Ecological Succession Models PDF

What is it? Natural, gradual changes in the types of species that live in an area; can be primary or secondary Gradual  Slow process  Causes of Succession 1. Initial or initiating causes: These are climatic as well as a biotic erosion, deposition, wind, fire, volcanic activit...

What is it? Natural, gradual changes in the types of species that live in an area; can be primary or secondary Gradual  Slow process  Causes of Succession 1. Initial or initiating causes: These are climatic as well as a biotic erosion, deposition, wind, fire, volcanic activities etc. are climatic factors. The biotic factors include the various activities of the living organism. 2. Ecesis or continuing causes: Invasion of organisms into a new habitat 3. Stabilizing causes: These are factors which stabilize a community in a particular area and climate of the areas the chief cause of stabilization (Clement 1916)  Types of Ecological Succession On the basis of different aspects: Primary Succession: The process of creating life in an area where no life previously existed. Secondary Succession: The process of re-stabilization that follows a disturbance in an area where life has formed an ecosystem. Autogenic Succession: Present environment is modified by interaction of community as well as its reaction with the environment that the present community is replaced by new community. Allogenic Succession: When existing community is not replaced by its own activities by the influence of any external condition. On the basis of nutritional and energy content: 1. Autotrophic Succession: a. It is a process in which early and complete dominance of autotrophic organisms like green plants, take place. b. In this case the inorganic environment is predominant and energy flow is maintained indefinitely. c. Organic contents supported by energy flow gradually increases. 2. Heterotrophic Succession: a. In this case heterotrophs like bacteria, actinomycetes, fungii, and animals predominate. b. Organic environment is predominant but the energy contents decline progressively.  Ecological Succession There are two main types of succession, primary and secondary. Primary succession is the series of changes that take place when there is no soil present. For example, after a volcano or destroyed coral reef. Secondary succession is the series of changes that take place when there is soil present. For example, after a fire, hurricane, flood, destruction by man, or tornado.  General process of Succession 1. Nudation: This is a process in which a barren area where no life exists, is created by several physical processes like land slide, erosion, erosion, deposition or other catastrophic events. a. Topographic: The gravity, water or wind causes erosion of soil. Communities growing in this soil thus may disappear with topographic factors. b. Biotic: Anthropogenic reasons for destruction of forests, grassland etc. for industry, agriculture and housing. Cont.. 2. Invasion a. Migration: Air, water or even birds excreta may bring seeds, spores or propagates in the barren area. b. Ecesis: After reaching the area the species establishes itself in the area as a result of adaptation with the prevailing environmental condition. c. Aggregation: As a result of reproduction number of species increases, they come close to each other to form aggregates by a process known as aggregation. Cont…. 3. Competition and coaction: Intra and interspecific completion for food and space. Individuals of a species interact with other’s life in various ways and this is known as coaction. 4. Reaction: The mechanism by which the living organisms modify the environment is known as reaction. 5. Stabilization: After a series of succession the terminal community becomes more or less stabilized for a longer period of time and it can maintain itself in equilibrium with climate of the area. This final community is known as “Climax community” or “Climax stage”  Pioneer Species- FIRST Examples of Pioneer Species Pioneer- FIRST species to grow Lichens-do not need soil to survive They can survive drought, extreme heat and cold, and other harsh conditions and start the soil building process. Lichens produce a weak acid that eats away at the rock and breaks it down into soil  Mosses  Pioneer Species- FIRST Algae- many types  Second Stage Second plants to become established after the disturbance (taller grasses, small shrubs). Shrubs  Third Stage- bushes Third species to become established Fourth Stage- usually small trees; depends on ecosystem Fourth species to become established  Final Stage-Climax Community Last species to appear; some say it isn’t really finished growing. A plant succession is accomplished with many steps, collectively these steps are known as sere. On the basis of nature of habitat the primary succession divided into two groups, viz. 1. Hydrach: If the initiation of plant succession is in water then it is called hydrach and the different steps are collectively known as hydrosere. 2. Xerach: If the plant succession starts at desert or extreme dry place is known as xerach and the different steps are collectively known as xerosere. 