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RESEARCH STATEMENT

Susan J. Mazer, Professor

Ecology, Evolution, and Marine Biology

University of California, Santa Barbara

Director, California Phenology Project

Western U.S. Coordinator, Project Baseline



OVERVIEW: Evolutionary processes and patterns in wild flowering plants

As an evolutionary ecologist and plant biologist, I’m captivated by the diversity of flowering plants and their ability to thrive in and adapt to environmentally challenging habitats. While detecting adaptation “in action” remains one of the central challenges of evolutionary biology, by investigating and measuring its components — genetic variation in fitness-related traits, phenotypic selection, and the direct and correlated responses to selection under natural conditions — we can observe its power and constraints.


My research aims to detect the process and outcome of natural selection within and among wild plant species, testing both long-standing and novel hypotheses and predictions concerning the mechanisms of evolutionary change. Most of my research focuses on traits known to influence plant survivorship or reproduction under natural conditions. I use a range of observational and experimental approaches to detect genetic and environmentally induced variation in ecologically important traits and to detect evidence for ongoing or past adaptation to challenging environments. These approaches include artificial selection experiments, manipulative experiments, ecophysiological surveys, common garden experiments, quantitative genetic analyses of variation in — and covariation among — functional traits within populations, phenotypic selection analysis of wild populations, and broad-scale comparative and phylogenetically informed studies that evaluate the outcome of evolution among species of temperate and tropical ecosystems. Quantitative genetics and the statistical evaluation of phenotypic selection gradients remain among the most powerful tools to use when simultaneously investigating the heritability and fitness consequences of a dozen or more continuously varying traits under natural conditions and when aiming to predict the phenotypic outcome of multivariate selection.
For the past 25 years, I have examined the efficacy of natural selection on traits that influence the ability of plants to persist in their natural habitats. This objective begins with identifying the ecological and evolutionary causes and consequences of variation in traits that are known to have a strong affect on individual fitness. Accordingly, my research has focused on traits such as seed size, plant age and size at maturity, floral development rate, floral display, flower size, phenology, sex allocation, mating system, and pollen performance. Subsequent steps include: conducting complex breeding designs to estimate genetic correlations among traits; measuring the direction and strength of natural selection in the field; and comparing patterns of selection with observed divergence between closely related taxa. Recent papers that represent these approaches include:
Dudley, L. S., A. A. Hove, S. K. Emms, A. Verhoeven, and S. J. Mazer. 2015. Seasonal changes in physiological performance in wild Clarkia xantiana (Onagraceae) populations: Implications for the evolution of a compressed life cycle and self-fertilization. American Journal of Botany, 102: 1-11.
Ivey, C. T., L. S. Dudley, A. A. Hove, S. K. Emms, and S. J. Mazer. 2015. Outcrossing and photosynthetic rates vary independently within two Clarkia species: implications for mating system evolution. Annals of Botany, submitted.

Mazer, S. J. and A. A. Hove. 2014. Winning in style: longer styles receive more pollen but do not intensify gametophytic selection in wild Clarkia populations. American Journal of Botany, submitted; special lissue on Pollen Ecology and Performance (co-editors, Susan Mazer and Joe Williams).

Hufford, K. M., S. J. Mazer, and S. A. Hodges. 2014. Genetic variation among mainland and island populations of a native perennial grass used in restoration. Annals of Botany Plants 6: plt044 doi:10.1093/aobpla/plt055

Hufford, K. M., S. J. Mazer, and J. P. Schimel. 2014. Soil heterogeneity and the distribution of native grasses in California: Can soil properties inform restoration plans? Ecosphere 5: 1 – 14.

Hove, A. A. and S. J. Mazer. 2013. Pollen performance in Clarkia taxa with contrasting mating systems: implications for male gametophytic evolution in selfers and outcrossers. Plants 2: 248-278.


A second approach to detecting the adaptive outcome of natural selection is to examine broad-scale patterns among functional traits and environmental conditions among dozens, hundreds, or thousands of species. In these studies, the unit of observation and analysis is typically a plant community or a clade, depending on the question. The distribution across habitats (or larger regions) of taxa that differ in life history or morphological traits can often tell us a great deal about how environmental conditions influence – through in situ natural selection or species-sorting among habitats – the attributes of the species that persist under different conditions. This approach is represented in three recent publications:
Mazer, S. J., S. E. Travers, B. I. Cook, T. J. Davies, K. Bolmgren, N. J. B. Kraft, N. Salamin, and D. W. Inouye. 2013. Flowering date of taxonomic families predicts phenological sensitivity to temperature: implications for forecasting the effects of climate change on unstudied taxa. American Journal of Botany 100: 1-17.

Davies, T. J., E. M. Wolkovich, N. Kraft, N. Salamin, J. M. Allen, T. R. Ault, J. L. Betancourt, K. Bolmgren, E. E. Cleland, B. I. Cook, T. M. Crimmins, S. J. Mazer, G. J. McCabe, S. Pau, J. Regetz, M. D. Schwartz, and S. E. Travers. 2013. Phylogenetic conservatism in plant phenology. Journal of Ecology 101: 1520-1530.



