Archives -- Research Reports

1995-1996 RESEARCH REPORTS

Effects of Predators (Trout, Stoneflies) and Nutrients on the Mean Levels, Overall Variability, and Spatial Heterogeneity of Invertebrates and Algae in Streams
Scott D. Cooper, Department of EEMB and Marine Science Institute, UCSB
Participants: K. Kratz, S. Diehl, S. Wiseman, T. M. Jenkins, S. Roll, J. Eichholtz, R. Scheinberg, N. Barbee, S. Stark,
E Gaylor, E. Dinger, M. Strunk, C. Lewis, P. Hosseini, Department of EEMB and Marine Science Institute

During the summer of 1995, my research group and I conducted experiments in the experimental stream facilities at SNARL. This research examined the effects of predators (brown trout, stonefly nymphs) and nutrients on the mean levels, overall variability, and spatial heterogeneity of lower trophic levels (stream invertebrates, algae). We set up four experimental treatments in the nine 50 m2 stream channels at SNARL: no trout and no stoneflies, trout only, stoneflies only, and trout plus stoneflies. We examined the effects of these treatments on benthic invertebrate abundance, invertebrate grazing activity, invertebrate drift, and algal biomass, as well as trout and stonefly growth, survival, and diets. We also examined the effects of predator manipulations on the spatial arrangement of patches of algae using geostatistical techniques. We found that both predators had negative effects on the grazing activity of mayflies on the substrate surface, resulting in higher algal biomass in treatments with predators. We are still analysing benthic, drift, and diet samples. The growth of one-year-old trout was higher in the presence of stoneflies than in their absence. This suggests that stoneflies facilitated the consumption of shared prey by trout, because they drive other prey out of refuges and into the drift. We analysed longitudinal patterns of spatial autocorrelation of algal biomass in pools and riffles, using two parallel rows of 100 ceramic tiles that had been colonized for 8 weeks. Although predators had effects on mean algal biomass, they did not affect the spatial pattern of algal biomass. The latter was mostly related to abiotic conditions such as differences in current speed and water depth. We also conducted a small-scale nutrient enrichment experiment in 24 0.2x2.4-m channels which were placed in Convict Creek at SNARL. We created a 1000-fold gradient of nutrient additions (phosphorus and nitrogen in a constant ratio continuously dripped into the channels) in two sets of 12 channels. Grazing invertebrates were allowed to colonize naturally in 12 channels, whereas grazer immigration was prevented in the other 12 channels. The experiment showed that algae were not nutrient limited above 20 micrograms phosphorus/L. Grazers colonized the channels open to drift and reduced algal biomass compared to grazer exclosures, except at the very highest nutrient input levels. At the end of the experiment, grazers were more abundant and emigrated less from channels with higher algal biomass. We finally conducted a small-scale predator-prey experiment in the same 24 channels as above. The treatments consisted of the presence and absence of predatory stoneflies in the presence and absence of absolute refugia for mayfly prey (shallow crevices underneath coarse substrate particles). The presence of stoneflies increased the rate at which mayflies emigrated from channels, but this rate was lower when mayflies had access to absolute refuges. When predators were present, mayflies reduced their grazing activity on the upper surfaces of substrates, especially when the undersides of substrates provided absolute refuges. Field personnel included the principal investigator, field and laboratory supervisors, and three full-time student assistants. We obtained additional help from seven part-time assistants during three periods of intensive sampling. Funding: National Science Foundation.

Livestock Grazing and Rangeland Stream Ecology
David B. Herbst and Roland A. Knapp, Marine Science Institute, UCSB
Participants: M. Embury, P. Kirchner, D. R. Dawson, SNARL

Livestock grazing in the limited riparian zone of arid Great Basin streams often results in a loss of vegetative cover and the degradation and erosion of stream channel habitats. Although changes in the riparian and physical environment of streams are well-documented, much less is known about the responses of in-stream aquatic communities to grazing-related impacts. For 3 years we have been monitoring the biological
characteristics of stream reaches exposed to different grazing practices to both evaluate differences in the ecological attributes of grazed and ungrazed areas, and the success of management in alleviating nonpoint source pollution problems. A loss of invertebrate species diversity and shifts in indicator groups consistently occurred at some grazed sites while others were unchanged relative to reference sites. Trout abundance also was decreased at some grazed sites but not others. Results suggest that physical monitoring alone is
insufficient to detect changes in aquatic ecosystem structure and function, and that bioassessment monitoring is sensitive and responsive to local and seasonal changes in rangeland stream environments. Funding:
UC Water Resources Center.

