Please write to jsexton2[at]ucmerced[dot]edu if you are unable access any of these publications. I would be happy to share a copy.
→Mandussi Montiel-Molina, Jorge A., Sexton, J.P., Frank, A.C., and J.M. Beman. Archaeal and bacterial diversity and distribution patterns in Mediterranean-climate vernal pools of Mexico and the western USA. (2021). Microbial Ecology. https://doi.org/10.1007/s00248-021-01941-2
Vernal pools are rare, temporary wetlands that host a great diversity of specially adapted life. They are also critically endangered in Mexico and California where 95-99% have been destroyed through development. Nevertheless, much remains unknown about these special ecosystems. Exploring the diversity of microbial life (bacterial and archaeal) in vernal pools across California and Baja California, we found that water and soil host distinct microbial communities within the same pools; that microbial communities differ according to the environmental differences and spatial distances between them; and that microbial community diversity increases at higher latitudes where pools receive higher rainfall.
→Jackie E. Shay, Lillie K. Pennington, Jorge A. Montiel-Molina, Daniel Toews, Brandon Hendrickson, and J.P. Sexton Sexton. (2021). Rules of plant species ranges: applications for conservation strategies. Frontiers in Ecology and Evolution. 9:700962. doi: 10.3389/fevo.2021.700962
Do general rules about plant species ranges exist? In this paper, we assess whether ecological and evolutionary rules of plant species geographic ranges may exist, and if so, how such rules can help with conserving plant biodiversity.
→Lillie E. Pennington, R.A. Slatyer, D. Ruiz-Ramos, S.D. Veloz, and J.P. Sexton. (2021). How is adaptive potential distributed within species ranges? Evolution. 75(9): 2152-2166.
Are there predictable hot spots of genetic variation that can boost adaptive potential for species in the face of global change? Combing the literature, we found that so far there are no strong patterns of adaptive potential between central and marginal regions or environments of species ranges. Nevertheless, few studies have tested this question in individual species ranges, and so it remains a major gap in our knowledge of the biology of species ranges. We advise that all populations of species ranges, central to marginal, should be considered as having high adaptive potential.
→Ezra J. Kottler, Erin E. Dickman, Jason P. Sexton, Nancy C. Emery, and Steven J. Franks. (2021). Draining the Swamping Hypothesis: Little Evidence that Gene Flow Reduces Fitness at Range Edges. Trends in Ecology & Evolution. 36(6): 533-544
There is a long-standing and popular idea that gene flow from central areas of species ranges swamps adaptation at species range boundaries, thereby creating species range limits. We argue that very little evidence exists supporting this hypothesis. In fact, most data point to gene flow being helpful to populations at the edges of species’ distributions.
→Rachel Meyer, Emily E Curd, Teia Schweizer, Zack Gold, Dannise Ruiz Ramos, Sabrina Shirazi, Gaurav Kandlikar, Wai-Yin Kwan, Meixi Lin, Amanda Friese, Jordan Moberg-Parker, Miroslava Munguia Ramos, Beth Shapiro, Jason Sexton, Lenore Pipes, Ana Garcia Vedrenne, Maura Palacios Mejia, Emma Aronson, Tiara Moore, Rasmus Nielsen, Harris Lewin, Paul Barber, Jeff Wall, Nathan Kraft, Robert Wayne (2021). The CALeDNA program: Citizen scientists and researchers inventory California’s biodiversity. California Agriculture. 75(1): 20-32.
What is eDNA? Environmental DNA, also known as “eDNA,” refers to DNA that is detected from a sample in any given environment (water, air, soil, etc.). For example, a gram of soil not only contains millions of microorganisms, but DNA strands of many species that have been shed over time and may persist for days to years. Thus, sampling eDNA can tell us not only what microorganisms live in a given space, but what species may live nearby, shedding their DNA along the way. In this paper we describe the CALeDNA program, which employs community science to to better understand the distributions of the great variety of organisms that live in California.
→Montiel, J.A., M.J. Beman, A.C. Frank, and J.P. Sexton. 2019. Visualizing diversity and distribution patterns for microbial communities in vernal pools. Pages 153-168 in R.A. Schlising, E.E. Gottschalk Fisher, G.M. Guilliams, and B. Castro (Editors), Vernal Pool Landscapes: Past, Present, and Future. Studies from the Herbarium Number 20, California State University, Chico, CA. Montiel et al. 2019
Vernal pool ecosystems are amazing ecological and evolutionary testing grounds. In this chapter, we discuss ways in which studying microbial organisms in vernal pools can improve understanding of how biological communities form, what binds them together and separates them, and how quickly communities can turn over across space (e.g.., between local pools or across an entire region) and time (e.g., days, months, or years).
