NORA UNDERWOOD

Department of Biological Science
Florida State University
Tallahassee, FL 32306-1100

Office: 2008 King Life Sciences Building
Telephone: 850-644-4167
email: nunderwood@bio.fsu.edu

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Current projects:

Our climate is changing rapidly, and effects of these changes are expected to be particularly strong at high altitudes. At the Rocky Mountain Biological Laboratory in the Colorado Rocky Mountains I am working with Dr. David Inouye (RMBL), Dr. Rebecca Irwin (NCSU) and Dr. Brian Inouye (FSU) to document the timing of flowering (flowering phenology) of for the plant community in montane meadows, the abundance, diverisity and phenology of the bee community, seed predator attack and climate variables. Our now over 40 year dataset on flowering phenology, and 6 year dataset on bees is allowing us to address a wide varieity of questions about the effects of climate on phenology, effects of climate change, links between plants and pollinators, and community level responses to climate.

 

  • Measuring and modeling the ecological consequences of associational effects (funded by NSF DEB)

Associational effects occur when neighboring resource organisms influence each other’s interactions with consumers or mutualists. In the context of interactions between plants and insect herbivores, associational effects are the effects of neighboring plants on a focal plant’s damage from herbivores. Because herbivores can influence plant growth and reproduction, it has been suggested that AE should influence population-level processes in plant-herbivore systems, including competition and natural selection for resistance.  But although it is clear that individual-level AE can occur, very little is known about whether or how AE influence population-level processes, and thus about their ecological or evolutionary importance. For this project I am collaborating with Dr. Brian Inouye (FSU), Dr. Stacey Halpern (Pacific University) and Dr. Peter Hamback (Stockholm University). Our overall goal in this project is to use a combination of mathematical models and empirical work to address whether and how associational effects influence the outcome of plant interspecific competition (coexistence and/or relative abundance). Work for this project is being done in the field at the North Florida Research and Education Center and at the Rocky Mountain Biological Laboratory in Colorado.

Planting a Nelder fan experimental design

 

Past projects:

  • The effect of insect herbivores on plant population dynamics (funded by NSF, USDA, and the L'Oreal Foundation)

 Knowledge about what controls plant population size is fundamental to our understanding of natural systems, and is also at the root of applied problems with invasive and weedy species. While the importance of competition with other plants is widely recognized, the effect of herbivores on plant populations is more contentious. In particular, biologists hold strong but opposing views about the role of insect herbivores in suppressing and regulating plant populations: some contend that insect herbivores have little effect, while others argue that insect herbivores can strongly limit plant population size. The persistence of these conflicting opinions indicates that the nature and prevalence of herbivore effects remains unresolved. Our goal in this project was to fully characterize herbivore effects on the population dynamics of a plant by incorporating effects of herbivores on both population growth rates and density dependence (change in growth rate with plant density) across the life cycle of the plant. In this project Stacey Halpern (Pacific University) and I used a combination of density manipulation experiments and demographic modeling to investigate whether and how insect herbivores affect population dynamics in the perennial herb Solanum carolinense.

  

Solanum carolinense in captivity

  • Induced resistance and herbivore population dynamics (funded by USDA)

Many plants are able to increase their level of resistance to herbivores in response to herbivore damage (induced resistance). I am interested in the consequences of induced versus unchanging (or constitutive) resistance strategies for herbivore population dynamics, since induced resistance is a potential source of density dependent regulation for herbivores. 

Although it has been suggested that induced and constitutive plant resistance should have different effects on insect herbivore population dynamics, there is little experimental evidence that plant resistance can influence herbivore populations over longer than one season. We (Underwood and Rausher 2000) used a density manipulation experiment and model fitting to examine the effects of constitutive and induced resistance on herbivore dynamics over both the short and long-term. We used likelihood methods to fit population dynamic models to recruitment data for populations of Mexican bean beetles on soybean varieties with no resistance, constitutive resistance or induced resistance. We compared model configurations that fit parameters for resistance types separately with models that did not account for resistance type. Models representing the hypothesis that the three resistance types differed in their effects on beetle dynamics received the most support. Induced resistance resulted in lower population growth rates and stronger density dependence than no resistance. Constitutive resistance resulted in lower population growth rates and stronger density dependence than induced resistance. Constitutive resistance had a stronger effect on both short-term beetle recruitment and predicted beetle population dynamics than induced resistance. The results of this study suggest that induced and constitutive resistance can differ in their effects on herbivore populations even in a relatively complex system.

