FIGURE 2.

The process of conversion of biotopes in niches. The figure represents nine successive stages of nichification of a biotope, whose constituents are depicted by target-like circles, to represent gradients. First row: (left), a small bacterial population finds a selective combination of traits able to sustain its growth (brown circle); the limits are those of the current niche; the color intensity reflects the bacterial abundance; (middle), the population is expanding and converting in niche the neighboring regions of the biotope; (right), the combination of traits defining the niche is shifting to the right, so that the niche moves into the biotope space. Second row: (left), an extinction event has eliminated the pioneering colonizer population; however, from the outside environment, a new small population of the same organism enters the biotope, recognizes the conditions of the ancient niche, and reinstalls itself; (middle), the sequential variants of the pioneering population emerge. This variation allows for the expansion of the niche; (right), a new invader of the biotope (blue circle) produces a new niche. Third row: (left), sequential variation of the new population expands the blue niche; (middle), niches of the brown and blue populations start to converge; (right), this convergence facilitates genetic exchanges between brown and blue populations, creating a new pink population (species?) advancing the exploitation of the biotope’s carrying capacity, which is almost entirely converted in a niche.