→Lowry, D.B., J.M. Sobel, A.L. Angert, T.-L. Ashman, R.L. Baker, B.K. Blackman, Y. Brandvain, K.J.R.P. Byers, A.M. Cooley, J.M. Coughlan, M.R. Dudash, C.B. Fenster, K. G. Ferris, L. Fishman, J. Friedman, D.L. Grossenbacher, L.M. Holeski, C.T. Ivey, K.M. Kay, V.A. Koelling, N.J. Kooyers, C.J. Murren, C. D. Muir, T. C. Nelson, M.L. Peterson, J. R. Puzey, M.C. Rotter, J.R. Seemann, J.P. Sexton, S.N. Sheth, M.A. Streisfeld, A.L. Sweigart, A.D. Twyford, M. Vallejo‐Marín, J.H. Willis, K.M. Wright, C.A. Wu, and Y.-W. Yuan. (2019). The case for the continued use of the genus name Mimulus for all monkeyflowers. Taxon. 68: 617–623
The plant Genus Mimulus, which has historically contained the “monkeyflowers,” has recently been changed so that monkeyflowers are contained within many genera. In this paper we argue for why Mimulus should be retained as the genus name for all monkeyflowers.
→Sexton, J.P. The adaptive continuum and how species succeed and fail (2019). Philosophy, Theory, and Practice in Biology.
A perspective paper discussing what it means to adapt, or fail to adapt, if we take a holistic view of adaptation–that is, adaptation occurring across the tree of life, from genes, to species, to biological lineages.
→Dickman, E.E., Pennington, L.K., Franks, S.J., and J.P. Sexton. (2019). Evidence for adaptive responses to historic drought across a native plant species range. Evolutionary Applications. 12: 1569-1582
We found evidence that monkeyflowers that lived during the great drought of 2011-2017 in the California Sierra Nevada evolved faster seed emergence times, allowing them to better escape drought. This adaptation may have come at a cost of losing genetic variation.
→Hirst, M.J., Griffin, P.C., Sexton, J.P., and A.A. Hoffmann. (2017). Testing the niche breadth-range size hypothesis: habitat specialization versus performance in Australian alpine daisies. Ecology. 98: 2708-2724.
Are rare species less able to inhabit a wide range of environments compared to common species? We tested this “niche breadth-range size hypothesis” in various field conditions in the Australian Alps at the seed and seedling stages of rare and common alpine daisies. We found mixed support for this idea. Some rare species did under-perform in novel conditions compared to common species, but there were clear exceptions. Whether a species will perform better in certain environments may be predictable from its distribution, but examining different life stages (e.g., seed viability versus seedling survival) can give different answers.
→Sexton, J., Montiel, J., Shay, J., Stephens, M., and R. Slatyer. Evolution of ecological niche breadth (2017). Annual Review of Ecology, Evolution, and Systematics. 48: 183-206.
What determines how specialized different species or life forms are, or the span of environments they can tackle? In this paper, we reviewed the topic of how “niche breadth” (the span of resources a species can use) evolves and made recommendations for future avenues of research.
→Hirst, M., Sexton, J.P., & A. Hoffmann. (2016). Extensive variation, but not local adaptation in an Australian alpine daisy. Ecology and Evolution. 6: 5459-5472.
Focusing on a wild daisy species endemic to southeastern Australia, this study demonstrates that both environmental (e.g., habitat type, soil type) and genetic (i.e., different source populations of plants) variation greatly influence the size, shape, and success of plants. However, although certain plant populations do better in certain environments, we found no evidence for local adaptation (e.g., a local advantage). Nevertheless, this extensive variation is no doubt useful in allowing such plant species to occupy a wide geographic range.
→Sexton, J. P., Hufford, M., Bateman, A., Lowry, D., Meimberg, H., Strauss, S.Y., and K.J. Rice. (2016). Climate structures genetic variation across a species’ elevation range: a test of range limits hypotheses. Molecular Ecology. 25: 911-928.
