Hirst, M.J., Griffin, P.C., Sexton, J. P., and A.A. Hoffmann. Accepted. Testing the niche breadth-range size hypothesis: habitat specialization versus performance in Australian alpine daisies. Ecology.
Sexton, J., Montiel, J., Shay, J., Stephens, M., and R. Slatyer. (2017). Evolution of ecological niche breadth. Annual Review of Ecology, Evolution, and Systematics
Hirst, M., Sexton, J. P., & A. Hoffmann. (2016). Extensive variation, but not local adaptation in an Australian alpine daisy. Ecology and Evolution.
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.
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.
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. 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., 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 know 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.