Bodega Marine Laboratory/Reserve
February 22-24, 2008 |
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Participant Abstracts
Do resource impacts predict invasion success in a coastal sage scrub community?
Leah J. Goldstein
Department of Ecology and Evolutionary Biology
University of California, Irvine
The successful invasion of exotic species in native communities has led to the generalization that exotic invasives are often better resource competitors than native species. Few studies have directly tested R* competition theory in the context of invasions by exotic plants, but R* (measured as resource availability in monoculture) indicates resource impacts and requirements, and so can lead to useful predictions about
invasion success. We hypothesized that 1) successful invaders will have a lower R* than native species, and 2) natives with a lower R* than exotic species should be able to resist invasion. We estimated R* for light, nitrogen, and water in monocultures of native coastal sage scrub shrub (CSS) species and in
monocultures of two exotic herbaceous species that are problematic invaders in CSS. Additionally, we measured invasion success by experimental invasion of exotics and native shrub seedlings into native and exotic monocultures. Exotic monocultures did not reduce resources below levels found in native
monocultures: native monocultures had lower light, lower soil moisture, and lower nitrogen availability. Experimental invasions supported the prediction that lower R* should provide invasion resistance, as exotic invaders had lower biomass in native shrub monocultures than exotic monocultures. In contrast to
predictions, however, native seedlings had lower biomass in exotic monocultures than native
monocultures. Rather than being strong competitors, exotics may rely on traits providing an advantage during transient conditions when resource availability is high. Comparisons of exotic R* with temporal
resource variability in native communities may help pinpoint windows of opportunity for invasives.
The Effect of Native Forb Abundance on Invasion Resistance in California Grasslands
Kris Hulvey
Department of Environmental Studies
University of California, Santa Cruz
Yellow starthistle negatively impacts California grasslands through losses of forage quality, native species, and landscape aesthetics. We conducted two experiments, one in pots at Stanford’s Jasper Ridge
Biological Preserve, and a second in the grasslands of McLaughlin Reserve, focused on the competitive interactions between starthistle, Centaurea solstitialis, and the native tarweed, Hemizonia congesta. We investigated whether tarweed abundance declines affect grassland vulnerability to starthistle invasion. This is important because changes in species abundance are more common than extinctions, and ecosystem functions such as invasion resistance may be mediated by such changes. In the first experiment, we
created grassland microcosms with varying tarweed abundance levels. We invaded half the microcosms with starthistle and gauged invasion resistance by measuring final starthistle biomass and flower number. To investigate possible mechanisms driving the relationship between tarweed abundance and invasion, we measured soil moisture, nutrient availability, and available light. In the second experiment, we invaded grassland plots containing a natural range of tarweed abundance levels with starthistle. We gauged
invasion resistance by measuring final starthistle abundance, biomass, and flower number, and
investigated mechanism by measuring soil moisture and available light. In pots, we found tarweed
affected invasion resistance, with increasing tarweed abundance resulting in less starthistle biomass and flower production. Soil moisture was the only measured factor that explained this relationship; pots with greater tarweed abundances used more water. In the field, it was uncertain if tarweed abundance affected invasion because few starthistle plants survived in any plot, possibly due to this year’s drought conditions.
Spatial and Temporal Variability in Survivorship affects Long Term Persistence of
a Subterranean Microparasite
Karthik Ram
Section of Evolution and Ecology
University of California, Davis
The long-term persistence and stability of host-pathogen interactions are often strongly affected by spatial distribution of the interacting populations. This is particularly true in seasonal systems where conditions for pathogen survival and host availability vary over time. My study occurs in the context of a trophic cascade which involves a microparasitic entomopathogenic nematode (Heterohabditis marelatus, hereafter EPNs) as the natural enemy of a root-feeding ghost moth caterpillar (Hepialus californicus) found on lupine
bushes (Lupinus arboreus). In the absence of EPNs, root-feeding caterpillars can kill and destroy large stands of lupines, especially in dry years. EPNs, when present, suppress such ghost moth outbreaks
thereby protecting the lupines. EPNs depend strongly on moisture for movement and persistence. Given the seasonal nature of the environment where moisture regimes and host availability vary dramatically, it is
unclear how EPNs persist. Our 13-year dataset shows considerable variation in EPN incidence among sites. I tested whether these differences were because of variation in survivorship. Using a known initial EPN number, I estimated the daily mortality rates for each of our sites. A negative binomial model fit the data well (Pearson’s X2/df = 0.898). I used these mortality rates in a fully stochastic model for
host-pathogen interactions in seasonal environments to calculate EPN extinction probabilities for a single season. Results from the survivorship experiment did not explain the full range of incidence patterns. Given the nature of these results, I hypothesize that dispersal is an important mechanism in explaining the
discrepancy between model predictions and field observations.
