Bodega Marine Laboratory/Reserve
February 26-28, 2010 |
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Participant Abstracts
Below-ground interactions between annual seeds and fungal pathogens
Erin Mordecai
Department of Ecology, Evolution, and Marine Biology
University of California, Santa Barbara
Seed banks are important for many annual plant species in California grasslands; however, the factors that impact seed survival in the soil are poorly understood. In particular, below-ground pathogens can mediate plant species interactions by reducing seed survival. Pathogens may have different impacts on grasses and forbs and on native and exotic species. Exotic grasses may promote pathogen growth by depositing thick thatch layers that harbor microbes and keep the soil relatively warm and moist. I examined the influence of season, thatch, and fungal pathogens on seed survival by placing the seeds of two exotic grasses, one native grass, and four native forbs in mesh seed bags in the summer of 2008 and the winter and spring of 2009. Seed bags were buried on serpentine hummocks in grasslands in Sedgwick Reserve, and treated with factorial combinations of thatch removal and fungicide addition. Overall, seed survival was much lower during the winter and spring than in the summer, as measured by seed germination in the lab. In the winter, seed survival improved with fungicide application. There was a strong season by fungicide interaction, as fungicide application had no effect in the summer. Thatch treatments also had no effect on seed survival. The effects of season and fungicide on survival varied somewhat across species, with five out of six species following the same general pattern. Seed mortality is therefore significantly higher in the winter than in summer, and winter mortality is partially ameliorated by fungicide. This supports the hypothesis that seeds that do not germinate with the first winter rains face fungal attack and low survival. Since forbs are much more likely than grasses to bank seeds between seasons, this overwinter mortality probably indirectly benefits exotic grasses over their native forb competitors.
Karen A. Stahlheber
Department of Ecology, Evolution, and Marine Biology
University of California, Santa Barbara
Invasive exotic species present significant threats to native plant abundance and diversity, and their success frequently relates to the availability of resources. Savanna trees in many locations increase nutrients and moderate the microclimate under their canopies, creating fertile islands. Oak trees are a common, highly valued part of many California grasslands, yet observations indicate the relative dominance of exotics and natives changes in their vicinity. To study this distribution, I surveyed vegetation composition, soil characteristics, and productivity around 11 Quercus agrifolia, 10 Q. lobata, and 6 Q. lobata snags at the Sedgwick Reserve in Los Olivos, CA. At each tree I ran transects oriented to the cardinal directions from the trunk into open grassland. Richness and diversity of both native and exotic plants declined beneath the canopy; however, total cover of exotics increased. Many exotic species attained their greatest cover underneath and at the edge of the canopy, creating a composition distinct from the nearby grassland. Dramatic differences in the soil conditions beneath the trees, especially moisture and organic carbon, correlate to these differences. Next to the trunks of dead oak trees, species diversity remained significantly lower than neighboring open grassland, indicating residual effects of past trees. Additionally, Q. agrifolia oak trees were associated with higher diversity immediately outside their canopies compared to the deciduous Q. lobata. Both deciduous and evergreen oak canopy environments favor exotic grasses and forbs at the
expense of native plants, an effect which may continue following the death of the tree.
Blair McLaughlin
Department of Environmental Studies
University of California, Santa Cruz
Questions on the importance of top-down vs. bottom-up effects have long occupied ecologists. Recent work has begun to delve into how these factors may shift in strength across both time and space,
challenging the traditional paradigm of classification and presenting new questions on the appropriate scale of study. We looked at bottom-up forces (competition for resources) and top-down forces
(herbivory) on Quercus lobata at the sapling stage, where a bottleneck to reproduction occurs. We found that the relative importance of these factors shifts across a precipitation gradient with top-down forces more important at the wetter end of the gradient and bottom-up forces more important at the dryer end of the gradient. Ours is the first study to look at the extent of variation in top-down vs. bottom-up factors in plant populations across a spatial precipitation gradient. Our field study looks at sapling recruitment
dynamics at 15 separate sites across the Q. lobata distribution, including oak savanna and woodland
community types spanning a precipitation range of 18-35 inches average annual rainfall. We present our field data in the context of a meta-analysis of planting experiments on Q. lobata seedling performance and dendro-chronological analysis of a subset of our samples. We argue that the strength of top-down vs. bottom-up limitation on sapling recruitment shifts across space depending on rainfall. Additionally, we include data on resurveyed sites to look at trends in recruitment over time. A better understanding of the importance of weather in shifting limitation in keystone species is integral to conservation ecology in
natural populations that span large spatial gradients, particularly in the context of a changing climate.
