Figure 1. - Comparison of size distribution of benthic molluscs in
Lake Chad benthos and in the gut of malacophagous fish species
(Synodontis clarias, S. schall, Hyperopisus bebe) (data from Lauzanne,
1975).
change also. Usually these changes are related to the
ability of growing animals to handle particular food
types. Most fish feed on plankton during at least part
of their life. Many fish larvae of non-planktivorous
species consume zooplankton or phytoplankton before
switching to larger prey.
According to Werner (1986), when ontogenic shifts
occur, they almost always involve shifts to larger
prey, as corroborated by theoretical and empirical
studies. This ontogenic niche shift involves trade-offs
of current growth, mortality and birth rates and is
closely related to the problem of optimal life histories.
An implication of the existence of a relationship
between body size and prey size is that juveniles