2015 Symposium Poster Presentation Abstracts
REMOVING SHRUB COMPETITION IN POST-FIRE REFORESTATION AREAS
Graduate Group in Ecology
Large, high severity fires are becoming increasingly more becoming increasingly more prevalent throughout the Sierra Nevada mixed conifer forests because of heavy fuel loads and forest densification due to past and current management practices. These large areas of severely burned forests require active reforestation in order to prevent a potential type-conversion to shrub fields. Typical reforestation efforts utilize a variety of tools (e.g. mechanical, chemical) to reduce shrub competition and promote conifer survival and growth. For years managers have carried out reforestation efforts without fully understanding how understory species richness and composition are altered by these practices. The objectives of this study were to (1) determine whether a difference in understory species richness exists between actively reforested areas and areas left to regenerate naturally after high severity fire in mixed-conifer forests; (2) assess whether differences in exotic species richness exist; and (3) identify the key environmental gradients driving understory species richness. Plots were installed throughout three different aged fires located in the South Fork of the American River canyon. All three experienced large, stand-replacing fire and had areas that were actively reforested and areas that were left alone to regenerate on their own. Preliminary results suggest that native understory plant species richness is significantly higher in reforested areas where removal of shrub competition took place. Non-native species show an initial increase in richness but this increase appears to lose its significance as time since disturbance increases. It appears that soil moisture and overstory shrub cover are the key driving factors in understory species richness levels but further analyses need to be carried out in order to confirm this.
ECOLOGICAL EFFECTS OF HEAVY METAL LEACHING IN THE BAHAMIAN LOBSTER FISHERY
Graduate Group in Ecology
Lobster condos are rapidly becoming the predominant fishing method for Bahamian lobster. Condos are comprised of corrugated sheet metal nailed to 2x6s, open on one or both ends and weighed down by cement blocks. Condos create artificial habitats for lobster and encourage congregations of a large number of individuals for the lobster fishery. Despite the predominance of condo use in The Bahamas, little work has been done looking at ecological impacts of condo habitats. Of primary importance is the possibility that the materials comprising the condos – chemically-treated wood and paint applied to sheet metal – leach hazardous chemicals into the marine system over time. Bioaccumulation of metals in tissues has served as a proxy for metal inputs into disturbed systems in previous marine studies. In order to provide a baseline for metal contamination, we conducted heavy metal isotopic analysis of wood from condos, primary production (seagrass & macro algae ), and lobster tissue to determine if concentrations of leached heavy metals are found in higher concentrations by condos. Metal leaching into nearby systems highlights that condos may be having direct (higher harvest) and indirect (metal toxicity) effects on lobster populations.
EFFECTS OF OCEAN WARMING AND ACIDIFICATION ON THE EARLY DEVELOPMENT OF AN ANTARCTIC FISH GYMNODRACO ACUTICEPS
Graduate Group in Ecology
While recent work has highlighted that marine fish, particularly during early life stages, can be vulnerable to ocean acidification (OA), we lack understanding of how life history strategies, environment, and concurrent ocean warming interplay with interspecific resilience. The protracted embryogenesis (~10 months) of the Antarctic dragonfish, Gymnodraco acuticeps, provides a unique opportunity to examine the impacts of potential synergistic stressors on embryo physiology over a fine time scale. Using an integrative, experimental approach, our research examined the impacts of near-future warming (-1°C [ambient], 2°C [+3°C]) and OA (400 [ambient], 650 [moderate], and 1000 [high] μatm pCO2) on survival, development, and metabolic processes over the course of 3 weeks in early development. Under increased pCO2 alone, embryos experienced mildly positive physiological effects, such as a higher proportion of more developed embryos at 3 weeks. However, under both warming and OA scenarios, dragonfish embryos experienced a dose-dependent, synergistic decreased in survival. We also found significant interactions between temperature, pCO2, and time in aerobic enzyme activity (Citrate synthase) and developmental rate, while temperature increased whole organism metabolic rate (O2 consumption) and development at the cost of increased mortality. Our findings suggest that developing Antarctic fish may only experience physiologically negative effects of OA under warming, but alterations in development and metabolism could cause negative ecological consequences due to changes in phenology (i.e. early hatching) in the highly seasonal Antarctic ecosystem.
