 |
 |
 |
||
Argentine ant (Linepithema humile) invasion along riparian corridors in southern California
Lauren Fah (in progress).
Current Student Research
Native black widow versus exotic brown widow spiders in urban southern California
Marty Lewis (in progress)
My research involves investigating potential competition between native black widow (Latrodectus hesperus) and the introduced brown widow (Latrodectus geometricus) which has been recently discovered in urban southern California. Both species are considered medically important because of highly potent toxins present in their venom. Since 2003, public anecdotal evidence claims that black widow numbers have been falling, while brown widow numbers have been on the rise. This suggests that the introduced brown widow species may be outcompeting black widows for necessary resources such as dwelling space. My project aims to investigate whether brown widows are actually over-numbering black widows in urban southern California, and whether the two species actually compete against another for dwelling space. If evidence of competition between the two species exists, then black widow populations may be experiencing local extinctions in urban southern California. Marty Lewis (in progress)
|
|
|
||
Argentine ant (Linepithema humile) invasion along riparian corridors in southern California
Lauren Fah (in progress).
My study focuses on the distribution of Argentine ants along riparian corridors intersected by urban development. Argentine ants are strongly associated with disturbed and human-modified habitats and are thought to be an urban edge effect in areas of dryer habitat types such as sage scrub and chaparral. I hypothesize that since much evidence shows their dispersal is correlated with water availability the spread of Argentine ants from an urbanized area into the bordering scrub and chaparral community should not be hindered if a continuous source of water, such as a river or stream, is present. In order to test this hypothesis I am investigating the distribution of Argentine ants along perennial and ephemeral steams. Perennial streams provide a constant moisture source for Argentine ants while ephemeral streams provide similar vegetation but an inconsistent source of moisture, which means at times this resource will be limited. I expect Argentine ants will be more persistent along perennial streams compared to ephemeral streams where they will be subjected to periods of stress due to dry conditions. I will also test for negative associations and impacts of Argentine ants on native ants along each stream type. I also plan to study the interplay between soil moisture levels and humidity levels and how each factor effects Argentine ant survival in a manipulated environment in the laboratory.
The effects of outdoor recreation on soil macrofauna communities in coast live oak forests (Quercus agrifolia) in southern California
Emily Ferril (in progress).
Decomposition processes are vital to every ecosystem on Earth because the rate of decomposition regulates the rate of primary production. Soil macrofauna (organisms 2-20 mm in body diameter) have an important role in decomposition processes, fragmenting organic matter and exposing greater surface area on which microbes or true decomposers can act, accelerating the decomposition rate overall. Picnicking, hiking and camping can cause major disturbances to the soil environment including; alteration of soil nutrient concentrations, pH, moisture, organic matter, structure and compaction. I hypothesize that soil macrofaunal communities in coast live oak forests where recreational use is common (high impact) will show decreased species richness and altered community composition in comparison to macrofaunal communities in lower impact areas. To test this hypothesis, I have selected nine sites located in San Diego and Orange counties where I will sample and characterize soil macrofaunal communities, while documenting differences in environmental factors among and within sites.
Ecological and anthropogenic variables influencing goldspotted oak borer, Agrilus auroguttatus, populations
Lauren Singleton (MS. in progress)
The goldspotted oak borer (Agrilus auroguttatus: Buprestidae, Coleoptera) was first documented in San Diego County in 2002 and was apparently introduced via infested firewood from southeastern Arizona. The goldspotted oak borer (GSOB) larvae feed on sapwood, which can lead to tree mortality. Since their introduction, approximately 21,500 coast live oak trees (Quercus agrifolia) have died due to GSOB larval feeding. I hypothesize that the change in GSOB population densities will correlate with specific biotic, abiotic, and anthropogenic factors that may predispose individual trees and certain stands of trees to the beetle. To test this hypothesis, I am measuring the change in GSOB populations and relative damage over a one year period at four high and four low beetle damage sites in San Diego County by counting adult emergence holes, quantifying tree crown damage, and trapping adult beetles. Biotic factors that I am measuring include coast live oak stand density and size class structure, phloem thickness, and woody plant species diversity. Abiotic factors include slope and aspect of individual trees, distance of an individual tree to the stand's edge, prevailing wind patterns, and mean distance to an aquifer at each site. Anthropogenic factors that I am interested in include tree distance from a fire pit, and dominant land use and human population density surrounding each stand. Since GSOB is a recently introduced invasive species, this research is one of the few ecological studies conducted on GSOB. The results from this study will hopefully reveal important correlations between ecological and anthropogenic variables and GSOB population growth that will allow land managers to prioritize eradication efforts in high risk areas.
