Donald R. Strong - US grants

GER-9553386 Stanton This proposal outlines a multi- disciplinary program of advanced training for doctoral students, to be coordinated through the Center for Population Biology at UC Davis. The CPB is a newly-formed group with established faculty of great accomplishment in graduate education and research; highly qualified applicants have been quickly attracted to our young doctoral program. Bringing diverse scholars together, the CPB facilitates interdisciplinary education in environmental biology within the context of contemporary population biology. A broadly synthetic field using sophisticated analytical techniques, population biology addresses ecological, evolutionary, behavioral, and genetic mechanisms at the heart of environmental biology. Our program pertains directly to biodiversity, endangered species, and processes of community restoration. GRT traineeships would provide the funds to increase PhD enrollment to levels that our faculty and support facilities are prepared to accommodate. Significant matching support has been pledged by UC Davis for this GRT initiative. A major component of our innovative approach is a consortial arrangement with San Francisco State University, which will direct diverse students into our PhD program in environmental biology. SFSU produces highly qualified and prepared Master's students, including large numbers of women and minorities.

9508673 STRONG This research focuses on a below-ground trophic cascade involving a root-feeding moth caterpillar, a bush lupine, a soil-dwelling entomopathogenic nematode, and predators on this nematode. It is the nematode predators that initiate this cascade. These predators are primarily the nematophagous fungi impertecti, which are speciose and abundant in soils. The trophic interactions are constructed as follows: Dead lupine killed by caterpillars are substrates for mushrooms that are putatively the reproductive stages of the nematophages. With opposite potential effect, leaves bearing copious alkaloids that are potent fungicides accumulate in thick blankets on the soil habitat of the nematophagous stages of the fungi. Neither the caterpillar, which consumes only wood low in alkaloid, nor the nematode appear to be affected by these alkaloids. The caterpillars are widely dispersed among lupine patches, yet their numbers are negatively correlated with nematode abundance. The nematodes suffer frequent local extinctions and are present only in areas where lupines flourish. However, where caterpillar densities are high, both lupine litter and the nematode-eating fungi are abundant. In these areas, there are a few nematodes. Soils are among the most poorly known habitats of life on earth. Underground insect herbivores, which are diverse, injurious to plants, and influential in ecosystems, have been studied to a degree in agriculture systems, but have had only had cursory treatment by ecologists. Population regulation of underground insect herbivores has been almost totally ignored by agriculturalists and ecologists alike. While underground insects are drawn from familiar above-ground groups, their natural enemies in the soil are distinctive. This research has clear linkages to understanding factors that regulate populations of below-ground herbivores in natural and agricultural communities.

ABSTRACT

Hastings, Alan M. , Susan L. Ustin, Edwin D. Grosholz, and Donald R. Strong

DEB 0083583

"Dynamics of an invasive non-native species and its biological, physical, and human impacts: Spartina alterniflora on the Pacific coast"

The PIs propose an integrative study of the dynamics of the invasive species, Spartina alterniflora (cordgrass), including a core mathematical/conceptual model, physical and biological feedbacks, and a study of the impacts on non-commercial human values. The core model is termed a "local-state, regional-state" model and the crucial innovation is the use of discrete time and continuous states and explicit inclusion of stochastically based on integro-difference equations, yielding substantial mathematical and computational advantages over reaction diffusion models. The state of the invasion will be a function of position along the shore, tidal height, age of Spartina, and densities of other species or human valuations in the system, and time. ENSO fluctuations, feedbacks, and non-reciprocal effects are included in the framework. Hypotheses concerning the biological bases of positive feedbacks, Allee effects, and density dependence will be tested experimentally and results integrated into the model.

Parameterization will be from a rich set of historical records and from remotely-sense images, references with GPS. Mixture analysis with data will inform the model of biochemical conditions of the cordgrass. Experiments will give data on demography, clonal growth, seed set, tide flow profile, sediment erodability, and shear stress. Sediment accretion will be quantified. Intensively studied sites will be extrapolated to the entire estuary using NASA's ASTER sensor on the Terra satellite. A map will be built of Pacific estuaries using daily MODIS satellite images. Food web and community effects will be studies experimentally. The ultimate faunal effects on the invasion will be measured in passerines and rallids. These observations will be combined with the overall model to develop long term prediction of the impact of Spartina on birds. Finally, these invasions are ideal for studying non-commercial values lost to the changes caused by Atlantic cordgrass. Integrating the valuation with the model will provide one of the first rigorous studies of invasive species on the value of ecosystem services.

I am researching how moisture influences a multi-predator trophic cascade in a
soil system. At my research site on the California coast, the entomophagous fungus
Beauveria bassiana is the most potent predator of root-feeding insects in dry summer
soil. During the rainy winter and spring, however, soil moisture increases sharply and the
entomopathogenic nematode Heterorhabditis marelatus becomes the primary predator as
B. bassiana decreases in predatory efficiency. Both prey on ghost moth (Hepialus
californicus) larvae, root-feeding herbivores that feed on the bush lupine Lupinus
arboreus. The lupine shows increased growth, seed set, and survivorship in the presence
of the nematode, which preys on H. californicus that would otherwise eat the lupine's
roots. The wet-season interactions in this food chain are known as an important example
of a terrestrial trophic cascade. My research seeks to develop a complete picture of this
food web by understanding predation on the herbivore during the dry season, and the role
that moisture plays in both predators' activities. I also propose testing whether the two
predators have equivalent impacts on the prey population, possibly leading to cascades
due to different predators in the wet versus dry season.

Abstract

Knowledge about the spread of diseases is vitally important to health, agriculture, and to natural communities of organisms. We propose to experiment with an insect disease that offers great potential for learning general principles of spread. We will work with entomopathogenic nematodes (EPNs) that kill caterpillars that eat the roots of plants. These nematodes can protect the plants by killing root feeding caterpillars.
Our preliminary mathematical models lead us to propose that the EPN population is caught between the point of extinction due to overexploitation and a the point of extinction due to underexploitation Finding the biological factors that create the area between over exploitation and underexploitation is the major objective of this project. The spread and dispersal of the EPN among lupine bushes is central to the area of over and underexploitation biology. Immigrants can rescue EPN populations that have or are headed for extinction. The field experiments are designed to answer questions about the conditions that lead to stability of the EPN population EPNs are among the most important natural enemies of root feeding insects in both cultivated and natural settings and are of substantial interest to agriculture and management

Ecologists have long been interested in the factors that control the decomposition of plant matter in terrestrial ecosystems. Decomposition is the primary process through which nutrients taken up by plants are recycled in the ecosystem. Although the physical environmental controls on decomposition have been well studied, relatively little is known about interactions among the animals that feed on detritus or how such interactions affect decomposition. Large detritivores, such as earthworms, millipedes and sow bugs, may improve the quality of food available for small soil animals such as nematodes and springtails. This project examines the interaction between a common sow bug, Porcellio scaber, and soil fauna. Porcellio scaber dramatically increases the breakdown of plant litter in this study system. The sow bugs may accelerate incorporation of plant litter into the soil, and benefit soil animals that depend on such influxes of detritus. Sow bug feeding may also benefit soil detritivores by improving the nutrient content of detritus and facilitating of microbe colonization. This work will test these hypotheses with field and laboratory experiments and demonstrate the overall impact of Porcellio scaber on soil fauna in a natural soil community and in controlled laboratory experiments. This study will contribute to a greater understanding of how carbon is cycled through decomposer foodwebs, and how species interactions contribute to variation in decomposition rates. This project will also support the dissertation research of a doctoral student.