Article: Stohlgren, T.J., D.T. Barnett, and J.T. Kartesz. 2003. The rich get richer: patterns of plant invasions in the United States. Frontiers in Ecology and the Environment 1(1): 11-14.


The emphasis in TIEE Issues is use of figures and tables for discussion and other types of student-active teaching and learning. These notes will give you ideas about using the figures in this paper in your ecology class. The Student-Active Teaching table will introduce you to a variety of approaches you can use in your class to actively engage your students. To see an essay on leading good discussions, go to Guided Class Discussions.

You can use these data and the overall disagreement to get your students to think more carefully about effects of invasive non-natives on native plants and communities, resilience and vulnerability of communities to invasive plants, and possible mechanisms regulating species diversity and introductions. Below are several ways you can use these figures and the table to stimulate discussion about these and related topics (use some of the questions below as well).

Note: Turn-to-Your-Neighbor is an easy and effective group approach you can use in large classes.

  1. Project or hand out Stohlgren et al.’s Figure 2. With the class as a whole or in small groups (no more than 5 students per group), ask students to first describe and then interpret this figure. (Ahead of time explain y, r, and p and the source of the data). For students working in groups, ask each group to present one question or comment they have about the figure. You can call on one group at random to describe and interpret the figure, and then ask for additional comments/questions.
  2. Project or hand out Stohlgren et al.’s Figure 1 and/or 2. Describe and interpret these figures yourself (including data sources) and the significance of this result. Then project or hand out Rejmanek’s Figure 1. Ask the class as a whole or students working in small groups to explain how this figure and the accompanying diagram differ from Stohlgren et al.’s data, e.g., what they learn and think about with these different data. Again, if students work in groups, ask for volunteers or call on a group at random when you bring them together for discussion.

Questions for discussion:

  1. Stohlgren et al. say that there may not be direct cause-effect relationship between diversity of native and non-native plants. Instead, both may be correlated to another factor or factors such as habitat heterogeneity. What do they mean by “direct cause-effect relationship” and why is the relationship they show “indirect?” Explain how diversity of non-native and native plants might be correlated to habitat heterogeneity. What does that mean?
  2. Why did Stohlgren et al. do this analysis? What questions were they asking and why? How might their findings change management of non-native plant invasions and conservation of species-rich areas?
  3. What question was Rejmanek addressing? Why is this interesting? Does his finding negate the results of Stohlgren et al.? Rejmanek includes a diagram with his figure; why? What is he doing with this diagram that is different from the data presentation of Stohlgren et al.?

Questions of scale

Another response to Stohlgren et al. by Renne and Tracy (2003) concerns the effect of scale on possible relationships between diversity and invisibility. The authors argue that the large scale of Stohlgren et al.’s analysis does not allow for control of environmental factors and that small scale studies do allow for isolation of such factors. They say that “…the ability to manipulate both local neighborhood interactions and environmental factors can elucidate their relative contribution towards community invisibility. Without these estimates, we fail to explain the processes affecting invasion patterns, and thus cannot offer effective management strategies.” This quote could lead to a good discussion about experimental design in regard to scale and application of results for management purposes.

Fig. 7 from from Stohlgren, T.J. et al. 1999. (Exotic plant species invade hot spots of native plant diversity. Ecol. Monogr. 69: 25-46) does address the scale issue and is included in the Figure section for that reason.