I characterized pollination success in a population of the invading species Hypericum canariense (Canary Island St. Johnswort) located in San Mateo County, CA.  I conducted timed pollinator observations together with field emasculation experiments to assess the source of pollen deposition on H. canariense flowers.  I quantified fruit production, seed weight and seed number per fruit across the invasion in order to evaluate seed production in increasingly younger cohorts of invaders.  I used GIS to show the placement of study individuals within the greater invasion, and to determine the distance of each individual from the initial introduction (invasion core).  Finally, I compared the heights of stigmas, anthers, and ovaries in greenhouse-reared core and edge flowers to check for any increases in the probability of self pollination among the youngest invaders at the invasion edge.  I found that unmanipulated flowers receive large amounts of self-pollen.  I also found that edge plants are producing significantly higher numbers of fruit than core plants but that seed weight and number per fruit are constant across the invasion.  Physical proximity of the anthers and stigmas did not differ between core and edge plants.  My findings are consistent with the idea that invading plants on the edge of an invasion may produce a higher amount of viable self fruit than plants closer to an invasion core due to evolutionary pressures that favor an increase in selfing rates with invasion expansion.

Courtney Angelo: Restoration of Danthonia californica, Elymus glaucus, and Nassella pulchra at Elkhorn Slough National Estuarine Research Reserve
PDF of Thesis
2005

California grasslands are one of the most invaded, endangered, and altered ecosystems in the world. Seven of the 10 million hectares of California’s grasslands are now dominated by exotic annual grasses of Mediterranean origin, replacing the native perennial bunchgrasses. Of all California grasslands, coastal grasslands remain the most intact floral assemblages, in which native species dominate in remnant patches. Thus, coastal grasslands have high potential for restoration and conservation purposes. We designed an experiment to evaluate at which life stages native perennial bunchgrasses need the most assistance for survival when competing with exotic annual grass species. In addition, our experiment evaluated which native perennial bunchgrass species and treatment are the most appropriate for restoration efforts. We used three plots, three native perennial bunchgrass species (Danthonia californica, Elymus glaucus, and Nassella pulchra), and three treatment types (weeding, mulching, and initial clearing). The three bunchgrass species responded differently, with D. californica growing the largest in terms of basal area and E. glaucus growing the tallest. Species also differed in survival and reproduction, with E. glaucus having the highest percent survival and D. californica reproducing the least. Species responded differently to the three treatments; however; weeding led to better establishment for all three bunchgrass species.

Emme Bruns: Maternal investment in and fitness of chasmogamous and cleistogamous progeny of the native perennial grass Danthonia californica
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2005

Theory predicts that mixed mating systems should be rare in plants, and yet it is documented in many species. Cleistogamy (permanently closed flowers) can be more cost-effective than chasmogamy (open-pollinated flowers) because reproductive structures are often smaller and less pollen needs to be produced. The maintenance of chasmogamous flowers is hypothesized to be due to higher fitness of the offspring, which could offset the increased effort put into their production. In addition, differences in fitness between chasmogamous and cleistogamous progeny may select for differential maternal investment in individual chasmogamous and cleistogamous seeds. Cleistogamy may also be maintained as a way to insure reproduction if percent seed set in chasmogamous seeds is low. We measured differences in reproductive effort and fitness between cleistogamous and chasmogamous flowers in the native bunchgrass, Danthonia californica. Seeds from both chasmogamous and cleistogamous flowers were counted, weighed, and planted in the greenhouse to measure germination and growth rates. D. californica individuals produced significantly more cleistogamous seeds than chasmogamous seeds, however there was greater maternal investment per seed for chasmogamous progeny. Overall, a significantly larger proportion of the total maternal reproductive effort was put into cleistogamous seed production. Plant size did not have a significant effect on the proportion of total effort invested in cleistogamous seeds. Chasmogamous spikelets had significantly lower percent seed set than cleistogamous spikelets in the upper nodes of the flowering culm, possibly indicating pollen limitation in the chasmogamous flowers. Chasmogamous progeny had significantly higher germination rates and germinated earlier than cleistogamous progeny. They also had a higher rate of new leaf growth and higher biomass, indicating that chasmogamous progeny may have some fitness advantages that could help offset the greater effort required for their production, and may help explain the maintenance of a mixed mating system in D. californica.