Cook, B. I., E. M. Wolkovich, T. J. Davies, T. R. Ault, J. L. Betancourt, J. M. Allen, K. Bolmgren, E. E. Cleland, T. M. Crimmins, N. B. Kraft, L. T. Lancaster, S. J. Mazer, G. J. McCabe, B. J. McGill, C. Parmesan, S. Pau, J. Regetz, N. Salamin, M. D. Schwartz, and S. E. Travers. Sensitivity of spring phenology to warming across temporal and spatial climate gradients in two independent databases. 2012. Ecosystems 15: 1283-1294.

In sum, I use a combination of field, greenhouse, and data-mining approaches to test both long-standing and new hypotheses concerning the evolution of ecological, life-history, reproductive, morphological, and physiological differences among populations and species. In addition, some of my empirical work tests the basic assumptions of mathematical models devised to explain evolutionary phenomena.
As part of my research in these areas, I am currently leading or co-directing three projects:


  1. Evolutionary diversification of mating system, phenology, life history, and physiological performance in Clarkia, a drought-adapted annual genus (2007-2013: $573,608). The synthesis of detailed studies of populations and cross-species comparisons – is represented by my recently completed NSF grant, The joint evolution of mating system, life history, physiology, and drought avoidance in Clarkia (Onagraceae): do genetic correlations contribute to mating system evolution? The major goal of this work is to evaluate the degree to whether natural selection favors shorter life cycles under compressed growing season and, if so, to determine whether there is correlated (indirect) selection on physiological rates (particularly gas exchange rates, water use efficiency and chlorophyll fluorescence) and on floral traits that influence the probability of self-fertilization, along with the genetic risks that strong inbreeding imposes. This work has been extended to include a variety of ongoing greenhouse experiments and was presented in two symposia at the 2014 Botanical Society of America meetings (Boise, ID).


(2) The California Phenology Project: tracking the effects of climate change on the seasonal cycles of iconic and ecologically important wild species (2010-2015: $430,000). Since 2010, I have been Field Director of the California Phenology Project (CPP: www.usanpn.org/cpp), the only statewide program in the U.S. dedicated to tracking the effects of climate change on the phenological patterns of wild plants. With a team of collaborators in the National Park Service, I designed and implemented phenological monitoring programs that continue to be run locally by national park staff, interns, and volunteers in seven California National Park units (Santa Monica Mountains, Joshua Tree, Sequoia, Golden Gate, John Muir National Historic Monument, Redwood, and Lassen). I have also developed strong partnerships for phenological monitoring with the UC Natural Reserve System (funded by UCOP), NatureBridge (the residential outdoor education program active in Yosemite, Golden Gate National Park, and the Santa Monica Mountains), and the California Native Plant Society. Among the participating national parks, more than 800 individual plants in 30 species have been georeferenced, mapped, and repeatedly visited to detect phenological transitions. As of June 2015, the California Phenology Project has contributed > 850,000 phenological observations to the USA National Phenology Network’s database, comprising more than 20% of the data in this national digital resource. I’m now analyzing the 7500 clearly defined phenological onset dates recorded by the CPP, along with thousands of additional records that my research group has culled from herbarium specimens.
As the CPP’s senior scientist, directing its field activities has included a novel opportunity to interact with the public and to explore the efficacy and quality of citizen-based science. Since 2011, I’ve personally led >35 one- to 3-day workshops attended by >650 educators (see CV for the full list of venues), national park staff, and naturalists, offering hands-on training in the standardized observation and recording of the phenological status of the CPP’s target species (www.usanpn.org/cpp/AllSpecies). I currently maintain and populate the CPP’s website, which is hosted by the USA National Phenology Network, for which I have served on the Board and Advisory Committee since 2007.
(3) Project Baseline: a national seed bank for the detection of short-term evolutionary change (2011-2014: $1,199,987). I’m the western U.S. field coordinator and Co-PI for Project Baseline, an NSF-funded project directed by Drs. Julie Etterson (U Minnesota), Steve Franks (Fordham University), and me (http://www.baselineseedbank.org/). We are creating the only seed bank in the world designed specifically for the study of short-term evolution. Project Baseline comprises the systematic and standardized collection, preservation, curation, and storage of millions of seeds to be made available to future biologists for the detection of evolutionary responses to anthropogenic and natural environmental changes. The > 3,000,000 seeds that my team at UCSB has collected to date (along with detailed georeferencing, habitat information, herbarium specimens, and photos) from 220 populations of 15 native species in California, Colorado, Utah, Oregon, and Washington are being stored at the National Center for Genetic Resources Preservation in Fort Collins, CO.
Below, I summarize these and other ongoing and recent projects, which comprise three themes:


  1. Evolutionary ecology and natural selection in wild plant species: detecting evidence for adaptation or evolutionary constraints within and among species




  1. Ecological and evolutionary patterns among species: cross-species analyses and predictions




  1. Phenological Monitoring and Climate Change: The USA-National Phenology Network and the California Phenology Project

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I. Evolutionary ecology and natural selection in wild plant species: detecting evidence for adaptation or evolutionary constraints within and among species
The research projects highlighted below address the following questions:


  • What do differences between closely related species tell us about the evolutionary significance of variation in ecologically important traits?




  • Do genetically based correlations among traits constrain their independent evolution? If so, what combinations of traits may evolve together under conditions predicted to occur under climate change?




  • How does a population’s or a taxon’s mating system affect or predict the evolution of its life history, physiological performance, pollen performance? Alternatively, how does selection on life history and physiological performance influence mating system evolution due to genetically based correlations between these traits and floral traits that promote selfing?




