Introduction

The debate about whether ecological systems behave in an equilibrial or nonequilibrial fashion is a thread that runs through the entire history of ecology. The debate between Clements’s super-organism (Clements, 1936) vs. Gleason’s individualistic assortment (Gleason, 1926) is one of the earliest well-known examples. The density-dependent (Nicholson & Bailey, 1935) vs. density-independent (Davidson & Andrewartha, 1948) regulation debate was very explicitly about equilibrial vs. nonequilibrial forces. This debate was so intense and long-lasting that a peace-making conference was called at Cold Spring Harbor (Cold Spring Harbor Symposium on Quantitative Biology (22nd), 1957). One could argue that the MacArthurian development of community ecology (MacArthur, 1968) and the subsequent backlash against it were also in this vein. The heated debate about null-models (Connor & Simberloff, 1979; Diamond, 1975) was basically sparked by a bold assertion of a specific version of the nonequilibrial view (namely complete randomness) as a challenge to the then prevailing equilibrial viewpoint. Most recently, niche vs. neutral theory is a battle between two very specific versions of the equilibrial and nonequilibrial theories respectively. Thus although the specific debate seems to mutate every couple of decades, the dominant points of contention in ecology have all had an underlying theme of equilibrial vs. nonequilibrial concepts at the center for close to 100 years now.

The noted historian of ecology, Sharon Kingsland, follows this recurring debate and interprets it as a battle of modelers, who like to find regular patterns, vs. field ecologists, who experience the variation in nature, (Kingsland, 1995). But I think this is perhaps imprecise. It is true that many of the earliest models introduced into ecology such as the Verlhulst-Pearl logistic equation (Verhulst, 1838) and the Lotka-Volterra competition equations (Lotka, 1925; Volterra, 1927) were highly deterministic, strong equilibrium, differential equation models. However, probabilistic, nonequilibrial models have been known in ecology and evolution at least since the 1920s (Arrhenius, 1921; Yule, 1924).