Life on the Edge: Morphological and Behavioral Adaptations for Survival on Wave-swept Shores

Wave-swept rocky shores serve as a home to a great diversity of organisms and are some of the most biologically productive habitats on earth. This burgeoning community exists in spite of the fact that the zone between the high and low tide marks can be one of the most physically harsh environments on earth. Large forces imposed by breaking waves and wide swings in temperature require the organisms living on rocky shores to adapt to a constantly changing environment or risk extirpation by physical forces. I have explored a number of hypothesized adaptations for survival on rocky shores and discuss how the results influence the evolutionary and ecological processes shaping shoreline communities. I developed a biophysical model to predict body temperatures for high shore littorine snails in order to address the role of evolved morphological and behavioral traits for controlling body temperature during extreme temperature exposures. The results demonstrate that while the behaviors of these snails allow them to reduce body temperatures by several degrees, the hypothesized roles of shell shape and color contribute relatively little to controlling body temperature. A similar biophysical model for predicting organismal body temperature was combined with a physiological study to examine the role of temperature stress in setting the distributional limits of an important mid-intertidal limpet, Lottia gigantea. With a temperature exposure protocol based on realistic field conditions, I measured sub-lethal and lethal temperature limits for this species, and found that the vertical distribution of L. gigantea may be set directly by high temperatures within certain microhabitats on the shore. The final section describes the role of behavior in barnacles in compensating for limits in the phenotypic plasticity of their feeding appendages. By directly monitoring the feeding activity of barnacles under breaking waves, I show that fast reaction times allow barnacles to avoid damaging water flows while still exploiting much of the available time for feeding. The studies in this thesis provide a number of new insights into the role of the abiotic environment in the evolution and ecology of organisms living on wave-swept rocky shores

Barriers to Flow: The Effects of Experimental Cage Structures on Water Velocities in High-energy Subtidal and Intertidal Environments

For decades, marine ecologists have used cages as biological enclosure or exclosure devices to manipulate movement, growth, and survival of organisms. The ability to control the densities of focal organisms makes these structures a powerful tool. However, cages can often produce artifacts that influence the outcome of experiments. Although a subset of these artifacts have been examined previously, the effects of cages on water motion have not been adequately addressed from a quantitative standpoint, especially in high-flow environments. We targeted this data gap by explicitly measuring the fractional degree of velocity reduction inside a variety of experimental cage structures across flow conditions spanning those typical of wave-swept shallow subtidal and intertidal zones. Cages decreased velocities inside by up to 47% and reduced high-energy impact forces by more than 40%. Associated cage controls, employed to mimic physical effects of cages without interfering with organism movement, often had effects on water flow similar to those of cages. However, the nearly half an order of magnitude change in velocities inside cages and their controls reveals the need to be vigilant in considering potential artifacts, especially those tied to secondary biological interactions. These artifacts may be reduced by maximizing mesh size, employing large plot sizes and low profile structures, using cage controls that best mimic effects of the full cage, and monitoring cage controls to avoid the establishment of high-density “consumer hotels” within them. Using such approaches, researchers can minimize experimental biases and simplify the explanation of experimental results

On the Prediction of Extreme Ecological Events

Ecological studies often focus on average effects of environmental factors, but ecological dynamics may depend as much upon environmental extremes. Ecology would therefore benefit from the ability to predict the frequency and severity of extreme environmental events. Some extreme events (e.g., earthquakes) are simple events: either they happen or they don\u27t, and they are generally difficult to predict. In contrast, extreme ecological events are often compound events, resulting from the chance coincidence of run-of-the-mill factors. Here we present an environmental bootstrap method for resampling short-term environmental data (rolling the environmental dice) to calculate an ensemble of hypothetical time series that embodies how the physical environment could potentially play out differently. We use this ensemble in conjunction with mechanistic models of physiological processes to analyze the biological consequences of environmental extremes. Our resampling method provides details of these consequences that would be difficult to obtain otherwise, and our methodology can be applied to a wide variety of ecological systems. Here, we apply this approach to calculate return times for extreme hydrodynamic and thermal events on intertidal rocky shores. Our results demonstrate that the co-occurrence of normal events can indeed lead to environmental extremes, and that these extremes can cause disturbance. For example, the limpet Lottia gigantea and the mussel Mytilus californianus are co-dominant competitors for space on wave-swept rocky shores, but their response to extreme environmental events differ. Limpet mortality can vary drastically through time. Average yearly maximum body temperature of L. gigantea on horizontal surfaces is low, sufficient to kill fewer than 5% of individuals, but on rare occasions environmental factors align by chance to induce temperatures sufficient to kill \u3e99% of limpets. In contrast, mussels do not exhibit large temporal variation in the physical disturbance caused by breaking waves, and this difference in the pattern of disturbance may have ecological consequences for these competing species. The effect of environmental extremes is under added scrutiny as the frequency of extreme events increases in response to anthropogenically forced climate change. Our method can be used to discriminate between chance events and those caused by long-term shifts in climate