  • Can we detect local adaptation in long-lived species early in their life? If so, what are the implications for restoration efforts in California grasslands?


The evolution of mating system, life history, and physiology in relation to drought in Clarkia (Onagraceae): do genetic correlations affect mating system evolution?
Source of current funding: National Science Foundation (2007-2013: $573,608, with supplements)

PIs: Susan Mazer and Leah Dudley

Collaborators: Dr. Simon Emms and Dr. Amy Verhoeven, University of St. Thomas, Minneapolis, MN (additional collaborative NSF award: $256,863).
Most flowering plant species rely on animals to pollinate their flowers, which usually results in cross-fertilization. Nearly 25% of angiosperm species, however, regularly self-fertilize; pollen is transferred within or between flowers of the same plant. In natural populations, chronic self-fertilization from generation to generation causes a reduction in genetic variation within individuals and their descendants, which can compromise a population’s ability to tolerate or to adapt to environmental change. Consequently, determining the primary biotic and abiotic factors responsible for the frequent evolution of self-fertilization observed among flowering plants remains a central problem in evolutionary biology.
Among the species that comprise my research group’s study system — the annual wildflower genus Clarkia (Onagraceae) — selfing has evolved from predominantly insect-pollinated, outcrossing progenitors at least 12 times. This provides the unusual opportunity to test (in a replicated fashion) predictions concerning the causes and consequences of the evolution of selfing. We are currently building on decades of previous work on Clarkia in California by focusing on two pairs of sister taxa with contrasting mating systems [Clarkia unguiculata (outcrossing) vs. C. exilis (selfing) and C. xantiana ssp. xantiana (outcrossing) vs. ssp. parviflora (selfing)]. By comparing multiple pairs of sister taxa, we aim to identify the morphological, life history, and physiological traits that consistently evolve along with self-fertilization.
When self-fertilization evolves in Clarkia, a number of other traits evolve simultaneously or soon afterwards, including those associated with more rapid development (Mazer et al., 2004, 2007, 2009, 2010, Delesalle et al. 2008, Dudley et al. 2007). For example, within each pair of sister taxa, the selfer flowers at an earlier age, produces successive flowers more rapidly, and produces smaller, short-lived flowers that complete their development more rapidly than their outcrossing counterparts.
Two hypotheses have been proposed to explain the joint evolution of these whole-plant and individual floral traits. The first is the accelerated life cycle hypothesis, which proposes that natural selection favors a short life cycle in environments with short growing seasons (or, for example, under conditions where a short life cycle enables plants to avoid drought stress). Under this hypothesis, natural selection independently favors genotypes with traits that promote early and rapid reproduction, including early maturation, synchronous flower production, short-lived flowers, and rapidly developing, self-fertilizing flowers. Populations or taxa occupying habitats with relatively long growing seasons would therefore evolve or sustain later maturation and outcrossing, while those adapted to shorter growing seasons would evolve early maturation and selfing.
The second hypothesis, the correlated response to selection hypothesis, similarly proposes that selection under a short growing season favors early maturation and reproduction. In addition, however, it states that rapid floral development and increased selfing evolve not independently but as correlated responses to selection due to genetic linkage (or pleiotropy) between genes influencing both whole-plant and floral development. In other words, regardless of whether high selfing rates are directly favored by natural selection, a high rate of self-fertilization will be “pulled along” as a correlated trait due to strong selection favoring early reproduction. Much of my effort is now directed towards testing these two hypotheses.
If selection on life history or physiological traits drives the rapid evolution of selfing due to strong genetic correlations, this would have cascading effects on the genetic structure of populations (i.e., higher homozygosity), potentially limiting their ability to adapt to future environmental change. Accordingly, our physiological comparisons between selfing vs. outcrossing species are helping us to detect whether there are genetic risks associated with selfing given the increasing frequency and intensity of droughts (and shorter growing seasons) expected in the southern Sierra Nevada. In addition, we are evaluating the genetic basis of the physiological differences that appear to have evolved with the evolutionary divergence of mating system in Clarkia. Prior to our work on this system (Mazer et al., 2010), there had been no published accounts of any physiological differences between closely related taxa that differ in mating system.
We are now also investigating whether selfing and outcrossing Clarkia sister taxa exhibit distinct physiological strategies and differ in their vulnerability to drought-stress. In each pair of selfing/outcrossing sister taxa, the selfer flowers earlier and produces smaller, faster-developing flowers than its outcrossing counterpart. If these early flowering selfing taxa avoid drought stress by completing their life cycle while soil moisture is relatively high, then they should be able to maintain higher transpiration rates and achieve faster photosynthetic rates than their outcrossing counterparts. In other words, selfers may be “drought-avoiders” while outcrossers are better able to tolerate the low soil moisture typical of late-spring in California. Together, these observations and inferences have motivated us to address the following questions and predictions:
1. How do abiotic conditions differ among sites occupied by selfing vs. pollinator-dependent taxa? We predict that the relatively early-flowering and highly selfing taxa will flower under conditions of higher soil moisture than their later-flowering, outcrossing counterparts.
2. Do autogamous and pollinator-dependent taxa differ physiologically? We predict that autogamous taxa should exhibit higher gas exchange rates and lower instantaneous water use efficiency (WUEi), due either to plastic responses to cooler conditions and moister soils or because these traits are evolutionary adaptations necessary to complete the life cycle more rapidly. To date, our field surveys have supported this prediction.
To initiate the comparative physiological study of our four focal taxa, we conducted a three-year field survey (2008 – 2010) of gas exchange rates, chlorophyll fluorescence, and fitness-related life history traits in multiple populations of each taxon in the southern Sierra Nevada. Within each taxon pair, populations of the highly selfing taxon flower and complete their life cycle before their predominantly outcrossing counterparts growing in sympatry or at similar elevations. As predicted, the selfing populations consistently exhibited higher rates of photosynthesis and transpiration than their outcrossing sister taxa, even when controlling statistically for leaf age and temperature (both of which influence gas exchange rates). Within taxa, high photosynthetic rates are positively correlated with lifetime fruit production, demonstrating the fitness advantage associated with higher rates of carbon assimilation.
These patterns are consistent with the hypothesis that selection has favored higher gas exchange rates in selfing Clarkia taxa, allowing them to achieve their faster life cycles and thereby escape seasonal late-spring drought. The ongoing analysis of our 2009 and 2010 field data and the analysis of our ongoing greenhouse experiments will help to distinguish between these hypotheses.
This project has included reciprocal training among the four PIs and has involved more than 60 undergraduates. Eight UCSB undergraduates completed their senior year honors theses in my lab while working on this project (Andrew Yamagiwa, Maxx Echt, Adrian Mayo, Lauren Capone, Bridget Bedsaul, Arrash Moghaddasi, Laura Barley, and Keith Rodriguez).
Papers published (or submitted) on this research from 2012-2015 are:

Hove, A. A. and S. J. Mazer. 2013. Pollen performance in Clarkia taxa with contrasting mating systems: implications for male gametophytic evolution in selfers and outcrossers. Plants 2: 248-278.


Dudley, L. S., A. A. Hove, S. K. Emms, A. Verhoeven, and S. J. Mazer. 2015. Seasonal changes in physiological performance in wild Clarkia xantiana (Onagraceae) populations. Implications for the evolution of a compressed life cycle and self-fertilization. American Journal of Botany, 102: 1-11.
Ivey, C. T., L. S. Dudley, A. A. Hove, S. K. Emms, and S. J. Mazer. 2015. Outcrossing and photosynthetic rates vary independently within two Clarkia species: implications for mating system evolution. Annals of Botany, submitted.
Mazer, S. J. and A. A. Hove. 2015. Winning in style: longer styles receive more pollen but do not intensify gametophytic competition in wild Clarkia populations. American Journal of Botany, in revision; special lissue on Pollen Ecology and Performance (co-editors, Susan Mazer and Joe Williams).

Local adaptation and effects of grazing among seedlings of two native California bunchgrass species: implications for restoration
Adaptation to environmental factors may influence the germination and establishment of focal species in ecological restoration, and this issue has generated intense interest among academic and commercial restoration ecologists. The use of local seed sources for restoration efforts is generally considered to be the “best practice” for reducing the potential that propagules will be poorly adapted to site conditions. Nevertheless, data are often lacking to determine the distance within which seed sources represent local genotypes. Short-term reciprocal transplant studies represent a class of tools to detect local adaptation of species targeted for restoration projects, among which the native perennial bunch grasses of California are a frequent choice.
To evaluate the importance of the provenance of seeds used in grassland restoration, Dr. Kristina Hufford and I conducted a reciprocal transplant of Nassella pulchra — a long-lived perennial often used in restoration — between two central California locations (Vandenberg Air Force Base and Sedgwick Ranch Reserve). Our primary goal was to test for adaptation to local environmental conditions over a three-year period. Experimental plots at Vandenberg Air Force Base were divided between grazed and ungrazed sites to evaluate the potential influence of livestock grazing on the detection or magnitude of local adaptation. During each year of the study, evidence of a home-site advantage depended on the location, traits studied, and population. At the end of the three-year study period, however, we detected consistent evidence of a home-site advantage for seedling biomass among grazed sites at Vandenberg and among the ungrazed plots at Sedgwick. In effect, local adaptation was only apparent in the final year of the study. Short-term (e.g., one- to two-year) reciprocal transplant studies are an effective tool to guide the selection of seed sources most likely to germinate and to become established at a restoration site, but such studies cannot rule out local adaptation, which may not be immediately detectable.
Papers published (or submitted) on this research from 2012-2015 are:

Hufford, K. M., S. J. Mazer, and S. A. Hodges. 2014. Genetic variation among mainland and island populations of a native perennial grass used in restoration. Annals of Botany Plants 6: plt044 doi:10.1093/aobpla/plt055

Hufford, K. M., S. J. Mazer, and J. P. Schimel. 2014. Soil heterogeneity and the distribution of native grasses in California: Can soil properties inform restoration plans? Ecosphere 5: 1 – 14.
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II. Ecological and evolutionary patterns among species: cross-species predictions and tests
Phenological sensitivity to temperature: taxonomic associations and the implications for forecasting the effects of climate change on unstudied taxa


    Many long-term studies in seasonal habitats have tracked inter-annual variation in first flowering date (FFD) in relation to climate, documenting the affect of warming on the FFD of many species. Despite these efforts, long-term phenological observations are still lacking for many species. This deficit motivated me to conduct a taxonomically informed analysis of a very large data set that comprised the focus of a recent NCEAS working group. The rationale for this analysis was as follows: If we could forecast responses based on taxonomic affinity, then we could leverage existing data to predict the climate-related phenological shifts of many taxa not yet studied.