BENTHIC MICROBIAL MAT EXPANSION AND NUTRIENT UPTAKE DURING LAKE LEVEL RISE IN ICE-COVERED LAKE VANDA, MCMURDO DRY VALLEYS, ANTARCTICA
Junior Specialist in Geology
Lake Vanda is a perennially ice-covered lake in the McMurdo Dry Valleys, Antarctica. The lake lacks macroscopic metazoans, but hosts benthic photosynthetic microbial mats with dm-scale pinnacles formed by microbial growth. Lake Vanda had a stratified water column with convecting layers separated by a pycnocline from 24 to 27m in 2014. The lake has no outflow and its water budget consists of melt water from the Onyx River and ice ablation from the lake surface. The water balance responds to regional climate change, and resulting lake level rise has submerged new areas. Colonization of these areas by microbial mats changes the flow of nutrients through this microbially-dominated landscape. The water column is considered P limited, and P annually sequestered in mat growth shallower than 19m was comparable to influx from the Onyx River at ~1.4 ug P m-2 yr-1 from 1998-2010 (Hawes et al., 2013). In this contribution, we document results from a drop camera survey of microbial mats on the bottom of Lake Vanda. Depth soundings, historical aerial photographs, and GPS shoreline tracks were georeferenced to a digital elevation model. Measurements were referenced to records of lake level to refine bathymetry and calculate change in benthic area through time. 34 drop camera sites across the lake demonstrate that pinnacles in microbial mats are present at depths of up to ~50m, but are absent to poorly developed below this depth. Our bathymetric reconstruction combines data from 2013 GPS shoreline tracks, new and preexisting depth soundings, and aerial photographs from 1964, 1972, 1983, and 1994. The resulting bathymetric model indicates that lake level rise has increased the wetted area of the lake at an average rate of ~6×104 m2 yr-1 since 1964, while lake volume has increased by 2×106 m3 yr-1 on average. Microbial mat growth observed by Hawes et al. (2013) would have required an average increase in P flux of 8×104 ug yr-1 to maintain a consistent growth rate with greater surface area colonization. This increasing flux requirement indicates that either 1) growth rates were not constant during the observed period of growth or 2) there has been an increase in P flux. This could come from either the Onyx River or diffusion across the density gradient from deeper parts of the lake where increasing lake level may have shifted the rate of decay relative to primary productivity.
MICROBIAL MAT MORPHOLOGY AS A RECORD OF ENVIRONMENTAL CHANGE IN PERENNIALLY ICE-COVERED LAKE JOYCE, ANTARCTICA
Geology Graduate Group
Microbial mats with diverse macroscopic growth forms are abundant in perennially ice-covered Lake Joyce in the McMurdo Dry Valleys of Antarctica. Lake levels rose by over 8.5 m between 1973 and 2014, and benthic cyanobacterial communities presently have depth-associated distributions. When observed in 2010, mats at <12m depth contained abundant Phormidium autumnale, Leptolyngbya antarctica, L. fragilis, and Pseudanabaena frigida morphotypes, whereas deeper mats lacked P. autumnale. Microscopy data indicate that different relative abundances of cyanobacterial morphotypes are associated with specific mat morphologies, and this is supported by preliminary 16S rRNA PCR analyses. Mats dominated by P. autumnale morphotypes had little topographic relief, whereas mats lacking P. autumnale commonly contained small peaks and branch-like bundles of filaments growing away from the mat surface. At 20-22 m depth, mats lack measureable photosynthetic activity and form dm-scale columnar stromatolites interpreted as having grown when lake levels were lower and thus illumination was higher. Calcite that precipitated within these stromatolites preserves variations in growth form with time from smooth prolate columns to branched and irregular columns. Crystals also contain cylindrical molds, which have diameters similar to the trichome widths of cyanobacteria living in Lake Joyce. Preserved community composition and stromatolite morphology co-vary. P. autumnale-sized molds are abundant in calcite forming the oldest smooth stromatolite layers, but are absent from younger layers with branched and irregular growth. This suggests that P. autumnale was present early in stromatolite growth, but disappeared from the community through time. Observations of both active mats and columnar stromatolites thus suggest that changes in microbial community composition influence growth forms and preserve a record of microbe-environment interactions consistent with longer-term environmental change in Lake Joyce. Kate Wall
MICROBIAL COMMUNITIES OF PINNACLED STRUCTURES IN ICE-COVERED ANTARCTIC LAKE VANDA
Microbiology Graduate Group
