Rabbitbrush and Caterpillars
Plants and insects are the key members of food webs because they are not only abundant and diverse, but they also provide food for many other animals higher up the food chain. We talk with Moria Robinson, Assistant Professor of Biology at Utah State University, about variations in these food webs as climate in the western U.S. dries and warms. In particular, we look at the interactions of rabbit brush and caterpillars.
Meet the Scientist: Moria Robinson
Moria Robinson is an Assistant Professor of Biology at Utah State University. She became hooked by insects in childhood after being gifted an insect net as a 10-year-old, has been fortunate enough to turn that love into a career. After chasing butterflies in her hometown of Vashon Island, Washington she moved on to major in Biology at Middlebury College, Vermont. During her college years a new love for the immature stages of butterflies and moths (caterpillars) was ignited in the lab of Dr. David Wagner (University of Connecticut), where she worked as a summer research assistant. She then went on to graduate school at the University of California, Davis to study ecology and evolution of native caterpillars and their hostplants in the lab of Dr. Sharon Strauss. Moria is now building her own research laboratory at Utah State University, where her and her students’ research ranges broadly from understanding climate change effects on native plants and caterpillar consumers, to evolution of caterpillar coloration, to plant-pollinator interactions across elevational gradients, to ecology of interactions between native trees, their belowground fungal partners, and invasive plant species. In her spare time she loves to hike, plan her dream native plant garden, and spend time with her partner and pups.
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Interview Excerpt - Changing Food Webs
Today we are talking with Moria Robinson, Assistant Professor of Biology at Utah State University, about plant and insect food webs. Changes in these food webs can be indicative of broader changes in climate.
Science Moab: Can you begin by describing what a healthy food web means?
Robinson: A lot of us probably learned about food webs in school when we might have drawn out the relationships between different organisms and species that eat each other. These food webs are ways that we can map out how healthy ecosystems function because these relationships between organisms that eat each other are how energy flows through ecosystems. We need a certain number or biomass or abundance of animals at the bottom of that food web to support animals at the top of that food web. We also need different safeguards in these food webs. So if a particular species disappears in a given year, maybe because its requirements aren’t met for temperature or climate or food, we need another species that can step in and fill that role. It can make sure that the abundance of animals below it in the food web doesn’t get too large, which can deplete other resources at a lower level and it can also provide itself as a resource to higher trophic levels in the food web. So things we look for in food webs are diverse communities of animals, so that if one is gone in a given year, another can fill the role.
Science Moab: What are some of these causes leading to a change in the food web?
Robinson: The way I like to think about this is from the bottom up. I think a lot about how plants allocate their energy among different functions that they have to do. plants need to grow and reproduce, but they also need to defend themselves against getting eaten. Under stressful circumstances, what we often find Is that plants will invest more in defense because if they get eaten, they won’t have a lot of resources like water or nutrients on hand to compensate and regrow from that. In these more stressful environments with lower precipitation, higher temperatures, plants may shift to investing more in defenses such as chemicals that are toxic to insects or leaf hairs that deter them and make it hard to eat the leaf. When this happens, we could expect a number of different outcomes for the food web. We might expect fewer insects eating those plants, but we also might expect that It’s just the specialized species eating the plants that are more able to counter those defenses of plants. So these are some of the ways we predict food webs might shift. They might become more specialized. We might lose generalists as plants invest more in defense. And this can have various outcomes for the stability of ecosystems, but that’s what we’re trying to understand. What are the changes we’ll see, and how will that influence the long term resilience of these complex food webs?
Science Moab: In your current project, what specific plants and or insects are you studying?
Robinson: The organisms that get me the most excited are the larval forms of butterflies and moths. These are really amazing animals to think about in the context of food webs because they are eating plants and then they are getting eaten by a wealth of other species. The work I’m doing now is thinking about which plant species on the Colorado Plateau are most important for supporting robust populations and diverse sets of caterpillar species because that in turn is what supports birds, rodents, and so many of these other animals that together form a healthy ecosystem.
I’m also studying rubber rabbitbrush, Ericameria nauseosa. It’ll be familiar to everyone by sight, it’s the silvery green plant that puts out incredible golden displays of flowers in the fall and even into October. This plant is neat because it provides important food for caterpillars and it also for pollinators. So this is a plant that links different kinds of ecosystem services to our landscape. It also has a wide range: it grows across elevation in the Moab area and really all across the West. It also grows in drier places and wetter places. Some of the questions I’m asking are, first, how do those sources of variation like elevation and also more fertile and less fertile soil types affect the characteristics of the plants, whether they’re tastier to caterpillars or not? And then how does that affect how abundant and diverse those caterpillars are in those plants? Then I’m measuring the different rates at which birds visit plants to look for caterpillars and whether certain plant species, rabbitbrush, sagebrush, mountain mahogany, are more important than others in supporting birds.
Science Moab: So you’re measuring what caterpillars and or moths birds are visiting the rabbitbrush, but are you also monitoring changes in rabbitbrush?
Robinson: Yes, we are really interested in looking at shifts in the plants themselves. So that could happen in a few different ways. We could have plants that persist in the same location. These are long lived perennial plants, but that change their traits through time as the environment changes. So the same individual that responds to a drier year by. Manufacturing more chemicals in its tissue, for example. We would call that a plastic response, the same individual responding differently.
But we could also see that certain individuals in the population might die out and be colonized by other individuals potentially that are moving up from the south. So we would think about that as range expansion or range shift. So we do have plans to try to monitor those changes through time and then try to understand what the consequences of those changes are for the rest of the ecosystem.