Ovipositional cues for a galling wasp, Tetramesa romana, on giant reed (Arundo donax)
Raymond Macias (in progress)
The giant reed (Arundo donax) is a globally important invasive plant species. Currently A. donax has invaded riparian habitats in central and southern California and south to Baja California. Large stands of A. donax alter stream flow patterns, increase erosion and flood damage, and cause the loss of biodiversity. Current practices for the control of A. donax employ the application of systematic herbicides, aerial application of herbicides, and mechanical removal. In 2005, a biocontrol program was initiated for A. donax using Tetramesa romana (Hymenoptera: Eurytomidae), a galling wasp monophagous on A. donax, as a possible biocontrol agent. The basic biology of T. romana has only recently been published, and so the factors that contribute to host selection of A. donax by T. romana are unknown at this time. I propose to study the ovipositional cues used by Tetramesa romana. I hypothesize that oviposition of T. romana in A. donax is stimulated by chemical and physical cues. I will investigate the chemical cue(s) of A. donax that stimulates oviposition in T. romana in a laboratory setting by first identifying which chemical fractions of the surface chemicals of A. donax are bioactive using thin layer chromatography then identifying specific bioactive chemicals using GC/MS. Also, I will identify the physical cues that stimulate oviposition of T. romana in a semi-natural experiment. I hypothesize that the environmental cues of time of day, temperature, and relative humidity influence oviposition of T. romana. To test this I will quantify oviposition behavior in a semi-natural environment (no manipulation) by conducting a behavioral assay, and quantify oviposition behavior under manipulated conditions in environmental chambers: time of day, temperature, and humidity.
Impact of Invasive Crayfish on the Benthic Community Structure in Southern California Depressional Wetlands
Matthew Schliebe (MS. in progress)The red swamp crayfish, Procambarus clarkii (Cambaridae: Decapoda), has become an important ecological pest outside of its native range of the southeastern United States. P. clarkii is found in both lotic and lentic systems and has also been known to tolerate degraded waters. P. clarkii is omnivorous and can function within several levels of benthic food web. Movement via anthropogenic factors has resulted in the spread of this species because P. clarkii is both common as a sport fish bait and an important human food source. P. clarkii are known to reduce the presence of native amphibians and crayfish, greatly impact gastropod abundance, reduce the diversity of select invertebrate taxa, and severely reduce submerged macrophyte coverage. P. clarkii also impacts the abiotic traits of the environment by increasing turbidity and resuspending nutrients. I expect that crayfish presence will increase several water chemistry parameters including turbidity, total suspended solids, total nitrogen and total phosphorus concentration. I hypothesize that P. clarkii will cause reduction in gastropod abundance resulting in a trophic cascade where algal density (the main component of a gastropod diet) will increase. I also expect that non-gastropod grazing taxa will increase in abundance due to the reduction in competition for food resources.
Past Student Research
Impact of boring insects on the reproductive success of Hespero yucca whipplei (our lords candle)
Danny Cuellar (January, 2011)
If plants and herbivorous insects are mutual evolutionary forces, we should be able to document this interaction in ecological time if the plant is consumed by few herbivore species and the herbivores are monophagous. This study investigated the impact of peduncle-boring insects on the reproductive success of Hesperoyucca whipplei by measuring plant size, peduncle height, the percent of flowers producing capsules, the number and size of fruit capsules, germination success and relating these variables to peduncle damage caused by peduncle-boring insects. Since peduncle-boring larvae tunnel through the peduncle they affect the flow of nutrients to the flowers and developing seeds. I found that peduncle damage caused by peduncle boring moth larvae negatively influenced germination success. Peduncle damage caused by weevil larvae reduced peduncle height and the number of pedicels. The effect of peduncle damage on seed set (number of seeds) was not significant in this study.
 |
 |
 |
||
An Investigation in Abiotic and Biotic Factors Influencing Ephemeroptera, Plecoptera and Trichoptera Microhabitat Selection in Streams
Emily Corona (January, 2010).