 Mexican bean beetle eggs... larva (note ferocious spines)...  and adult
  • The influence of variance in quality within plant populations on herbivore dynamics and spatial distributions (funded by NSF)

The quality of individual plants as food for herbivores (and thus the mean quality of plant populations or communities) can influence both individual herbivores and herbivore populations. However, assemblages of plants vary not only in mean quality, but also in the variance around that mean (CV). In the hopes of gaining a better understanding of how plant quality affects herbivore populations, I have recently been working on experiments and models that focus on variance in plant quality, rather than the mean.. In particular, I am exploring the effect of variance in quality among plants on the movement and long-term population dynamics of insect herbivores. I have been working with a spatially-explicit computer model to examine how herbivore movement influences the interaction of variance in plant quality with herbivore population dynamics in space and time. This model will provide a framework for understanding how variance in quality affects herbivore populations in systems where quality varies among phenotypes, genotypes or species. I am also using field experiments at the Bodega Marine Reserve (Sonoma Co, CA) to examine how the degree of genetically based variation in quality in wild strawberry populations affects strawberry aphid movement and population dynamics. I am looking at  how aphid movement responses to individual plant quality are affected by population variance in plant quality, and using longer-term experiments to follow aphid population dynamics on plant populations with different levels of quality variance. Aphid dynamics on these populations are being characterized by direct observation of multiple generations and by fitting population dynamics models to the observed time series. These experiments should indicate how aphid population dynamics on monocultures of individual plant genotypes combine to produce dynamics on mixtures of genotypes of different qualities. Understanding the consequences of among-plant variance in quality for herbivore population dynamics may allow us to extend our knowledge of the effects of plant-quality characters on individual herbivores to an understanding of how populations or communities of plants affect populations of herbivores in space and time. Results of this research should also allow critical examination of the hypothesis that agricultural mixtures of plant varieties (genotypes) should host lower pest populations than monocultures. Ultimately, I am thinking of linking genetic variance in plant quality and herbivore population dynamics as a step towards incorporating plant population genetics into the study of plant-herbivore dynamics, thus allowing connections between ecological and evolutionary processes in these systems.

meep meep!mmmm!

Strawberry Aphid (Chaetosiphon fragaefolii) Fragaria chioloensis (picture © Br. Alfred Brousseau, Saint Mary's College)
  • Effects of plant characters on plant "apparency" to herbivores.

Many plant characters are thought to influence the likelihood that herbivores and seed predators locate individual hosts or patches of hosts. Although the influence of plant characters on the apparency of plants to attackers bears on many important issues in plant-insect interactions, there have been relatively few studies examining the influence of specific characters on apparency. In a short study, I considered the effects of two such characters, isolation from nearest neighbors and fruit display size, on attack rates of an Incurvariid caterpillar that develops in the fruits of a common woody shrub (Monochaetum amabile) in the mountains of Costa Rica. Working with a group of OTS graduate course students, we measured the size of the fruit and flower display of individual plants or plant patches (where patches consist of individual plants that are contiguous), and the proportion of fruits that were attacked. As expected, we found that plants or patches isolated from other plants or patches had lower levels of galling than plants closer to other plants, suggesting that gallers are less likely to locate isolated plants. However, contrary to our expectation, we found that larger displays of flowers and fruits decreased galling rates, suggesting that large numbers of developing buds may saturate the ability of gallers to lay eggs.

                    

Monochaetum, flowers and fruits Monochaetum habitat (view from near Cuerici Biological Station
  • Effects of patchy disturbance on the distribution and pollination of a rare endemic plant

My collaborator on this project (Brian Inouye) and I have been examining the effect of disturbance (in the form of gopher mounds) on the recruitment and performance of Mimulus angustatus at the Las Posadas State Forest, Napa Co, CA. M. angustatus produces a tiny rosette and then a variable number of flowers that are huge relative to the rest of the plant. Through observations and experiments we have found that this Mimulus is far more common on gopher mounds (or in other disturbed areas), germinates at far greater rates on mounds, and has more and larger flowers on mounds. Flowers on mounds also receive more pollen than those off mounds, and outcrossed flowers produce more seeds. Other small annuals in the same meadows (such as Lasthenia californica) appear to do much better in undisturbed areas. We are interested in pursuing questions such as how disturbance affects plant color and how this may influence pollinator visits, whether levels of disturbance from year to year are sufficient to maintain this small population, and whether the effects of gopher mounds are due to reduced competition, nutrient availability, etc.

                  

Mimulus angustatus  Fresh gopher  mounds Patches of Mimulus in the field
  • Interaction of induced resistance and herbivore movement: spatial distribution of herbivores, plant damage and plant resistance (funded by USDA)

Induced resistance is a type of phenotypic plasticity in which plants change their level of resistance to herbivores in response to herbivore damage. By definition inducible resistance adds a source of variance to the interaction between plants and their herbivores. The temporal variability of inducible resistance can affect temporal herbivore population dynamics, and it has been predicted that induced resistance should also affect spatial variance in distributions of herbivores and damage to plants. Because many herbivores can move away from plants of low quality, herbivore movement should mediate the interaction of induced resistance with spatial distributions of herbivores, herbivore damage and plant resistance. To test these ideas, I am using models (in collaboration with Kurt Anderson and Brian Inouye), and experiments using tomato and a pest caterpillar (Spodoptera).

Graphs look smart!

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