I have always enjoyed thinking about factors and mechanisms that maintain and generate diversity, and the study of plant evolution has become a central focus of my research. I believe that evolutionary problems are best answered using an interdisciplinary approach, and thus my research bridges concepts from ecology, physiology, reproductive biology, genetics, and systematics in the study of plant evolution.
I believe in using research as a teaching tool and have developed an undergraduate student-led research program in geoecology over the last fourteen years. Much of my research to date has been aimed at getting undergraduate students excited about inquiry-based learning and providing them with the critical thinking skills needed to succeed in their post-graduation pursuits. I love working with undergraduate students and giving them their first taste for research—supplying them with the tools they need to conduct ecological research, from the initial development of hypotheses via field observations, to publishing results in peer-reviewed journals, and all of the steps in between, including securing funding.
See here for past research conducted during my time at College of the Atlantic, Maine (2004-2008; 2010-2016) and San Jose State University, CA (2008-2010).
At Cal Poly, I plan to continue my current research on the evolutionary ecology of edaphically-specialized plants (including Lasthenia, Layia, Streptanthus, Chorizanthe, and Monardella, as well as others) and to establish new projects with Master’s and undergraduate students examining how edaphic, climatic, and topographic features contribute to the diversity, ecology, and evolution of vascular plant, bryophyte, and lichen species and their communities in California and elsewhere. In addition, I look forward to getting involved in applied research, particularly in projects relating to the restoration of habitats with ‘harsh’ soils and the conservation of plants that are restricted to such habitats. I am also interested in phytoremediation, the use of native plants to clean soils that are contaminated with heavy metals due to anthropogenic activities such as mining.
Current Projects on the California Flora
1) Seed Longevity and Climate Tolerance of San Joaquin Woolly Threads (Monolopia congdonii)
Monolopia congdonii (Asteraceae) is a federally-listed endangered annual plant species. Its historic range included most of the San Joaquin Valley where it was once broadly distributed, however, the species now only consists of small, scattered populations. The mission of the current project is to provide land managers information to assist with species recovery and management. The primary objectives are to: 1) determine the seed viability curve and estimate maximum seed longevity based on seed viability analysis from herbarium specimens and old seed collections, and 2) examine plant response to simulated climates analogous to the Mojave Desert and Sonoran Desert to determine effects of projected climate change on the species. Research will include herbarium, growth chamber, and field work.
Graduate Student: Paul Excoffier (Fall 2017-current)
Undergraduate Student: Christopher Howington (Fall-Spring 2017-2018), Peter Walsh (Fall-Spring 2017-2018), Dylan Stephens (Spring-Summer 2019)
Collaborator: Ryan O’Dell (Bureau of Land Management)
2) Causes and Consequences of Intraspecific Variation in Milkwort Jewelflower (Streptanthus polygaloides)
Streptanthus polygaloides is a serpentine endemic found only on the western slopes of the Sierra Nevada Range in California. The species can hyperaccumulate nickel (>0.1% of dry leaf tissue, i.e., at least 1000 ppm) and is one of only two nickel-hyperaccumulating species confirmed from continental North America. Streptanthus polygaloides consists of four sepal color morphs found along an elevational gradient. The morphs are also distinct with respect to their soil-tissue ion relations. We plan to better characterize these morphotypes in terms of their ecology, ion accumulation, taxonomically important traits, and inter-morph reproductive compatibility. If morphotypes are ecologically distinct, differ in taxonomically important traits, and show reduced reproductive compatibility, they may be worthy of both taxonomic subdivision and—depending on the abundance of each taxon—subsequent listing for conservation.
Graduate Student: You?
Undergraduate Students: Peter Walsh (Fall 2017-Fall 2018), Christopher Howington (Fall 2017), Anthony Ferrero (Fall 2017-Spring 2019), Charlotte Miranda (Spring 2018), Teiana Cataldo (Fall 2018-Spring 2019)
Collaborator: Dr. Robert Boyd (Auburn University, AL)
3) Ecological Speciation in Rayless Tidytips (Layia discoidea)
A potentially fascinating example of the relationship between adaptation and reproductive isolation yet to be studied lies in the progenitor-derivative species pair of Layia glandulosa (non-serpentine) and L. discoidea (serpentine endemic). Unlike Mimulus, in which hybrid lethality has been documented between copper-tolerant and -intolerant taxa, there is complete fertility between artificial crosses of the serpentine-intolerant and serpentine-endemic Layia species; however, natural hybrids are not found in nature, suggesting that partially or completely reduced hybrid fitness in one or both parental habitats may be responsible for the diversification. Additionally, it is unknown whether the flower shape (discoid- vs. ray-flowered) plays a role in pollinator preferences or whether potential differences in flowering time, especially when populations occur along contact zones, contribute to pre-zygotic isolation. We plan to conduct 1) greenhouse studies to better explore the nature of adaptation to serpentine soils in Layia discoidea, 2) field studies to better characterize their phenology and plant-pollinator interactions, and 3) a reciprocal transplant study in the field or in the greenhouse using field collected soils to examine the factors contributing to reproductive isolation between the two Layia species.