Mary Goldman: Timing of gamete release in an intertidal alga, Silvetia compressa.
PDF of Thesis
2005

Natural selection on a fine scale causes local adaptation while gene flow homogenizes genotypes across microhabitats through dispersal. I investigated the interaction between dispersal and local adaptation across the intertidal cline from shore to sea for the brown algae, Silvetia compressa. Previous research at Scott’s Creek, CA, has shown that individuals of S. compressa within this population are locally adapted to tidal height. Since only a few meters separate the upper and lower edge of the species distribution, why doesn’t gene flow counteract natural selection? I quantified and timed the release of gametes of randomly selected individuals at the extremes of the distribution (i.e. the upper and lower tidal limit). Sampling occurred from November 2004 to April 2005 on days when the entire distribution was exposed. Both eggs and sperm are released simultaneously as an alga is uncovered by water; thus as the tide declines, the individuals at the upper edge release gametes before lower edge individuals. Although the precise timing of gamete release varied between individuals within a given tidal height and across different sampling days, the overall pattern showed earlier release of gametes by upper edge individuals when compared to lower edge individuals. Timing of gamete release differed significantly between the upper and lower edge of the distribution, limiting dispersal across the gradient and promoting local adaptation.

Kristofer Orre: The Effects of Grazing on Native and Exotic Seed Banks at Elkhorn Slough National Estuarine Research Reserve
PDF of Thesis
2005

Grazing has been suggested as a technique to maintain or even promote native success in California’s heavily invaded grasslands. Varying responses of different plant species to this approach may translate into differences in seed bank species composition. These seed banks provide a long-term signature of historical grazing, and stimulation of this soil seed bank has been suggested as a restoration technique when native seeds are present. In May and September of 2004, soil samples were collected to determine if a native seed bank still persists in the heavily invaded grassland of Elkhorn Slough National Estuarine Research Reserve. In addition, I determined if the seed bank differed between historically different grazed areas. I hypothesized that species shown to respond positively to grazing would have higher abundance in regions of historically higher grazing intensity, and species known to respond positively to the absence of grazing would have higher abundance in regions of historically lower grazing intensity. The seed banks of both grazed regions were dominated by non-natives and showed no significant difference in individual abundances, except for one species (Lolium multiflorum). However, there were differences between the two collection dates for total species richness, species diversity, graminoid (grass, sedges, and rushes) richness, evenness, and four of eight species abundances analyzed. All were found to be significantly higher in September. This study emphasizes the importance of species level analysis, and consideration of sampling time when analyzing soil seed banks.

Jodi Stewart: HPLC of the invasive species Hypericum canariense to assess rapid evolutionary changes in defensive chemistry.
PDF of Thesis
2005

The 'Evolution of Increased Competitive Ability' (EICA) hypothesis in invasion biology proposes that introduced plants may become invasive because they no longer have to invest in costly anti-herbivore compounds. The EICA hypothesis is part of a larger hypothesis known as the 'Enemy Release Hypothesis' (ERH) or 'Natural Enemies Hypothesis' (NEH). The ERH predicts that invasive species will be released from their natural enemies in their introduced range and experience a competitive advantage. In the case where a plant species leaves behind herbivores and pathogens for which the plant has evolved defensive mechanisms, the selective pressure maintaining the defense may weaken and the resources allocated elsewhere. The reallocation results in increased competitive ability. This study investigated the predications of the EICA hypothesis using HPLC analysis of the plant species Hypericum canariense. The relative concentration of the compound hypericin, induced by the herbivore Spodoptera exigua (beet armyworm), followed the prediction of the EICA hypothesis. This pattern was not found for quercitrin, the other target compound investigated.