Lake Vanda is a perennially ice-covered lake in Wright Valley of the McMurdo Dry Valley region of Antarctica. Lake Vanda is stratified, with saline waters at the bottom and fresher waters near the top. The bottom waters are anoxic, while the fresher waters in the photic zone are saturated with oxygen. Throughout the photic zone, the lake floor is covered with thick microbial mats. The absence of disturbance and grazing metazoans makes Lake Vanda a unique environment reminiscent of the earth’s early biosphere. A consistent feature of the benthic mats in Lake Vanda are pinnacles, which vary in size and number throughout the photic zone. Cross sections of the pinnacles show internal laminations, with characteristic pigmented layers. These layers consist of outer orange/brown layers, followed by an inner green layer which transitions to pink toward the internal portion of the pinnacle. These layers can be easily separated in the field, and were analyzed separately using culture independent methods in order to gain an understanding of how the microbial content differs between layers. Pinnacle structures are dominated by cyanobacteria, primarily from the order Osccilatoriales. Limnothrix, Leptolyngbya and Phormidium provided the majority of the cyanobacterial taxa. These taxa are most similar by BLAST to cyanobacteria found in other cold environments. The majority of sequences from the outer layers of the pinnacles belonged to Leptolyngbya, while inner layers consisted of both Leptolyngbya and Phormidium. Other abundant bacterial phyla were Proteobacteria, Bacteroidetes, Chloroflexi, and Planctomycetes. Rarefaction curves and diversity indices indicated undersampling of some samples. Principle component analysis shows clustering of sample subsections, though differences between samples were not statistically significant by Unifrac analysis. Differences in nutrient availability may account for the differences in microbial communities in the pinnacle subsections. The most interior pinnacle subsections showed enrichment of a bacterial group, the Melainobacteria, that clusters with the cyanobacteria but which as been found to be non-photosynthetic.
CONSUMER DIVERSITY AND FLOW VARIABILITY INFLUENCE WATER FILTRATION IN FOULDING COMMUNITIES
Ecology Graduate Group
Environmental heterogeneity is predicted to influence biodiversity-ecosystem functioning relationships. When environmental conditions vary across space or time key trait differences between community members can be expressed, potentially enhancing resource complementarity. In this study we investigated how temporal heterogeneity in water flow rates interacts with sessile suspension feeding invertebrate diversity to determine clearance rates of phytoplankton. In the absence of flow nine individual consumer species differentially filtered seven cultured phytoplankton species across a large range of cell sizes, providing evidence for feeding trait differentiation. We conducted a series of 24-hour feeding experiments using recirculating flow chambers, supplied with cultured phytoplankton, and run under constant and variable flow rates across a range of consumer diversity. Preliminary results suggest that suspension feeder diversity enhanced filtration, but this relationship saturated quickly and depended on specific combinations of consumer traits. However, consumer polyculture treatments tended to filter a greater range of phytoplankton cell sizes than most monocultures. Flow rate treatments evoked more subtle responses and depended on consumer composition, reinforcing the idea that in order for heterogeneity to enhance complementarity it must be coupled with sufficient trait diversity.
2015 Symposium Oral Presentation Abstracts
STRATEGIC POLLINATOR HABITAT SPATIAL ANALYSIS AND DESIGN
Geography Graduate Group
Habitat fragmentation and destruction are cited as the main reasons for pollinator declines, yet existing remedies are not spatially strategic. My research aims to help solve current geographic shortcomings affecting urban bee populations to ensure ecosystem services. Reconciling scales perceivable by pollinators versus practical landscape analysis is not simple. Bee life history, flower visitation and pollinator abundance data is used to answer geographic questions with scientific solutions.
INTERACTIONS BETWEEN LARGE HERBIVORES AND TERMITES DRIVE MULTI-SCALAR PATTERNS IN COMMUNITY STRUCTURE IN A KENYAN SAVANNA
Ecology Graduate Group
Understanding the causes and controls of community heterogeneity and structure has long been a goal of ecologists. In African savannas, both megaherbivores and termites are keystone taxa demonstrated to have profound impacts on plant communities and ecosystem function. Termites create mounds that create landscape heterogeneity by locally enriching soil, shifting plant palatability and community structure, and altering herbivory. Meanwhile, megaherbivore browsing can lead to reductions in tree and shrub density and diversity. Elephants in particular are known to radically affect landscape heterogeneity through changes in woody stands. While the effects of termites and megaherbivores have been studied separately, little work has been done to assess their potential interactions. Megaherbivores and termites may either compete for woody material or facilitate its availability, and may affect plant community structure either additively or synergistically.