Mono Lake Benthic Ecology and Environmental Physiology
David B. Herbst, Marine Science Institute, UCSB
Participants: C. Culbertson and L. Miller, USGS, Menlo Park; D. Blinn and J. Naquin, Northern Arizona University;
R. Castenholz, University of Oregon

Continued research at Mono Lake has included monitoring of the abundance of the alkali fly population, the primary food source for many shorebirds visiting this saline lake. We examined changes related to changes in lake levels and provide feedback for lake management planning. Research also included studies of the rate of colonization of artificial substrates by algae and fly larvae and pupae (as a monitoring tool and in relation to small-scale surface orientation). In addition, salinity effects on the microbial community of Mono Lake were investigated suing as response variables, (1) the growth response of the filamentous green alga Ctenocladus and (2) the rate of nitrogen fixation in the microbial community of shallow sediments. All results played a role in the recent decision of the State Water Resources Control Board to raise the level of Mono Lake and to restore the ecosystem. Funding: Mono Lake Foundation.

Biogeography of Great Basin Aquatic Invertebrates
David B. Herbst, Marine Science Institute, UCSB
Participant: University of Nevada Biodiversity Center, Reno, Nevada

Aquatic habitats throughout much of the Great Basin are isolated islands in a sea of desert. On the Sheldon Wildlife Refuge in northern Nevada are a variety of habitats including ephemeral lakes, spring systems, and perennial streams that flow for a few miles then disappear into desert sand. Few collections of aquatic invertebrates have been made from this region and there is great potential for the discovery of relict, isolated and endemic species, and extensions in the ranges of known species. Aquatic collections in this half-million acre refuge will contribute to documenting the biodiversity of the Great Basin and prioritizing refuge habitats for protection. Funding: E. L. Wiegand Foundation.  

Impacts of Livestock Grazing on the Spawning Habitat and Population Structure of Golden Trout
Roland A. Knapp, Marine Science Institute, UCSB and SNARL
K. Matthews, USDA Pacific Southwest Research Station
Participants: V. Vredenburg, J. Muck, USDA Pacific Southwest Research Station

The goal of this project is to increase our understanding of the impacts of livestock grazing on the spawning habitat and population structure of golden trout in their native streams (Golden Trout Wilderness, Inyo National Forest, California). The native streams of the golden trout are generally heavily degraded by cattle grazing, and trout populations in these streams are characterized by high densities and slow-growing fish; however, little is known about the regulation of these populations. Our results show that golden trout have very specific spawning habitat requirements, only utilizing particular water depths, water velocities, and substrate sizes for nest construction and egg deposition. In addition, preferred spawning habitats are much more common in heavily-grazed areas than lightly-grazed or ungrazed areas, because cattle grazing decreases bank stability and results in wider, shallower streams. As a result of increased spawning habitat availability, nest density and density of juvenile trout is also much higher in heavily grazed than in lightly-grazed or ungrazed areas. These results suggest that by increasing the amount of spawning habitat available to golden trout, livestock grazing may have indirectly resulted in increased densities and slower growth rates of golden trout in their native streams. Our results have important consequences for grazing management and stream restoration strategies in the Golden Trout Wilderness and other meadow-stream ecosystems in the western United States. Funding: USDA Pacific Southwest Research Station.

