Life Sciences Commons^™

A Student’S Perspective On Engagement In Ecological Research During Their First Semester In College, Natalie M. Aguirre, Karagan L. Smith, Cristian M. Garcia, Cheryl Swift, Stephen D. Davis

Biology

Pepperdine University and Whittier College jointly initiated a new first-year seminar series in the fall of 2016 that engaged students in authentic research, their first semester on campus. The goals are listed below. Assessment of these goals included both qualitative focus groups and quantitative survey questionnaires administered by an outside assessment agency, WestEd.org.

Ninety-two percent of students reported that their first-year seminar improved learning in concurrent courses and ninety to ninety-three percent of students said their first-year seminar increased their interest in STEM. In addition, students self-reported a significant improvement in all aspects of their ability to plan and conduct …

Post Drought Recovery In Malosma Laurina After Severe Dieback During California’S Historic Drought Of 2012-2016, Karagan L. Smith, Guinevere X. Mesh, Natalie M. Aguirre, Gabriella N. Palmeri, Helen I. Holmlund, Stephen D. Davis

Biology

Malosma laurina is a species of chaparral shrub that dominates coastal exposures of the Santa Monica Mountains of southern California. Between 2012 and 2016, protracted drought with half normal rainfall over a five-year period (175 mm), led to severe dieback, exceeding 50% whole plant mortality at some sites. The drought dissipated in 2017 with an annual rainfall that exceeded the 140-yr normal by 108 mm. As a result of this elevated annual rainfall in 2017, we were interested in documenting the potential for full recovery of Malosma laurina as a keystone species of coastal chaparral shrub communities. We tested the …

A Comparison Of Water Potential, Photosynthetic Rate, Electron Transport Rate, And Stomatal Conductance Between Native Malosma Laurina And Exotic Schinus Molle, Karagan L. Smith, Agatha C. Heng, Viridiana Hernandez-Lopez, Stephen D. Davis

Biology

Schinus molle is a relatively new invasive chaparral shrub in the Santa Monica Mountains and has only recently been observed to displace native shrubs like Malosma laurina. To investigate the probable cause of S. molle’s competitive displacement of M. laurina, we compared their water status, photosynthetic rates, electron transport rates, and stomatal conductance to water vapor diffusion during the fall months of 2016. We hypothesized that S. molle would physiologically outperform M. laurina indicated by higher photosynthetic rates, electron transport rates, stomatal conductance rates, and less negative water potential. We found that there was no significant difference between dry …

The Effect Of Drought On The Comparative Fitness Of Purple Needle Grass (Stipa Pulchra) In The Presence Of An Invasive Weed, Grace M. Palmer, Taylor M. Purdy, Stephen D. Davis

Biology

Studies on the relative health of Stipa pulchra, a California native perennial bunchgrass, were conducted at the transplant garden on the Drescher campus of Pepperdine University in the Spring semesters of 2016 and 2017. Following the trend of other perennial native grasses, Stipa pulchra is dwindling due to competition with Avena fatua and other invasive species introduced by human activities. In 2016, in the midst of historic five-year drought in California, stomatal conductance, dark adapted fluorescence, water potential, and height of S. pulchra and A. fatua were recorded and compared. As hypothesized, the wild S. pulchra exhibited greater overall fitness-- …

Resistance To Xylem Cavitation In Evergreen Ferns Correlates With Seasonal Dehydration Levels, Not Mechanical Strength, Helen I. Holmlund, Kaitlyn E. Sauer, Breahna M. Gillespie, Jarmila Pittermann, Stephen D. Davis

Biology

Ferns in the Santa Monica Mountains of southern California display a range of responses to severe drought. In this study, we further characterized the traits that may contribute to fern survival in a mediterranean-type climate. Due to anatomical differences between ferns and angiosperms, we predicted that ferns would exhibit no correlation between stipe mechanical strength and vulnerability to water stress-induced cavitation of stipe xylem. However, we predicted that ferns would show a correlation between seasonal water stress (minimum water potential) and cavitation resistance. Our results support these hypotheses; however, we must increase our sample size of evergreen fern species in …

Malosma Laurina Dieback Associated With Fungal Induced Loss In Hydraulic Conductivity And Photosynthesis, Gabriella N. Palmeri, Shaquetta R. Reese, Helen I. Holmlund, Frank W. Ewers, Stephen D. Davis

