Characterizing deep-water oxygen variability in the Southern California Bight and seafloor community responses
Natalya D. Gallo, Scripps Institution of Oceanography
UC San Diego
When scientists study climate change, the focus is usually on changes to mean conditions. However, animals live in temporally variable environments, which influence organism exposure histories and vulnerabilities to climate change. One manifestation of climate change, decreasing ocean oxygen, has been recorded over the last 30 years in nearshore, upper-slope depths in the Southern California Bight. How these changes compare to the magnitude of natural variability experienced by seafloor communities at short timescales was unknown. An autonomous nanolander collected high-frequency T, O2, pH, and salinity data and benthic community responses 100–400 m deep off San Diego to determine timescales of natural environmental variability, changes in variability with water depth, and community responses to variability. The diurnal oxygen range at all depths exceeded the annual long-term trend in oxygen loss. Depths of 200 and 400 m showed high oxygen variability relative to the mean, which may help buffer against deoxygenation stress by providing periods of relatively high oxygen conditions across daily and weekly timescales. Communities do not respond to large natural O2, T, and pH variability occurring over shorter time-scales, but day-night differences are apparent. Over five-month, seasonal timescales, community responses do correlate with differences in environmental conditions. The transition from fish-dominated to invertebrate-dominated communities is associated with lower oxygen conditions, suggesting a useful ecological indicator of hypoxia. Small and easy to use with small boats, nanolanders are powerful tools for studying environmental variability and seafloor community responses, and improve our understanding of community vulnerability to climate driven environmental change.
Sex-specific foraging strategies of a sexually dimorphic marine predator, the northern elephant seal
Sarah Kienle, Ecology and Evolutionary Biology
UC Santa Cruz
Many sexually dimorphic species exhibit intraspecific niche divergence, often resulting in the sexes occupying different ecological niches. However, little is known about the foraging behavior of wide-ranging, deep-diving marine predators. We documented sex-specific foraging strategies in a large, sexually dimorphic marine predator, the northern elephant seal (Mirounga angustirostris). We coupled satellite telemetry, diving behavior, and foraging success metrics from 39 adult male and 152 adult female seals and showed that males and females differed in most key foraging metrics. Males are benthic continental shelf predators with small foraging areas and high foraging success, as measured by mass and energy gain. Males were extremely consistent in their feeding behavior, showing little to no flexibility. Females are primarily mesopelagic predators with large foraging areas and moderate to low foraging success. Females show more behavioral flexibility than males; females vary feeding strategies by season, where females on the post-breeding foraging trip (February–May) have small foraging areas, short pelagic foraging dives with low efficiency, and low foraging success compared to females on the post-molt trip (May–January). There was little to no overlap between male and female foraging strategies, indicating the sexes act as different ecological species in benthic and mesopelagic North Pacific habitats. There is a trade-off between survival and foraging success: males have a lower survival rate than females but higher foraging success. Males may adopt a riskier foraging strategy to attain and maintain the large body sizes required to compete for mating opportunities, while females may adopt a risk-adverse strategy to maximize lifetime reproductive fitness.
Pinniped taphonomy: Observations from a northern elephant seal breeding colony provide new insights into the taphonomic processes of pinnipeds
Ana M. Valenzuela-Toro, Ecology and Evolutionary Biology
UC Santa Cruz
The fidelity of reconstructions of ancient communities relies on how closely fossil assemblages capture the ecological attributes of the original living communities. Therefore, understanding the processes that occur between the death of organisms and their final burial and potential fossilization are critical, constituting the core of taphonomy. In particular, taphonomic studies on bone assemblages of living populations have provided valuable insights about the properties of the source population. Actualistic studies on vertebrate taphonomy have been focused on terrestrial mammals, and little is known about the taphonomic processes affecting the record of marine mammals. Pinnipeds (seals, sea lions, fur seals) exhibit an extensive fossil and archaeological record, the interpretation of which is often impeded by the lack of research on their taphonomic processes. I present the preliminary results of a taphonomic study performed in a modern breeding colony of northern elephant seals (NES; Mirounga angustirostris) located at Año Nuevo State Park, San Mateo County, California. We performed direct observations along linear transects. We recorded more than 350 isolated bones and 30 pinniped carcasses in variable states of decomposition and levels of completeness. Most of the remains were identified as belonging to NES pups, followed by adult and subadult California sea lions (Zalophus californianus), revealing some differences with respect to the source community. Overall, these results underline the need for new and more exhaustive studies incorporating knowledge of the functional anatomy and natural history of the species, to elucidate the taphonomic processes involved in modern, archaeological, and fossil assemblages containing pinnipeds.
