A New Ecology - Systems Perspective - Chapter 6

Else_SP-Jorgensen_ch006.qxd 4/12/2007 17:59 Page 103 6 Ecosystems have complex dynamics (growth and development) Openness creates gradients Gradients create possibilities What you gain in precision, you lose in plurality (Thermodynamics and Ecological Modelling, 2000, S.E. Jørgensen (ed.)) 6.1 VARIABILITY IN LIFE CONDITIONS All known life on earth resides in the thin layer enveloping the globe known as the ecosphere. This region extends from sea level to ,10km into the ocean depths and approximately the same distance up into the atmosphere. It is so thin that if an apple were enlarged to the size of the earth the ecosphere would be thinner than the peel. Yet a vast and complex biodiversity has arisen in this region. Furthermore, the ecosphere acts as integrator of abiotic factors on the planet accumulating in disproportionate quantities particular elements favored by the biosphere (Table 6.1). In particular, note that carbon is not readily abundant in the abiotic spheres yet is highly concentrated in the biosphere, where nitrogen, silicon, and aluminum, while largely available, are mostly unincorporated. However, even in this limited domain the conditions for living organisms may vary enormously in time and space. The climatic conditions: (1) The temperature can vary from ,270 to ,55 centigrade. (2) The wind speed can vary from 0km/h to several hundred km/h. (3) The humidity may vary from almost 0–100 percent. (4) The precipitation from a few millimeter in average per year to several meter per year, which may or may not be seasonally aligned. (5) Annual variation in day length according to latitude. (6) Unpredictable extreme events such as tornadoes, hurricanes, earthquakes, tsunamis, and volcanic eruptions. 103 Else_SP-Jorgensen_ch006.qxd 4/12/2007 17:59 Page 104 104 A New Ecology: Systems Perspective Table 6.1 Percent composition spheres for five most important elements Lithosphere Atmosphere Hydrosphere Biosphere Oxygen 62.5 Silicon 21.22 Aluminum 6.47 Hydrogen 2.92 Sodium 2.64 Nitrogen 78.3 Oxygen 21.0 Argon 0.93 Carbon 0.03 Neon 0.002 Hydrogen 65.4 Oxygen 33.0 Chloride 0.33 Sodium 0.28 Magnesium 0.03 Hydrogen 49.8 Oxygen 24.9 Carbon 24.9 Nitrogen 0.27 Calcium 0.073 The physical–chemical environmental conditions: (1) Nutrient concentrations (C, P, N, S, Si, etc.) (2) Salt concentrations (it is important both for terrestrial and aquatic ecosystems) (3) Presence or absence of toxic compounds, whether they are natural or anthropogenic in origin (4) Rate of currents in aquatic ecosystems and hydraulic conductivity for soil (5) Space requirements The biological conditions: (1) The concentrations of food for herbivore, carnivore, and omnivore organisms (2) The density of predators (3) The density of competitors for the resources (food, space, etc.) (4) The concentrations of pollinators, symbiants, and mutualists (5) The density of decomposers The human impact on natural ecosystems today adds to this complexity. The list of factors determining the life conditions is much longer—we have only men-tioned the most important factors. In addition, the ecosystems have history or path dependency (see Chapter 5), meaning that the initial conditions determine the possibili-ties of development. If we modestly assume that 100 factors are defining the life condi-tions and each of these 100 factors may be on 100 different levels, then 10200 different life conditions are possible, which can be compared with the number of elementary par-ticle in the Universe 1081 (see also Chapter 3). The confluence of path dependency and an astronomical number of combinations affirms that the ecosphere could not experience the entire range of possible states, otherwise known as non-ergodicity. Furthermore, its irreversibility ensures that it cannot track back to other possible configurations. In addi-tion to these combinations, the formation of ecological networks (see Chapter 5) means that the number of indirect effects are magnitudes higher than the direct ones and they are not negligible, on the contrary, they are often more significant than the direct ones, as discussed in Chapter 5. What is the result of this enormous variability in the natural life conditions? We have found ,0.53107 species on earth and it is presumed that the number of species is Else_SP-Jorgensen_ch006.qxd 4/12/2007 17:59 Page 105 Chapter 6: Ecosystems have complex dynamics (growth and development) 105 double or 107. They have developed all types of mechanisms to live under the most var-ied life conditions including ones at the margin of their physiological limits. They have developed defense mechanisms. For example, some plants are toxic to avoid grazing, others have thorns, etc. Animals have developed horns, camouflage pattern, well-developed auditory sense, fast escaping rate, etc. They have furthermore developed integration mechanisms; fitting into their local web of life, often complementing and creating their environmental niche. The multiplicity of the life forms is inconceivable. The number of species may be 107, but living organisms are all different. An ecosystem has normally from 1015 to 1020 individual organisms that are all different, which although it is a lot, makes ecosystems middle number systems. This means that the number of organisms is magnitudes less than the number of atoms in a room, but all the organisms, opposite the atoms in the rooms, have individual characteristics. Whereas large number systems such as the number of atoms in a room are amenable to statistical mechanics and small number problems such as planetary systems to classical mechanics or individual based modeling, middle number problems contain their own set of challenges. For one thing this variation, within and among species, provides diversity through co-adaptation and co-evolution, which is central both to Darwinian selection and network aggradation. The competitive exclusion principle (Gause, 1934) claims that when two or more species are competing about the same limited resource only the best one will survive. The contrast between this principle and the number of species has for long time been a para-dox. The explanation is rooted in the enormous variability in time and space of the con-ditions and in the variability of a wide spectrum of species’ properties. A competition model, where three or more resources are limiting gives a result very different from the case where one or two resources are limiting. Due to significant fluctuations in the dif-ferent resources it is prevented that one species would be dominant and the model demonstrates that many species competing about the same spectrum of resources can coexist. It is, therefore, not surprising that there exists many species in an environment characterized by an enormous variation of abiotic and biotic factors. To summarize the number of different life forms is enormous because there are a great number of both challenges and opportunities. The complexity of ecosystem dynamics is rooted in these two incomprehensible types of variability. 