Populists in the Pluralist Heaven:

At the aggregate level there are fewer theories that describe group mobilizations and
those that do focus on the bene ts side. Olson (1982), while focusing more on the con-
sequences of group mobilizations, has the implication that groups should accumulate over
time, independent of other reasons to form. Shortly thereafter, the Virginia School (Mueller
and Murrell 1986; Coughlin, Mueller and Murrell 1990; Mitchell and Munger 1991) began
modeling the incentives of government o cials to attract groups and their money, conclud-
ing that legislators would o er policy in exchange for electoral resources: states that spend
more should attract more groups. Gray and Lowery (1996), referring to this as the \hey kid,
wanna buy some crack" model, substitute biological models of species density and diversity
for rational choice models. Their model, dubbed the Energy-Stability-Area model (ESA)
has three key components: the carrying capacity, or area, of a state, indicated by the size
of its economic activity; the energy available for groups to consume, measured by the size of
government output; and the stability of the environment, measured by the uncertainty over
which party will be in control. Analyzing state interest group populations in 1975, 1980 and
1990 they nd some support for the ESA model and little for its competitors.
These inquiries focus primarily on what groups are trying to in uence: their share of
government money. By increasing the potential bene ts for groups to form, states that are
larger in economic terms and have more government activity should have more groups that
have successfully mobilized. The other component of the bene t side is the ability to exert
in uence, which is a ected by which political institutions are available to groups. By altering
these institutions, the incentives to become active are also altered. Walker (1991) discusses
the ways in which groups overcome the obstacles to mobilization and suggests that political
4