Going with the flow, or not: how larvae contend with dynamic ocean environments
Helen Killeen, Coastal and Marine Science Institute
The vast majority of marine animals reproduce by releasing free-floating eggs or larvae directly into the water column. While ubiquitous, this life history characteristic has tradeoffs. For example, dispersing fish larvae can exploit productive regions distant from adult habitats, but they are also susceptible to being swept away from suitable settlement locations by strong ocean currents. The balance between benefits and drawbacks of life as plankton determines larval mortality rates and subsequent recruitment to adult populations. To examine whether larvae are able to mediate their chances of being advected from suitable habitat in strong currents, I quantified marine fish larval distributions on the central coast of California where currents are seasonally very strong. Observed distributions showed that larvae are able to stay close to shore even when currents moving offshore were strong. Different species exhibited different distributions, suggesting that species-specific behavior and depth preference play a role in retaining larvae nearshore. These findings contradict the prevailing assumption for this region that advection of larvae from shore limits marine fish populations. Further research examining the importance of other abiotic and biotic factors for larval mortality rates will improve our understanding of this poorly understood life history stage and the population dynamics of marine species.
The consequences of grazing disturbance on the genetic diversity of eelgrass meadows
Nicole M. Kollars, Evolution and Ecology
Eelgrass meadows, comprised of the seagrass Zostera marina, serve as an essential winter food source for Pacific brant geese. Previous research has shown that the genetic diversity (the number of unique clones) of eelgrass is important in helping eelgrass populations recover from the biomass removal caused by grazing. However, we do not know how the act of grazing affects the genetic diversity of the eelgrass. Does grazing reduce, maintain, or enhance genetic diversity? To address this question, I conducted a field experiment in Bodega Harbor, CA, that mimics grazing disturbance and measures how changes in disturbance intensity affect the number of unique clones present in the meadow. Preliminary results showed that a “normal disturbance” level (i.e., clipped twice during the grazing season) did not affect the clonal diversity of meadows. However, samples from the “absence of disturbance” and “intense disturbance” treatments still need to be genotyped. Because the genetic diversity of eelgrass is important to its persistence, understanding the direct impacts of geese on the genetic diversity of eelgrass is essential to understanding how changes in grazing intensity will affect the long-term sustainability of eelgrass populations.
Learning from the past: a life cycle approach to understanding California mussel declines
Lauren L.M. Pandori, Ecology and Evolutionary Biology
California mussels (Mytilus californianus) are a critical foundation species which support a diverse assemblage of associated species in the intertidal zone. Mirroring global trends among habitat-forming species, M. californianus biomass and cover have declined 30-50% in southern California since the 1970s, leading to reductions in species diversity of 58% on average. Proposed contributors for declines include changes in larval transport, increased human disturbance, and increased environmental stress likely to occur as a consequence of the warming climate. Given that thermal sensitivity and exposure differ across life stages, we developed a life stage-structured population dynamics model for California mussels with the objectives of: (1) investigating the effects of temperature on demographic rates, (2) identifying vulnerable life stages, and (3) predicting growth and extinction risks under a future climate scenario. We conducted experiments at Kenneth M. Norris Rancho Marino Reserve (Cambria, CA) and Crystal Cove State Park (Newport Beach, CA) that monitored thermal conditions, mussel distributions, and four demographic rates: fecundity, recruitment, survival, and growth. We found that thermal conditions and patterns of growth differed across tide heights, leading to differing patterns of vulnerability. Data collected will be used to develop a life stage-based population dynamics model to predict growth and extinction risks under changing thermal conditions.
Impacts of Mexacanthina lugubris, a dark unicorn in Southern California intertidal communities
Piper Wallingford, Ecology and Evolutionary Biology
The effects of climate-driven range shifts are well documented, but the impacts of range-shifting species on native communities are relatively unknown. In Southern California, the dark unicorn whelk Mexacanthina lugubris has been shifting northward from its native Baja California, Mexico range, which could lead to increased competition with endemic whelks and increased predation on shared prey species. To assess the effects of M. lugubris on local intertidal communities, we surveyed 10 Southern California sites over the course of a year to determine spatial overlap with native species and conducted feeding experiments to assess competitive interactions with native whelks and predation of native mussels and barnacles. Finally, thermal tolerance trials were run to predict how future climate change could alter species’ distributions and competitive ability. We found that M. lugubris was able to utilize space higher in the intertidal compared to local competitors and was often more abundant than native species in areas where establishment occurred recently. Additionally, M. lugubris had a greater impact on prey than native competitors and was more robust in the face of thermal stress. Understanding the potential for competition with local species can help determine how expanding species may impact communities, and whether these impacts could increase under future warming.
