Hopland Research and Extension Center

Mammalian herbivores can exert large influences on plant communities and ecosystems through their activities as consumers, disturbance agents, and producers of metabolic wastes.  However, studies have reported such widely disparate results that attempts to generalize about their effects have been hindered.  At the community level, herbivores have been shown to both increase and decrease plant species richness and rates of succession.  At the ecosystem level, herbivores can either accelerate or decelerate nutrient cycling.  In some cases, the community effects of herbivores give rise to ecosystem effects, while in others; ecosystem effects either give rise to community effects or do not substantially alter plant communities.  Attempts to understand the causes of such varying and often opposing results will be critical for efforts to generalize about the influence of herbivores on plant communities and ecosystems.  To address this issue, I have established a large-scale exclosure experiment in oak savanna habitat at three sites in northern California: Sonoma State University's Fairfield Osborn Preserve, Stanford University's Jasper Ridge Biological Preserve, and the University of California's Hopland Research and Extension Center (Riley Ridge Biological Study Area).

This project is designed to improve our fundamental understanding of the European red fox invasion in northern California by studying co-occurrence patterns among canids and exploring their relationship to urban, natural, and agricultural landscapes.  This study is being conducted in oak woodlands surrounding the San Francisco Bay area, which are being extensively modified for vineyard and suburban residential development.  Our research involves a combination of field and laboratory work, including surveys using a scat detection dog and genetic analyses to identify scats to species.  A GIS of land use and land cover, integrated with spatial statistical software, will be used to test hypotheses of red fox habitat correlates and impacts to native gray foxes.  A model of red fox habitat use and areas of potential spread will be developed in conjunction with existing economic models of development in northern California.  This study will provide information on the pattern of invasion, as well as the limitations to red fox establishment imposed by competitors, predators, and patterns of land-use.

This project is designed to assess geographic variation in genetic and behavioral measures within the Lark Sparrow (Chondestes grammacus).  By capturing, color marking, and blood sampling individuals from multiple breeding populations, including Mendocino County, we can determine if there is evidence to support any subspecific divisions, regional dialects, or a loss in genetic diversity in the much declined eastern populations.  Though the Hopland Research and Extension Center was not visited last year as part of this assessment on account of unforeseen permit delays, we hope to incorporate data from this population this year at the end of June.  This will allow us to not only add another population to our analysis, but will also provide a within-state comparison to more northerly populations in Tehama County.

In 1959, Dr. H. Howard initiated what a very long-term study on voles (Microtus californicus) at HREC.  When I joined UCD in late 1995, I began to consider what additional information could be gleaned from these long-enclosed plots.  My work is based on the premise that extreme isolation of a species known to exhibit substantial multi-year cycles in population numbers may have led to demographic bottlenecks in these vole populations.  Fundamentally, I am investigating loss of genetic variation in isolated vole populations, as well as a specific morphological response to reduced genetic variation.  This response - fluctuating asymmetry - may occur when animals are unable to compensate for "environmental abuse" during development.  To date my work has documented minimal loss of genetic variation, but we have not completed collecting samples for morphological analyses.  HREC pens are highly suitable to this project because of the duration of isolation (46years, or somewhat more than 60 Microtus generations), and the presence of pitfall traps that allow simulated emigration (this prevents populations from expanding exponentially, a dynamic known as the "fence effect").

The project's goals are to determine how egg temperature and female attentiveness of passerine birds varies with incubation stage (embryo age) and ambient temperature.   The research will test a mathematical model that describes relative investment in parental self-maintenance versus embryo developmental rate, and the extent to which performance for either is compromised by integration of both functions.  The project also examines whether exposure of newly-laid eggs to ambient temperatures above physiological zero induces embryonic development in the absence of incubation.  If so, eggs that experience preincubation development should require less incubation time to hatch than non-exposed eggs subject to similar incubation patterns.

Infection of egg contents has been demonstrated during the laying period of the Western Bluebird (Sialia mexicanus). We propose to measure the changes in hatchability and microbial penetration of the egg with increasing length of exposure to ambient temperatures. The rate of microbial infection during the laying period will be determined for the shell, albumen, and yolk using PCR with general Eubacterial and fungal primers. An analysis of incubation behavior indicates nest attendance during the laying period is common; the effect of this partial incubation on hatching success and microbial infection will be determined experimentally. The results may provide a new paradigm for understanding variation in the onset of incubation.

DNA technology will be applied to experimental use of the Coyote Lure Operative Device (CLOD) to determine whether coyotes that visit and consume CLOD contents at Hopland are the same individuals that kill sheep and lambs.  Swabs of sheep and lambs killed at Hopland will be sent to the USDA NWRC for DNA analysis to identify specific coyotes responsible for kills.  These will be matched to DNA samples from saliva taken from CLODs distributed in pastures at HREC from June  through April, as well as to blood samples taken from coyotes live-captured and released on the Center during the spring, in order to determine whether sheep-killing coyotes will predictably and repeatedly activate CLODs and ingest their contents.  CLODs will be filled with non-toxic mixtures containing sucrose or other rewards that stimulate repeat visits and/or appropriate biological markers.