Title
When Biocontrol Isn’t Effective: Making Predictions and Understanding Consequences
ABSTRACT PAGE
The Issue
Invasive species cause significant ecological and economic harm, and therefore effective management strategies are of utmost importance. One common yet controversial method proposed to control invasive plant species is biological control. This issue explores how relatively short-term ecological research can be combined with matrix modeling to evaluate the likely success of biological control. Students will incorporate actual research data into a modeling program to determine the effects of biocontrol on the population growth rate of an invasive species. Further, they will explore the consequences of introducing an actual biological control agent and discuss the associated risks and benefits. This issue, particularly Figure Set 2, is most appropriate for use in an upper-level ecology or population ecology course.
Ecological Content
biological control, demography, herbivory, indirect effects, invasive species, matrix modeling, population ecology, plant tolerance, trophic cascades
Student-active Approaches
think-pair-share, jigsaw
Student Assessments
essay quiz, one minute paper, concept map
Authors
Michele R. Schutzenhofer1 and Tiffany M. Knight2 Washington University in St. Louis, St. Louis, MO 63130
1- mrschutzenhofer@mckendree.edu
2- tknight@biology2.wustl.edu
Acknowledgements
The authors would like to thank E.A. Pardini and the students in the Population Ecology course at Washington University in St. Louis for encouraging the continued development of this activity and Washington University and the National Research Initiative of the USDA Cooperative State Research, Education and Extension Service, grant number #05-2290, for financial support.
Citation Schutzenhofer, M. R. and T. M. Knight. February 2009, posting date. When Biocontrol Isn’t Effective: Making Predictions and Understanding Consequences.
Teaching Issues and Experiments in Ecology, Vol. 6: Issues
Figure Set #1 [online]. http://tiee.ecoed.net/vol/v6/issues/figure_sets/biocontrol /abstract.html
FIGURE SET HEADER for Set #1
Figure Set 1: What are the effects of herbivory on individual plant survival and growth?
Purpose: To interpret graphical results and to examine how herbivory affects individual plant survival and growth.
Teaching Approach: Think-pair-share
Cognitive Skills: (see Bloom's Taxonomy) -- Knowledge, Comprehension
Student Assessment: One minute paper
BACKGROUND for Set #1 (back1.html)
Invasive species are species that have been introduced from their native range into an area where they do not have an evolutionary history. Further, invasive species are categorized as highly problematic species, causing both economic and ecological harm (Pimentel et al 2005). There are numerous invasive plant species that have been introduced to the United States that are problematic and need to be managed, including bush honeysuckle (Lonicera maackii), garlic mustard (Alliaria petiolata), and spotted knapweed (Centaurea maculosa). Typical management strategies often include hand-pulling, mowing, chemical spray, or a combination thereof. For some species, these management strategies can be an effective means to reduce the abundance of invasive species, ultimately reducing the negative effects they have on native species and communities. In other cases, typical management strategies are not enough to reduce invasive species’ abundance or are too costly to employ. When such traditional management techniques prove inadequate (based on cost or effectiveness), biological control is often considered a feasible alternative. In plants, for instance, biological control consists of introducing enemies (herbivores), often referred to as biological control agents, from the plant’s native range. The herbivores are meant to “damage” the invasive plant species by consuming plant tissue, reducing plant resources, and therefore curbing its population growth.
One invasive species that is considered highly problematic is Lespedeza cuneata (common name: sericea lespedeza or Chinese lespedeza). Lespedeza cuneata is a perennial legume native to eastern Asia. It was introduced in to the United States in the 1930s to stabilize areas that had been strip mined. It was also recommended the Department of Transportation in many states to use for quickly stabilizing roadsides. While the plant grows quickly in poor soil and requires little maintenance, it is those same traits that also make it an invasive threat. Lespedeza cuneata does not stay put. From the initial plantings, L. cuneata has spread by the movement of animals, hay, and equipment used to cut hay, and through the blowing wind. It can now be found throughout the eastern and Midwestern United States. It encroaches on our native prairies, savannas, glades, woodlands and forests. Normal grassland management practices such as grazing and burning do not adequately control L. cuneata and can actually increase its spread.
Lespedeza cuneata produces prolific amounts of seed, and some of that seed can remain dormant in the soil and germinate at a later time, making it very difficult to eradicate the species once it establishes. Further, L. cuneata makes two different types of seeds: cleistogamous seeds
FIGURE SET HEADER for Set #2
Figure Set 2: What are the effects of herbivory on population growth rate?
Purpose: To understand how a demographic matrix model works using a modeling program (R). To use demographic modeling to calculate population growth rate for control plants and then modify the model to understand how herbivory treatments change the results. Students will find that individual level consequences (examined in figure set 1) do not always translate into population level consequences. Students will then calculate an elasticity matrix to understand that not all vital rates contribute equally to the population growth rate.
Teaching Approach: Think-pair-share
Cognitive Skills: (see Bloom's Taxonomy) -- Knowledge, Comprehension, Interpretation Student Assessment: essay quiz
BACKGROUND for Set #2 (back2.html)
FIGURE SET HEADER for Set #3
Figure Set 3: Indirect effects of biological control of knapweed.
Purpose: To allow students to teach each other about the cascading effects resulting from an introduced biological control agent, involving the invasive knapweed, the biological control agent (gall flies), mice, and hantavirus.
Teaching Approach: Jigsaw
Cognitive Skills: (see Bloom's Taxonomy) — Comprehension, Interpretation, Synthesis
Student Assessment: essay quiz, concept map
BACKGROUND for Set #3 (back3.html)
Background
For Instructor and Students
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