Graduate Student: You?
Undergraduate Student: Sam Farrow (Fall 2017-Spring 2018); Alex Pena (Winter 2019-current)
4) Ecological Speciation in the Maritime Goldfields (Lasthenia maritima)
The factors contributing to reproductive isolation between the guano-endemic, Lasthenia maritima, and its close relative and coastal bluff-specialist, L. minor, is little-known. There is evidence for greater self-compatibility within the guano-endemic, resembling the trends shown for some metal-tolerant species; however, it is unclear whether other isolating barriers, such as differences in pollinators or flowering times, or hybrid inviability and reduced fitness of hybrids in parental habitats, also contribute to isolation. Further, the physiological bases for guano adaptation are also unknown. Whether it is the high nutrient content (nitrogen, phosphorus), low pH (due to uric and other acids), or another chemical or physical factor of guano, that drives selection on these substrates needs further investigation. We plan to conduct greenhouse- and field-based studies to investigate the reproductive isolating barriers between the two species and better characterize the nature of guano adaptation in L. maritima.
Graduate Student: You?
Undergraduate Student: Sam Farrow (Fall 2017-Spring 2018)
Collaborator: Dr. Mike Vasey (San Francisco Bay National Estuarine Research Reserve and San Francisco State University)
5) Ecology & Adaptive Significance of Nickel Hyperaccumulation in Streptanthus poygaloides & Noccaea fendleri
Hyperaccumulation of nickel (Ni) (>0.1% of dry leaf tissue, i.e., at least 1000 ppm) is a fascinating phenomenon seen in less than 500 serpentine-associated species worldwide. Various hypotheses have been brought forward to explain this unusual physiology, with the defense hypothesis being the most-discussed in the literature. Investigation of other adaptive roles for Ni-hyperaccumulation is exciting from an evolutionary standpoint. Studies have shown that most hyperaccumulators localize Ni in the leaves, specifically in the vacuoles of guard cells or subsidiary cells, suggesting an osmotic-regulation role for this ion. Because serpentine habitats are often exposed to extreme drought, it is tempting to speculate that this ion may be used as an osmoticum to maintain a favorable water potential gradient. Our recent studies also show that Ni may contribute to increased flowering in Ni-hyperaccumulating plants, making them more fit under growing conditions with high concentrations of Ni. We hope to initiate several studies to investigate aspects of the evolutionary ecology, including cross-kingdom interactions, of the only known California taxa to hyperaccumulate Ni, S. polygaloides (accumulating up to 20,000 ppm of Ni) and N. fendleri subspecies – formerly, Thlaspi montanum – (accumulating up to 5,000 ppm of Ni).
Graduate Student: You?
Undergraduate Students: Peter Walsh (Fall 2017-Spring 2018), Christopher Howington (Fall 2017-Spring 2018), Anthony Ferrero (Fall 2017-Spring 2019), Teiana Cataldo (Fall 2018-Spring 2019)
Collaborator: Dr. Bob Boyd (Auburn University)
6) Understanding the Cost of Tolerance to Serpentine Soils
Serpentine outcrops provide edaphic “islands” within the California chaparral and are characterized by remarkable floras with a high degree of endemism. Serpentine soils provide outright hostile conditions for plant growth. Hence, species that colonize this unusual substrate have to overcome the “serpentine syndrome” involving an array of hostilities. Many species avoid California’s serpentine outcrops altogether while others exhibit various stages of accommodation to the substrate. This range of responses suggests a compelling question related to the distribution of species on California serpentines: why do some taxa give rise to serpentine endemics or ecotypes while others maintain a single species across serpentine and non-serpentine soils? There is considerable evidence that the evolution of tolerance to extreme edaphic conditions can involve a physiological cost (i.e., tradeoff between tolerance and growth, including reproduction). We hypothesize that there is a relatively higher cost to the tolerance found in species and ecotypes that are endemic to serpentine soils relative to the cost of tolerance found in widespread, undifferentiated species that occur both on and off of serpentine. Thus, only lineages experiencing a high cost to tolerance will be subjected to strong divergent selection across the serpentine and non-serpentine boundary. To study this, we will select species pairs with various levels of accommodation (i.e., endemic, indifferent, intolerant) to serpentine soils. Competition experiments will be conducted on and off of serpentine soils to determine whether there is a higher cost to serpentine tolerance in species/ecotypes endemic to the substrate.