I examined the these interactions using the Kenya Long-term Exclosure Experiment (KLEE), which has excluded different combinations of large mammalian herbivores from replicated 4-ha plots for the past 20 years. I compared termite mound density, plant community composition, and plant community structure across large herbivore treatments. Using structural equation models, I analyzed how these keystone groups interact to influence plant community structure.
I found that termites and megaherbivores interact in profound ways that strongly affect plant community structure and ecosystem heterogeneity. Megaherbivores (elephants, mostly) reduce tree density, and this leads to a reduction in termite mound density. Multivariate analysis shows plant communities on termite mounds are strikingly different from background plant communities, but that these differences are significantly reduced by the presence of megaherbivores. Therefore, megaherbivores reduce the landscape heterogeneity produced by termites by both a) reducing termite mound density, and b) reducing the ecological footprint of individual termite mounds. Overall, these results provide strong evidence for interactions between these two keystone taxa, which differ in body size by nearly ten orders of magnitude. This system is now being further studied to explore the factors influencing large-scale patterns in nutrient cycling, plant community composition, and community structure.
BOTH SIDES OF THE COIN: HOST AND PATHOGEN INFLUENCE DISEASE OUTCOME IN AN EMERGING AMPHIBIAN DISEASE
Ecology Graduate Group
The emerging disease chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), has devastated amphibian populations worldwide, leading to the decline of hundreds of species. Despite these striking declines, chytridiomycosis has extremely variable impacts on different amphibian hosts. Some species are known to act as asymptomatic carriers of Bd, and yet relatively little is known about host physiological and immune responses that allow these species to effectively combat disease. To further understand amphibian host responses to fungal infection, we conducted an experimental exposure trial with a disease-susceptible species, the wood frog (Lithobates sylvaticus), and a disease-resistant species, the American bullfrog (L. catesbeianus). These two amphibian species were each exposed to two isolates of Bd known to differ in virulence, Section Line Lake (SL) Bd, which has a high virulence phenotype, and Carter Meadow (CM) Bd, which has demonstrated only mild virulence in previous exposure trials with other amphibian species. Over the course of the seven week experiment, wood frogs exposed to SL Bd suffered significantly higher mortality (overall survival rate = 0.17) than frogs exposed to CM Bd or sham controls, both of which experienced no mortality. In contrast, there were no differences in American bullfrog survival attributable to Bd exposure treatment despite the fact that American bullfrogs were exposed to Bd doses three times greater than that of wood frogs. Furthermore, there was evidence of sublethal, negative effects on body mass in SL Bd-exposed wood frogs but not in CM Bd-exposed or control groups of that species. Thus, our results provide strong evidence that both the amphibian host and Bd isolate greatly influence the disease outcome of amphibian-Bd interactions.
In continuing this work, we will evaluate host responses to pathogen exposure by characterizing gene expression in frog tissues that were harvested at multiple time points (three, seven, and 10 days post-exposure) through the course of the experimental exposure trial. Gene expression profiling, to be conducted using RNA sequencing, allows for the simultaneous quantification of thousands of gene products within a tissue of interest. In addition, RNA sequencing of ventral skin tissue harvested from infected animals should allow for the simultaneous characterization of Bd pathogen gene expression. Bioinformatics analyses of gene expression profiles of exposed and unexposed host animals will highlight immune genes and other pathways involved in chytridiomycosis disease resistance, while comparison of the two pathogen isolates will reveal genes contributing to virulence. Such knowledge will deepen our fundamental understanding of host-pathogen interactions and will ultimately contribute to the development of effective conservation strategies for both wild and captive amphibians at risk from disease.
CONTEXT-DEPENDENCY OF PREDATOR CONSUMPTIVE AND NON-CONSUMPTIVE EFFECTS IN AN ESTUARINE FOOD CHAIN: IMPACTS OF COPPER POLLUTANTS AND ENVIRONMENTAL FACTORS
Ecology Graduate Group
Predators eat and scare their prey, and the relative importance of these actions play large roles in determining community structure. The relative strength of these predator consumptive and non-consumptive effects are often context-dependent. Despite this recognition, we are only beginning to understand the impact of anthropogenic stressors such as chemical pollutants on these species interactions. We conducted laboratory experiments to examine the impact of copper on an estuarine food chain of predatory crabs, invasive whelks, and basal barnacle resources. In the absence of copper, crab cues reduced whelk consumption rates of barnacles. Copper altered the relative strength of predator consumptive and non-consumptive effects. Specifically, intermediate copper levels decreased the strength of predator consumptive effects whereas extreme copper levels weakened predator non-consumptive effects. We also conducted a field experiment in San Francisco Bay to investigate whether differences in pollutant levels and environmental factors among three sites would influence species interactions. The strength of predator non-consumptive effects varied among sites. Namely, crab non-consumptive effects may have been weakened at the site with warmer waters. Our results support the notion that predator-prey interactions are often context-dependent, and may especially be influenced by human-caused stressors such as chemical pollutants.
