Ecology: the biology of interaction. 3.08. Succession. Basic concepts

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3.07. Productivity of Different Biomes

D. Shabanov, M. Kravchenko. Ecology: Biology of Interaction Chapter 3. Biogeocenology and Community Ecology

3.09. Trends in Successions

{ "title": "3.08. Succession. Basic Concepts", "summary": "", "body": "Have you ever found yourself in an abandoned field or a deserted garden? You probably guess that by their appearance, you can tell when they were abandoned. How is this possible? An ecosystem left to itself (in these examples, an artificial agricultural ecosystem - an agrosystem) begins to change. Knowing the rate of such changes, one can estimate how long it has been since it was abandoned.\n\nNow imagine a river flowing through a wide valley. The channel of such a river forms loops - meanders. Where the channel makes a turn, the flowing water erodes the bank it hits, forming a coastal cliff. And on the opposite edge of such a bank, a sandy beach grows. Right at the water, the sand is bare, a little further - it is overgrown with grass, even further - the grass forms a dense turf, and finally, at some distance from the shore, shrubs grow. It is easy to understand that this transition from one community to another (ecocline) reflects the dynamics of changes in each individual section of the shore over time. Where the shrubs are growing now, once only a beach was forming, creating a new section of the shore... The river loops grow and eventually connect with each other. The channel plots a shorter path, and its former sections form oxbow lakes. Over time, the oxbow lakes turn into floodplain lakes, fill with sediments, and become parts of the floodplain meadow. The examples we have given show the ability of ecosystems to change over time - to succeed (from Latin successio - succession, inheritance).\n\nSuccession is a sequential change of communities in one habitat. It is a directed process controlled by the community, leading to a certain state. Succession in biogeocenoses is a longer process than seasonal changes but not as long as ecosystem evolution. Ecocline, therefore, is a succession observed in space.\n\nUsually, in the course of succession, one can distinguish transient stages, which are called serial communities (or simply series), and the final stable state - the climax community (climax). The doctrine of succession was developed in the 1920s by Frederick Clements, an American ecologist, who considered succession as an analogue of ecosystem ontogenesis.\n\nThe reason for succession is not only a change in habitats by some external factors (for example, by flowing water, as in the case of a river meander), but also the whole set of interactions between components of communities, and sometimes - the impact of human activity.\n\n\"A characteristic dynamics of communities described for the end of the XIX - beginning of the XX centuries in the heather peat bogs of Scotland. The owner of these lands used them to hunt numerous Scottish grouse - grouse. In 1892-1893, several pairs of gulls settled on the heather. Taken under protection by the owner, they already formed a large colony at the beginning of our century, numbering 1.5-2 thousand pairs. The birds abundantly fertilized the soil, the hygroscopic material of their nests accumulated moisture. As a result, a gradual swamping began, which led to the gradual disappearance of heather and its replacement by hard grasses. The lands began to be used as hayfields. However, later the grasses were displaced by sedge, and later - by horse sorrel and other weeds. In parallel, there was a decrease in the number of grouse; on the swamped areas, ducks appeared - a species less valuable as a hunting trophy. All this led to the abolition of protection of gulls; moreover, their nests began to be deliberately destroyed. By 1917, there were about 30 pairs left, the heather began to recover gradually, the ducks disappeared, and the grouse reappeared. However, even by this time, the restoration of the initial community was incomplete: on the heather moor, grasses and some weeds remained - a \"trace\" of the succession series \"(I.A. Shilov, 1998).\n\nThe main reason for succession is the lack of equilibrium between production and respiration in the ecosystem, i.e., the nonequilibrium of the ecological balance. This leads to a change in the stock of organic matter in the ecosystem and, ultimately, to a change in the community. Having arranged diverse ecosystems on the plane of \"production-respiration\" (Fig. 3.8.1), we can make sure that only those in which production and respiration balance each other are stable.