Biology

Widespread Malosma laurina (Laurel Sumac) dieback is occurring throughout the Santa Monica Mountains. M. laurina is a keystone species within the SMM and its deep roots provide necessary slope stability to the hillsides; therefore, M. laurina’s health is of ecological importance. This study examines whether M. laurina dieback is associated with decreased stem water transport due to the prevalence of a pathogenic fungus within the water transport tissue. Stem samples from dieback and healthy control M. laurina were cultured for fungal growth. 100% of samples from water transport tissue from dieback adult plants contained a fungal pathogen from the …

Premature Seed Germination And High Seedling Mortality In A Chaparral Shrub (Adenostoma Fasciculatum) Caused By Severe Drought In Calfiornia, Lexe Evans, Teal Speece, Stephen D. Davis

Biology

The Santa Monica Mountains (SMM) represents one of five Mediterranean-type environments in the world. With sustained summer droughts, this ecosystem is prone to frequent wildfires, a phenomenon that has affected the SMM with regularity once every 32 years. Adenostoma fasciculatum (chamise), is a chaparral shrub well adapted to wildfire cycles because typically its seeds are triggered to germinate by high fire temperatures, smoke, and charate. In the winter of 2015, we were surprised to discover seedlings of A. fasiculatum emerging at an unburned chaparral site without the occurrence of fire. We hypothesized that drought induced canopy dieback at some microsites, …

Recent Dieback In A Keystone Chaparral Species Is Caused By A Fungal Pathogen, Botryosphaeria Dothidea, Adriana Borges, Frida Morales, Emily Pierce, Mariah Taylor

Biology

Due to the recent drought in Southern California, the abundance of a keystone species, Malosma laurina, within the Santa Monica Mountains (SMM) has been dwindling. This species has a rooting depth that exceeds 13 m, so it typically has little difficulty tapping into the water table. Recently, this species has undergone extensive dieback, which might be attributed to the unprecedented drought in California and predisposition fungal pathogen Botryosphaeria. dothidea. While this fungi appears to be innocuous to M. laurina when the plant is healthy, it is more susceptible to invasion under water stress due to the dry and …

Extensive Dieback In Malosma Laurina In Coastal Exposures Of The Santa Monica Mountains Associated With Unprecedented Drought In California, Gina S. Gilderman, Kaitlyn E. Sauer, Gabriella Palmeri

Biology

Throughout coastal exposures of the Santa Monica Mountains (SMM) there is a recent emergence of widespread dieback in Laurel Sumac (Malosma laurina). M. laurina is a keystone species of chaparral that dominates the SMM. A significant trait of M. laurina is an extensive root system exceeding 12 m in depth. We hypothesized that M. laurina was weakened by unprecedented drought in California (2013-2015) and predisposed to fungal pathogens. An initial study conducted in the summer of 2015 revealed all stem samples taken from dieback adult M. laurina plants were infected with Botryosphaeria dothidea, while zero stem samples taken …

Novel Seed Germination In Response To California’S Historic Drought May Deplete Soil Seed Banks, Amanda M. Burns, Victoria M. Lekson, Helen I. Holmlund, Stephen D. Davis

Biology

We observed novel seed germination, without a fire cue, in an obligate seeding species of chaparral (Ceanothus megacarpus) during historic drought in California (2014). We hypothesized that premature germination was promoted by drought-induced canopy dieback among adults that allowed high radiation loads to reach normally shaded soils, cracking seed coats, facilitating water uptake. We hypothesized that because premature seed germination was late in the season (April, when December is typical) roots would not have time to penetrate deep moisture resources before the onset of summer drought, leading to excessive mortality and eventual depletion of soil seed banks. We …

Comparative Foliar Water Uptake And Leaf Hydrophobicity In Island Versus Mainland Ferns, Victoria M. Lekson, Helen I. Holmlund, Nicole A. Nakamatsu, Amanda M. Burns, Stephen D. Davis

Biology

In 2014, Southern California experienced the worst drought in the last 1,200 years. In this study, the mechanisms of drought tolerance for eight species of ferns in the Santa Monica Mountains were assessed with a focus on foliar water uptake and hydrophobicity of frond (leaf) surfaces. We measured gravimetric foliar water uptake and angle of contact for a drop of water on a frond. Seasonal shifts were tracked as a method of following drought response patterns.