Impacts of Non-native Trout on Lake Ecosystems in the Sierra Nevada
Roland A. Knapp, Marine Sciene Institute, UCSB and SNARL
Participants: K. Matthews, V. Vredenburg, J. Muck, D. Paron, USDA Pacific Southwest Research Station; R. Jellison,
T. Jenkins, P. Kirchner, M. Embury, E. Wenk, Marine Science Institute, UCSB

This research project is designed to elucidate the impacts of non-native trout on lake ecosystems in the Sierra Nevada. Historically, nearly all Sierran lakes were fishless. Starting in the 1850Õs and continuing to the present day, however, trout have been stocked into nearly all suitable waters. Because trout are effective predators, these introductions have resulted in precipitous declines in species adapted to fishless lakes, including amphibians, and some zooplankton and benthic invertebrates. In some cases (e.g., amphibians), these declines have been severe enough that some species may soon be listed under the Endangered Species Act. In order to better understand the impacts of introduced trout on lake ecosystems, we are sampling all lakes in several watersheds in the Sierra Nevada for fish, amphibians, zooplankton, and benthic invertebrates. The information generated by this sampling effort will be used to model the population viability of the mountain yellow-legged frog, and the distribution of trout that would result from several alternative trout stocking practices. Our study will increase our understanding of causes underlying amphibian declines, and will have important consequences for the future management of high mountain lake ecosystems. Funding: USDA Pacific Southwest Research Station.

Colonization Dynamics: Resource Levels, Intraspecific Interactions, and Predator Impacts on Prey Populations
Kim W. Kratz, Department of EEMB, UCSB
Ph.D. Advisor: Scott D. Cooper, Department of EEMB, UCSB

This research project used small in situ stream channels in Convick Creek. The research involved 1) an investigation of invertebrate predator impacts on prey populations along a resource gradient and 2) the influence of refugia on predator-prey dynamics. Funding: National Science Foundation .

Vertical Mixing and Resource Supply to Phytoplankton
Sally MacIntyre, Marine Science Institute, UCSB
Participants: R. Jellison, K. M. Flynn, J. R. Romero, D. Heil , C. Saltikov, Marine Science Institute, UCSB

My research project addresses the importance of vertical mixing to phytoplankton ecology. I used turbulent microstructure profilers to determine where the water column was mixing and the intensity of the turbulence. With accompanying profiles of chlorophyll a and nutrients, we assessed the vertical circulation of
phytoplankton and their exposure to fluctuating irradiance, as well as rates of nutrient flux. By performing measurements in different parts of lake basins, we will determine whether nutrient fluxes are forced by Kelvin-Helmholtz billowing in the thermocline or by other processes such as boundary mixing or upwelling. Measurements were made in Lake Biwa, Japan, in 1993, as part of the Lake Biwa Transport Experiment (BITEX), the first international, interdisciplinary limnological study on the scale of an oceanographic
experiment. Field studies were conducted at Mono Lake, CA during the spring, summer, and fall of 1995 and included periods of calm, as well as stormy periods, with winds gusting to 20 m/s. Particularly exciting is our finding that nutrient flux across the thermocline is two to three orders of magnitude higher in nearshore areas, where the thermocline intercepts the sediment-water interface, than in offshore waters. Funding: National Science Foundation.

Monitoring of Limnology and Plankton in Mono Lake
John M. Melack, Marine Science Institute and Department of EEMB, UCSB
Robert Jellison, Marine Science Institute, UCSB
Participants: D.Heil, P. Kirchner, Marine Science Institute, UCSB

Mono Lake is a large, hypersaline, highly productive alkaline lake lying just east of the Sierra Nevada. In addition to its recreational, scenic, and water resource values, it contains large populations of an endemic brine shrimp and the alkali fly which are important food sources for migrating birds. Although saline lakes are common throughout the world and provide important ecological resources for many species, they are much less studied than freshwater ecosystems. Limnological monitoring conducted from 1979-1996
represents one of the longest continuous studies of any hypersaline ecosystem and, in addition to addressing current environmental concerns in the Mono Basin, provides insight into the functioning of saline ecosystems. Funding: Los Angeles Department of Water and Power.