Causes and consequences of intraspecific variation in Daphnia life history: how can “superfleas” be explained?
Kelsey Lyberger, Evolution and Ecology
How variation is maintained in natural populations remains a fundamental question in ecology. Previous studies have found that Daphnia clones exhibit substantial variation in vital rates, including so called “superflea” clones, which are younger yet larger at maturity. The existence of superfleas contradicts classic life-history theory, which assumes there are tradeoffs between growth and reproduction. One explanation is that, as resource abundance varies, individuals face a tradeoff between being well adapted to high- or low-resource environments. I tested this mechanism in a laboratory setting by measuring life-history traits of the two Daphnia clones found in McLaughlin Natural Reserve’s Otter Pond under high and low resources. I found support for the hypothesis that superfleas are only super when resources are high. To further investigate this question in a natural environment, I monitored changes in genotype frequency, population sizes, and resource abundance in replicate enclosures in Otter Pond. I found the superflea clone took over regardless of starting genotype frequency. However, small, short-term fluctuations in resources do not explain changes in genotype frequency, and a longer time frame is needed to determine whether longer-term, seasonal resource availability explains the coexistence of the two clonal types.
Seasonal foraging-mode shifts of Oncorhynchus mykiss in a Mediterranean stream
Gabriel Rossi, Integrative Biology
For stream dwelling fishes, behavioral flexibility can allow individuals to survive and grow under changing contexts of food availability, competition, predation, and experience. Juvenile salmon and steelhead engage in a range of foraging tactics, including drift foraging—where fish hold focal points in the water column and make short forays to intercept drifting prey; search foraging— where foraging is not associated with a focal point, and benthic foraging—where benthic prey are captured by forceful attacks at the substrate. Diel shifts in foraging behavior have been observed in many salmonids but seasonal, population-scale behavioral shifts in response to ecological gradients have been studied more rarely. In fisheries management, habitat suitability has traditionally been based on fish response to hydraulic and physical habitat factors while food web dynamics, biotic interactions, and foraging mode have been notably excluded. Yet these ecological interactions have profound effects on the growth and success of juvenile salmonids and, therefore, on the recovery of imperiled adult populations. This study evaluates the phenology of steelhead (O. mykiss) foraging behavior and benthic invertebrate drift in a Mediterranean stream between May and August of 2016. This study seeks to identify whether a phenological pattern of juvenile steelhead foraging behavior and within-pool movement exists during the spring-fall period, and, if so, to explore some drivers of that pattern. Finally, I will synthesize some of the implications to seasonal foraging mode shifts on water and habitat management outcomes.
Translocating sub-soil to the surface reveals independent effects of microclimate and plant inputs on microbial access to soil carbon
Eric Slessarev, Ecology, Evolution and Marine Biology
UC Santa Barbara
Depth within the soil profile is a major control on the residence time of soil carbon. Both plant inputs and microclimatic fluctuations decline with depth in the soil profile; both may influence microbial access to C, and thus C residence times. I assessed the influence of plant inputs and microclimate separately by translocating subsurface soil samples (50–60 cm depth) to the surface for 18 months across three NRS reserves, and then either excluded plant inputs or allowed plant growth in the translocated soil. Translocated soil increased in microbial biomass after 18 months of surface exposure without plant inputs, while water extractable organic carbon concentrations remained unaffected. Allowing plant growth increased microbial biomass further while also increasing water extractable organic carbon. Respiration pulses from wetting dry, translocated soil were smaller on a relative basis than pulses from dry subsurface soil that remained in-situ, indicating acclimation to repeated wetting and drying cycles at the surface. These results show that climatic fluctuations at the soil surface are sufficient to increase the availability of native soil C, promote growth of microbial biomass, and change the sensitivity of microbes to hydrologic perturbations.