My study investigates if larval Ephemeroptera, Plecoptera and Trichoptera (EPT) species' distributions can be predicted with respect to microhabitat. My study tests if individuals select microhabitats differently with other species present versus absent. EPT are the three most important orders utilized to evaluate water quality since individuals are highly sensitive to specific stressors such as anthropogenic pollution, high chemical or metal concentrations, etc. My study will provide some insight into species' establishment. If a species is absent, is it because of water quality or a missing factor, e.g. a specific habitat is absent or another species is absent or present?
 |
 |
 |
||
Nesve Yayalar (May, 2009)
Eucheira socialis westwoodi is the only known lepidopteran that exhibits division of labor. Early studies showed that colonies of larvae have a male biased sex ratio, and that larvae exhibit sex-specific behavioral differences. The objectives of my study were to test for an effect of work effort on larval growth and survivorship and to compare work effort between male and female larvae in colony of two different sex ratios. I found that males worked more than females as measured by the number of minutes spinning silk on the nest. Work effort in males, but not females, was negatively correlated to pupal weight and larval survivorship, suggesting that male work effort constitutes a sex-specific cost to social living. This project contributes to our understanding of the early stages of the evolution of cooperation and sociality and provides evidence of altruistic behavior among larval E. s. westwoodi.
 |
 |
 |
||
Bioassessment in California ecoregions: exhibits how much information is required to assess biotic stream health?
Coventry O. Dougherty (May, 2008)
Bioassessment standardization efforts have resulted in protocols that measure large suite of chemical and physical habitat parameters that may or may not be informative of freshwater system health. Chemical, physical habitat and benthic macroinvertebrate data from five California ecoregions were obtained from the United States Environmental Protection Agency's STORET Data Warehouse to characterize the freshwater environment of an ecoregion and identify a subset of ecoregion-specific chemical and physical habitat parameters that correlate with benthic macroinvertebrate community assemblages. Non-parametric multivariate analyses based on these data indicated that there were ecoregion-specific characteristics. However, some ecoregions could not consistently be distinguished from one another suggesting that predefined terrestrial ecoregions may not accurately overlay onto freshwater systems. Chemical and physical habitat data differentially explained ecoregion patterns in benthic macroinvertebrate abundances and biological metrics. Further investigation and validation is required before ecoregion-specific recommendations can be made for reducing the number of measured parameters.
Impacts of recreational trail use on arthropod community composition in California coastal scrub habitat
Dennis E. Miller (December, 2007)
Construction and use of hiking trails into native landscapes has been shown to alter native habitat allowing establishment of non-native species along trails, which withstand the continued disturbance of trail use. No study has yet documented the ability of non-native arthropods to spread through recreational trails. I trapped ground dwelling arthropods and adult Diptera along three trials in Point Mugu State Park, California. Three trap arrays were placed along each trail 500 m apart with paired arrays placed 100 m into the habitat. Non-native ground dwelling arthropods were found at all trapping locations along the trails suggesting that these species are able to further their ranges into native habitat along trails. Non-native arthropods were also found at all paired off trail trapping locations perpendicular to the trails, indicating that the trail itself is acting as the new habitat edge. Adult Diptera showed significant community dissimilarity among trapping locations. Ground dwelling arthropods only showed dissimilarity among the communities if the eight identified non-natives were removed from analysis. These results suggest that non-native species found throughout the testing locations have caused biotic homogenization among the ground dwelling population that has not yet impacted the aerial adult Diptera.
