A New Ecology - Systems Perspective - Chapter 4

Else_SP-Jorgensen_ch004.qxd 4/12/2007 17:23 Page 59 4 Ecosystems have directionality “From the way the grass bends, one can know the direction of the wind.” (Chinese Quotation) All nature is but art unknown to thee; All chance, direction which thou canst not see; All discord, harmony not understood; All partial evil, universal good; And, spite of pride, in erring reasons spite, One truth is clear, Whatever IS, is RIGHT. (Alexander Pope, 1773) 4.1 SINCE THE BEGINNINGS OF ECOLOGY Ecosystems have directionality! This is an extraordinary statement, although the reader might at first wonder why.After all, one observes directional behavior everywhere: A bil-liard ball, when struck by another ball, will take off in a prescribed direction. Sunflowers turn their heads to face the sun. Copepods migrate up and down in the water column on a daily basis. Yet, despite these obvious examples, scientists have increasingly been trained to regard instances of directionality in nature as having no real basis—epiphenomenal illusions that distract one from an underlying static, isotropic reality. Before embarking on how ecological direction differs from directionality observed elsewhere, it is worthwhile describing the ecological notion of succession (Odum, 1959). The classical example in American ecology pertains to successive vegetational communities (Cowles, 1899) and their associated heterotrophs (Shelford, 1913)— research conducted on the shores of Lake Michigan. Both Cowles and Shelford had built on the work of the Danish botanist, Eugenius Warming (1909). Prevailing winds blow-ing against a shore will deposit sand in wave-like fashion. The most recent dunes have emerged closest to the lake itself, while progressively older and higher dunes occur as one proceeds inland. The assumption here, much like the famed ergodic assumption in thermodynamics, is that this spatial series of biotic communities represents as well the temporal evolution of a single ecosystem. The younger, presumably less-mature com-munity consisted of beach grasses and Cottonwood. This “sere” was followed by a Jack pine forest, a xeric Black oak forest, an Oak and hickory moist forest, and the entire pro-gression was thought to “climax” as a Beech-maple forest. The invertebrate and verte-brate communities were observed to segregate more or less among the vegetational 59 Else_SP-Jorgensen_ch004.qxd 4/12/2007 17:23 Page 60 60 A New Ecology: Systems Perspective Line Chart 50 45 40 35 30 25 20 15 10 5 0 -5 60 65 70 75 80 85 90 95 100 year Figure 4.1 Increase over time in the number of plant species found on the newly created island of Surtsey. zones, although there was more overlap among the mobile heterotrophs than among the sessile vegetation. Other examples of succession involve new islands that emerge from the sea, usually as the result of volcanic activity. One particular ecosystem that was followed in detail is the sudden emergence in 1963 of the approximately 2.8 km2 island, Surtsey, some 33 km south of the large island of Iceland in the North Atlantic. Figure 4.1 depicts the rise in the number of plant species found on the island. (Other measures of succession on Surtsey will be given below). 4.2 THE CHALLENGE FROM THERMODYNAMICS Now one might well ask how the directionality of these ecosystems differs in any quali-tative way from, say the billiard ball mentioned in the opening paragraph of this chapter? For one, the direction of the billiard ball is a consequence of the collision with the other ball, the Newtonian law of momentum and the Newtonian-like law of elasticity. The ball itself remains essentially unchanged after the encounter. Furthermore, if the ball is highly elastic, the encounter is considered reversible. That is, if one takes a motion picture of the colliding balls and the movie is shown to a subject with the projector operating in both the forward and reverse modes, the subject is incapable of distinguishing the original take from its reverse. Reversibility is a key attribute of all Newtonian systems, and until the mid-1960s all Newtonian laws were considered strictly reversible. Early in the 20th cen-tury, Aemalie Noether (1918) demonstrated how the property of reversibility was fully Else_SP-Jorgensen_ch004.qxd 4/12/2007 17:23 Page 61 Chapter 4: Ecosystems have directionality 61 equivalent to that of conservation, i.e. all reversible systems are conservative. There is no fundamental change in them, either before or after the event in question. This pair of fundamental assumptions about how objects behaved set the stage for the first challenge to the Newtonian worldview. In 1820 Sadie Carnot (1824) had been observing the performance of early steam engines in pumping water out of mines. He observed how the energy content (caloric) of the steam used to run the engines could never be fully converted into work. Some of it was always lost forever. This meant that the process in question was irreversible. One could not reverse the process, bringing together the work