Artificial ecosystem selection

Abstract

Artificial selection has been practiced for centuries to shape the properties of individual organisms, providing Darwin with a powerful argument for his theory of natural selection. We show that the properties of whole ecosystems can also be shaped by artificial selection procedures. Ecosystems initiated in the laboratory vary phenotypically and a proportion of the variation is heritable, despite the fact that the ecosystems initially are composed of thousands of species and millions of individuals. Artificial ecosystem selection can be used for practical purposes, illustrates an important role for complex interactions in evolution, and challenges a widespread belief that selection is most effective at lower levels of the biological hierarchy.

Figure 1

Results of soil ecosystem and aquatic ecosystem selection experiments. (a) Above-ground biomass of Arabidopsis thaliana plants grown in ecosystems inoculated with 6.0 g of soil. Open, upward-pointing triangles represent mean of 15 microcosms (± 1 SE) selected for high biomass. Solid, downward-pointing triangles represent selection for low biomass. Asterisks indicate generations in which biomass differed significantly (bootstrap test, P < 0.05). There were no significant differences between mean plant biomass in either of the two paired control treatments in the soil ecosystem experiments. (b) The 0.06-g soil inoculum experiment, symbols as described in a. (c) pH of aquatic microcosms selected for high or low pH. Means of 24 aquatic microcosms (± 1 SE), symbols analogous to those given in a.

Figure 2

Results of ecosystem artificial selection experiments (as in Fig. 1) expressed as deviations from overall means. Symbols are the same as in Fig. 1. (a) Difference between above-ground biomasses of Arabidopsis thaliana grown in ecosystem microcosms selected at high or low biomass, 6.0-g inoculum. (b) Difference between above-ground biomasses, 0.06-g inoculum treatment. (c) Difference in pH of aquatic microcosms selected for high or low pH.

Figure 3

Discriminant function analysis of 10 soil nutrient variables in the 6.0-g inoculum size treatments, generations 13 and 14 combined. Open, upward-pointing triangles represent soils in microcosms selected for high biomass. Filled, downward-pointing triangles represent selection for low biomass. Circles represent soils from microcosms inoculated with autoclaved slurries and selected at random. The first discriminant function is largely attributable to soil NH₄⁺ content. The second discriminant function is most strongly attributable to soil K, Zn, and P content. (Wilk's λ, 0.00828; F (20, 156) = 77.895; P < 0.0001).