A

Figure 2 (a) Sketch of a typical 'leaf' of Utricularia floridana, with detail of the interior of a utricle containing a captured invertebrate. (b) Schematic of the autocatalytic loop in the Utricularia system. Macrophyte provides necessary surface upon which periphyton (speckled area) can grow. Zooplankton consumes periphyton, and is itself trapped in bladder and absorbed in turn by the Utricularia.

Figure 2 (a) Sketch of a typical 'leaf' of Utricularia floridana, with detail of the interior of a utricle containing a captured invertebrate. (b) Schematic of the autocatalytic loop in the Utricularia system. Macrophyte provides necessary surface upon which periphyton (speckled area) can grow. Zooplankton consumes periphyton, and is itself trapped in bladder and absorbed in turn by the Utricularia.

hair- like triggers at its terminal end, which, when touched by a feeding microheterotroph, opens the end of the bladder, and the animal is sucked into the utricle by a negative osmotic pressure that the plant had maintained inside the bladder. This feeding upon microheterotrophs helps the Utricularia to grow and increase its surface area (process A). In nature the surface of Utricularia plants is always host to a film of diatomaceous algal growth known as periphyton, so that more surface area encourages the growth of more periphyton (process B). More periphyton in its turn means more food to support the growth of any number of species of small microheterotrophs (process C). The autocatalytic cycle is closed when it is noted that a greater density of microheterotrophs provides more resources for the Utricularia to grow (process A again) by capturing and absorbing more abundant zooplankton (Figure 2b).

Unlike in chemistry, the actors in ecology are more complex, malleable entities with capabilities to undergo small, incremental alterations. Such malleability substantially enhances the repertoires of autocatalysis and enables it to exhibit some very nonmechanical behaviors. This is especially the case when autocatalysis involves processes that can change in stochastic and nonpredict-able ways. An important characteristic of causal cycles (e.g., autocatalysis) is that when random events impinge upon them, they usually yield nonrandom results. This is the consequence of the first and foremost attribute of autocatalysis - its generation of selection pressure.

To see how autocatalysis generates selection, one begins by considering a small spontaneous change in process B. If that change either makes B more sensitive to A or a more effective catalyst of C, then the transition will receive enhanced stimulus from A. In the Utricularia example, diatoms that have a higher P/B ratio and are more palatable to microheterotrophs would be favored as members of the periphyton community. Conversely, if the change in B makes it either less sensitive to the effects of A or a weaker catalyst of C, then that perturbation will likely receive diminished support from A. Hence, the response of this causal circuit is decidedly not symmetric, and out of this asymmetry emerges a direction. This direction is not imparted or cued by any externality; its action resides wholly within the system. As one might expect from a causal circuit, the resulting directionality is in part tautologous, that is, autocatalytic systems respond to random events over time in such a way as to increase their degree of autocatalysis. It should be emphasized that this directionality, by virtue of its internal and transient nature, should not be conflated with teleology. There is no externally determined or preexisting goal toward which the system strives. Direction arises purely out of the immediate response by the internal system to a novel, random event impacting one of the autocatalytic members.

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