Using functional traits to build native grassland communities that are resistant to exotic annual grasses
Maddie Nolan, Ecology, Evolution and Marine Biology
UC Santa Barbara
Grasslands in California’s coast ranges were historically dominated by a diverse mixture of bunchgrasses and forbs. Yet today, these lands are dominated by exotic annual grasses and forbs, particularly where past agricultural activities disrupted the root systems of perennial plants. Without human intervention, these former agricultural sites remain dominated by exotic species, with little to no natural succession back to native species assemblages over many decades. Throughout California, restoration activities in these habitats have focused on the reestablishment of a small number of species, particularly the perennial bunchgrass Stipa pulchra. However, plant richness in California grasslands arises from forb and not grass diversity, so the failure of grassland restoration could be due, in part, to a lack of forbs in restored communities. Apart from being lower in species richness, restored communities that do not have native forbs could be missing important functional traits that help restored grasslands resist reinvasion by exotic annual grasses. My research proposes to quantify the diversity of functional traits across native grassland species and the common exotic annual grass Avena fatua. The information can be used to create theoretical assemblages of native grassland species that functionally overlap with Avena fatua and resist the establishment of this noxious exotic species. This research could provide valuable insights into the mechanisms controlling the continued dominance of Avena fatua and other exotic annual grasses in California grasslands.
Physiological sensitivity to historic drought and deluge years for eastern Sierra Nevada conifers
Katherine Ross, Environmental Studies
UC Santa Cruz
Projections of future precipitation trends in California suggest greater interannual variability, while higher temperatures increase risk of drought. By comparing spatial and temporal variation in photosynthesis, growth, and water status between unusually wet and dry years, across an elevation gradient, this study improves our understanding of the mechanistic pathways by which dominant conifer species respond to climate change. Recent years provide a rare opportunity to quantify conifer sensitivity to high and low precipitation extremes likely to become more common, as well as interactions between elevation and annual differences in precipitation reflecting within range differences. Photosynthesis, stem water potential, and CO2 response curves were measured for Abies magnifica, Pinus contorta, and P. jeffreyi at four sites along a 500 m elevation gradient in the eastern Sierra Nevada near Mammoth Lakes. Measurements from 2016–2018 started at the end of a historic drought and included the especially wet winter of 2017. Stomatal conductance was significantly greater earlier in the season in 2016 and 2018, but reached a maximum later in the season in 2017. Photosynthesis followed a similar pattern, but was only significantly lower later in the season in 2016. By contrast, no differences were found between elevations. Needle length was lower for the 2014 and 2015 cohorts than those from later years, but only for the lowest two elevations. Interactive effects of elevation, species, and year on photosynthetic carbon gain and needle biomass may help explain tree response patterns to extreme drought. These findings can inform future forest management strategies.
Clinal variation and plasticity in California poppy in response to climate change
Elizabeth Ryan, Ecology, Behavior and Evolution
UC San Diego
Predicting plant species responses to climate change can be complicated by population-level variation in plasticity. Yet predictive species distribution models assume current distributions are determined solely by climate, not biotic factors, and species do not have distinct populations with varied potential to adapt to climate change. We examined clinal variation in phenological traits and fitness, and plastic responses to environmental change, for 21 populations of California poppy along a clinal gradient across California characterized by a threefold increase in precipitation. Plants were grown in treatments approximating the precipitation regimes of the wettest and driest sites, and in the presence or absence of home soil. Phenological plant traits (emergence timing, flowering timing, growing season length) and fitness (biomass and seed production) both exhibited clinal variation. Southern populations emerged later, flowered earlier, had shorter growing seasons, and had higher fitness (biomass and seed production) than northern populations. Northern populations exhibited greater plasticity in emergence timing when grown in home soil, and four of the twenty-one populations produced more biomass in the presence of home soil. While flowering timing did not respond plastically to either precipitation or soil treatment, ample water precipitation lengthened growing season more for plants from northern populations, but increased growth (i.e. biomass) more for plants from southern populations. Thus, arid, warm populations that tolerate conditions north of current distributions are particularly promising candidates for assisted migration. Current predictive modeling approaches may be insufficient for species exhibiting clinal variation and high population-level variation in plasticity.
16 Seasonal fluctuations in natural selection help maintain genetic diversity
Ben Wasserman, Ecology and Evolutionary Biology
UC Santa Cruz
Natural selection allows populations to adapt to their environments. The selection caused by changing environments may fluctuate over time. The effects of such fluctuating selection on the long-term evolution of populations is not well understood. Moderate fluctuations in the strength and direction of selection may lead to the persistence of genetic diversity in a population, whereas large fluctuations may lead to the loss of alleles and a reduction in genetic diversity. We tested whether fluctuations in natural selection due to seasonal environmental shifts can function to maintain genetic diversity in a system where stable selection would drive a population to fixation. We studied how differences in the annual rainfall and subsequent lagoon breaching affect the evolution of armor morphology and the underlying genes in threespine stickleback (Gasterosteus aculeatus), which are known to correlate with freshwater or marine residency in other stickleback populations. In stickleback inhabiting intermittently ocean-connected estuaries, we found that traits and genotypes associated with freshwater and marine residency fluctuate seasonally as predicted over four years—less armored during the dry summer and fall, and more armored in the wet winter and spring. We will discuss the importance of interannual variation in breaching intensity for the maintenance of genetic diversity.