Responses of a Saline Lake to Environmental Change
John M. Melack, Marine Science Institute and Department of EEMB, UCSB
Robert Jellison, Marine Science Institute, UCSB
Participant: D. Heil, Marine Science Institute, UCSB

Saline lakes constitute nearly half of inland waters by volume and provide ecologically important aquatic habitats in arid regions of the world. They often have high rates of algal productivity which support aquatic invertebrates and large numbers of birds. At Mono Lake, California environmental concern has focused on the impacts of higher salinity associated with smaller lake sizes caused by the diversion of freshwater streams that used to flow into Mono Lake. In 1994, state agencies decided to gradually raise the surface elevation of Mono Lake to approximately six meters above the historic low in 1982. This action provides a unique opportunity to study the effects of environmental change on a large saline lake. Ecological studies of the lake's biota during the period of rising lake levels and decreasing salinity will complement prior laboratory studies focused on the effect of increased salinity on Mono Lake's biota. Funding: National Science Foundation.  

Aquatic Insects in the Springs of the Great Basin
Marilyn Myers, Department of Environmental Science, Policy, and Management, UC Berkeley
Ph.D. Advisor: Vince Resh, Department of Environmental Science, Policy, and Management, UC Berkeley

By the end of the 1995 field season, I had visited over 100 springs in Inyo and Mono Counties in the vicinity of SNARL. I gathered water chemistry information (temperature, pH, conductivity, dissolved oxygen, alkalinity, and hardness) on about 35 springs and collected aquatic invertebrates from all springs. I have identified caddisflies (Trichoptera) to species level. Forty different species in 12 families have been identified. Limnephilids and lepidostomatids have the greatest number of species represented. Springs with well-developed riparian areas supported the greatest number of species. Other groups of invertebrates will be identified at least to generic level as work continues. In the springs visited, grazing by ungulates is the major human impact observed. Funding: Departmental Funds; Walker Fund; Harvey I. Magy Memorial Scholarship; White Mountain Research Station.

Snow Algae Studies at SNARL
William H. Thomas, Scripps Institution of Oceanography, UC San Diego
Participants: T. Thomas, A. M. Thomas, and A. K. Thomas, MRD/SIO, UC San Diego; B. Duva, University of Massachusetts

Microscopic algae, that color old snowfields red or green, were abundant in early summer of 1993 and 1994 in the Tioga Pass area of the Sierra Nevada. We postulated that surface algal blooms would decrease albedo, the proportion of sunlight reflected back from the snow, and thus snow melting would be increased. Significant negative correlations were found between albedo and algal cell numbers in the snow, but albedo was not decreased over the whole Tioga Pass watershed because the algae occurred in discrete patches. Thus water supply from snow melting was not affected by algae. Dirt on the snow also decreased albedo. Snow bacterial abundances and growth rates were higher in red snow containing algae than in white snow. Bacterial growth rates were also less than algal photosynthetic rates. Thus bacteria seemed to be dependent on algae for much of their nutrient supply and were ultimately associated with algae, often attached to algal cells. About 30% more ultraviolet radiation is found at the elevation of Tioga Pass than at sea level, and the Sierra is a high-UV environment. In experiments where snow algae were contained in UV-transmitting quartz tubes, UV radiation inhibited red snow (collected from open, sunlit areas) photosynthesis about 25%, whereas green snow (collected from forested, shady locations) photosynthesis was inhibited by 85%. These differences may be due to different habitats, or may be genetic, since different species were found in the two snow types. These studies are some of the first to examine the microbial ecology of snow, and we plan to assess the effects of UV on the complete algal-bacterial system in future field studies at Tioga Pass and at SNARL. Funding: Donation to SIO; Southern California Edison Company.

