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New Paper in ‘PLoS One’

Multi-phase US spread and habitat switching of a post-Columbian invasive, Sorghum halepense

Sezen, Barney, Atwater, Pederson, Pederson, Chandler, Cox, Cox, Dotray, Kopec, Smith, Schroeder, Wright, Jiao, Kong, Goff, Auckland, Rainville, Pierce, Compton, Lemke, Philips, Kerr, Mettler, Paterson (pdf)

I’m happy to announce that PLoS One has accepted Uzay Sezen’s paper documenting the population genetics of colonizing Johnsongrass (Sorghum halepense).

Using a panel of almost 500 Johnsongrass accessions from 70 sites throughout the US, Dr. Sezen showed that Johnsongrass was introduced to the US at two locations. It has subsequently colonized much of North America, demonstrating surprising genetic variation even at range margins.

Johnsongrass populations have also differentiated strikingly along habitat boundaries, with genetic clusters segregating strongly between crop populations and those found in roadsides and other disturbed environments.

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New Paper in ‘Annual Reviews’

The mechanisms and consequences of interspecific interactions among plants

Aschehoug, Brooker, Atwater, Maron & Callaway (pdf)

I’m very pleased to announce that Annual Reviews of Ecology, Evolution and Systematics has accepted our review article documenting recent advances in our understanding of interspecific plant interactions.

I am proud to have been a part of this group. Erik spearheaded this effort and has worked very hard to bring the finished product together. I look forward to the publication of our review in November!

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New Paper in ‘Ecology’

Intraspecific diversity buffers the inhibitory effects of soil biota

Luo, Callaway & Atwater (link)(pdf)

WenboFig

In sterilized soil, bluebunch grew the same regardless of the soil that was used. In unsterilized soil, bluebunch did not grow well in soil from the low-richness plots.

Congratulations to Wenbo Luo for recently having a paper accepted to Ecology! In this paper, Wenbo shows that soil microbes inhibit the growth of related bluebunch wheatgrass plants (Pseudoroegneria spicata).

To do this, he collected soil from bluebunch populations varying in their genetic diversity. He then grew bluebunch seedlings in that soil and compared their growth.

Seedlings did not grow well in soil from populations with low genetic diversity. This effect went away when the soil was sterilized, suggesting that soil microorganisms were responsible.

Soil feedbacks such as these are thought to result from adaptation by soil pathogens. Wenbo’s results suggest that soil pathogens specialize not only on species but on related individuals. This also provides a mechanism affecting the high productivity we see in genetically diverse bluebunch wheatgrass populations.

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WSSA 2016 – San Juan

I presented the results of my environmental niche modeling work at the 2016 Weed Science Society of America Meeting in San Juan, Puerto Rico. I attended the meeting with my advisor, Jacob Barney, and Dan Tekiela, a graduate student in Jacob’s lab.

The weather was lovely and we had an excellent time escaping winter’s grip to enjoy some sunshine and sea air! We also had a fantastic conference, meeting new people and learning about the exciting work that WSSA members are doing.

Congratulations to Jacob for winning the Outstanding Early Career Weed Scientist award!

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New Paper in ‘Oecologia’

An exotic invasive plant selects for increased competitive tolerance, but not competitive suppression, in a native grass

Fletcher, Callaway & Atwater (pdf)

Fig2new

At each of four sites, bluebunch from knapweed invaded plots (I) had much better ability to tolerate knapweed than those from uninvaded plots (U). However they were not better at suppressing knapweed.

Many congratulations to Rebecca Fletcher, who just had a paper accepted into Oecologia. Her paper shows that spotted knapweed, an invasive plant, selects for bluebunch wheatgrass plants that are tolerant of knapweed competition, but not for ones that are better at competitively suppressing knapweed.

This is the first direct test of the hypothesis that neighbor suppression does not provide fitness benefits to competing plants. Her finding is important because it challenges long-held notions of what makes a plant a good competitor. Becky performed this research as an undergraduate student at the University of Montana, on a grant she wrote for the Montana Integrative Research Experience for Students (MILES) program.

 

 

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New Paper in ‘Weed Research’

Propagule pressure alone cannot always overcome biotic resistance: The role of density-dependent establishment in four invasive species

Barney, Ho & Atwater (link)
I am very pleased to announce that we have just had a paper accepted for publication into Weed Research. This paper documents Master’s Student Matt Ho’s research into the role of propagule pressure in invasion. He found that negative density-dependent germination probability causes diminishing returns for species that broadcast a large number of seeds. His results suggest that site conditions and species interactions play an important role in determining invasion probability even when propagule pressure is intense.