Graduate Student: You?
Undergraduate Student: ?
7) Evolution of Plant Communities: The Role of Adaptive Evolution versus Ecological Sorting Processes in the Formation of Serpentine Chaparral
Tolerance to serpentine may involve multiple functional traits relating to morphology and ecophysiology, making the study of serpentine chaparral an ideal model system to enhance our understanding of the relative importance of adaptive evolution and ecological sorting processes in the evolution of plant communities. We plan to conduct a comparative study of functional traits related to serpentine-tolerant species and their serpentine-intolerant congeners from several common chaparral lineages to address the following questions:
1) What are the key traits relating to functional morphology and ecophysiology that differ between serpentine species and their closest relatives found on non-serpentine soil
2) Do the findings support the hypotheses of convergent evolution (i.e., traits giving adaptation to serpentine have evolved independently in different lineages) or exaptation (i.e., traits were already present in the ancestors and ecological sorting processes have allowed the formation of serpentine chaparral) or both?
The research will involve field measurements of functional traits as well as common garden studies involving hydroponic and greenhouse experiments to characterize potentially adaptive traits relating to the tolerance of heavy metals (Ni, Cr), nutrients imbalances (N, Ca:Mg), and water stress, features that appear to be distinct in the preliminary work conducted to date.
Graduate Student: You?
Undergraduate Student: You?
Collaborators: Dr. David Ackerly (UC Berkeley), Dr. Charley Knight (Cal Poly)
8) Endemism and Rarity in California’s Flora: Are Most Endemic and Rare Species Edaphic Specialists?
California is home to 6,523 minimum-rank native plant taxa, more than 35% (2,273) of which are endemic to the state. Out of these endemic taxa, 58% (1,314) are considered rare by the California Native Plant Society. Our preliminary analysis of reported substrate affinities for rare, endemic taxa indicates that at least 36% are edaphic specialists. Approximately 12% of California endemics are exclusively found on serpentine soils. Comparatively little is known about other substrate affinities (e.g., carbonitic, volcanic, and gabbroic soils) present in the California flora. Using GIS and other data sources, including California Native Plant Society, California Natural Diversity Database, Jepson Online Interchange for California Floristics, we plan to determine the range of substrate affinities within the California-endemic taxa to gain a greater understanding of the abiotic factors governing biodiversity and rarity in California.
Collaborators: Nick Jensen (Rancho Santa Ana Botanic Garden), Dr. Shannon Still (UC Davis Arboretum & Public Garden), Dr. Erin Riordan (UC Berkeley), David Baxter (UC Berkeley), and Josh Steele (Rancho Santa Ana Botanic Garden).
9) Role of Climate and Geology on the Diversity of Lichens and Bryophytes in California
Serpentine-vascular plant relationships have been the focus of many ecological and evolutionary studies; however, studies of serpentine-associated bryophytes and lichens are limited. Although bryophyte and lichen taxa endemic to serpentine are rare, the limited research to date has shown that serpentinite and other ultramafic rocks harbor distinct assemblages of species relative to those found on nearby non-ultramafic rocks and often contain metal-tolerant and locally rare species. Because cryptogams are generally slow-growing and are readily out-competed by vascular plants, they often reach their greatest diversity in habitats that are unsuitable for vascular plant growth. For vascular plants, alpha diversity (i.e., within site or local species richness) and beta diversity (i.e., community differentiation among sites, i.e., species turnover among sites) often increase with increasing productivity (i.e., biomass) resulting from higher precipitation (1, 2) and decreasing latitude (3), but it is unclear whether such relationships exist for bryophytes and lichens. In vascular plants, high productivity leads to increased habitat specialization because productivity intensifies the competitive pressure resulting from a larger regional species pool (i.e., higher gamma diversity) (1, 2). In collaboration with lichenologists and bryologists we plan to investigate how productivity (via precipitation) influences alpha and beta diversity of bryophytes and lichens found on adjacent, chemically distinct rock types along a rainfall gradient in California.