done by the engine with the dispersed heat and create steam of the quality originally used to run the engine. (See also the discussion of the second law of thermodynamics in Chapter 2). But the steam, the engine, and the water were all material things, made up of very small particles, according to the atomic hypothesis that had recently been formulated. Elementary particles should obey Newtons laws, which always gave rise to reversible behaviors. Whence, then, the irreversibility? This was a conundrum that for a while placed the atomic hypothesis in jeopardy. The enigma occupied the best minds in physics over the next half century. How it was “resolved” demonstrates volumes about common attitudes toward scientific belief. Ludwig von Boltzmann (1872) considered the elements of what was called an “ideal gas” (i.e. a gas made up of point masses that did not interact with each other) to obey Newton’s laws of motion. He then assumed that the distribution of the momenta of the atoms was normally random. This meant that nearby to any configuration of atoms there were always more equivalent distributions (having same mass and momentum) that were more evenly distributed than there were configurations that were less evenly distributed. Any random walk through the distributions would, therefore, would be biased in the direction of the most probable distribution (the maximum of the normal distribution). Ergo, without violating conservation of mass or momentum at the microlevel, the system at the macrolevel was biased to move in the direction of the most even distribution. This was a most elegant model, later improved by Gibbs (1902). It is worth noting, however that the resolution was a model that was applicable to nature under an exceed-ingly narrow set of conditions. Nonetheless, it was accepted as validation of the atomic hypothesis and Newtonian reversibility everywhere, and it put an end to the controversy. This rush to consensus was, of course, the very antithesis of what later would be exposited as logical positivism—the notion that laws cannot be verified, only falsified. Laws should be the subject of constant and continual scrutiny; and scientists should always strive to falsify existing laws. But when conservation, reversibility, and atomism were being challenged, the response of the community of scholars was precisely the opposite—discussion was terminated on the basis of a single model that pertained to con-ditions that, in relation to the full set of conditions in the universe, amounted to “a set of measure zero”! Such inconsistencies notwithstanding, the second law does indeed provide a direction for time and introduces history into science. The second law serves as a very significant constraint on the activities of living systems and imparts an undeniable directionality to biology (Schneider and Sagan, 2005). Else_SP-Jorgensen_ch004.qxd 4/12/2007 17:23 Page 62 62 A New Ecology: Systems Perspective 4.3 DECONSTRUCTING DIRECTIONALITY? Events in biology have been somewhat the reverse of those in physics. Whereas physics began with directionless laws and was confronted with exceptions, biologists had origi-nally thought that phylogeny took a progressive direction over the eons, culminating in the appearance of humankind at the apex of the natural order—the so-called “natural chain of being.” Evolutionary biologists, however, have sought to disabuse other biolo-gists of such directional notions (Gould, 1994). At each turn in its history, a biotic system is subject to random, isotropic influences. What looks in retrospect like a progression has been merely the accumulation of the results of chance influences. Complexity simply accrues until such time as a chance catastrophe prunes the collection back to a drastically simpler composition. We thus encounter a strong bias at work within the community of scientists to deny the existence of bias in nature (a statement which makes sense only because humanity has been postulated to remain outside the realm of the natural). Physicists and (perhaps by virtue of “physics envy”) evolutionary theorists appear keen to deny the existence of direction anywhere in the universe, preferring instead a changeless Eleatic world-view. It is against this background that the notion of direction in ecology takes on such importance. Directionality, in the form of ecological succession, has been a key phenomenon in ecology from its inception (Clements, 1916). By ecological succession is meant “the orderly process of community change” (Odum, 1959) whereby communities replace one another in a given area. Odum (ibid.) do not equivocate in saying, “The remarkable thing about ecological succession is that it is directional.” In those situations where the process is well known, the community at any given time may be recognized and future changes predicted. That is, succession as a phenomenon appears to be reproducible to a degree. Of course, it was not long after the ideas of community succession came into play that the opinion arose that its purported direction was