Grazing Impacts on Golden Trout
Vance Vredenburg, PSW, U.S. Forest Service
Ph.D. Advisor: Mary Power, UC Berkeley
Participants: R. A. Knapp, Marine Science Institute, UCSB; K. Matthews, J. Muck, U.S. Forest Service

The purpose of this study is to determine whether cattle grazing affects the availability of spawning habitat and population structure of the California golden trout. The study was conducted in two creeks in the Golden Trout Wilderness Area, Inyo National Forest. Funding: PSW/U.S. Forest Service

Remote Sensing and Change in Snow Properties
Robert E. Davis, Department of the Army, Hanover, NH
Participants: J. Dozier's research group, ICESS, UCSB; S. Burak, Snow Survey Associates

The broad goal of this research is to advance knowledge of the spatial distributions of snow properties and processes in complex landscapes. Use of the Reserve toward this goal involved carrying out field and
laboratory experiments to measure changes in snow properties, testing models to predict the changes in snow properties over time, and developing links between these models and remote sensing measurements.
Investigations toward this goal were carried out at a variety of spatial scales. In laboratory experiments we melted snow to examine how initial conditions and melt schemes affected the intensity and timing of the ionic pulse of trace chemical species. Near the other end of the scale range we related weather conditions over a large area to the release of avalanches by explosive triggering. Results of these efforts were published. Additional publications on the avalanche data are currently in preparation. At intermediate spatial scales, we are continuing research to develop links between remotely sensed products, such as snow extent maps, and spatially distributed snow process modeling. Most of this work used Mammoth Mountain as the test area for intensive studies, and the Black Cap watershed in the Kings River basin as the test area for broad hydrologic studies. Funding: Army Corps of Engineers Projects 2A762784AT42 and Civil Works Remote Sensing (363) Work Unit 32712.

Carbon Dioxide Emission Study, Mammoth Lakes Area
Christopher D. Farrar, U.S. Geological Survey
Participants: J. Neil and J. Howle, U.S. Geological Survey

Research on the carbon dioxide emissions in the Mammoth Lakes area is being conducted as part of the U.S. Geological Survey Volcanic Hazards Program. SNARL has been used as a base for conducting parts of the reconnaissance and field surveys that are aimed at identifying areas of anomalously high CO2 concentrations in soil gas. Our surveys have focused on Mammoth Mountain, especially the areas where coniferous forest has been killed by excessive concentrations of soil gas CO2 (up to 95 vol%). Less intensive surveys have been made near Hot Creek Gorge, Fumarole Valley, Hot Bubbling Pool, and Casas Diablo. On Mammoth Mountain the high rate of CO2 emission at the land surface probably began in 1990 but was triggered by seismicity and magmatic intrusion to shallow depths beneath Mammoth Mountain in 1989. Our work is focused on mapping areas of high CO2 in soils, quantifying emission rates, quantifying the total amount of CO2 discharged to the atmosphere, identifying the source of the CO2 , and assessing the volcanic hazard implications of CO2 emissions. Our early results (Farrar, et. al., 1995) indicate that concentrations of soil gas CO2 range between 20 and 95 vol% in areas where confierous forest has been completely killed. There are four general areas of tree-kill on Mammoth Mountain that total about 40 hectares but appear to be still enlarging in size. The source of CO2 is either directly from degassing magma or from carbonate rocks heated by magma. A preliminary estimate of total CO2 emission from Mammoth Mountain is 1200 metric tons per day and is comparable to the CO2 discharge from Kilauea in Hawaii during periods of low level eruptive activity. Funding: USGS Volcano Hazards Program.

Snowmelt Research
Bob Harrington, Hydrology and Water Resources, University of Arizona
Participants: R. Bales, University of Arizona; J. Dozier, R. Kattelmann, ICESS, UCSB

Monitoring of snowmelt runoff and chemistry was conducted at the SNARL snowmelt research site on Mammoth Mountain. Roger Bales and Jeff Dozier examined the process governing release of pollutants stored in the snowpack, and determined the spatial variability of snowpack properties and snowmelt runoff. The extremely deep (5.2 meters) snowpack during the winter of 1994-1995 provided an excellent set of data for looking at hydrologic processes that take place under heavy snow conditions. Rick Kattelmann and I observed slightly elevated concentrations of ionic solute at the onset of spring melt, followed by extremely dilute flow from the melting snowpack. Funding: National Science Foundation; NASA Earth Observing System Interdisciplinary Science Investigations Program.

