believe that mouthbrooding likely evolved several times among the tilapias
as an adaptation to stable and competitive conditions (Balon 1980,1981a).
If there has been this polyphyletic origin, it must be questioned as to whether
to separate the generic names on this basis. An outline of our theories and
some essential terms formulated by Balon (1979a, 1979b,1980,1981a) and
of the theoretical framework we propose to apply will be given f~st. We will
then consider the tilapias with some comparisons to related taxa and con-
clude with some practical considerations.
Although most terms we will use are by now established, confusion still
exists as to precise meanings of some, or how some may be applied in
particular circumstances. A number of recent reviews or textbooks, in
addition to those cited above, have more than adequately discussed the basic
ecological and epigenetical framework used later, so we refer interested
readers to those sources (e.g., MacArthur and Wilson 1967; Emlen 1973;
Ricklefs 1973; Lq5vtrup 1974; May 1976; Gould 1977; Steams 1976,1977;
Krebs 1978; Pianka 1978).
Review of TerminologyThe life history of any species (more properly, of individuals) is the sum
of a number of events and processes with ecological and evolutionary con-
sequences. Recent usage has introduced the term "strategy" in such dis-
cussions. While there is some confusion over both the etymology and appli-
cation of this term, it can be a useful shorthand reference to evolutionary
considerations. We do not propose to defend its uncritical acceptance or
application, but find it a useful heuristic tool, at least in the early stages of
discussing the evolution of life history patterns. For it is surely the evolution-
ary questions that will be of greatest interest at the level of the comparative
approach we use. We employ the term and assume the phrase "as ifW,i.e.,
animals would be expected to respond to natural selection "as if" they were
attempting to maximize fecundity, or minimize predation, or minimize
energy expenditure, and so on. In all cases, the more formal argument could
be made (Dawkins 1976) in a more orthodox fashion, to lead to the same
conclusion.
A conventional consideration of life histories would likely discuss the
biology of these species in terms of fecundity, growth and development, age
at maturity, parental care, and longevity (Emlen 1973; Ricklefs 1973). The
assumption is that natural selection acts so as to maximize the fitness of
individual animals (but see Dawkins 1978) by adjusting some or all of these
parameters in accordance with the ecological conditions faced, to produce an
integrated whole, the life history strategy (= style).
The Pitfalls of "r" and "K"A concept often applied to life histories, frequently uncritically or even
inappropriately, is that of the so-called "r- and K-continuum" (MacArthur
and Wilson 1967; Wilson and Bossert 1971; Emlen 1973; May 1976; Pianka