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10

Other Species Concepts

Ecological Species Concepts

Turesson’s species concept was not widely adopted, but ecological concepts have
been proposed from time to time. Mayr himself ventured one in his 1982 history:

A species is a reproductive community of populations (reproductively isolated from

others) that occupies a specific niche in nature.^1

He did this with neither preamble nor follow-up, and the requirement for the
“niche” here seems to have been allowed to quietly drift away, as he does not insist
on it elsewhere. A prior instance of another partial ecological concept occurs in
Ghiselin, who referred to species as

The most extensive units in the natural economy such that reproductive competition

occurs among its parts.^2

The competition here is for genetic resources, and comes in the context of a strong
selectionist account of evolution at various levels. Ghiselin calls it the “hypermodern
species concept” and says that species are economic entities analogous to firms.^3
Van Valen, in a paper that discussed the “odd” reproductive dynamics and evolu-
tion of American oaks (gen. Quercus), proposed that in these plants at any rate a
species was an ecological type. He offered a definition as “a vehicle for conceptual
revision, ... not a standing monolith”:

A species is a lineage (or a closely related set of lineages) which occupies an adaptive

zone minimally different from that of any other lineage in its range and which evolves

separately from all lineages outside its range.^4

This is self-consciously a mixture of the Mayr and Simpson definitions, and Van
Valen justifies it in terms of evolution acting on phenotypes, controlled by “ecology
and the constraints of individual development.” It is therefore a definition founded on
a particular view of evolution. He reprises Simpson’s notion of a lineage, and defines
a population in genetic terms. The novel element here is the idea of the “adaptive
zone,” which he describes as

(^1) Mayr 1982, 273, italics original.
(^2) Ghiselin 1974, 538.
(^3) Ghiselin 1974. See Ghiselin 1997, chapter 9.
(^4) Van Valen 1976, 233.