General Papers
However, there is a tendency towards a dichotomy, with the utilisation of the extremities of this continuum, which is well illustrated by the Bajocian Otoitidae. There, the Emilieia / Otoites dimorphic group, in its relatively short life span, show trends towards increased size and greater differentiation between dimorphs (in size, shell form, ornament and with a tendency towards mutual exclusion), in diverse faunas in which it is generically significant, but specifically rather rare. It is suggested that these trends are the result of intra specific, sexually based resource partitioning (a response to intense competition in temporally homogenous environment): a classic K-strategy.
In contrast, the Sphaeroceratitidae (Chondroceras & Sphaeroceras), over a long time span, show decreases in size and ornament, with a strong convergence in sexual dimorphs, which are almost identical. They form very rare components in high-low diversity faunas, with restricted horizons at which they are almost totally dominant. This suggests that they are an 'opportunistic species' responding to a fleeting environment, such as 'algal meadows': a typical r-strategy.