Phylogeography of carpenter ants from the California Channel Islands: an evolutionary reconstruction based on phylogenomics
Ida Naughton, Ecology, Behavior and Evolution
UC San Diego
The California Channel Islands support a wealth of biodiversity and are home to numerous threatened and endemic species. While the plants and vertebrates of this archipelago have received considerable attention from biologists in recent decades, an understanding of the insect fauna remains incomplete. With relatively modest capacities for over water dispersal, ants tend to exhibit intriguing biogeographic patterns. On the Channel Islands, for example, ants provide apparent examples of relictual distributions, disjunct distributions, and island endemism. Carpenter ants (Camponotus) are a historically old and hyper diverse ant genus with a worldwide distribution; just over twenty species of Camponotus occur in California, including numerous taxa that are endemic to the California Floristic Province. Here I present the preliminary results of a comparative phylogeographic study of eight Camponotus taxa that occur on the Channel Islands. I sampled workers of eight taxa of carpenter ants in several locations on each island in which they occur, and across their range in the California Floristic Province, including six UC NRS reserves. For each sample, I extracted total genomic DNA, constructed DNA libraries using KAPA DNA Hyperprep kits, and enriched pooled libraries for ~1510 ultraconserved elements. I sent pooled, enriched libraries to the Vincent J. Coates Genomics Sequencing Laboratory at UC Berkeley for 150 bp pair end sequencing on a HighSeq 4000. Preliminary analyses reveal interesting patterns of differentiation and help clarify the taxonomic status of several putative island endemics.
Joshua tree aesthetics: a history of grazing and its charismatic yucca
Julia Sizek, Anthropology
As for many potentially endangered species, the protection of Yucca brevifolia forges strong ties between the plants and their habitat. Under future climate regimes, scientists anticipate that current distributions of Joshua trees—based on past climatic conditions—will no longer align with their future habitats. In this paper, I examine one habitat where the charismatic yucca thrives, showing that the landscape supporting dense, aesthetically pleasing stands of Joshua trees was one indelibly shaped by large-scale grazing in the East Mojave. Following a history of desert aesthetics that links idealized desert landscapes to intensive grazing regimes over the last 150 years, I argue that grazing landscapes labeled as Joshua tree woodland or Joshua tree shrubland became an aesthetic expectation for the East Mojave that persists today. Contributing to social scientific literature on contemporary anthropogenic change and historical ecology, I argue that understanding the historical change of Joshua tree habitat can reshape our understanding of the charismatic yucca under anticipated climate change regimes and Anthropocene ruination, unsettling relationships between past and future.
Understanding how dark-eyed juncos (Junco hyemalis) differentiate between local and foreign song
Felisha Wong, Ecology and Evolutionary Biology
UC Los Angeles
The purpose of this research is to determine how dark-eyed juncos (Junco hyemalis) respond to different populations’ songs, how these songs differ, and what components of songs individuals use to discriminate among the songs of different populations. I will record the songs of male dark-eyed juncos in three urban populations and three natural habitat populations: UC Los Angeles; UC San Diego; UC Santa Barbara; the San Jacinto James Reserve; the Angeles National Forest; and the San Bernardino National Forest. I will construct playback recordings of each location’s songs and expose males from each population to songs from all six populations. I will measure a range of aggression traits, including: (1) male’s closest approach to the speaker; (2) delay before approaching within 1 m and 5 m; (3) delay before the male’s first flyover; (4) number of flyovers; (5) time spent singing in response; and (6) time spent within 1 m and 5 m of the speaker. Each population’s songs will also be analyzed to determine differences in frequency, trill rate, song length, and syllable length. After determining these differences, recordings will be manipulated to control for one of these variables and played back to each population to see which elicits the most aggressively reactions. I predict that each population will respond more aggressively to the songs from their own population than to those from a foreign population and that the songs from each urban location will be more similar to each other than to those from natural habitats.