plants and insects. More specifically most of my work is experimental and addresses two broad questions: 1) how do human land-use activities and restoration practices shape diversity and composition of natural communities? And 2) how do interactions between plants and animals shape each other’s ecology and evolution? Below are quick summaries of my research projects.
Humans are the masters at modifying habitats for our own benefit. For example, agriculture (both farming and grazing) alone covers over 40% of the Earth’s land. This destruction and degradation of native ecosystems is the leading cause of the ongoing sixth mass extinction. But even when we abandon land to let it recover, many organisms fail to return, leaving a legacy of past environmental damage. In the beautiful and highly threatened longleaf pine savanna ecosystem, my colleagues and I are studying how past and present human land-use activities impact biodiversity. Some of my research in this system showed that farmlands which were abandoned over 60 years ago still have very different plant communities with lower diversity than nearby savanna remnants with no history of agriculture. Habitat restoration that makes these areas more savanna-like, by removing trees, increases plant diversity but does not erase the fingerprint of past land-use on plant communities. Restoration also increases seed production of native plants and makes these same plants more likely to establish when seeds are added. These results together highlight that it can be difficult for habitats to recover from intensive land-use activities so we should cherish and preserve the remnants of more pristine habitats that still exist. And, that active restoration can possibly help the species restricted to these remnants to persist and spread, but we still have much to learn about that. We are continuing our work with plants in this system but also moving on to understand how soil microbes, pollination, and bees are impacted by land-use activities.
Because of the scarcity of tallgrass prairies in the Midwestern US, efforts to restore these diverse and endangered habitats are becoming increasingly widespread. However we still have a great deal to learn about what factors are important in shaping outcomes when restoring prairie plant communities. I’ve been working with Jen Lau, Emily Grman, and Lars Brudvig on an experiment at Kellogg Biological Station in SW Michigan where we’ve established 12 new prairies. And we’ve manipulated a wide range of factors to better understand the causes and consequences of variation in prairie plant communities. As an initial study, I focused on the impacts of herbivores and edge effects and I found that the most native plants established in the middle of restoration plots and when small mammals and birds were excluded. More to come on this front.
In the 400 million years that animals have been eating plants it’s pretty clear that herbivores have driven evolutionary change in plants, especially when considering all the specialized defensive traits that plants have, like spines and toxic chemicals. However few studies have tested if herbivores cause plants to evolve on contemporary timescales (<100 years). For my PhD research, in collaboration with Marc Johnson and others, I focused on understanding if, and how, intense grazing by rabbits shapes plant evolution. To do this, I took advantage of a long-term experiment set up by Mick Crawley in the grasslands of Silwood Park, England where he established new rabbit exclosures year after year for decades (see photo above for an example). By studying plants collected from exclosures that varied in age from 1 year to over 20 years we could infer the evolutionary impacts of rabbits on plants over time. We found that some species evolved to grow more slowly and have taller morphology following the removal of rabbits, while other species did not change. We also discovered that fungi that live inside of grasses (called fungal endophytes) increased in frequency over time following rabbit exclusion, opposite to what we expected since they are thought to serve a defensive role. Finally, in some research from a more ecological perspective, we found that removing rabbits changed plant communities and reduced some aspects of diversity, especially the total amount of evolutionary history within the community (I haven’t published that one yet, but you can check out chapter 5 of my thesis if you’re feeling brave).
It is tempting to assume that variations within species (for example: size, color, and behavior) are not all that important ecologically, especially when compared to the differences we see among species. However, a rapidly body of research suggest that, at least in some cases, variation within species can have dramatic impacts on the performance, abundance, and diversity of other species. I tested some of these questions with a field experiment with plants and aphids. I found that populations of aphids evolved over the time period of 6 weeks and that different genotypes (clonally reproducing lineages) of aphids had quite different impacts on plant they were feeding on (see this blog post I wrote about this research). In some cases knowing what genotype of aphid was on the plant was just as important as knowing if that plant had aphids or not, so quite strong evidence that we should think twice about ignoring genetic variation. Also, I’ve been part of a working group testing similar question by compiling data from many studies. We’ve found that variation within species in aquatic systems can have similar impacts on communities and ecosystems as swamping species or removing species. Going forward I think this work will
Around 10,000 years ago humans starting farming and inadvertently initiated perhaps the largest replicated evolutionary experiment on Earth. Over time farmers domesticated hundreds of crops as they selected plants that grew the best generation after generation. Then later breeding programs sped up this evolutionary change. In research led by Martin Turcotte we explored the ecological consequences of this evolutionary change on the interactions between insects and plants by studying 29 crops and their wild relatives. We found that, on average, crops were eaten more by caterpillars but not aphids compared to wild relatives and that the evolutionary dynamics on crops and wild plants where different. Check out Martin’s further work on this topic.
Habitat loss typically isn’t complete, a farm field here a shopping mall there, with little bits of habitat left in between. Surviving in these fragmented chunks of habitat is challenging for most species because they are small and isolated, and living within these patches means always being close to the potentially inhospitable environment that surrounds the fragments. One mitigation for this problem is to connect these fragmented habitat with corridors, narrow strips of habitats that connected otherwise isolated patches. Corridors often increase movement, population sizes, and diversity, but few studies had looked at how they impact species interactions. We studied interactions between plants and insects at the Corridor Project, a massive field experiment where we can test how habitat corridors impacts ecological interactions. We found that corridors did not impacts how much plant got eaten by insects (primarily grasshoppers) but that plants in the middle of patches, where it’s warmer, got eaten more and as a result produced less fruits. We also studied complicated interactions between plants, aphids, ants, and grasshoppers where ants are attracted to plants because of aphids (they collect the honeydew) and the ants then keep away the grasshoppers. Plants in big warm patches where there are lots of grasshoppers most benefited from the protection of ants, but again, these interactions where not impacted by corridors. The main message from this work is that in fragmented habitats, species interactions may be more impacted by unexpected factors and those responses could be a result of shifts in webs of interacting species. And finally, it’s important to consider the relative importance of factors in fragmented landscapes; connectivity doesn’t impact all aspect of ecology and sometimes the edges inherent in small habitats are more important.