Climate Change Enhances the Negative Effects of Predation Risk on an Intermediate Consumer

Predators are a major source of stress in natural systems because their prey must balance the benefits of feeding with the risk of being eaten. Although this \u27fear\u27 of being eaten often drives the organization and dynamics of many natural systems, we know little about how such risk effects will be altered by climate change. Here, we examined the interactive consequences of predator avoidance and projected climate warming in a three-level rocky intertidal food chain. We found that both predation risk and increased air and sea temperatures suppressed the foraging of prey in the middle trophic level, suggesting that warming may further enhance the top-down control of predators on communities. Prey growth efficiency, which measures the efficiency of energy transfer between trophic levels, became negative when prey were subjected to predation risk and warming. Thus, the combined effects of these stressors may represent an important tipping point for individual fitness and the efficiency of energy transfer in natural food chains. In contrast, we detected no adverse effects of warming on the top predator and the basal resources. Hence, the consequences of projected warming may be particularly challenging for intermediate consumers residing in food chains where risk dominates predator-prey interactions

Geographic Variation in Temperature Tolerance as an Indicator of Potential Population Responses to Climate Change

The temperature tolerances of individuals in geographically separated populations of a single species can be used as indicators of each population\u27s potential to persist or become extinct in response to climate change. We evaluated the population-level variation in temperature tolerance in populations of several marine invertebrate taxa, including bryozoans, tunicates, bivalves, and gastropods, separated by distances of \u3c 200 km to \u3e 5000 km. We then combined physiological thermotolerance data with current temperature data and climate change predictions to predict which of these populations may be most vulnerable to future changes. In a trans-continental comparison of four subtidal epibenthic species, we show that populations on the east coast of the United States, which experienced higher habitat temperatures than those on the west coast, had higher thermal tolerances but lived closer to individuals\u27 tolerance limits. Similarly, temperature tolerances varied between western and eastern Atlantic populations of the mussel Mytilus edulis; however, these differences only emerged after repeated exposures to high temperatures. Furthermore, the less thermotolerant M. edulis population in the western Atlantic was more susceptible to temperature increases, as evidenced by a recent range contraction. Thus, for both the subtidal epibenthic and intertidal mussel species, we identified the western Atlantic as a ‘hot spot’ of populations susceptible to climate change compared to those in the eastern Pacific and eastern Atlantic, respectively. Finally, because current tolerances are not the sole indicators of individuals\u27 abilities to cope with temperature increases, we also assessed the possibility for acclimatization to facilitate the persistence of populations via the buffering of temperature effects. We show that, for four populations of intertidal Littorina snail species in the northwest Atlantic, most populations were able to overcome geographic differences in temperature tolerance via acclimation. When acclimation capacity is low, the potential for “rescue” may depend on the particular species\u27 life-history strategy and dispersal ability. For example, although individuals from the coldest-adapted population of Littorina littorea were unable to acclimate as quickly as those from more southern populations, this species has a pelagic larval stage and, thus, the greatest dispersal potential of these littorines. Together, these studies highlight the importance of considering variation in temperature tolerance between populations within species to improve the forecasting of changes in the abundances and distributions of species in response to climate warming

Dislodged But Not Dead: Survivorship of a High Intertidal Snail Following Wave Dislodgement

Waves breaking on rocky shorelines impart large forces on intertidal organisms, sometimes dislodging individuals. Dislodged individuals may be deposited in habitats that have a greater risk of predation or that prevent return to preferred regions on the shore. Thus, dislodgement is often assumed to be lethal. We experimentally dislodged Littorina keenae snails from high in the intertidal zone to test the likelihood of survival. Under a variety of wave conditions, we measured return rates to the high shore of 54–90%, so in this species, dislodgement is not equal to death. Snails showed a strong preference for returning to the approximate tidal height from which they were dislodged, but we found no evidence of widespread homing behaviour back to the original site of dislodgement