Fog is becoming more important due to limited ground water. Fog is far more common on Santa Cruz Island off the coast of California …

Differential Survival Of Chaparral Shrub Species In Response To Severe Drought, Hannah Dario, Stephen D. Davis

Biology

In this experiment, we examined how the plants in the Santa Monica Mountains are responding to the driest period in recorded history for California. Our hypothesis was that plant species with the deepest roots would have highest survivorship. We thought this because deep-rooted shrubs will have greater access to soil moisture. This hypothesis was tested by collecting data on plant survival, in a mixed chaparral stand, containing eleven species, growing in the Green Valley Preserve off of Stunt road, in the Santa Monica Mountains. The chaparral stand was 21 years old, having last burned in 1993 (Old Topanga Canyon Fire). …

Leaf Mechanical Strength Corresponds To Tissue Water Relations In Twelve Species Of California Ferns, Breahna M. Gillespie, Stephen D. Davis, Jarmila Pittermann

Biology

The dominant vegetation types in southern California’s coastal foothills are chaparral and costal sage scrub. Chaparral shrubs have mechanically strong evergreen leaves whereas coastal sage scrubs bear mechanical weak, facultative deciduous leaves. What about the ferns that live in the understory of these vegetation types, especially considering their adaptations to a summer dry, Mediterranean-type climate? We tested the hypothesis that some fern leaves are stronger than others and mechanically strong leaves are associated with greater dehydration tolerance. Twelve fern species were examined. Tissue water relations were assessed via pressure volume curves using Scholander-Hammel pressure chambers. We estimated osmotic potential at …

Relationship Between Dehydration Tolerance Of California Ferns And The Mechanical Strength Of Their Stipes, Helen I. Holmlund, Stephen D. Davis

Biology

In recent years, experts in plant physiology have begun to explore the functional traits of ferns, especially in regards to their tissue-water relations. However, to our knowledge, no scientist had yet examined the relationship between fern biomechanics and physiology. We examined the mechanical properties of fern stipes (stems) and attempted to relate those properties to ecological and physiological traits. Based on our knowledge of fern anatomy, we hypothesized that stipe mechanical strength would not correlate with water-stress resistance as it does in seed-bearing plants.

We assessed mechanical strength using Modulus of Elasticity (MOE) and tissue-water relations using pressure-volume curves. Water-stress …

Plasticity In Cavitation Resistance And Mechanical Strength Of Stem Xylem In Heteromeles Arbutifolia, Adults Versus Post-Fire Resprouts, Iolana N. Kaneakua, B. A. Bergman, F. W. Ewers, S. D. Davis

Biology

Background/Questions/Methods

Many species of chaparral shrubs of California undergo vigorous resprout success after wildfire. We hypothesized that the water transport properties of resprouts, as well as their biomechanical strength would differ from adults. In addition, we hypothesized that irrigated and shaded resprouts would display reduced cavitation resistance and biomechanical strength in comparison to controls and adults. We tested these hypotheses by using a centrifuge method to compare the vulnerability of xylem to water stress induced cavitation. We used 50% loss in hydraulic conductivity due to water stress (PLC₅₀) as our estimate of vulnerability to cavitation. A Universal Materials …

Foraging Preference By Wild Deer On Toyon Populations From Santa Catalina Island Versus The Santa Monica Mountains, Amelia I. Clark, Rodney Honeycutt, Anjel Helms, Stephen Davis

Biology

Post-fire regeneration of Toyon (Heteromeles arbutifolia), a chaparral shrub on Santa Catalina Island is impeded by mule deer (Odocoileus hemionus), a non-native species introduced during the 1930’s. Mainland and island populations of Toyon were examined for potential differences in defense mechanisms that act as natural deterrents to over-browsing by ungulate herbivores, with the hypothesis that island populations, void of natural ungulate herbivores, may lack such defense mechanisms. Several characteristics of leaf morphology, including number and length of spines, leaf area and depth, and tensile strength of leaves, were compared between island and mainland populations. Leaves of Toyon from Santa Catalina …