New Paper in ‘Ecography’

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

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


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.


New paper in ‘Ecology’

Testing the mechanisms of diversity-dependent overyielding in a grass species

Atwater & Callaway (2016)(link)
007-boxplotsEDI’m very pleased to announce that Ray Callaway and I have just had a paper published in Ecology. In this paper, we find that genetically diverse populations of bluebunch wheatgrass (Pseudoroegneria spicata) yield about 50% more biomass than populations with low diversity.

This diversity-dependent “overyielding” is thought to occur because diverse plant communities function more efficiently than communities with low diversity. There is thought to be less demand for shared resources in diverse communities and less disease (e.g. by soil fungi). As a result, overyielding in species-diverse communities is often associated with changes in soil nutrients, and the yield of low-diversity communities can be “rescued” by killing soil pathogens.

However, we find that diversity-dependent overyielding in bluebunch wheatgrass populations was not related to changes in soil nutrients, and was unaffected by fungicide applied to the soil. We conclude that overyielding in genetically diverse populations may not be caused by the same processes that cause overyielding of species diverse communities.



WSSA 2015 – Lexington


Two phases of invasion: Initial invasion (red) appears to have been in warmer climates. Later in invasion (blue) Johnsongrass has expanded to cooler climates.

On Thursday, at the Weed Science Society of America meeting in Lexington, I presented the results of a large scale survey of phenotypic differentiation in 499 accessions of Johnsongrass (Sorghum halepense) from 70 populations throughout the United States. Jacob Barney — my postdoctoral advisor — was initially scheduled to present, but I took his place when a scheduling conflict prevented his attendance.

I had a great meeting and met a lot of wonderful people. Special congratulations to Kate Venner, Sandeep Rana, and John Brewer from the lab upstairs for their recognitions and accomplishments at the meeting.