    I examined phenological time series of 1226 species occurrences (1031 unique species in 119 families) across seven sites in North America and England where intensive observations of the timing of flowering had been recorded for several decades and where climatic data were available to link phenological data to inter-annual and month-to-month variation in temperature and rainfall. My primary goals were, first, to determine whether family membership (or family mean FFD) can be used to predict the sensitivity of a species’ FFD to standardized inter-annual changes in temperature and precipitation during seasonal periods before flowering and, second, to determine whether families differ significantly in the direction of their phenological shifts. I found that the most striking pattern observed among species both within and across sites is also mirrored among family means across sites; earlier-flowering families advance their FFD in response to warming more than later-flowering families. By contrast, we found no consistent relationships among taxa between mean FFD and sensitivity to precipitation.



    Based on the patterns observed in these analyses, family membership can be used (with some caution) to predict whether an otherwise unstudied species will exhibit high vs. low sensitivity to temperature in seasonal, temperate zone plant communities. The particularly high sensitivity of earlier-flowering families (and the absence of earlier-flowering families not sensitive to temperature) appears to reflect high phenotypic plasticity in flowering time, which would be adaptive in environments where earlier-season conditions are highly variable among years. A combination of long-term demographic studies along with measures of species’ phenological sensitivities to inter-annual variation in climate, however, is necessary to determine unambiguously the adaptive significance of the interspecific variation detected in this study.


Mazer, S. J., S. E. Travers, B. I. Cook, T. J. Davies, K. Bolmgren, N. J. B. Kraft, N. Salamin, and D. W. Inouye. 2013. Flowering date of taxonomic families predicts phenological sensitivity to temperature: implications for forecasting the effects of climate change on unstudied taxa. American Journal of Botany 100: 1-17.
Does mating system affect the evolution of pollen performance across species?
Studies of sexual selection in plants historically have focused on pollinator attraction, pollen transfer, gametophytic competition, and post-fertilization processes. Pollen performance (germination and pollen tube growth rates) in particular is thought to be strongly subject to intrasexual selection (i.e., favoring genotypes that aggressively compete for access to eggs), but the role of mating system in this process has not been rigorously evaluated.
I recently published a paper to draw attention to this gap and to propose avenues of future research; in this work, I proposed four predictions derived from the inference that pollen performance should coevolve with mating system as an adaptive response to: (a) the competitive environment among pollen genotypes and (b) variation among the female genotypes regularly encountered by a given pollen genotype, both of which differ between selfing and outcrossing taxa (Mazer et al., 2010). First, due to the greater opportunity for intense selection among pollen genotypes in outcrossing relative to selfing taxa, pollen should evolve to germinate and to grow more rapidly in outcrossers. Second, due to stronger selection on pollen performance in outcrossing than in selfing taxa, heritable variation in pollen tube growth rate is more likely to be purged in outcrossers. In selfers, by contrast, genetic variation in pollen performance may accumulate more easily because selfing reduces the number of pollen genotypes deposited on any given stigma, thereby relaxing selection on male gametophytic traits. A literature review provided support for this prediction (Mazer et al., 2010). Third, due to the high probability that the pollen of outcrossing individuals will be exposed to multiple pistil genotypes, pollen of habitually outcrossing taxa should evolve to perform more consistently across female genotypes than that of selfing taxa. Fourth, epistatic interactions between pollen and pistil genotypes should be more likely to evolve in selfers than in outcrossers.
In the first test of the first prediction (above), we evaluated pollen performance in natural populations of the outcrossing C. unguiculata and its selfing sister species, C. exilis, as well the outcrossing C. xantiana ssp. xantiana and its selfing sister subspecies, C. x. ssp. parviflora (Hove and Mazer, 2013). We found that the joint evolution of mating system and pollen performance traits has occurred in C. unguiculata and C. exilis, with the former producing more rapidly-germinating pollen. This is among the first studies to seek differences in pollen competitive ability between outcrossing and selfing wild taxa.
The paper we published on this research is:

Hove, A. A. and S. J. Mazer. 2013. Pollen performance in Clarkia taxa with contrasting mating systems: implications for male gametophytic evolution in selfers and outcrossers. Plants 2: 248-278.