Evaluation of Water Resources throughout the Sierra Nevada
Rick Kattelmann, ICESS, UCSB

As part of the Sierra Nevada Ecosystem Project, a comprehensive assessment of the state of the environment of the Sierra Nevada was undertaken, including general conditions of streams, lakes, and riparian areas. This assessment relied on the compilation of thousands of scientific papers, unpublished reports, and various sets of data. Field surveys provided a common frame of reference for the diverse array of information that was compiled from literature sources. Aquatic and riparian systems were found to be the most altered and impaired habitats of the Sierra Nevada. Dams and diversions have dramatically altered streamflow patterns throughout most river basins in the range. Changes in water quantity have adverse impacts on aquatic organisms and water quality in most river systems. Riparian areas have been damaged by placer mining, grazing, water development, roads, timber harvest, residential construction, and recreational activities. The disturbance of riparian areas has accelerated sediment yield, which is a widespread water quality problem. Aquatic systems of the Sierra Nevada appear to be highly resilient and responsive to the cessation of disturbance and active restoration. Funding: Sierra Nevada Ecosystem Project, UC Davis; U.S. Forest Service Collaborators.

EOS NASA Project
John M. Melack, ICESS and Department of EEMB, UCSB
Jeff Dozier, ICESS, UCSB
Participants: V. B. Aizen, E. Lolctionova, Russian Academy of Sciences; R. Kattelmann and W. Rosenthal, ICESS, UCSB

An extension of a decade long study of Sierran catchments, applications of remote sensing of snow with optical and microwave systems, hydrological and hydrochemical modeling and experimental studies. Funding: NASAÕs Earth Observing System Program.  

Nearfield Crustal Strain Across Active Faults in California
Arthur G. Sylvester, Department of Geological Sciences, UCSB
Participants: M. Morse, N. Takeuchi, E. Johnson, B. Lockee, B. Olson, J. Eastman, Geological Sciences, UCSB

We resurveyed existing USGS and UC Santa Barbara benchmarks in Long Valley in the Mammoth Lakes region of the eastern Sierra Nevada to determine whether recurring vertical displacement has occurred recently across the Hilton Creek fault, and whether measurable tilting has occurred in and around the caldera in places not presently monitored by USGS tiltmeters. We found that displacement has not occurred across the Hilton Creek fault in McGee Creek canyon over the period 1993 to 1995, whereas uplifting has taken place across at a rate of 1-2 mm/yr since 1982. On the other hand, we resurveyed 6 dry tilt arrays in Long Valley and found that they have tilted radially outward from 10 to 15 microradians per year in the last 5 years. The tilt directions and magnitudes are very similar to those determined by tiltmeters, but the dry tilt data fill some important gaps. Funding: U.S. Geological Survey; PresidentÕs Undergraduate Research Fund.  

BRDF Measurements of Snow and Ice
Zhengming Wan and William Snyder, Department of Geological Sciences and ICESS, UCSB
Participants: L. Zhang, J. Feng, X. Wu, Department of Geological Sciences and ICESS, UCSB

This project involves measuring the reflectance of snow and ice in infrared wavelengths for land surface temperature measurements. Funding: NASA.  

Effects of Induction of Wound Responses of Nicotiana attenuata on Herbivore and Plant Performance
Rick Karban, Department of Entomology, UC Davis

During this past spring I initiated an experiment to evaluate the effects of induction of wound responses of Nicotiana attenuata on herbivore and plant performance. Nicotiana attenuata synthesizes nicotine when it is damaged by herbivory. This response can also be induced by application of methyl jasmonate to the roots of plants. Methyl jasmonate appears to act as the signal that moves through the plant and inducess other defensive responses as well. I induced some plants with minute concentrations of methyl jasmonate and kept other plants as water controls. Jasmonate treated plants had higher whole-plant concentrations of nicotine, confirming previous laboratory findings. Plants treated with jasmonates also suffered less damage by cutworm larvae. Data evaluating the effects of this treatment on plant fitness are still being collected. An important herbivore of Nicotiana attenuata in some years is the tobacco hornworm, Manduca quinquemaculata. This year populations of hornworms were low at the reserve. Adult moths were preferentially attracted to tall N. a. plants and those that were in close proximity to other flowering species. Hornworm larvae were placed on plants that had been treated with methyl jasmonate and on untreated controls. Although sample sizes were small, the results suggested that hornworm growth was retarded on plants tested with jasmonates.

