(This exercise is based on De Deyn, G. B., C. E. Raaijmakers, H. R. Zoomer, M. P. Berg, P. C. de Ruiter, H. A. Verhoef, T. M. Bezemer, and W. H. van der Putten. 2003. Soil invertebrate fauna enhances grassland succession and diversity. Nature 422: 711–713.)
(Note: The reference above links directly to the article on the journal’s website. In order to access the full text of the article, you may need to be on your institution’s network [or logged in remotely], so that you can use your institution’s access privileges.)
Ecologists studying succession have traditionally emphasized the effects of plants on each other, not usually considering how the activity of animals affects successional change. In recent decades, more attention has been paid to the role of animals in succession. The recent studies show that the faunal composition of communities is often important in succession. These studies, however, generally focus on symbiont and pathogenic microbes or on vertebrate herbivores. In the present study, a group of scientists from the Netherlands Institute of Ecology examined the effects of soil invertebrates on succession.
The researchers established three different grassland communities: an early succession community (from an agricultural grassland), a mid-succession community (one that had undergone nature-restoration management for the last 20 years), and a climax community (a species-rich natural grassland community). The climax community is sometimes called the target community.
Table 1 The compositions of the soil fauna of the early-succession, mid-succession, and climax communities. (Click to enlarge.)
Question 1
What are the major differences in the compositions of the fauna shown in Table 1?
Figure 1 The effect of soil fauna on the shoot biomass of plants from the early succession, mid-succession, and target (= climax) grassland communities. (The data given are the averages of the three different soil fauna). The y-axis is the change in shoot biomass in the soil fauna–added treatment as compared to the control. “n.s.” denotes non-significant, and “*” denotes P < 0.05.
Question 2
The researchers added soil fauna from the target (climax) community to plants from each of the three types of communities, and investigated the effects of these additions. What conclusions about both the effects of soil nematodes and the time course of effects can you draw from the data shown in Figure 1?
Figure 2 The effects of soil fauna from the early, middle, and target communities on a group of plants from the early and mid-succession communities. Growth for both grasses (above the horizontal 0 line) and roots (below the horizontal 0 line) is shown. (The letters “a” and “b” represent significant differences at P < 0.05 level; if one treatment has an “a” and the other has a “b,” they are significantly different from each other.)
Question 3
The investigators also looked at the effects of adding soil fauna from the early, middle, and target communities to the same plants from the early and mid-succession communities (lumped together). The results are shown in Figure 2. What conclusions can you draw from the data shown in Figure 2?
Figure 3 The evenness of plant species abundance (as measured by the Simpson's evenness index) for the control (no soil fauna) versus treatment (combined data from all three soil faunas). Significance is denoted by “*”.
Question 4
The soil fauna appeared to selectively inhibit the growth of the dominant species. Thus, one might expect the species composition of the plots treated with the soil fauna to have a more even species distribution than the controls. What conclusions can you draw from Figure 3?