Graduate Student: Michael Mulroy (Fall 2019-)
10) Examining local adaptation to soils or microclimate in three common chaparral shrubs
In 2009, we reciprocally transplanted 6-month-old seedlings of Adenostema fasciculatum, Ceanothus cuneatus and Eriodictyon californicum to serpentine and sandstone soils, and cool northerly and warm southerly slopes to see if these common species were locally adapted to their respective soils and microclimate. At the age of 2 years, none of the species manifested higher survival or growth on ‘home’ compared with ‘away’ soils or slopes, indicating an absence of local adaptation with respect to seedling recruitment. Our results did not, of course, rule out local adaptation at either earlier (e.g., seed germination and early establishment) or later life stages (e.g., reproduction) than those we were able to study in our experiment. We plan to revisit the transplant experiment and look for evidence for local adaption in the adult shrubs that have now reached reproductive maturity. We will assess total reproductive effort as well as characterize other ecophysiological traits (water use efficiency, photosynthesis, etc.) to determine if the adult shrubs are locally adapted to their home (soils and slope) environment.
Graduate Student: You?
Undergraduate Student: You?
11) The Role of Fire on Plant-Soil-Aspect Relationships in the Poly Canyon, San Luis Obispo, California
Fire plays a key role in the ecology of chaparral and grasslands of California. Seeds of many plants germinate only in the year after a fire, and so the age, reproduction, dispersal potential, and community composition of plants are controlled by the infrequent occurrence of fire. Prescribed fires are difficult to plan and execute and are often cancelled or postponed, hence controlled experimentation using prescribed fire is rarely successful. As a result, research that has been done on the fire ecology of these ecosystems in California has been largely opportunistic, taking advantage of naturally occurring fires. More than 97 acres of accessible public lands burned in the Poly Canyon Fire in the Fall of 2017, creating a rare opportunity to examine the role fire plays in generating and maintaining plant diversity on different soils and aspects found within Poly Canyon. Vegetation monitoring plots have been set up to determine short- and long-term patterns of plant diversity on north- and south-facing aspects of chemically-distinct serpentine and metavolcanic soils following the fire. Additionally, a reciprocal transplant study will be conducted to determine if seedling recruitment occurs only from seed produced on particular soil types or on particular slope aspects, or whether seed produced in a particular habitat can successfully germinate and establish in other soil types or on slopes with different aspects. Finally, how the nutrient rich fire retardant (Phos-Check) influences native and nonnative plant interactions on serpentine and metavolcanic soils will also be investigated. Results from this study will provide useful information for understanding how fire influences plant diversity on common but distinct soil types/aspects found in central coast California and generate guidelines for science-based management of chaparral ecosystems. This information will contribute to both the restoration of degraded chaparral and to the ability of resource managers to predict and plan for shifts in species distributions in response to climate change.
Graduate Student: You?
Undergraduate Students: Chris Howington (Fall 2017-Summer 2018), Gabi Orta (Fall 2017-Spring 2018), Peter Walsh (Fall 2017-Spring 2018), Anthony Ferrero (Fall 2017-Spring 2018), Zach Raposo (Fall 2017-Summer 2018), Charlotte Miranda (Fall 2017-Spring 2018), Morgan Morris (Fall 2017-Spring 2018), Cora Bishop (Fall 2017-Spring 2018), Jackie Duerksen (Fall 2017-Spring 2018), Freddie Mayer (Fall 2017-Spring 2018), and other undergraduate student volunteers
Collaborators: Luka Negoita
12) Impacts of multiple nutrient element enrichment on native and alien plant species from California’s serpentine grasslands: Implications for better management of a threatened habitat
California’s serpentine soils are an important refuge for rare species, supporting over 200 plant taxa with highly restricted ranges, 111 of which have threatened, endangered, or special conservation status. The unique biogeochemistry of the substrate, characterized by nutrient imbalances, is responsible for the prevalence of rare, native species, exclusion of alien species, and ecotype formation within those species that do not grow on serpentine soil. In recent decades, human activities have greatly increased the amount of bioavailable nutrients in the biosphere, mostly through fertilizer use and fossil fuel combustion. For example, atmospheric deposition as high as 20 kg N ha-1yr-1 have been documented on serpentine outcrops in the Bay Area. Understanding the ecological implications of such increases in nutrient deposition is critically important, particularly in this rare and unique ecosystem of high conservation value. Alien grasses, supposedly restricted from serpentine habitats due to nutrient deficiencies, are better able to invade the substrate under N enrichment. Such recent invasions, especially on serpentine grasslands in the Bay Area, are progressively eliminating native species associated with serpentine habitats. While some attention has been paid to N enrichment and its effects on patterns of plant growth and diversity on serpentine grasslands and other nutrient-poor grassland communities, no study to date has examined the effects of multiple nutrient enrichment of N, Ca, and P (all naturally limiting on serpentine soils) on the growth of co-occurring native versus alien species or how such enrichment could potentially impact plant diversity of serpentine grasslands. We are currently conducting a greenhouse study of the effects of multiple nutrient enrichment on native and invasive grasses on serpentine soil to better understand the interactions between multiple nutrient elements and their influence on vegetation dynamics in California’s serpentine soils.