illusory. Gleason (1917) portrayed suc-cession in plant communities as random associations of whatever plant species happened to immigrate into the area. Others have pointed out that “seres” of ecological communi-ties almost always differ in terms of the species observed (Cowles, 1899). The ecosystem ecologist takes refuge in the idea that the functional structure nonetheless remains pre-dictable (Sheley, 2002). The question thus arises as to whether ecological succession is orderly in any sense of the word, and, if so, what are the agencies behind such order? We begin by noting that the directionality of ecosystems is of a different ilk from those mentioned in the opening of this chapter. With regard to all three of those examples, the direction of the system in question was determined by sources exterior to the system—by the colliding billiard ball in the first instance, and by the sun as perceived by the sunflower and copepod. It will be argued below, however, that the directionality of an ecosystem derives from an agency active within the system itself. Surely, external events do impact the system direction by providing con-straints, but any one event is usually incremental in effect. On rare occasions an external event can radically alter the direction and the constitution of the system itself (Prigogine, 1978; Tiezzi, 2006b), but this change is every bit as much a consequence of the system Else_SP-Jorgensen_ch004.qxd 4/12/2007 17:23 Page 63 Chapter 4: Ecosystems have directionality 63 configuration as it is of the external event (Ulanowicz, 2006a). The direction an ecosystem takes is both internal and constitutional. Most change seen elsewhere is neither. 4.4 AGENCIES IMPARTING DIRECTIONALITY It remains to identify the agency behind any directionality that ecosystems might exhibit. Our natural inclination is such a search would be to look for agencies that conform to our notions of “lawful” behaviors. But such a scope could be too narrow. It would behoove us to broaden our perspective and attempt to generalize the notion of “law” and consider as well the category of “process”. A process resembles a law in that it consists of rule-like behaviors, but whereas a law always has a determinate outcome, a process is guided more by its interactions with aleatoric events. The indeterminacy of such action is perhaps well illustrated by the artificial example of Polya’s Urn (Eggenberger and Polya, 1923). Polya’s process consists of picking from an urn containing red and blue balls. The process starts with one red ball and one blue ball. The urn is shaken and a ball is drawn at random. If it is a red ball, then the ball is returned to the urn with yet another red ball; if a blue ball is picked, then it likewise is returned with another blue ball. The question then arises whether the ratio of red to blue balls approaches a fixed value. It is rather easy to demonstrate that the law of large num-ber takes over and that after a sufficient number of draws, the ratio changes only within bounds that progressively shrink as the process continues. Say the final ratio is 0.3879175. The second question that arises is whether that ratio is unique? If the urn is emptied and the process repeated, then will the ratio once again converge to 0.3879175? The answer is no. The second time it might converge to 0.81037572. It is rather easy to show in Monte-Carlo fashion that the final ratios of many successive runs of Polya’s process are uniformly distributed over the interval from 0 to 1. One sees in Polya’s Urn how direction can evolve out of a stochastic background. The key within the process is the feedback that is occurring between the history of draws and the current one. Hence, in looking for the origins of directionality in real systems, we turn to consider feedback within living systems. Feedback, after all, has played a central role in much of what is known as the theory of “self-organization” (e.g. Eigen, 1971; Maturana and Varela, 1980; DeAngelis et al., 1986; Haken, 1988; Kauffman, 1995). Central to control and directionality in cybernetic systems is the concept of the causal loop. A causal loop, or circuit is any concatenation of causal connections whereby the last member of the pathway is a partial cause of the first. Primarily because of the ubiquity of material recycling in ecosystems, causal loops have long been recognized by ecologists (Hutchinson, 1948). It was the late polymath, Gregory Bateson (1972) who observed “a causal circuit will cause a non-random response to a random event at that position in the circuit at which the random event occurred.” But why is this so? To answer this last question, let us confine further discussion to a subset of causal circuits that are called autocatalytic (Ulanowicz, 1997). Henceforth, autocatalysis will be considered any manifestation of a positive feed-back loop whereby the direct effect of every link on its downstream neighbor is positive. Without loss of generality, let us focus our attention on a serial, circular conjunction of ... - tailieumienphi.vn