Integrating Ecology, Climatology, & Phylogeny to Understand Responses to Climate Change
A second project derived from the NCEAS working group mentioned above examined inter-annual variation in both first flowering dates and first leafing dates among >1600 species observed in North American and European studies designed to detect the link between phenology and inter-annual variation in climate. Studies of the sensitivity (the sign and magnitude of response) of plant phenological schedules to climatic factors have relied on standardized observations available from large observational networks. The ability to make broad generalizations from these data about natural populations and communities worldwide, however, may limited. For example, observational networks focused on communities or field sites typically under-represent the species diversity of naturally occurring communities and often have strong geographic and climatic biases.
In this project, we measured and compared the sensitivity of first flowering date (FFD) and first leafing date (FLD) to temperature- and precipitation-based climate predictors using data from an observational network of phenological observations in Europe (PEP725: >100,000 time series; 56 taxa) and a new database we created comprising observations of wild species across Europe and North America (NECTAR: 1,938 time series; 1,627 taxa).
We detected high and consistent sensitivity to inter-annual variation in temperature; increased temperatures result in earlier FFD and FLD. This pattern was seen in most species in the PEP725 database (83.6% of all time series) and among species located in the cooler and highly seasonal sites in NECTAR (70%-100%). In other words, plants respond most strongly to inter-annual changes in temperature in cooler and more seasonal environments. We also found that sites characterized by relatively early-flowering species were also those where the plant species were the most sensitive to temperature (similar to the patterns reported in Mazer et al., 2013).
In general, the relationships between climate and phenology observed in the PEP725 data are also found among the NECTAR sites, supporting the use of networks such as PEP725 to inform and predict the response of phenology to climate change. These relationships, however, do not apply to the taxa monitored in the NECTAR sites that fall outside the PEP725 climatic envelope. There remains a critical need for observations from regions outside of the mesic, temperature seasonal mid-latitudes that have been targeted for monitoring to date.
The paper we published on this research is:
Cook, B. I., E. M. Wolkovich, T. J. Davies, T. R. Ault, J. L. Betancourt, J. M. Allen, K. Bolmgren, E. E. Cleland, T. M. Crimmins, N. J. B. Kraft, L. T. Lancaster, S. J. Mazer, G. J. McCabe, B. J. McGill, C. Parmesan, S. Pau, J. Regetz, N. Salamin, M. D. Schwartz, and S. E. Travers. Sensitivity of spring phenology to warming across temporal and spatial climate gradients in two independent databases. 2012. Ecosystems 15: 1283-1294. DOI: 10.1007/s10021-012-9584-5.

Project Baseline, a living plant genome reserve for the study of evolution
Source of funding: National Science Foundation (2011-2015: $1,199,987)

PIs: Julie Etterson (University of Minnesota-Duluth), Susan Mazer (University of California, Santa Barbara), and Steve Franks (Fordham University)


A powerful approach to understanding evolution in natural populations is to monitor it in action, particularly in response to environmental change. However, in only a few cases can we determine whether these changes are a function of genetically based evolution vs. environmentally induced phenotypic plasticity.
The most direct way to distinguish between these influences on phenotype is to raise ancestors and their descendants side-by-side in a common environment. This has been done in a few instances where propagules (e.g. seeds or eggs) have been recovered (e.g. seeds frozen in tundra soils) after long-term storage. A collection of propagules collected according to a thoughtful sampling scheme and archived for the long term, would enable future investigators to use this “resurrection” approach to unequivocally document microevolution during a period of rapid environmental change and to investigate the roles of alternative evolutionary processes. With such a seed bank, evolutionary biologists would be able to cultivate genetic material representing populations from the past and compare them to modern assemblages using long-established and new genetic approaches, as well as ones yet to be developed, to dissect the underlying mechanisms of evolutionary change.
This project comprises a national effort to use a standardized set of protocols collect, preserve and archive seeds to be made available to future biologists for studies of evolutionary responses to anthropogenic and natural changes in the environment. For ~50 species of diverse life-histories, seeds are being collected from multiple populations across the species’ geographic range and from 100-200 individuals per population. This sampling plan will capture genetic variation both within and among populations. Seeds are being archived at the USDA National Center for Genetic Resources Preservation; tested for viability, genetic diversity, and seed quality; and stored in liquid nitrogen. All accessions will be made available to future researchers to test for genetically based changes that occur in the upcoming decades. (See attached brief published in Science).
Papers published (or in press) on this research from 2012-2015 are:
Schneider, H. E. and S. J. Mazer. 2015. Geographic variation in climate as a proxy for climate change: forecasting evolutionary trajectories from species differentiation and genetic covariance. American Journal of Botany, in press.
Etterson, J. R. S. J. Franks, S. J. Mazer, R. G. Shaw, N. Soper Gorden, H. Schneider, J. J. Weber, K. Winkler, and A. E. Weis. 2015. Project Baseline: an unprecedented resource to study plant evolution in space and time. American Journal of Botany, in press.
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III. Phenological Monitoring and Climate Change: The USA-National Phenology Network and the California Phenology Project
Phenology is the study of seasonally occurring plant and animal life cycle events, or “phenophases.” In natural habitats, the annual timing of these events is strongly influenced by recent (i.e., winter or spring) temperature and precipitation, both of which are driven by the combination of weather and climate. Phenophases influenced by regional climate include the timing of spring bud break, leaf-out and flowering, seed germination, seedling emergence, emergence of beneficial and detrimental insects, and animal migrations. These events are relatively simple to record and to track, and are vital to both the scientific and public interest (with or without climate change.)

Changing phenological cycles affect the abundance and diversity of organisms, their interactions and ecological functions, and their effects on fluxes of water, energy, and chemical elements at various scales. Indeed, the asynchronous responses of interacting species — such as plants and their pollinators, or plants and their specialist herbivores — to climate change have been shown to have cascading affects on plant and animal abundances and demographic dynamics. Moreover, phenological data and models are useful in agriculture, drought monitoring, and wildfire risk assessment, as well as management of wildlife, invasive species, agricultural pests, and other risks to human health and welfare, including allergies/asthma and vector-borne diseases.