Morgan W. Kelly
Population Biology Graduate Group
University of California, Davis
The rapid pace of anthropogenic climate change represents an unprecedented threat to the planet’s biological diversity. Models predicting species’ responses to climate change have focused on range shifts rather than adaptation. However, there is a growing appreciation that most species will exhibit some combination of adaptation and range shifts. The ability to adapt to a changing climate will depend on the magnitude of genetic variation for environmental tolerance and also on how this variation is distributed among populations within a species. We are using the intertidal copepod Tigriopus californicus to examine the potential for an evolutionary response to climate change and to test hypotheses about patterns of quantitative genetic variation in edge vs. center populations. Our results indicate that T. californicus is locally adapted to thermal conditions, with the greatest thermal tolerance in populations from southern California. Our data also show a narrow range of variation in thermal tolerance within populations as compared to the species as a whole. We are now using selection experiments to measure heritable variation in thermal tolerance within populations. After five generations, all selected lines had greater thermal tolerance than unselected controls; however, lines from southern populations showed a smaller response, suggesting decreased
heritability of thermal tolerance in these populations. Our results suggest that in species with strong
local adaptation, range-wide occurrence data may fail to predict population-level variation in environmental tolerance. Our data also suggest that populations from equator-ward populations may have a diminished capacity to adapt to climate change.
Amy Concilio
Department of Environmental Studies
University of California, Santa Cruz
Bromus tectorum is an exotic annual grass that was introduced into the U.S. from Eurasia in the late 1800s. It has since spread through much of the Great Basin Desert, displacing native shrub and
bunchgrass communities and altering fire regimes. At high elevation, B. tectorum is only present in small populations. However, agents of global change may facilitate its spread. My dissertation research will explore how altered precipitation patterns, increased temperature, and increased Nitrogen (N) deposition might affect B. tectorum spread in the eastern Sierra Nevada, CA. In 2008, study plots were set up in three dominant microhabitats and exposed to varying levels of simulated spring rain coupled with ambient and increased N-deposition. B. tectorum generally responded with increased growth and fecundity when given supplemental water, and the combined effect of supplemental water and N additions increased B.
tectorum growth over ambient conditions in Artemisia tridentata microhabitats. No differences in native plant species composition were apparent after one year of treatments. However, these preliminary results suggest that B. tectorum may become more widespread at high elevations with a shift from winter snow to spring rain and that increased N-deposition may further exacerbate the problem. This year, I will measure B. tectorum response to changing snowpack, increased rain-on-snow events, and increased spring rain at varying elevations. Collectively, data from the two years of study will help identify times and places across the landscape that may be most prone to cheatgrass invasion under future climatic and edaphic
conditions.
Nicole Molinari
Department of Ecology, Evolution, and Marine Biology
University of California, Santa Barbara
Global change is projected to be the main driver of ecosystem change and biodiversity loss over the next century. Ecosystem change may be mediated through the promotion of non-native species by particular global change scenarios. Many of California’s grasslands have already been affected by the presence of non-native plant species and global environmental changes could exacerbate these impacts. California’s grasslands are largely thought to be water and nitrogen limited. Alterations in precipitation and nitrogen cycling are therefore likely to influence the restoration potential of non-native dominated sites as well as the persistence of native plant communities. My research seeks to understand how rainfall reduction and
repackaging (fewer, more intense events), along with nitrogen deposition will alter invasibility and diversity in remnant native grasslands compared to adjacent non-native dominated grasslands at Sedgwick
Reserve. I am adding seeds of the dominant non-native grass, Bromus diandrus, to native sites and seeds of the native bunchgrass, Nassella pulchra, to non-native sites while altering rainfall amount and
distribution, along with increasing nitrogen deposition. Data collected thus far suggests that the non-native annual grass, B. diandrus, will be favored under both increased nitrogen deposition and decreased
rainfall. By contrast, repackaged rainfall patterns appear to decrease the success of this non-native
species. Alternatively, few N. pulchra individuals established in non-native dominated sites regardless of treatment. Currently, N. pulchra seedlings are being planted into each treatment to assess the effects of global change on the success of this native bunchgrass once already germinated.
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