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Participant Abstracts
Due to close proximity, hosts and epiphytes potentially exert strong ecological influences on each other. In the case of kelp, associated epiphytes may negatively impact the host due to shading and blocking nutrient uptake. However, an epiphyte can reduce the susceptibility of its host to herbivory. This research examines whether an epiphytic bryozoan, Membranipora membranacea, provides an associational refuge from herbivory for its host giant kelp. I hypothesized that the presence of Membranipora reduces the grazing damage on kelp inflicted by small grazers. Individual invertebrate grazer species were tested in the laboratory to determine their feeding preferences for kelp with or without Membranipora. Almost all grazers (Norris’ topsnail, top snails, Lacuna snails, amphipods, and kelp isopods) were found to have a strong preference for kelp without the bryozoan. However, kelp crabs showed a preference for kelp encrusted with Membranipora. Field surveys indicate a slight reduction of grazing on kelp blades heavily encrusted with Membranipora in areas dominated by small grazers in the canopy. These results suggest that while some protection from herbivores may be gained when Membranipora is present, it is unlikely to outweigh the overall costs of hosting the epiphyte.
Excessive loading of fine sediment is one of the most serious impacts of land-use on stream ecosystems in arid and semi-arid environments. Detrimental direct effects of excessive fine sediment are well documented for fish, invertebrates, and buried periphyton. Periphyton growing on clear surfaces may also be indirectly affected by deposited fine sediment, but these indirect effects remain poorly known. Two hypothesized mechanisms for indirect effects of fine deposited sediment on periphyton include hydraulic changes resulting from a smoothed riverbed, and changes in ambient grazer biota resulting from embedded substrates. We manipulated fine sediment in experimental channels and quantified periphyton accrual, metabolism, and nutrient uptake under both natural and reduced grazer conditions. Grazers were reduced by electric fence chargers surrounding experimental tiles in each sediment treatment, allowing us to contrast the indirect effect of altered food web dynamics from the direct effect of altered hydraulic conditions. Results after thirty and sixty days suggest periphyton was not affected by hydraulic contrasts imposed by our sediment manipulation. While periphyton accrual, metabolism, and nutrient uptake did not differ among sediment manipulations, ambient grazing stimulated greater nitrogen uptake and greater metabolism per unit mass. Our results suggest under low flow summer conditions grazer effects outweigh any indirect hydraulic effects of a smoother bed due to deposited fine sediment, and food web composition and/or dynamics can alter nutrient cycling in a coastal river.
Chaparral is a quintessential Mediterranean-type shrubland in California. Although it covers vast areas in the mountains of interior California, there are several more restricted stands of chaparral along the central California coast called “maritime chaparral.” Maritime chaparral is rich in rare endemic species. Because of its limited distribution, concentration of local endemics, and threats of urbanization in this region, maritime chaparral is designated as a protected sensitive natural community under CEQA and the California Coastal Commission protects maritime chaparral as an Environmentally Sensitive Habitat Area. These regulatory protections have resulted in a land use policy storm that threatens to become increasingly costly and acrimonious. At issue is the difficulty in distinguishing “maritime” from “interior” chaparral. In this study, I hypothesize that maritime chaparral distribution is influenced by the moderating effects of coastal fog on drought effects caused by California’s long, hot summer. Using data from four core research sites established along a heavy fog to no fog gradient, I demonstrate that water potentials in Arctostaphylos are much less negative (less drought stress) in maritime versus interior habitats. Further, by the end of the dry season, water potential metrics help to clarify the status of a potentially questionable chaparral site. Other ecophysiology parameters (such as PSII fluorescence) reinforce these findings. Subject to further studies designed to validate these patterns and identify causal mechanisms, the use of ecophysiology tests in contentious cases might provide objective criteria to help resolve this “maritime versus interior” land use policy question and help diffuse this dilemma. The Angelo Coast Range Reserve in Mendocino County contains a relict population of old-growth coast redwood trees. These redwoods grow at the eastern edge of the redwood range, tucked behind coast range mountains that prevent marine fog from bringing a water subsidy into the forest during the summer months. To understand if redwoods growing outside of the belt suffer from severe drought stress during the summer, I measured the level of water stress in 6 redwood saplings diurnally following a multiple-day heat wave in July 2006. Additionally, I sampled stem water for isotopic analysis to identify the water source used by each sapling and sampled 3 cohort of leaves from each sapling diurnally to evaluate isotopic differences in leaf water between the leaf age classes. I found that despite the severe heat experienced by the saplings in the 10 days prior to sampling, the saplings showed no signs of drought stress. The isotopic composition of the stem water revealed that the redwoods were likely using predominately South Fork Eel River water, a consistently available water source throughout the summer season. Additionally, I determined that the redwood leaf cohorts maintain consistent differences in water isotope composition overnight, showing significant leaf water isotopic enrichment in younger leaves. Due to the arrangement of redwood foliage along branches, the age of leaf cohorts is correlated with position and further investigation is required to interpret whether the age of the leaf or its position along the branch influences evaporative enrichment in redwood leaves.
Individuality can reveal itself in a variety of ways—behavior, physical appearance, scent, voice—but how do individualistic traits evolve? Individual distinctiveness aids individual recognition, which is critical for many functions that occur within groups of social animals. We predict these needs will be greater in larger social groups, and therefore that evolution will favor increases in individual distinctiveness in species with larger social group sizes. Using the alarm calls of ground-dwelling sciurid rodents (ground squirrels and their relatives), we describe, quantify, and compare vocal distinctiveness and address adaptive questions about how and why individuality evolves. The latest results from UC Reserve species and other species will be discussed.
Physiological responses to environmental changes can occur at several organizational levels (molecular, cellular, organismal) and over several time-scales. Behavioral responses may complement or even override physiology, requiring an integrative approach to relate laboratory results to ecological consequences. Here, we assess both physiological and behavioral responses of leopard sharks (Triakis semifasciata) to laboratory salinity changes. Sharks were acclimated to 60%, 80%, or 100% seawater for 48 hours (short-term) or 3 weeks (long-term). Plasma samples were analyzed for osmolyte concentrations to assess organismal osmoregulatory status. To assess underlying molecular mechanisms, we identified several proteins that were up- or down-regulated in osmoregulatory tissues (gill, rectal gland) during salinity change using a proteomics approach (i.e., 2-dimensional electrophoresis and mass spectrometry). The functions of these proteins were assessed using bioinformatics databases and pathway analysis software. Behavioral responses (swimming activity) were monitored using focal animal surveys and point sampling. Changes in plasma osmolality, sodium, and chloride concentrations lagged behind changes in the salinity of the water, and the osmotic gradient between shark and environment was greatest at 24 hours. Sharks remained hyperosmotic but hypoionic to the medium in short and long-term experiments. In the short-term swimming activity increased in lower salinities. Meanwhile, individuals in 60% seawater in the long-term treatment responded behaviorally by reducing their activity by ~50%, suggesting a long-term behavioral tradeoff for increased costs of osmoregulation. These multi-level laboratory results provide a baseline for comparison with ongoing field studies to evaluate tradeoffs between physiology and behavior in wild sharks inhabiting dynamic estuarine systems. Previous |