Islands often have high levels of endemic species that are easily threatened by introduced plants and animals. Over 20 percent of the native plant species on Guadalupe Island, Mexico are endemic, though non-native goats have led to the disappearance of some. Eradication of goats on the island has been proposed, but the ability of native vegetation to recover in the absence of the introduced herbivore is unknown. This study looked at the composition of the seed bank and the effect of fire on seedling germination in three habitats of the island: the cypress forest, the spring and the pine forest. Soil samples from the three habitats were burned with either organic material from the habitat or newsprint in the case of the spring, where organic material was not available. These burned soil samples were placed in random order with unburned, control flats of soil. Seedlings were monitored and identified over a period of two months. Informal surveys were conducted
in the field in the cypress, spring and pine habitats to determine the above ground composition of plants. More species diversity exists above ground in the habitats than was found in the flats, indicating that some species have low densities of seed in the soil. Therefore, reseeding efforts would increase the rate of recovery of the vegetation on of the island. Furthermore, some species, including the exotic Mesembryanthemum nodiflorum, were found in the seed bank but not in the field. M. nodiflorum growth should be monitored in the three habitats for a potential population explosion after the removal of goats. Fire was found to affect some morphospecies, but overall has neither a strongly positive nor strongly negative effect on the vegetation of the island, suggesting that use of fire as a tool in management should only be undertaken for specific goals. Overall this study shows the importance of pre-eradication investigation for developing a management plan.

(no abstract - see full thesis)

Haivan Ngo: Pathogenicity and host range of soilborne fungi associated with Ammophila arenaria
PDF of Thesis
2003

Ammophila arenaria (European beachgrass) is currently invading coastal dune systems in California.  A previous study found that the invasive success of A. arenaria is not explained by a release from pathogenic fungi, instead soilborne fungi increased seedling mortality and reduced plant biomass.  This study investigated whether four fungal species, Fusarium culmorum, F. oxysporum, Phytophthora sp., and an unidentified species in the Pleosporales that were isolated from the previous study were responsible for the disease symptoms.  Two inoculation experiments of these fungi on seedlings of A. arenaria led to reduce biomass in comparison to controls.  Moreover, the inoculated treatment showed a trend for shorter culm height and greater number of dead leaves.  These results suggest that the four fungi tested contribute to the measured reduction in A. arenaria growth, providing further evidence that its invasive success is not attributed to a release from pathogenic fungi.  A survey of fungal incidence in the co-occurring host species showed that the host range of these fungi spans beyond A. arenaria.  Host range of the four soilborne fungi associated with A. arenaria was explored via inoculation experiments on three plant species: Cakile maritima, Camissonia cheiranthifolia, and Chorizanthe pungens var. pungens.  Fungal inoculation experiments on co-occurring species resulted in reduced biomass in comparison to controls, indicating that these species have a wide host range and therefore can be considered as generalist pathogens on the plant communities at Sunset State Park.  Furthermore, the results from this study suggest that although invasive species may escape specialist enemies from home range, it may not escape generalist enemies that have a broad range.  Secondly, escaping specialist and generalist enemies does not mean that the species cannot acquire new generalist enemies in home range.

Alex Fields: Compost Use in Tropical Agroecosystems
PDF of Thesis
2002

Our study was initiated with the goal of determining nontraditional methods of biomass use that could provide a sustainable approach to increasing crop yield in tropical agroecosystems. The results of our study indicate that the use of composted mulch and compost extracts can provide positive benefits when added to vegetable cropping systems, especially when used in combination with inorganic fertilizers. The targeted use of small amounts of inorganic fertilizers (especially P) combined with organic matter applications may be an important step towards introducing tropical farmers to organic matter technology. In order to increase the chances of incorporating these methods of organic matter preparation into current management practices, future studies should also focus upon increasing farmer participation in the research process. Increased contact between farmer’s and researchers will provide valuable information about which types of organic materials are readily available on local farms and will help determine the general attitude towards the use of compost and compost extracts.