Designing and providing the infrastructure to promote long-term phenological data collection and data archiving has been the primary role of USA-National Phenology Network (USA-NPN) and the California Phenology Project, two large-scale efforts in which I have focused my activities since 2007. Since 2005, an interdisciplinary group of scientists have worked (with the help of an NSF Research Coordination Network grant) to establish a national network to engage federal agencies, NGOs, educational institutions, and citizen scientists in phenological monitoring. A primary goal of the USA-NPN is to enhance climate change adaptation strategies by building and supporting the first coordinated effort by scientists, naturalists, and the general public to detect and to predict the effects of climate change on the seasonal cycles of plants and animals by accumulating and analyzing frequent observations of the natural world.
The California Phenology Project
Source of current funding: U.S. National Park Service Program (2011-2015: $430,436)

PI: Susan Mazer

The U.S. National Park Service’s Climate Change Response Program recently funded the design and implementation of the first statewide phenological monitoring program anywhere in the United States: the California Phenology Project (CPP). The resulting collaboration — the California Phenology Project (CPP) — is a partnership between my research group at UCSB, the California Cooperative Ecosystem Studies Unit (CESU), plant ecologists at each of the six pilot parks, and the USA-National Phenology Network.

In California, our network is currently being initiated in seven of the state’s 19 National Parks and Recreation Areas (Joshua Tree National Park, Santa Monica Mountains National Recreation Area, Sequoia-Kings Canyon National Park, Golden Gate National Recreation Area, John Muir National Historic Monument, Redwood National Park, and Lassen Volcano National Park). In addition, we have written Standard Operating Procedures for park-based phenological monitoring that may be used at all California National Park units, as well as by other landholders (such as the UC Natural Reserve System) (Matthews et al., 2013, 2014).



My responsibility is to direct all of the field activities associated with this project, including:

  • To lead (with project staff) annual 2- to 5-day visits among participating parks to conduct training sessions for resource managers and interpretive staff and to identify, to map, and to label at each park 125-150 individual plants in 4-5 species for recurrent monitoring;

  • To establish a statewide phenology network that serves the needs of resource managers, public educators and outreach staff, including the design of collaborative research projects with national park staff and university partners;

  • To conduct multiple workshops each year to train park staff and members of the public to use the USA National Phenology Network’s protocols for recording and uploading of phenological data. I delivered >35 training workshops (most of which were full-day events including lecture, guided discussions, and hands-on instruction in phenological monitoring) from 2012-2015.

  • To conduct park-level and regional floristic assessments to select ecologically important plant species, communities, and habitats for monitoring in California National Parks and the UC Natural Reserve System;

  • To create plant species profiles and phenophase definitions of target species and to disseminate them to the public through on-line venues, workshops, and parks;

  • To test protocols developed by the USA-National Phenology Network and to adapt or adjust them to the species selected for monitoring in California;

  • To develop and to test educational tools and materials to engage citizens and students to record and use phenological data to detect the effects of climate change on plants and wildlife;

  • To create a website (www.usanpn.org/cpp) that allows users to obtain educational and training materials that will facilitate monitoring and public participation; and

  • To ensure that phenological data recorded in California are managed using standards in use by the National Park Service Inventory & Monitoring Program and the USA-National Phenology Network.

The California Phenology Project was initiated in fall 2010 and a project coordination team comprised of staff from each pilot park and the principal project partners discussed the project and our progress in twice-monthly to monthly teleconference calls. The publications designed to enable CPP partners (both within and outside of the National Parks) to replicate the methods used within in each park are the following:
Haggerty, B., E. R. Matthews, K. L. Gerst, A. G. Evenden, and S. J. Mazer. 2013. The California Phenology Project: tracking plant responses to climate change. Madroño 60: 1-3.
De Beurs, K. M., R. B. Cook, S. Mazer, B. Haggerty, A. Hove, G. M. Henebry, L. Barnett, C. L. Thomas, and B. R. Pohlad. 2013. Phenology in Higher Education: ground-based and spatial analysis tools. In M. D. Schwartz (ed.), Phenology: An Integrative Environmental Science, Chapter 31. Springer Science+Business Media B. V.
Matthews, E. R., K.L. Gerst, S. J. Mazer, C. Brigham, A. Evenden, A. Forrestel, B. Haggerty, S. Haultain, J. Hoines, S. Samuels, and F. Villalba. 2013. California Phenology Project: Report on pilot phase activities, 2010-2013. Natural Resource Report NPS/PWRO/NRR—2013/743. National Park Service, Fort Collins, CO.
Matthews, E. R., K. L. Gerst, Mazer, S. J., C. Brigham, A. Evenden, A. Forrestel, B. Haggerty, S. Haultain, J. Hoines, S. Samuels, and F. Villalba. 2014. California Phenology Project (CPP) plant phenological monitoring protocol: Version 1. Natural Resource Report NPS/PWR/NRR—2014/763. National Park Service, Fort Collins, CO.
Elmendorf, S., K. Jones, B. Cook, J. Diez, C. Enquist, M. Jones, R. Kao, S. Mazer, A. Miller-Rushing, D. Moore, M. Schwartz, and J. Weltzin. 2015. National Ecological Observatory Network. TOS Science Design, Plant Phenology. NEON Doc. #: NEON.DOC.000917vA. 30 pp.
In addition to preparing these detailed summaries of the content, scope, and protocols of the California Phenology Project, as of June 2013, four species were sufficiently intensively monitored to be able to detect strong associations between recent climatic conditions and the onset dates of distinct phenological stages. These four species — Baccharis pilularis (coyotebrush: Asteraceae), Quercus lobata (valley oak: Fagaceae); Sambucus nigra (blue elderberry: Caprifoliaceae); and Eriogonum fasciculatum (California buckwheat: Polygonaceae) — are widespread in California, enabling us to capture a good deal of climatic varaition among the sites where they were monitored.
I examined the effects of monthly climate parameters during a four-month window (December to March), including mean minimum temperatures (Tmin), total monthly precipitation, and their interactions, on the onset dates of four phenophases per species. I found that stepwise regressions explained a high proportion (30-99%) of the variation in the onset date of each phenophase, demonstrating the efficacy of this model in predicting the phenological behavior of these species. Species and phenophases differed, however, with respect to the strength and the direction of the relationship between each month’s conditions (Tmin and/or precipitation) and the timing of vegetative and reproductive phenophases. In sum, due to the wide climatic variation represented among the monitored sites and years (2011-2013), and the sensitivity of each of these species to climatic conditions, I could detect significant associations between local, recent winter conditions and the onset dates of subsequent phenophases, although interactions between monthly conditions were also common. These patterns permit preliminary predictions regarding how these species will respond to future winter warming and intensifying drought in California.
The paper published on this research from 2012-2015 is:
Mazer, S. J., K. L. Gerst, E. R. Matthews, and A. Evenden. 2015. Species-specific phenological responses to winter temperature and precipitation in a water-limited ecosystem. Ecosphere, 6(6):98. http://dx.doi.org/10.1890/vES14-00433.1
As the educational component of this effort, two graduate students and I created a suite of educational tools that span the range from primary school through university seminars and lectures. With funding from the U.S. Fish and Wildlife Service, USGS, and the California Cooperative Ecosystem Studies Unit, we have written and tested a variety of educational products to connect UCSB students and California residents with our natural environment and its cycles by observing, recording, and reporting seasonal changes in biological activities (www.usanpn.org/cpp/education). One of these products was published recently.
Haggerty, B., A. Hove, S. Mazer, L. Barnett. 2013. Flight of the pollinators: plant phenology from a pollinator’s perspective. Chapter 9, In Trautmann, Fee, Tomasek and Bergey, Citizen science: 15 lessons that bring biology to life, 6-12. National Science Teachers Association, Arlington, VA.

