Erin C. Riordan

Influence of environmental heterogeneity on genetic diversity and structure in an endemic southern Californian oak

Understanding how specific environmental factors shape gene flow while disentangling their importance relative to the effects of geographical isolation is a major question in evolutionary biology and a specific goal of landscape genetics. Here, we combine information from nuclear microsatellite markers and ecological niche modelling to study the association between climate and spatial genetic structure and variability in Engelmann oak (Quercus engelmannii), a wind‐pollinated species with high potential for gene flow. We first test whether genetic diversity is associated with climatic niche suitability and stability since the Last Glacial Maximum (LGM). Second, we use causal modelling to analyse the potential influence of climatic factors (current and LGM niche suitability) and altitude in the observed patterns of genetic structure. We found that genetic diversity is negatively associated with local climatic stability since the LGM, which may be due to higher immigration rates in unstable patches during favourable climatic periods and/or temporally varying selection. Analyses of spatial genetic structure revealed the presence of three main genetic clusters, a pattern that is mainly driven by two highly differentiated populations located in the northern edge of the species distribution range. After controlling for geographic distance, causal modelling analyses showed that genetic relatedness decreases with the environmental divergence among sampling sites estimated as altitude and current and LGM niche suitability. Natural selection against nonlocal genotypes and/or asynchrony in reproductive phenology may explain this pattern. Overall, this study suggests that local environmental conditions can shape patterns of genetic structure and variability even in species with high potential for gene flow and relatively small distribution ranges.

Land Use Compounds Habitat Losses under Projected Climate Change in a Threatened California Ecosystem

Given the rapidly growing human population in mediterranean-climate systems, land use may pose a more immediate threat to biodiversity than climate change this century, yet few studies address the relative future impacts of both drivers. We assess spatial and temporal patterns of projected 21st century land use and climate change on California sage scrub (CSS), a plant association of considerable diversity and threatened status in the mediterranean-climate California Floristic Province. Using a species distribution modeling approach combined with spatially-explicit land use projections, we model habitat loss for 20 dominant shrub species under unlimited and no dispersal scenarios at two time intervals (early and late century) in two ecoregions in California (Central Coast and South Coast). Overall, projected climate change impacts were highly variable across CSS species and heavily dependent on dispersal assumptions. Projected anthropogenic land use drove greater relative habitat losses compared to projected climate change in many species. This pattern was only significant under assumptions of unlimited dispersal, however, where considerable climate-driven habitat gains offset some concurrent climate-driven habitat losses. Additionally, some of the habitat gained with projected climate change overlapped with projected land use. Most species showed potential northern habitat expansion and southern habitat contraction due to projected climate change, resulting in sharply contrasting patterns of impact between Central and South Coast Ecoregions. In the Central Coast, dispersal could play an important role moderating losses from both climate change and land use. In contrast, high geographic overlap in habitat losses driven by projected climate change and projected land use in the South Coast underscores the potential for compounding negative impacts of both drivers. Limiting habitat conversion may be a broadly beneficial strategy under climate change. We emphasize the importance of addressing both drivers in conservation and resource management planning.

Association of genetic and phenotypic variability with geography and climate in three southern California oaks

PREMISE OF THE STUDY Geography and climate shape the distribution of organisms, their genotypes, and their phenotypes. To understand historical and future evolutionary and ecological responses to climate, we compared the association of geography and climate of three oak species (Quercus engelmannii, Quercus berberidifolia, and Quercus cornelius-mulleri) in an environmentally heterogeneous region of southern California at three organizational levels: regional species distributions, genetic variation, and phenotypic variation. METHODS We identified climatic variables influencing regional distribution patterns using species distribution models (SDMs), and then tested whether those individual variables are important in shaping genetic (microsatellite) and phenotypic (leaf morphology) variation. We estimated the relative contributions of geography and climate using multivariate redundancy analyses (RDA) with variance partitioning. KEY RESULTS The modeled distribution of each species was influenced by climate differently. Our analysis of genetic variation using RDA identified small but significant associations between genetic variation with climate and geography in Q. engelmannii and Q. cornelius-mulleri, but not in Q. berberidifolia, and climate explained more of the variation. Our analysis of phenotypic variation in Q. engelmannii indicated that climate had more impact than geography, but not in Q. berberidifolia. Throughout our analyses, we did not find a consistent pattern in effects of individual climatic variables. CONCLUSIONS Our comparative analysis illustrates that climate influences tree response at all organizational levels, but the important climate factors vary depending on the level and on the species. Because of these species-specific and level-specific responses, todays sympatric species are unlikely to have similar distributions in the future.

