such ecological (rather than evolutionary) shifts in life history features.
The bearing species have a relatively lower fecundity, larger ova (with
higher yolk density), a longer growth interval, later age at maturity (with
overlap between guilds), and possibly (the data are few) greater longevity
than the guarding species (see also Lowe-McConnell, this volume). The
bearers lack the larval period in their ontogeny (Balon 1977), an adaptation
for increased protection of the young. The young are released in an advanced
state of development (as juveniles), at a relatively large size (up to 15 per cent
adult body size) (Figure 1). The guarding species have significantly higher
fecundity, with correspondingly smaller, less energy-rich eggs (Fishelson
1966a; Fryer and Iles 1972 ; Hanon 1975 ; Balon 1977). Their development
includes an abbreviated but distinct larval (alevin) period. Maturation (onset
of the adult period) is relatively earlier, the growth interval shorter, and life
span appears to be shorter (again, these data are not strong) (see also Shine
1978).GUARDER
(ALTRICIAL)0
e
BEARER
(PRECOCIAL)Figure 1. Diagrammatic representation of developmental intervals in idealized guarding (altricial) and bearing (preco-
cial) tilapiine fishes (adapted from Fishelson 1966a; Fryer and Iles 1972; Axelrod and Burgess 1973; Peters 1973;
Balon 1977,1981a). Durations of intervals as indicated by vertical extent in the diagram, are not to scale.