Complex life cycles drive community assembly through immigration and adaptive diversification

Most animals undergo ontogentic niche shifts during their life. Yet,
standard ecological theory builds on models that ignore this complexity.
Here, we study how complex life cycles, where juvenile and adult
individuals each feed on different sets of resources, affect community
richness. Two different modes of community assembly are considered:
gradual adaptive evolution and immigration of new species with randomly
selected phenotypes. We find that under gradual evolution complex life
cycles can lead to both higher and lower species richness when compared to
a model of species with simple life cycles that lack an ontogenetic niche
shift. Thus, complex life cycles do not per se increase the scope for
gradual adaptive diversification. However, complex life cycles can lead to
significantly higher species richness when communities are assembled
through immigration, as immigrants can occupy isolated peaks of the
dynamic fitness landscape that are not accessible via gradual evolution.