Herbivory through the ages: Revealing responses to global change with historical specimens
Global climate change has increased outbreaks of insect herbivores that eat plants across multiple habitats, including crop systems, forests, and urban areas. However, less is known about how chronic, non-outbreak herbivores respond to changes in the earth’s climate. Chronic herbivores are those that munch on your tomato plant, presumably reducing its growth and fruit production, but not killing it. Chronic herbivory by insects is the most prevalent kind of herbivory worldwide.
In this ongoing project, I use herbarium (pressed plant) specimens to document chronic herbivory on plants over the last 200 years. I am asking a variety of questions about historical interactions between plants and insects, from how they change across space, from the equator to boreal forests, to how herbivory rates have shifted over time as humans have become the dominant force for change on the planet. Initially, this project is focusing on plant species native to forests in the northeastern US, including blueberries, and conspecifics in France. This work is housed at the Harvard University Herbaria and the Museum National d’ Histoire Naturelle, Paris.
Funding: NSF Postdoctoral Fellowship Program, NSERC CRSNG, Harvard University Herbaria
Specimen images above and those I have posted to social media are from the Northeastern Botanical Collection’s digitization project of New England plant specimens. For details about this collection, email Mikaela Schmull at firstname.lastname@example.org or see the Harvard Herbaria digitized collections.
Understanding the effects of urban warming on insect herbivores and their host trees
For over a century, people have wondered why plants in cities have more insect herbivores than plants of the same species living outside cities. I studied the extent to which urban warming—heat released by sidewalks, asphalt, and other hard surfaces in cities—drives this pattern by sampling insects on street trees across a gradient of urban temperatures. I found that urban warming increased abundance of a common pest known as a scale insect (Parthenolecanium quercifex) by 13 times. I also found evidence that these effects were a result of P. quercifex evolving to tolerate urban heat and disruption of its interactions with parasitoid wasps*. Overall, this study revealed that insect pests and warming combined to reduce street tree growth. This work continues in Steve Frank’s lab at North Carolina State University, where it has become a major focus of research. A full summary of this work is here.
*Parasitoid wasps often eat insect pests. Most are smaller than a millimeter. They live in almost all habitats worldwide, including cities.
Funding: EPA STAR Fellowship Program, Southeastern Climate Science Center, USGS, NSF, Garden Club of America, North Carolina State University Department of Entomology
Measuring microclimate: The need for standard methods in ecology
Ecologists have recorded a lot of climate data over the past decades, mostly in an effort to understand how living things respond to climate change. Some of these observations are collected using expensive instruments that are located at permanent or semi-permanent sites. However, these weather stations are often too spread out to provide data useful for, for example, understanding temperatures experienced by frogs in a particular stream.
Instead, ecologists have increasingly turned to inexpensive data loggers to measure climate at these smaller scales. We do so with a general sense of how accurate these tools are; data loggers are tested for accuracy and precision in laboratories by the companies that make them. But ecologists deploy these tools across deserts, tropical forests, tundra, and cities, all far cries from the laboratories in which data loggers are tested. As a result, we do not know how accurate our climate data actually are.
I teamed up with other ecologists and a climatologist to address this issue. We set up a controlled experiment to test the accuracy of data loggers across habitats. Based on our results, we will provide a set of recommendations and best practices for collecting climate data in field ecology.
Funding: Southeast Climate Science Center, USGS