Graduate Student: You?
Undergraduate Students: Mary Devlin (Winter 2018-Summer 2018), Amber Williams (Summer 2018), Dylan Stephens (Fall 2018-Spring 2019), Morgan Morris (Fall 2018), Sophie Parr (Fall 2018), Amanda Gersoff (Winter 2019)
Collaborators: Luka Negoita
Current Projects in South Africa
1) Examining the role of substrate chemistry and climate on the diversity of lichen species in South Africa
Lichens are symbiotic organisms that tolerate a range of substrates and environmental conditions and are widely used for environmental monitoring. Lichenology is a seriously understudied science in South Africa with no taxonomists/systematists or ecologists resident in the country. The South Africa lichen checklist contains 1750 taxa, with more macrolichens (foliose and fruticose species) than microlichens (crustose species) being reported. Because, when fully studied, macrolichens generally comprise about one third of an area’s lichen biota, this suggests that the microlichen biota of South Africa (especially rock inhabiting species) is seriously understudied and that over 1000 taxa remain to be discovered. Our project examined how climate (particularly rainfall and temperature) interacts with substrate (rock and soil) chemistry to influence the diversity of saxicolous (rock-dwelling) and terricolous (soil-dwelling) lichen species in South Africa. We collected lichens from adjacent ultramafic (serpentinite) and non-ultramafic rock outcrops distributed along a rainfall gradient to examine how diversity is influenced by both substrate chemistry and climate. A team of four researchers each from USA and South Africa traveled over 3000 km in the mountainous area of north-eastern and north-central South Africa, systematically surveying lichens on and off of serpentinite rocks. We collected over 1000 specimens which we are currently identifying to species. We are also proce
ssing the rock samples from which the lichens were collected to get mineralogical data. A number of species apparently new to science or South Africa have been discovered during the course of our visit. Our study will inform conservation efforts by showing the edaphic diversity that should be protected to conserve South Africa’s lichen diversity. Since rainfall patterns may be altered by climate change, our research will also provide insight on how climate change may affect South Africa’s lichen biota. Our study will also go some way to addressing the lack of lichenological activity in South Africa by focusing on saxicolus microlichens as well as involving and training local scientists.
2) Biological crusts of serpentine and other metal rich substrates in South Africa
Collaborators: Dr. Arthurita Venter (North-West University, South Africa), Dr. Anatoliy Levanets (North-West University, South Africa), Dr. Stefan Siebert (North-West University, South Africa)
See a paper resulting from a previous collaboration.
Current Projects in Sri Lanka
1) Vascular Plants and Lichens of Serpentinite Outcrops of Sri Lanka
In Sri Lanka, five ultramafic rock outcrops occur along a Precambrian suture zone at the boundary of the Vijayan and Highland Series, metamorphic remnants of two ancient tectonic plates. The geochemistry of these outcrops, particularly of Ussangoda along the southern coast, has received some attention in recent years, providing a better understanding of their geologic and edaphic nature. The floristics of these ultramafic outcrops, especially of Ussangoda, have also received some attention. Three of the other five outcrops have only been subjected to one day of botanical survey and, therefore, rare or endemic species may have been overlooked, especially if they were not in flower or fruit at the time of the survey. The limited sampling of these outcrops may have also hindered observations of morphological or phenological features indicative of genotypic differences between serpentine and non-serpentine populations. The remaining two outcrops have not been surveyed and it is unknown what floristic diversity they may harbor. During 2016-2017 we conducted systematic surveys of vascular plants in all five serpentine outcrops and collected soil and rock samples to better characterize the substrate. We are currently in the process of identifying the species, preparing tissue samples for elemental analyses, and analyzing the soil samples for heavy metals and essential nutrients. In collaboration with two lichenologists we have also begun a survey of lichens on the ultramafic outcrops and adjacent non-ultramafic rocks.
Collaborators: Dr. Denise Fernando (LaTrobe University, Australia), Dr. Siril Wijesundara (National Institute of Fundamental Studies, Kandy, Sri Lanka), Dr. M. C. M. Iqbal (National Institute of Fundamental Studies, Kandy, Sri Lanka), Dr. Gothamie Weerakoon (The Field Museum, Chicago), Dr. Udeni Jayalal (Sabaragamuwa University, Sri Lanka), Mr. Asiri Weerasinghe (Sugarcane Research Institute, Uda Walawe, Sri Lanka)