How do plant genes flow across a species range? In a Sierran monkeyflower we found evidence that gene flow occurs most strongly between populations having similar climates rather than being determined by spatial distance between populations or whether populations occur near the center or edge of their species range. We also found that populations living on the edge of their distribution tend to have as many or more plants living in them, compared to central populations. This work signals the importance of climate in maintaining genetic variation as well as the equal importance of peripheral populations as sources of genetic variation.
→Sexton, J. P., & E. E. Dickman. (2016). What can local and geographic population limits tell us about distributions? American Journal of Botany, 103(1), 129-139. Sexton & Dickman 2016
In this paper we compare and contrast the benefits of studying plant populations at the their local margins and the margins of the species range. We also demonstrate in Sierran monkeyflower case studies how both of these types of population limits can signal severe growth and fitness reductions.
→Sexton, J. P., & Griffith, A. B. (2015). Evolutionary conservation under climate change. In T. L. Root, Hall, K. R., Herzog, M., & Howell, C. A., Biodiversity in a Changing Climate: Linking Science and Management in Conservation. University of California Press.
In this chapter we review how natural resource managers can use evolutionary ideas to help maintain wild plant and animal populations under climate change.
→Ferris, K., Sexton, J. P., & Willis, J. (2014). Speciation on a local geographic scale: the evolution of a rare rock outcrop specialist in Mimulus. Philosophical Transactions of the Royal Society B, 369(1648), 20140001. Ferris et al. 2014
This study reports how two closely related plant species (fern-leaved monkeyflower; cut-leaf monkeyflower) that look very similar (i.e., have dissected leaves) and “act” very similar (i.e., live only in the same type of habitat of the western slope of the Sierra Nevada, but separated by > 100 km), likely evolved independently and both specialized on rocky seeps. They are both close relatives to the common yellow monkeyflower.
→Sexton, J. P., Hangartner, S. B., & Hoffman, A. A. (2014). Genetic isolation by environment or distance: which pattern of gene flow is most common? Evolution, 68(1), 1-15. Sexton et al. 2014
The Molecular Ecologist
In a review of the landscape genetics literature, we found that differences in environment (aka “isolation by environment”) seem to most often explain genetic differences between populations. That is to say, gene flow most frequently occurs between populations inhabiting similar environments or ecosystems, rather than just how close populations are to each other spatially (aka “isolation by distance”). This is likely due to the forces of natural selection and/or the way environments can shape or influence mating patterns in nature.
→Grossenbacher, D. L., Veloz, S. D., & Sexton, J. P. (2014). Niche and range size patterns suggest that speciation begins in small, ecologically diverged populations in North American monkeyflowers (Mimulus spp.). Evolution, 68(5), 1270-1280. Grossenbacher et al. 2014
In this study we found evidence that new plant species most often start as small populations within the ranges of another species. Furthermore, as new species arise, they occupy distinct ecological niches from their widespread sister species.
→Sexton, J.P. (2014) Species range limits. Encyclopedia of Earth. http://editors.eol.org/eoearth/wiki/Species_range_limits
What are species range limits? See this article for a brief description in the Encyclopedia of Earth.
→Sexton, J. P., Ferris, K. G., & Schoenig, S. E. (2013). The fern-leaved monkeyflower (Phrymaceae), a new species from the northern Sierra Nevada of California. Madroño, 60(3), 236-242. Sexton et al. 2013
We described a new, rare species of monkeyflower in California from Butte and Plumas Counties.
→Slatyer, R. A., Hirst, M., & Sexton, J. P. (2013). Niche breadth predicts geographical range size: a general ecological pattern. Ecology Letters, 16(8), 1104-1114. Slatyer et al. 2013
In a review and meta-analysis of the literature, we found that species with greater niche breadth (for example, broader diet or broader climate tolerance) have wider distributions on Earth (i.e., larger species ranges).
→Peterson, M. L., Rice, K. J., & Sexton, J. P. (2013). Niche partitioning between close relatives suggests trade-offs between adaptation to local environments and competition. Ecology and Evolution, 3(3), 512-522.
Peterson et al. 2013
We tested whether two plant species–one common and one rare–in the Sierra Nevada are adapted to the local environments where you find them. We found that a rare monkeyflower outperformed a common monkeyflower in its home habitat (rocky seeps) by developing quickly before soils dry up. The absence of the rare monkeyflower in more common habitats may be explained by a trade-off in fast development versus ability to compete with other plant species.