Relationship of Plant Root Traits to Resource Competition and Stress Tolerance
J. H. Richards and L. A. Donovan, Land, Air, and Water Resources, UC Davis
Participants: G. Kyser, K. Fort, C. Davis, L. A. Donovan, J. P. Davis, G. Dodd, N. Pergarn, UC Davis

Plant distributions along ecological gradients may be related to tradeoffs between traits associated with stress tolerance and resource competition. This project will be an interspecific comparison of two woody shrubs, Sarcobatus vermiculatus and Chrysothamnus nauseosus, that differ in their distributions along a nutrient resource and toxic ion gradient in the Mono Lake basin. Resource competition is defined as a negative interaction between neighboring plants as mediated through resources (e.g. nutrients and water). Stress tolerance is defined as greater ability to survive and maintain growth as resource levels are decreased and/or some non-resource stress increases (e.g. toxic ions). The hypotheses to be tested are that the two shrubs rank differently for stress tolerance and ability to compete for resources, and that differences in below ground traits (growth rate, morphology, architecture, and plasticity) will be associated with these rankings. Competition will be measured in the field gardens by measuring the ability of plants to suppress the growth of neighboring plants, as well s the plants' ability to garner resources such as nitrogen and water. Stress tolerance will be measured in field gardens and in a sand-culture irrigation system as the ability to survive and maintain growth in response to decreased nutrients and increased toxic ion concentrations. Predicted and measured values for root growth rate, morphology (specific root length, root length density, diameter, root hair length, and mycorrhizal infection), branching architecture, and plasticity will be compared. This comparison will contribute to our understanding of the relationship between belowground form and whole plant function and, thus, our understanding of factors such as competition and stress tolerance that shape ecosystem form and function. Funding: USDA /University of Florida.

Biological and Physical Processes Determining the Development of an Alkaline Playa Sand-dune Ecosystem
Catherine A. Toft and Deborah Elliott-Fisk, Department of Evolution and Ecology, UC Davis
Participants: T. Trapp, D. Brown, T. Brown, UC Davis

The goal of this research, which we are conducting on the north shore of Mono Lake, CA, is to understand the biological and physical processes determining the development of an alkaline playa sand-dune ecosystem. The site is typical of highly saline alkaline Great Basin lake-bed playas, which were produced by the recession of pluvial lakes during past climate changes and, in some, from anthropogenic alterations of the lakesÕ water budgets. We are investigating aspects of a conceptual model of desert succession that emphasizes abiotic, plant, and animal ecosystem components on a time scale appropriate to the development of desert ecosystems (i.e. centuries). We have chosen sites, or are sampling transects, along the playa-to-diverse-dune gradient where the substrate became available for colonization at time scales ranging from 10 years up to many hundreds of years ago. We are 1) quantifying ecosystem characteristics (soil and water chemistry, stratigraphy, substrate and landform age, plant and animal diversity and density) along a continuous 2200-m horizontal gradient from the current, lake shore to mature stabilized dunes, and 2) testing experimentally the relative importances of crucial processes that guide and constrain the development of terrestrial ecosystems in deserts. The experiments test hypotheses regarding physical and physiological constraints for plants in migrating to, germinating on, establishing on, and propagating on highly saline, highly alkaline, and dry substrates that have very limited nutrient availability. Results of this study will allow a major advance in the understanding of succession in desert ecosystems, a topic of long-standing and unresolved debate. More importantly the project will rigorously test hypotheses about biogeochemical, ecophysiological, and plant- and animal-population mechanisms operating at several stages during the development of semi-stabilized dunes in desert playa environments. The results of the study can be directly applied to ecosystem restoration and revegetation in the western United States, particularly where saline, alkaline, or chemically unfavorable substrates have been desiccated by diversions of water for agricultural or urban uses. Applications to other desert locations are also envisioned as we increase our understanding of the interactions between abiotic and biotic constraints to the success of plants in these environments. Funding: USDA Competitive Grants.