Emily Smith Putnam: Effects of Restoration of Costal Dune Through Removal of the Invader Ammophila arenaria on the Whole Community and Rare and Endangered Species, Chorizanthe pungens var. pungen
PDF of Poster
2002

This study examines the potential impacts of invasive species, such as Ammophila arenaria, on whole ecosystems as well as rare and endangered species, such as Chorizanthe pungens var. pungens. A survey was undertaken to compare costal dune communities that had been invaded, restored after invasion, and those that had never been invaded. Seven transects were placed across the four community types (i.e. Natural, Long Restored, Recently Restored, and Ammophila) and two by two meter quadrants were used to estimate percent cover of each species in each of the four different habitats. A DCA analysis was used to compare whole communities and showed an overall community difference among the sites, particularly between Ammophila and Natural sites. The ANOVA analysis showed community type differences in percent native cover (F3,24=14.6492, p<.0001), species richness (F3, 24=14.8329, p<.001), bare ground (F3,24=16.76, p<.0001), and C. pungens var. pungens coverage (F3,24=8.3349, p<.0006). The Natural and Long Restored sites had significantly more percent native cover and species richness, and less bare ground than the Recently Restored sites. The Ammophila sites had significantly less of percent native species, bare ground, and C. pungens var. pungens than all other sites. Overall, the Long Restored areas were very similar to the Natural site, but the restoration sites have not yet been completely restored to the natural conditions. These results indicate that removal of A. arenaria from invaded dunes at Sunset State Beach has been very successful in restoring natural community characteristics and the rare plant C. pungens var. pungens. However, restoration may not be entirely completed, so other restoration methods, including transplantation of seeds from the Natural area to the Restored areas of species that are lacking in the Restored areas and removal of the nonnative Catile maritima, should be explored.

Erin Avery: Nutrient Input Effects From Fire Retardant on Exotic Species, Species Richness, and Species Diversity in a Coastal California Grassland.
PDF of Thesis
2001

California grasslands have undergone an extensive transformation in floristic composition over the past 250 years. Introduced species have spread widely, largely replacing native annuals and perennials. Nutrient inputs, such as fertilizers and atmospheric deposition, have been found to facilitate invasion of grasslands by introduced species, as well as cause declines in species richness and species diversity. It has been hypothesized that an ammonium-phosphate-based fire retardant, Phos-Chek, commonly used to combat wildfires in backcountry areas, may be a substantial source of nutrient inputs when applied to grasslands. This hypothesis is based on the fire retardant’s composition as well as field observations following an application to a coastal California grassland. Exotic thistle species were found to respond vigorously and species richness and diversity appeared to decline. Based on the assumption that the Phos-Chek fire retardant acts as a nutrient input, the purpose of this study was to determine how the fire retardant impacts exotic species (specifically exotic thistle and exotic annual grasses), species richness, and species diversity in a coastal grassland in central California. While phosphate levels were not analyzed, this study found that the fire retardant significantly increased ammonium and nitrate levels in the soil, therefore providing essential nutrients for plants. The nutrient inputs resulted in increased growth of exotic annual grasses, but had no effect on exotic thistles. The increased exotic grass growth led to declines in short statured forbs, as well as declines in species richness and species diversity.

Alexandra (Sandi) Engel: Pollinator visitation of French and Scotch Brooms
2000

Published in: Parker, I. M., A. Engel, K. A. Haubensak, and K. Goodell. 2002. Pollination of Cytisus scoparius and Gensita monspessulana, two invasive shrubs in California. Madrono 49:25-32.

Mutualistic interactions between natives and non-natives, and between different introduced species, can play an important role in the invasion process. The facilitation of a new introduced species by a previous invader could either accelerate an invasion or exacerbate its impact, providing a positive feedback loop in heavily invaded ecosystems. Open grasslands in Marin County, California, are being invaded by two closely related,
introduced legumes, Cytisus scoparius (Scotch broom) and Genista monspessulana (French broom). These non-clonal shrubs have been shown to be non-autogamous and pollen limited, underscoring the potential importance of pollinators to their fecundity and spread. The flowers of both are fused
shut and require forced "tripping" by a pollinator. We measured floral characters to make predictions about which species would be most attractive, and most accessible, to bee visitors. Cytisus flowers were an order of magnitude larger, suggesting that they should be more attractive and rewarding than Genista flowers. However, Cytisus flowers also required significantly more force to open, suggesting that less powerful pollinator species might be excluded from visiting. We then tested these predictions by quantifying visitation rates and directly observing pollinators at two sites where the invaders co-occur. Consistent with the mechanical assay, pollinators were more successful at accessing flowers of the small-flowered
Genista than the large-flowered Cytisus ; however, Cytisus was more frequently visited than Genista, suggesting that pollinators preferred the larger and more rewarding species.

