The Illinois Invasive Species Awareness Month blog brings you the third installment of catchy invasive species slogans! http://illinoisisam.blogspot.com/2012/08/the-hunt-for-invasive-species-slogans.html
“Spread the word, not the weed” was one of my favorites.
In 1948 two researchers looked at polyploidy (additional sets of chromosomes) in 175 weedy species in California and found about equal numbers of diploid and polyploid weeds. They concluded that polyploidy had little to do with weediness in general, but might be useful in more specific comparisons within families or genera (Heiser and Whitaker, 1948).
Polyploidy can lead to a plant having different growth and reproductive characteristics and often leads to plants either being sterile or to becoming a different species that is no longer able to breed with the parent species. Some polyploids are able to hybridize with other related species that the diploid parent wasn’t able to cross with.
You can read all the details about why a polyploid might be expected to be more successful as an invader in an article by Beest et al. (2011). It has to do with some polyploids producing more seeds or more vegetative propagules, becoming adapted to new environmental conditions, and a host of other factors.
In the case of spotted knapweed, Centaurea stoebe, diploid and tetraploids exist in its native Europe, but only tetraploids occur in its invasive range in the United States. In a common garden experiment, tetraploids from the US had much greater seed production and seedling establishment and therefore a high population growth rate, than either European diploids or tetraploids. This indicates that it isn’t ploidy level, but rather some other evolutionary driver that makes American populations so successful (Hahn et al., 2012).
Although polyploidy certainly can increase the probability of invasiveness, it clearly isn’t the cause in every case. Who ever said ecology had easy answers though?!
Beest, Mariska te, Johannes J. Le Roux, David M. Richardson, Anne, K. Brysting, Jan Suda, Magdalena Kubešová and Petr Pyšek. 2011, The more the better? The role of polyploidy in facilitating plant invasions. Annals of Botany doi: 10.1093/aob/mcr277. Available online: http://aob.oxfordjournals.org/content/early/2011/10/30/aob.mcr277.full
Hahn, M.
Heiser, Charles B. Jr. and Thomas W. Whitaker. 1948. Chromosome number, polyploidy and growth habit in California weeds. American Journal of Botany 35 (3): 179-186.
Water hyacinth, Eichornia crassipes, is known as the world’s worst aquatic weed because of its prolific growth. It lowers biodiversity in tropical waterways, shelters pests like mosquitos, and causes eutrophication. But all that biomass could have its uses. Patel summarizes research on using water hyacinth in wastewater treatment, production of biofuels, animal feed and many other uses.
Dense growth of water hyacinth in a Florida waterway
Patel, S. 2012.
You might think that plants growing in gardens would face fewer pest problems as gardeners vigilantly defend them against unsightly leaf damage and flower mangling. For introduced ornamental plants this could be just the boost they need to escape the garden walls and become invasive. However, a study comparing herbivory on native and non-native plants in garden and natural settings, found no difference in herbivory for plants grown in different settings. Native plants did suffer more insect damage than introduced plants, but it didn’t matter where they grew.
Matter, S.
Following up on research that demonstrated that garlic mustard’s (Alliaria petiolata) production of chemicals detrimental to other plants declined the longer a population had been established, Lankau now reports on the ability of a native plant to resist the phytotoxins.
Clearweed, Pilea pumila, commonly occurs in areas invaded by garlic mustard. In habitats where many native species are present, Alliaria petiolata produces more sinigrin, a compound that kills the mycorrhizal fungi that help plants obtain more nutrients. Clearweed growing with the more toxic garlic mustard has evolved some resistance to the chemical.
The author speculates based on his transplant studies that using more resistant plants in restoration projects could lead to greater establishment success of the natives. The two studies also show that over long periods of time some invasive plants may come to co-exist with native plants.
Lankau, R. A. 2012. Coevolution between invasive and native plants driven by chemical competition and soil biota. PNAS, published ahead of print June 25, 2012, doi:10.1073/pnas.1201343109
Lankau, R. A., V. Nuzzo, G. Spyreas and A. S. Davis. 2009. Evolutionary limits ameliorate the negative impact of an invasive plant. PNAS 106 (36) 15362-15367.
A greenhouse study on native and non-native grasses from the Great Basin looks at changes in soil nutrient levels and soil microbes among species. The researchers found that although both native and non-native grasses condition soils, the changes caused by native plants tended to favor the growth of other species, while conditioning by the non-native grasses tended to favor only their own growth. The non-native grasses studied included Bromus tectorum, Taeniatherum caput-medusae, Agropyron cristata, and Aegilops triuncialis. These were compared to the native grasses Elymus elymoides, Pseudoroegmeria spicata, and Vulpia microstachys.
Perkins, L.
Goats seem to be the hottest new weed control method. They have been used for weed control probably since they were first domesticated, but companies offering rental goats specialized in weed control are, growing like weeds. Goats offer an alternative to herbicides, but they can be costly to use because of the care and maintenance required. Of course spray equipment requires a lot of care and maintenance too, so maybe the investment evens out. The public seems to enjoy watching goats work much more than they like to see spray equipment being used!
Below is just a sampling of companies now offering goat rental services for weed control. The only rental we are personally familiar with is EcoGoats, so please check references before choosing a company. Add your favorite goat rental to this list!
EcoGoats, MD, http://www.eco-goats.com
Green Goat Rentals, ID and WA, http://www.greengoatrentals.com/
Rent-a-Ruminant, WA, http://www.rentaruminant.com/
The Goat Lady, WA, http://www.thegoatlady.org/
Goats R Us, CA, http://www.goatsrus.com
The Goat Girls, MA, http://www.thegoatgirls.com/
I’ve been steeped in the nuances of assessments of plant invasiveness the last few months as the Maryland Invasive Plant Advisory Committee develops an assessment for non-native terrestrial plants that grow or could grow in Maryland. Most assessments look at a plant’s ability to establish and spread and the impact the plant can have at the population, community and ecosystem levels. Some also include economic impacts including impacts to trade, agriculture, and built environments. When it comes to establishment, geography and climate play an important role in determining where a species can survive. A new paper published in Biological Invasions models how climate and human influences affect the distribution of Japanese honeysuckle, Lonicera japonica. It finds that human influences extend the predicted range based solely on climate. So if you want to figure how much risk a plant might have of invading your region, consider both climate change and distribution by people.
Carolyn M.