6.2 ECOSYSTEM DEVELOPMENT Ecosystem development in general is a question of the energy, matter, and information flows to and from the ecosystems. No transfer of energy is possible without matter and information and no matter can be transferred without energy and information. The higher the levels of information, the higher the utilization of matter and energy for further development of ecosystems away from the thermodynamic equilibrium (see also Chapters 2 and 4). These three factors are intimately intertwined in the fundamental nature of complex adaptive systems such as ecosystems in contrast to physical systems, that most often can be described completely by material and energy relations. Life is, therefore, both a material and a non-material (informational) phenomenon. The self-organization of life essentially proceeds by exchange of information. Else_SP-Jorgensen_ch006.qxd 4/12/2007 17:59 Page 106 106 A New Ecology: Systems Perspective E.P. Odum has described ecosystem development from the initial stage to the mature stage as a result of continuous use of the self-design ability (E.P. Odum, 1969, 1971a); see the significant differences between the two types of systems listed in Table 6.2 and notice that the major differences are on the level of information. Table 6.2 show what we often call E.P. Odum’s successional attributes, but also a few other concepts such as for instance exergy and ecological networks have been introduced in the table. Table 6.2 Differences between initial stage and mature stage are indicated Properties (A) Energetic Production/respiration Production/biomass Respiration/biomass Yield (relative) Specific entropy Entropy production per unit of time Eco-exergy Information (B) Structure Total biomass Inorganic nutrients Diversity, ecological Diversity, biological Patterns Niche specialization Organism size Life cycles Mineral cycles Nutrient exchange rate Life span Ecological network (C) Selection and homeostasis Internal symbiosis Stability (resistance to external perturbations) Ecological buffer capacity Feedback control Growth form Growth types Early stages ..1 or ,,1 High High High High Low Low Low Small Extrabiotic Low Low Poorly organized Broad Small Simple Open Rapid Short Simple Undeveloped Poor Low Poor Rapid growth r-strategists Late or mature stage Close to 1 Low Low Low Low High High High Large Intrabiotic High High Well organized Narrow Large Complex Closed Slow Long Complex Developed Good High Good Feedback controlled K-strategists Else_SP-Jorgensen_ch006.qxd 4/12/2007 17:59 Page 107 Chapter 6: Ecosystems have complex dynamics (growth and development) 107 The information content increases in the course of ecological development because an ecosystem integrates all the modifications that are imposed by the environment. Thus, it is against the background of genetic information that systems develop which allow inter-action of information with the environment. Herein lies the importance in the feedback organism–environment, that means that an organism can only evolve in an evolving envi-ronment, which in itself is modifying. The differences between the two stages include entropy and eco-exergy. The conservation laws of energy and matter set limits to the further development of “pure” energy and matter, while information may be amplified (almost) without limit. Limitation by matter is known from the concept of the limiting factor: growth continues until the element which is the least abundant relatively to the needs by the organisms is used up. Very often in developed ecosystems (for instance an old forest) the limiting ele-ments are found entirely in organic compounds in the living organisms, while there is no or very little inorganic forms left in the abiotic part of the ecosystem. The energy input to ecosystems is determined by the solar radiation and, as we shall see later in this chap-ter, many ecosystems capture ,75–80 percent of the solar radiation, which is their upper physical limit. The eco-exergy, including genetic information content of, for example, a human being, can be calculated by the use of Equations 6.2 and 6.3 (see also Box 6.3 and Table 6.3). The results are ,40MJ/g. A human body of ,80 kg will contain ,2 kg of proteins. If we presume that 0.01 ppt of the protein at the most could form different enzymes that control the life processes and therefore contain the information, 0.06 mg of protein will represent the information con-tent. If we presume an average molecular weight of the amino acids making up the enzymes of ,200, then the amount of amino acids would be 63102836.231023/200<231017, that would give an eco-exergy that is (1025 moles/g, T5300K, 20 different amino acids): 58.314380,000330031025 3231017 ln 2051.231012 GJ It corresponds to 1.53107 GJ/g. These are back of the envelope calculations and do not represent what is expected to be the information content of organisms in the future; but it seems possible to conclude that the development of the information content is very, very far from reaching its limit, in contrast to the development of the material and energy relations (see Figure 6.1). Information has some properties that are very different from mass and energy. (1) Information unlike matter and energy can disappear without trace. When a frog dies the enormous information content of the living frog may still be there a microseconds after the death in form of the right amino-acid sequences but the information is useless and after a few days the organic polymer molecules have decomposed. (2) Information expressed for instance as eco-exergy, it means in energy units, is not conserved. Property 1 is included in this property, but in addition it should be stressed that living systems are able to multiply information by copying already achieved successful information, which implies that the information survives and ... - tailieumienphi.vn