Katy Hayden: Plasticity in cyanogenesis of Trifolium repens L: Inducibility, fitness costs and variable expression.

PDF of Thesis
2000
Published in: Hayden KJ, Parker IM. 2002. Plasticity in cyanogenesis of Trifolium repens L.: inducibility, fitness costs and variable expression. EVOLUTIONARY ECOLOGY RESEARCH 4 (2): 155-168.

The polymorphism for cyanogenesisthe production of cyanide by damaged tissue in white clover (Trifolium repens L.) has long been a model system for studying the maintenance of genetic variability. The prevailing model holds that opposing selective forces maintain the polymorphism; cyanogenesis protects the clover from herbivory, but incurs a cost of defense at lower temperatures and under drought. To date, most studies of cyanogenesis have focused on presence/absence of the trait, although there is evidence of variability in expression within individuals. It is known that inducibility in some plant defense systems alleviates costs by initiating or increasing expression of a costly defense only when it is most needed. It follows, then, that defenses might also be downregulated when they are likely to be most costly. We used a modified Feigl-Anger assay to quantify the degree of cyanogenesis (both cyanoglucoside and__-glucosidase enzyme) in clones of T. repens, under different environmental conditions historically associated with the costs and benefits of the polymorphism. Neither simulated herbivory nor herbivory by the snail Helix aspersa resulted in a significant increase in expression of cyanogenesis (cyanoglucoside or enzyme). Therefore, we conclude that cyanogenesis is not an inducible defense. However, drought stress led to an apparent decrease in activity of _-glucosidase in samples with amplified linamarin concentrations. Further, genotypes showed significantly weaker expression when grown in cold than when grown in warm temperatures. These results suggest that some conditions that favor acyanogenic plants may also result in a decreased expression in cyanogenic morphsa plasticity that changes our understanding of the selective forces at work in this system.

Joseph M. Rodriguez: The colonization by Verbascum thapsus of an altitudinal ecocline in the Sierra Nevada: an experimental test of local adaptation through increased frost tolerance.
PDF of Thesis
2000
Published in: Parker IM, Rodriguez J, Loik ME. 2003. An evolutionary approach to understanding the biology of invasions: Local adaptation and general-purpose genotypes in the weed Verbascum thapsus. CONSERVATION BIOLOGY 17 (1): 59-72.

Invasive species are the second leading cause to the depletion of biodiversity in the United States. Attempts to create predictive models to identify potential invaders or habitats that may be susceptible to invasion have been thwarted when they are generally applied. Instead, concentration on particularly successful invading species in specific environments may alleviate the inadequacy of our current understanding of biological invasions. An important but understudied area in invasion ecology is testing the possibility of genetic adaptation occurring within the introduced species that enhance their colonization of a new range. This research aims to comprehend the mechanisms responsible for the altitudinal expansion of the noxious weed Verbascum thapsus in Yosemite National Park. I identified 10 populations of V. thapsus in and outside of the park. These populations occurred along an altitudinal ecocline that ranges from 25 meters of elevation on Santa Cruz Island, off the California coast, to 2466 meters on the eastern slope of the Sierra Nevada. The progeny of 10 plants from each population were grown in two controlled chambers kept at day/night temperatures of 15/5 and 25/15æC. High-altitude individuals are expected to demonstrate faster growth rates in cold conditions than are the low-altitude representatives. In addition, I am using fluorimetry to test the prediction that high-altitude plants express greater cold tolerance (resistance to cell damage). If the results correspond to my predictions, this research will represent one of the first demonstrations of adaptation in an invasive species and will provide National Park resource managers with a more comprehensive understanding of this problematic weed.