Conservation of terrestrial habitat for California tiger salamanders (Ambystoma californiense)
Christopher A. Searcy
Section of Evolution and Ecology
University of California, Davis
Across its range, the California tiger salamander is listed as either endangered or threatened under the U.S. Endangered Species Act. As a result, there is much concern about protecting appropriate habitat for this species. This is challenging, because California tiger salamanders spend over 95% of their adult lives in mammal burrows, making it very difficult to determine which portions of the landscape they are
utilizing. This study sought to determine the distribution of California tiger salamanders across the
terrestrial landscape using an array of 164 drift fences at the Jepson Prairie Reserve. A total of 10,042
salamanders were caught over the course of two years using this drift fence array. In addition, data on a number of habitat parameters, such as distance from shoreline of the pond, elevation, mammal activity, and vegetation were collected from each fence. Model selection was used to search for correlations
between the density of salamander captures and these habitat parameters, revealing that salamander density is influenced by both distance from the shoreline of a breeding pond and elevation above the pond surface. This indicates that higher conservation priorities and mitigation values should be assigned to land that is closer to breeding ponds and at a higher elevation. In addition, it was shown that California tiger salamander densities vary both between years and between ponds. It is thus important to understand both spatial and temporal heterogeneity before making conservation decisions for this species.
Evolution of Anti-predator Defenses in Larvae of a Native Frog in Response to an Invasive Predator
Katherine M. Pease
Department of Ecology and Evolutionary Biology
University of California, Los Angeles
Invasive species are widely recognized as a serious ecological threat; the evolutionary impacts of
invasions may be equally as threatening, yet remain relatively unstudied. Invasive species can act as a strong selection pressure, causing evolution in native species through predation, competition, or
parasitism. The proposed project will determine whether Pacific treefrog (Pseudacris regilla) tadpoles are adapting to the invasive predator, the red swamp crayfish (Procambarus clarkii) in the Santa Monica
Mountains of southern California. I will examine differences in the anti-predator adaptations (morphological and behavioral) between tadpoles from streams with crayfish and tadpoles from streams without crayfish. Preliminary results show that tadpoles from streams with crayfish are significantly different in morphology than tadpoles from streams without crayfish. I will determine if the predator is acting as an agent of natural selection by performing predation experiments and comparing survival rates of prey that coexist with the predator to prey that are naïve to the predator. In order to determine whether the anti-predator traits are inducible and/or heritable, I will conduct a common garden experiment, rearing tadpoles in the lab from field-collected eggs in the presence and absence of predator cues. Finally, I will determine the population genetic structure of P. regilla to determine levels of gene flow and whether there are natural or human
barriers to gene flow. The proposed study will show whether a native species is able to adapt to a novel
invasive predator and has broader implications for understanding and predicting interactions between
native and invasive species.
Evolutionary genetics of self-incompatibility in three California species (Papaveraceae)
Timothy Paape
Department of Ecology, Behavior and Evolution
University of California, San Diego
I am examining the evolutionary genetics of the gametophytic self-incompatibility (GSI) locus of the
Papaveraceae plant family. The S-locus in this family has previously been characterized at the molecular level in two species, Papaver rhoeas and P. nudicaule. The limited sequence data from these species has enabled the amplification of 65 sequences that represent potential alleles from a homologous S-locus from Argemone munita, Romneya coulteri, and Platystemon californicus, all of which are California natives. The S-locus of this family represents a non-homologous system of self-recognition from other plant families possessing GSI including the Rosaceae, Solanaceae, and Scrophulariaceae. I am currently conducting greenhouse and natural population studies in the three California species that will determine allelic
function, number of alleles, levels of sequence divergence, and sites of positive selection within each sampled species. Previous studies of S-loci have revealed extensive trans-specific evolution in which the age of the alleles often pre-dates the speciation event that separated various taxa. Preliminary
genealogical analyses have showed that the potential S-alleles from the California species exhibit an
overall lower range of diversity than the four published Papaver alleles. Greenhouse crosses have also revealed that some individuals possess linked polymorphism that may or may not also be involved in SI.
I am designing in vitro assays to test the function of suspected alleles and potential duplicates.
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