Stability and selective extinction in complex mutualistic networks
We study species abundance in the empirical plant-pollinator mutualistic networks exhibiting broad degree distributions, with uniform intra-group competition assumed, by the Lotka-Volterra equation. The stability of a fixed point is found to be identified by the signs of its non-zero components and those of its neighboring fixed points. Taking the annealed approximation, we derive the non-zero components to be formulated in terms of degrees and the rescaled interaction strengths, which lead us to find different stable fixed points depending on parameters, and we obtain the phase diagram. The selective extinction phase finds small-degree species extinct and effective interaction reduced, maintaining stability and hindering the onset of instability. The non-zero minimum species abundances from different empirical networks show data collapse when rescaled as predicted theoretically.