Energy Supply Limits on the Reproductive Activities of Male Ground Squirrels
Gwen Bachman, Department of Zoology, University of Oklahoma
Participants: T. Clark, M. Embree, S.Ibarguen, Department of Zoology, University of Oklahoma

The project's primary goal is to assess whether and how energy supply limits the reproductive activities of male ground squirrels. We hope to determine (i) the relationship between individual variation in male reproductive behavior and daily energy expenditure, and (ii) the extent to which individual reproductive activity is limited by stored energy reserves and intake during the mating period. These questions will be examined in two species of ground squirrels with contrasting forms of intrasexual competition: the thirteen-lined ground squirrel (study site in Oklahoma) and the Belding's ground squirrel (study site at SNARL). The mating system of the 13-lined squirrel emphasizes mate searching behavior with minimal male-male combat, whereas the Belding's mating system is thought to emphasize male fighting ability. These tactics are common features of many mammalian systems. A sample of males were followed throughout the breeding period with the aid of radio transmitters mounted on collars. Location and activity of males was noted every 10-15 minutes for 9-10 hours each day. We also measured energy expenditure and body composition changes in males differing in activity level and experimental treatment. In this first year, we provided some males with access to extra food for part of each day to examine whether food availability and foraging time limited mating effort or mating success. Funding: National Science Foundation; Visiting Professorships for Women.

Begging Energetics in House Wrens
Mark Chappell, Department of Biology, UC Riverside
Robert Gibson, Department of Biology, UC Los Angeles
Gwen Bachman, Department of Zoology, University of Oklahoma

Our main goal is to evaluate the effectiveness of begging as an honest communication of offspring need. To do this, we are combining laboratory based measures of the energetic expenditures associated with begging with field observations of nestling begging and parental response. In brief, we have discovered that the energetic cost of begging is significant, in that chicks of all ages (2 to 10 days) show large increases in oxygen consumption during begging activity. The increase may be as much as 2-3 x resting levels. However, the energy cost of begging is very low as a fraction of daily energy consumption, since chicks beg for only a small fraction of time (perhaps 15 seconds for every 10 minutes during the day). Beg costs are also low as a function of return (i.e., food provided by parents). The cost of an average beg is much less than 1% of the energy contained in a typical food item. Finally, experiments and observations with chicks in nest boxes reveals that chicks beg ÔhonestlyÕ, in that they increase the intensity of begging when hungry and decrease begging when well fed. These results have implications for theoretical analyses of signal evolution. Funding: Academic Senate, UC Los Angeles (Gibson), UC Riverside (Chappell).

The Role of Air Sacs in Sage Grouse Sound Production
Marc Dantzker, Department of Biology, UC San Diego
Ph.D. Advisor: Jack Bradbury, Department of Biology, UC San Diego

The vocal display of the male sage grouse, Centrocercus urophasianus, has various acoustic characteristics that make it unique among vertebrates. The mechanism by which they make these sounds is not known; however, it is clear that the paired membranous air sacs which inflate through the chest wall during phonation are responsible for the bulk of acoustic radiation, if not the primary vibration. Such paired air sacs are restricted in birds to just a few species of grouse. Acoustic models suggest that dual sound-source systems may have biologically relevant complex interference patterns. We examined the acoustic radiation patterns of calling male sage grouse using a microphone array. We found evidence for directional, asymmetric sound fields unlike those previously measured in any system. Our continued research will focus on resolving the consequences of these radiation patterns on sexual selection and mate choice in the sage grouse.

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