032-Fig3-FINAL-Ed

Invasion probability increases as the number of seeds (aka propagule size) increases. When germination is density dependent (solid line), invasion probability increases much more gradually than when it is not (dashed line). This means that site conditions play a very important role in determining invasion probability, even when propagule pressure is high.

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NEPPSC 2016 – Philadelphia

Pictured, left to right: Big Dan, Morgan, Little Dan (top); Jacob and Benjamin Franklin (bottom)

I recently presented the results of my niche modeling work at the 2016 Northeastern Plant Pest and Soils Conference in Philadelphia. I went the the conference along with most of the rest of my postdoc advisor’s (Jacob Barney’s) lab and we had a great time. I met a lot of people, including the First American, Benjamin Franklin, who looked great despite being only a week away from his 310th birthday.

At the conference, I presented the results of our study of climatic niche shifts in introduced species. Jacob and I have found that species experience major niche shifts as they cross continents. This work is in preparation for submission.

Also, congratulations are in order for “Little” Dan Tekiela, who won the Robert D. Sweet Outstanding Graduate Student Award and placed first in the Student Paper Contest. Virginia Tech also won the NEPPSC quiz bowl, besting teams from Cornell, Penn State, UMass, Maine, NC State, and Delaware, as well as the EB-ESA Linnaean Games. Graduate students Morgan Franke and Dan Tekiela both gave excellent presentations of their research.

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New Paper in ‘Ecography’

Reconstructing changes in the genotype, phenotype, and climatic niche of an introduced species

Atwater, Sezen, Goff, Kong, Paterson & Barney (link)

022-JGUltra-Ecography-Fig-A6

The climate occupied by initial invaders (black, dashed) resembled the home climate (black, solid). As the invasion progressed, Johnsongrass moved into cooler habitats in the US (grey, solid & dashed). Noteably, these are not climates Johnsongrass occupies in its native range in Eurasia, although they are available. How invasive species change their climatic niches in their introduced ranges is a mystery.

Invasive species must deal with enormous environmental variation in their introduced ranges. Some evolve rapidly, and others tolerate a wide variety of conditions. We examined how one invader, Johnsongrass, has responded to environmental variation in North America. This devastating agricultural weed is ever-present in the fields, roadsides and railways of the United States.

Almost 500 individual Johnsongrass plants collected from 70 locations in the United States show enormous variation in their size and shape. Plants from cool, wet climates grow especially large, growing 10 feet tall and gaining almost 5 pounds of dry weight in a single year. Plants from agricultural habitats grew much larger and taller than those from roadside habitats and meadows, and responded differently to growing conditions.

These results paint the clearest picture to date of how an introduced species changes genetically and phenotypically as it encounters habitat variation in their introduced range. Local adaptation and phenotypic plasticity play important roles in the ability of Johnsongrass to invade the United States.

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Hokie Half 2015

The 2015 Hokie Half Marathon is officially vanquished! I set a PR (1:38:22) and had a lot of fun.

The weather was absolutely beautiful and there over 1200 runners. It was a great time. Thank you to my cheer squad for keeping me going!

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ESA 2015 – Baltimore

On Thursday at the 2015 Ecological Society of America meeting, I presented preliminary data from an analysis of the global distributions of 1135 introduced species. We find that species experience massive niche shifts as they cross continents. The magnitude of these niche shifts depends upon the methods used to remove sampling bias.

These data have significant implications for our ability to use native-range data to predict future distributions in the introduced range — a critical issue in the development of invasive species risk assessments. Fortunately, I was able to finish my talk just before a fire alarm cleared out the convention center!

Big ups to Dan and Morgan, the students in my post-doc lab, for giving great talks. Dan presented his study of non-additive effects of dual invaders, and Morgan presented her work on restoring autumn olive-invaded surface mine sites. Surface mining in Appalachia involves complete mountaintop removal. The topology, plant communities, and “soil” of these sites are 100% artificially reconstructed and have to be seen to be believed. Jacob, my advisor, presented our work on evaluating genetic and phenotypic variation in 70 US populations of Johnsongrass, a devastating invader.