  Mutualistic interactions are vital constituents of ecological and
socio-economic systems. Empirical studies have found that the patterns of
reciprocal relations among the participants often shows the salient features of
being simultaneously nested and modular. Whether and how these two structural
properties of mutualistic networks can emerge out of a common mechanism however
remains unclear. We propose a unified dynamic model based on the adaptation of
niche relations that gives rise to both structural features. We apply
Hutchinson's concept of niche interaction to networked cooperative species.
Their niche relation evolves under the assumption of fitness maximization.
Modularity and nestedness emerge concurrently through the accumulated local
advantages in the structural and demographic distribution. A rich ensemble of
key dynamical behaviors are unveiled in the dynamical framework. We demonstrate
that mutualism can exhibit either a stabilizing or destabilizing effect on the
evolved network, which undergoes a drastic transition with the overall
competition level. Most strikingly, the adaptive network may exhibit a profound
nature of history-dependency in response to environmental changes, allowing it
to be found in alternative stable structures. The adaptive nature of niche
interactions, as captured in our framework, can underlie a broad class of
ecological relations and also socio-economic networks that engage in bipartite
cooperation.