Superconductivity and Field-Induced Magnetism in Pr2−x_{2-x}Cex_xCuO4_4 Single Crystals

We report muon-spin rotation/relaxation (muSR) measurements on single crystals of the electron-doped high-T_c superconductor Pr$_{2-x}$Ce$_x$CuO$_4$. In zero external magnetic field, superconductivity is found to coexist with Cu spins that are static on the muSR time scale. In an applied field, we observe a Knight shift that is primarily due to the magnetic moment induced on the Pr ions. Below the superconducting transition temperature T_c, an additional source of static magnetic order appears throughout the sample. This finding is consistent with antiferromagnetic ordering of the Cu spins in the presence of vortices. We also find that the temperature dependence of the in-plane magnetic penetration depth in the vortex state resembles that of the hole-doped cuprates at temperatures above ~ 0.2 T_c.Comment: 4 pages, 5 figure

Heat-Shock Protein 70 (Hsp70) Expression in Four Limpets of the Genus \u3cem\u3eLottia\u3c/em\u3e: Interspecific Variation in Constitutive and Inducible Synthesis Correlates With \u3cem\u3ein situ\u3c/em\u3e Exposure to Heat Stress

Limpets of the genus Lottia occupy a broad vertical distribution on wave-exposed rocky shores, a range that encompasses gradients in the frequency and severity of thermal and desiccation stress brought on by aerial emersion. Using western blot analysis of levels of heat-shock protein 70 (Hsp70), we examined the heat-shock responses of four Lottia congeners: Lottia scabra and L. austrodigitalis, which occur in the high-intertidal zone, and L. pelta and L. scutum, which are restricted to the low- and mid-intertidal zones. Our results suggest distinct strategies of Hsp70 expression in limpets occupying different heights and orientations in the rocky intertidal zone. In freshly field-collected animals and in specimens acclimated at ambient temperature (≈14 °C) for 14 days, the two high-intertidal species had higher constitutive levels of Hsp70 than the low- and mid-intertidal species. During aerial exposure to high temperatures, the two low-shore species and L. austrodigitalis exhibited an onset of Hsp70 expression at 28 °C; no induction of Hsp70 occurred in L. scabra. Our findings suggest that high-intertidal congeners of Lottia employ a “preparative defense” strategy involving maintenance of high constitutive levels of Hsp70 in their cells as a mechanism for protection against periods of extreme and unpredictable heat stress

Warm Microhabitats Drive Both Increased Respiration and Growth Rates of Intertidal Consumers

Rocky intertidal organisms are often exposed to broadly fluctuating temperatures as the tides rise and fall. Many mobile consumers living on the shore are immobile during low tide, and can be exposed to high temperatures on calm, warm days. Rising body temperatures can raise metabolic rates, induce stress responses, and potentially affect growth and survival, but the effects may differ among species with different microhabitat preferences. We measured aerial and aquatic respiration rates of 4 species of Lottia limpets from central California, and estimated critical thermal maxima. In a variety of microhabitats in the field, we tracked body temperatures and measured limpet growth rates on experimental plates colonized by natural microalgae. Limpet species found higher on the shore had lower peak respiration rates during high temperature aerial exposure, and had higher critical thermal maxima. Using our long-term records of field body temperatures, we estimated cumulative respiration to be 5 to 14% higher in warm microhabitats. Growth rates in the field appear to be driven by an interaction between available microalgal food resources, low tide temperature, and limpet species identity, with limpets from warmer microhabitats responding positively to higher food availability and higher low tide temperatures. Stressful conditions in warm microhabitats make up a small portion of the total lifetime of these limpets, but the greater proportion of time spent at non-stressful, but warm, body temperatures may result in enhanced growth compared to limpets living in cooler microhabitats

Factorized Point Process Intensities: A Spatial Analysis of Professional Basketball

We develop a machine learning approach to represent and analyze the underlying spatial structure that governs shot selection among professional basketball players in the NBA. Typically, NBA players are discussed and compared in an heuristic, imprecise manner that relies on unmeasured intuitions about player behavior. This makes it difficult to draw comparisons between players and make accurate player specific predictions. Modeling shot attempt data as a point process, we create a low dimensional representation of offensive player types in the NBA. Using non-negative matrix factorization (NMF), an unsupervised dimensionality reduction technique, we show that a low-rank spatial decomposition summarizes the shooting habits of NBA players. The spatial representations discovered by the algorithm correspond to intuitive descriptions of NBA player types, and can be used to model other spatial effects, such as shooting accuracy.Engineering and Applied Science