A SIREN SONG OF COLUMBINES
Ecology Graduate Group
Plants have a myriad of defense strategies – both direct and indirect. A sticky columbine attracts and murders (!) non-interacting insects, with which it attracts predatory bodyguards (assassin and stilt bugs), which reduce damage the plant by a caterpillar. While this sounds idiosyncratic, over 100 genera of plants entrap insects via sticky or hooked trichomes.
IMPORTANCE OF FUNCTIONAL TRAITS AND NEIGHBORS FOR UNDERSTANDING PLANT RESPONSES TO HERBIVORES
Ecology Graduate Group
Herbivores play an important role in determining the abundance of plant species. However, attempts to generalize about the influence of herbivores on plant populations have had mixed success because species responses are determined not only by the effects of herbivores, but also by their interactions with plant neighbors and the surrounding environment. In a coastal California grassland, we used a 14-year-old exclosure experiment to examine the response of six plant species (Heracleum maximum, Cirsium vulgare, Ranunculus californica, Iris douglasii, Baccharis pilularis, and Lupinus arboreus) to a large mammalian herbivore – tule elk (Cervus elaphus nannodes). We explored whether species with stress-tolerance functional traits were less influenced by elk than species with resource-acquisition functional traits. In addition, for two species (Cirsium and Heracleum), we assessed the possibility that plant-plant interactions mediate the influence of elk. The abundance or cover of our six plant species varied greatly in their responses to elk herbivory, so we examined these responses from a functional trait perspective rather than by species functional group. We found that herbivores increased the abundance of plant species with higher specific leaf area (SLA), whereas they had no effect on species with lower SLA. In contrast, leaf size and dry matter content were poor predictors of species response to herbivores. Native shrub and tall forb interactions differed based on species. Heracleum was shorter in the presence of herbivores, and taller if it was associating with a native shrub. Cirsium was negatively affected by elk herbivory and shrub neighbors; it was taller when it wasn’t found near a shrub neighbor, especially in the absence of herbivores which suggests that native shrubs compete with Cirsium and may be important factors influencing invasion success. Our results suggest that functional traits alone may not fully predict that response of plant species to herbivory and that incorporating plant-plant interactions into conceptual models of the influence of herbivores may help explain species response.
PREDATORS GOING GREEN: FLOWERS REDUCE THE CONSUMPTIVE EFFECTS OF OMNIVOROUS BEETLES RESPONSIBLE FOR A TROPHIC CASCADE
Ecology Graduate Group
Changing plant traits may induce omnivores to alter their predation rates. We assessed the consumptive effect of beetles on prey in the presence of alternative plant stages – vegetative or reproductive. Flowers reduced beetle predation on prey.To examine the potential for beetles to induce a trophic cascade, we conducted a mesocosm experiment that measured the impacts of beetles on plants. In the absence of flowers, beetles indirectly benefited below-ground plant growth.
EMERGING PERSPECTIVES ON SALT MARSH HARVEST MOUSE CONSERVATION AND MANAGEMENT – DUCKS, DIKES, AND DEMOGRAPHICS
Ecology Graduate Group
The salt marsh harvest mouse (Reithrodontomys raviventris) is an endangered species that is endemic to the San Francisco Bay Estuary. The primary threat to this species is habitat loss. About 90% of its historical tidal habitat has been altered or lost. The majority of monitoring for this species occurs sporadically, often occurring only once a year at any given site. This project represents the first efforts for long term, monthly monitoring of salt marsh harvest mouse populations in the wild. Here we present data from the first year of monitoring at wetlands in the Suisun Marsh complex, during a California drought. The wetlands monitored include tidal wetlands and wetlands managed for waterfowl (diked). Management activities in the diked wetlands we monitored range from no recent activity, to hydrological manipulation, to discing, and burning. This fine scale monitoring has revealed novel, and sometimes surprising, aspects of salt marsh harvest mouse populations, demographics and behavior that will contribute to the conservation of this species.