Research Coordination Network for Phenology and Climate Change
Source of funding: National Science Foundation ($499,000)

PIs: PI (Mark Schwartz, University of Wisconsin); Co-PIs: Susan Mazer and Jake Weltzin (USA-National Phenology Network, Tucson, AZ)

Duration of grant: October 2011 – March 2013
I was a Co-PI on a recently completed five-year NSF-funded Research Coordination Network grant (Lead PI: Mark D. Schwartz, University of Wisconsin, with Co-PI Jake Weltzin, Director of the USA National Phenology Network) to design and to implement the first National Phenology Network (NPN) in the U.S. The USA-NPN is a partnership between academic communities, federal agencies, educators, and volunteers.
The RCN helped the USA-NPN to achieve the following objectives: 1) to promote progress and leadership in the study of phenology; 2) to inform and guide USA-NPN design and implementation with sound science; 3) to develop and field test protocols for data collection and management by students, the public, and scientists; 4) to synthesize, prioritize, and integrate research projects that take advantage of USA-NPN data at all levels; 5) to identify and address key gaps in theory and data that limit phenological research; 6) to inspire new multi-disciplinary experimental designs and models to increase the utility and relevance of phenological research; and 7) to develop new on-line resources to increase awareness and access to phenological data.

The RCN created four products: 1) a meta-database of existing phenological data in the USA, now available at: www.usanpn.org; 2) a broadly-vetted and tested set of data-collection and -management protocols, now in use by the USA-NPN and all participating partners; 3) lists of target species representative of U.S. biomes and customized for each of four network tiers; and 4) enhancement of the USA-NPN Web page with new software and tools that facilitate communication among and access to data by the research and education communities. Annual workshops each addressed focal issues such as the integration of past phenological data collected with differing protocols, exchange of information with international phenological monitoring programs.


Tracking Spring on a Changing Planet:

Phenology and climate change across the University of California Natural Reserve System: The UCNRS Phenology Network
Source of funding: University of California, Office of the President: $40,000

PI: Susan Mazer

Duration of grant: July 2011 – June 2015
In the long-term, particularly in California where climate change is expected to continue altering the timing of seasonal temperature and precipitation, we expect that the inter-annual rhythms of flowering, pollination, and fruit production will change in the coming decades, as will the animals that depend on these processes. Despite the potential for phenological studies to detect early warning signs of the affects of climate change, and despite their applications to other science and education efforts, there is currently no concerted effort among UC researchers, educators, and institutions to conduct phenological research.
The purpose of this project is to initiate such an effort across the UC Natural Reserve System (UCNRS), beginning with seven pilot reserves across three UC campuses (Sedgwick Ranch, Hastings, Stunt Ranch, Carpinteria Salt Marsh, Valentine/SNARL, Coal Oil Point, Rancho San Marino). As described above, phenological monitoring is easy to conduct and straightforward to teach, so the prospective roles of both professional and citizen scientists in contributing to a large-scale effort to track phenological changes is both heartening and realistic.
I am now working with Monica Pessino in the Ocean o’ Graphics graphic design and production studio of the Marine Science Institute to create web pages summarizing the phenological monitoring program in the UC Reserves that have dedicated volunteers or staff members to this continuing effort (Sedgwick Ranch Reserve, Stebbins Reserve, Norris Rancho Marino Reserve, Sierra Nevada Aquatic Research Lab, and Valentine Reserve).

Mazer - Research -




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