Morphological Traits and Invasive Potential of the Alien Euphorbia terracina (Euphorbiaceae) in Coastal Southern California

ABSTRACT Euphorbia terracina L., also known as terracina spurge, is a Mediterranean Basin perennial that has recently become invasive in southern California and is actively spreading at a virtually exponential rate along coastal areas in Los Angeles County. The National Park Service (NPS) is undertaking measures to treat and control further spread of current populations, but little is known about the plants ecology and impact on native plant communities. This study reviewed the existing information on E. terracina and investigated populations established in Solstice Canyon in coastal Los Angeles County. Populations of E. terracina were compared in two different habitats in Solstice Canyon: in an open site along an old road and a shaded riparian site subject to past disturbance. Both open-disturbed and shaded sites had high aboveground biomass densities, with the highest density in the open, disturbed site. Sites differed in biomass allocation and specific leaf area (SLA) between sites, with plants at the open site having significantly lower specific leaf area than those at the shaded site. Open site plants also had high SLA compared to native coastal sage scrub species. Euphorbia terracina produces large quantities of seeds that do not show dormancy. Seeds germinated well under low light intensities without mechanical or chemical treatment. Euphorbia terracina possesses numerous traits — success in disturbed sites, phenotypic plasticity, high SLA compared to native species, high reproductive output, and seeds lacking dormancy — that have been associated with invasive species and likely contribute to both its success and the difficulty in treatment and control of established populations.

Best practices for reporting climate data in ecology

A large number of published ecological studies fail to include basic information about the climate data used. In the interest of reproducibility and transparency, we offer recommendations for best practices that we urge Editors, authors, and reviewers to adopt in future publications.

Threats of future climate change and land use to vulnerable tree species native to Southern California

Author(s): Riordan, EC; Gillespie, TW; Pitcher, LH; Pincetl, SS; Jenerette, GD; Pataki, DE | Abstract: Climate and land-use changes are expected to drive high rates of environmental change and biodiversity loss in Mediterranean ecosystems this century. This paper compares the relative future impacts of land use and climate change on two vulnerable tree species native to Southern California (Juglans californica and Quercus engelmannii) using species distribution models. Under the Intergovernmental Panel for Climate Changes A1B future scenario, high levels of both projected land use and climate change could drive considerable habitat losses on these two already heavily-impacted tree species. Under scenarios of no dispersal, projected climate change poses a greater habitat loss threat relative to projected land use for both species. Assuming unlimited dispersal, climate-driven habitat gains could offset some of the losses due to both drivers, especially in J. californica which could experience net habitat gains under combined impacts of both climate change and land use. Quercus engelmannii, in contrast, could experience net habitat losses under combined impacts, even under best-case unlimited dispersal scenarios. Similarly, projected losses and gains in protected habitat are highly sensitive to dispersal scenario, with anywhere from g 60% loss in protected habitat (no dispersal) to g 170% gain in protected habitat (unlimited dispersal). The findings underscore the importance of dispersal in moderating future habitat loss for vulnerable species. Copyright

Utilizing public Internet-connected cameras for a cross- continental plant phenology monitoring system

Development of inexpensive, automated ground methods is necessary to advance precision plant phenology monitoring across large spatial extents. We propose the use of free, publicly available, Internet-connected cameras, often associated with nonscientific monitoring, to monitor plant phenology at continental scales. We provide a methodology to detect changes in vegetation greenness and determine timing of spring and fall events from over 1100 public cameras across North America from February 2008 – 2009. Manual image segmentation facilitated spring detection for both deciduous and understory vegetation occurring within a single camera view. Deciduous spring green-up was highly correlated with visual ground truths, despite signal noise introduced by varying image exposure and automatic color correction. Compared to co-occurring satellite remote sensing products, public cameras had an equivalent or higher ability to detect spring with fewer days lost to cloud cover.