\n\n[IMG_1]\nFig. 3.8.1. Ordination (arrangement) of different types of ecosystems on the plane of \"production - respiration\"\n\nIf in some community production exceeds respiration (for example, in the initial culture of algae - a solution of mineral salts in which phytoplankton organisms are populated), an autotrophic succession begins in it. An excess of organic matter accumulates in such an ecosystem, changing its properties and creating an environment for the reproduction of heterotrophs. Production in the community decreases, respiration increases, and eventually, these two quantities reach equality.\n\nHeterotrophic succession (Fig. 3.8.2) begins with a state in which the respiration of the community exceeds production. Gradually, heterotrophs destroy the excess of organic matter, and the system reaches an equilibrium between respiration and production.\n\n[IMG_2]\nFig. 3.8.2. An example of heterotrophic succession: dynamics of the number of various protozoa in hay infusion\n\nA characteristic case of autotrophic succession can be considered the colonization of organisms by a territory where there are no reserves of organic matter. Consider the following example. On a bare rocky rock, lichens settle, gradually corroding the stone with the help of acids secreted by them. In the cracks of rocks, soil appears. Mosses begin to grow on the rock, and then grasses. Forming a turf of intertwined dead stems and rhizomes, grasses retain detritus and even collect dust. After a very long time, shrubs appear in place of the former rocks, and then a forest. This was a primary succession - a succession that occurred where there were no reserves of organic matter from previous communities (Fig. 3.8.3).\n\n[IMG_3]\nFig. 3.8.3. An example of primary succession: silting of a lake\n\nAfter some time, the forest that grew during the primary succession is destroyed by a fire. A burnt area is formed. On the burnt area, remnants of forest soil (abundantly sprinkled with ash) and even seeds of many plant species are preserved. Already next year, the burnt area will be overgrown with grasses (for example, fireweed is very characteristic in such conditions). After a few years, shrubs and young trees will appear in place of the burnt area, and after a few decades or a century, a forest will develop here, reminiscent of the one that grew here before the fire. Secondary succession occurs in habitats where remnants of organic matter from previous stages of development of a given ecosystem have been preserved (Fig. 3.8.4).\n\n[IMG_4]\nFig. 3.8.4. An example of secondary succession: overgrowing of a burnt area with mixed forest\n\nHeterotrophic succession requires a supply of organic matter for its occurrence. Most examples of heterotrophic succession that we can observe unfold not on the scale of biogeocenoses, but within relatively small ecosystems. For example, they include the bodies of dead animals or the trunks of fallen plants. The succession occurring in such temporary ecosystems is called destructive - they do not lead to a climax, but simply destroy the habitat in which they occur. Sometimes, one can observe ecoclines even in heterotrophic successions. Dig up the fallen needles and the upper layer of soil in a coniferous forest. From the top, the needles are almost not damaged, and the deeper - the more they are transformed by bacteria, fungi, and detritivorous animals. Each fallen needle goes through this path of destruction, corresponding to the sequence of layers of coniferous litter.\n\nClements was a supporter of the monoclimax concept. Currently, the polyclimax concept has prevailed, according to which for each region there is a certain climatic or zonal climax, and, in addition, certain edaphic (i.e., due to soil features) or local climaxes can be stable. A cyclic climax is also described, in which the ecosystem passes through a set of certain states that replace each other in a circle. Sometimes these changes are determined by catastrophic events that regularly occur at a certain stage of ecosystem development. So, a spruce forest, having reached a certain maturity, can be regularly destroyed by pests; chaparral can regularly burn down in fires.\n\nOne can consider both general and particular successions. So, in a fruit garden, polyphagous insects - pests live on young trees: cockchafers, black beetles, loopers, silkworms, and leafrollers. When the trees begin to bear fruit, fruit-eating pests appear: codling moths, flower-eaters, and weevils. As the garden ages, it is inhabited by stem pests (bark beetles, woodworms, and glassy worms)." }

3.07. Productivity of Different Biomes

D. Shabanov, M. Kravchenko. Ecology: Biology of Interaction Chapter 3. Biogeocenology and Community Ecology

3.09. Trends in Successions