Food Web Assembly Rules for Generalized Lotka-Volterra Equations
a, Food web with two trophic levels only; a staircase of coexistence with balanced species richness at levels 1 and 2 . b, Three trophic levels. The number of intermediate species must equal the total number of basal and predator species. Intermediate species dominate ecosystem biodiversity. c, Four trophic levels. n2 (n3) must at least match basal (predator) species richness n1 (n4), indicated by thin black lines in green and orange bar. Solid green (orange) bars show the minimal upper bound to species richness in trophic level one (two). Species richness n2 and n3 can increase even further by co-evolution of intermediate species (shaded region). Note the applicable assembly rules shown for the different cases.