→Sexton, J. P., Strauss, S. Y., & Rice, K. J. (2011). Gene flow increases fitness at the warm edge of a species’ range. Proceedings of the National Academy of Sciences of the United States of America, 108(28), 11704-11709.
Sexton et al. 2011
In this study we pollinated Sierran monkeyflowers growing in the warmest region of the species range using local pollen, pollen from cooler elevations, or pollen from other populations from a similar, warm elevation. Planting seeds back in the warm environment, we found that plants with parents from different populations, but from similar, warm environments were most successful. Thus, wild populations can benefit from gene flow from similar, stressful environments and this may be an effective conservation approach.
→Epanchin-Niell, R. S., Hufford, M. B., Aslan, C. E., Sexton, J. P., Port, J. D., & Waring, T. M. (2010). Controlling invasive species in complex social landscapes. Frontiers in Ecology and the Environment, 8(4), 210-216.
Espanchin-Niell et al. 2010
Who your neighbor is and what they do to control invasive species (e.g., yellow starthistle, kudzu, and cane toads) can matter as much as your management actions. In this paper we cover how and why coordination and cooperation among neighbors is essential for managing biological invasions.
→Sexton, J. P., Schwartz, M. W., & Winterhalder, B. (2010). Incorporating sociocultural adaptive capacity in conservation hotspot assessments. Diversity and Distributions, 16(3), 439-450. Sexton et al. 2010
Are more just societies better at preserving nature? In this paper we discuss how and why human health and well-being should be factored in to make regional conservation strategies most effective.
→Sexton, J. P., McIntyre, P. J., Angert, A. L., & Rice, K. J. (2009). Evolution and ecology of species range limits. Annual Review of Ecology, Evolution, and Systematics, 40, 415-436. Sexton et al. 2009
What causes organisms to stop expanding their distributions? We reviewed the topic of the causes of species range limits (also known as species distribution limits) in this paper and made recommendations for future avenues of research.
→Aslan, C. E., Hufford, M. B., Niell, R. S., Port, J. D., Sexton, J. P., & Waring, T. M. (2009). Practical challenges and solutions to private stewardship of rangeland ecosystems: Yellow starthistle control in California’s Sierra Nevada foothills. Rangeland Ecology and Management, 62(1), 28-37. Aslan et al. 2009
In this survey of Sierran foothill ranchers, we found that gaps between science and practice contribute to limitations to the control of the invasive plant, yellow starthistle. These gaps resulted from incomplete education/information, ineffective weed control in variable landscapes, inconsistent application of methods, and lack of long-term planning.
→Bower, M., Sexton, J. P., & Carne-Cavagnaro, V. (2006). Agricultural invaders, pests, and disease in California’s changing climate. In Climate Change: Challenges and Solutions for California Agricultural Landscapes (Cavagnaro, T.R., Jackson, L.E. and Scow, K.M., eds.). CEC-500-2005-189-SF.
In this report we reviewed literature on agricultural weeds, pests, and disease-causing microbes and how they may be impacted by climate change in the context of California agriculture.
→Sexton, J. P., Sala, A., & Murray, K. (2006). Occurrence, persistence, and expansion of saltcedar (Tamarix spp.) populations in the Great Plains of Montana. Western North American Naturalist, 66(1), 1-11. Sexton et al. 2006
In this field study we explored the northern invasion front of the invasive shrub–saltcedar (aka tamarisk)–in eastern Montana. We found that saltcedar invaded e. Montana from multiple introductions in the 1960s and that its populations have increased over time in terms of shrub stand size and the number of stands. Saltcedar increases are likely due to intentional plantings, habitat disturbance, and habitat alterations due to river flow control.
→Sexton, J. P., McKay, J. K., & Sala, A. (2002). Plasticity and genetic diversity may allow saltcedar to invade cold climates in North America. Ecological Applications. Ecological Applications, 12(6), 1652-1660. Sexton et al. 2002
In this study we found that seedlings of the invasive shrub, saltcedar (aka tamarisk), had different growth habits (e.g., differences in root investment up north) between populations in colder Montana climates and hotter Arizona climates. These findings illustrate how colonizing populations can evolve and shift growth habits quickly (within a few decades) within their newly colonized species ranges.