3. Mesarch: Where adequate moisture conditions are present 4. Lithosere: Initiating on rocks 5. Psammosere: on sand 6. Halosere: in saline water or soil  Primary Succession 6/5/03 M-DCC / PCB 2340C 18  Secondary Succession SECONDARY SUCCESSION begins in habitats where communities were entirely or partially destroyed by some kind of damaging event. When an existing community has been cleared by a disturbance such as a fire, tornado, etc...and the soil remains intact, the area begins to return to its natural community. Because these habitats previously supported life, secondary succession, unlike primary succession, begins on substrates that already bear soil. In addition, the soil contains a native seed bank. Since the soil is already in place, secondary succession can take place five to ten times faster than primary succession. 19 Phases Process Events Initiation Nudation Creation of a bare area Migration Immigration of species or propagules to the new area Ecesis Successful establishment of species due to adjustment with prevailing conditions Reaction Modification of the habitat by organisms Continuation Competition Inter and intra specific competitions, leading to establishment of new species Termination Stabilization Final community maintains equilibrium with the habitat conditions Types of climax Climatic Climax If there is only a single climax and the development of climax community is controlled by the climate of the region, it is termed as climatic climax. For example, development of Maple-beech climax community over moist soil. Climatic climax is theoretical and develops where physical conditions of the substrate are not so extreme as to modify the effects of the prevailing regional climate. Edaphic Climax When there are more than one climax communities in the region, modified by local conditions of the substrate such as soil moisture, soil nutrients, topography, slope exposure, fire, and animal activity, it is called edaphic climax. Succession ends in an edaphic climax where topography, soil, water, fire, or other disturbances are such that a climatic climax cannot develop. Catastrophic Climax Climax vegetation vulnerable to a catastrophic event such as a wildfire. For example, in California, chaparral vegetation is the final vegetation. The wildfire removes the mature vegetation and decomposers. A rapid development of herbaceous vegetation follows until the shrub dominance is re-established. This is known as catastrophic climax. Disclimax When a stable community, which is not the climatic or edaphic climax for the given site, is maintained by man or his domestic animals, it is designated as Disclimax (disturbance climax) or anthropogenic subclimax (man-generated). For example, overgrazing by stock may produce a desert community of bushes and cacti where the local climate actually would allow grassland to maintain itself. Subclimax The prolonged stage in succession just preceding the climatic climax is subclimax. Preclimax and Postclimax In certain areas different climax communities develop under similar climatic conditions. If the community has life forms lower than those in the expected climatic climax, it is called preclimax; a community that has life forms higher than those in the expected climatic climax is postclimax. Preclimax strips develop in less moist and hotter areas, whereas Postclimax strands develop in more moist and cooler areas than that of surrounding climate.  Theories about climax concept 1. MONOCLIMAX THEORY: (Clemets, 1916, 1935) According to this theory within a given region all land surfaces eventually tend to be occupied by a single kind of community which is climax. Climax is determined by regional climate. Given a stable climate the climax community is stable indefinitely. Criticized by many ecologist. The idea of stability or equilibrium state” never reach and succession infact variable, approaching a variable rather than a constant 2. POLYCLIMAX THEORY: According to Transley (1935) climax is controlled by many (not one-climate) factors and this concept is popularly known as “Polyclimax theory” 3. CLIMAX-PATTERN HYPOTHESIS: R.H.Whittaker (1935). It was postulated that communities developing at a particular place are in accordance with all the factors of environment. Different climax types are orderly organized parallel to the environmental gradient. One big community changes according to soil, slope and other habitat factors. Models in succession In the following diagram two models of succession are represented in this diagram A, B, C, and D are species and arrows indicate ‘is replace by’ Given below are two models of succession. A, B, C, and D are species and arrows indicate ‘is replace by’ Apparent competition is a form of competition between species, or a group of organisms indirectly competing with another species or group of organisms, which both of them serve as prey of a predator. Based on the mechanism, the types of competition include apparent competition, exploitation competition, and interference competition. In apparent competition, species compete indirectly with each other as prey. Example: Apparent competition between nettle aphids (prey A) and grass aphids (prey B); both are prey to Coccinellidae (predator). The increase in the population of grass aphids (prey B) attracted more Coccinellidae (predator) in the area, resulting in the increased predation of Coccinellidae of nettle aphids (prey A). Apparent competition can be described as a type of indirect competition in which the competing organisms have the same predator. Usually, this type of competition will commence when one of the prey species populations begins to grow. The more prey that is present, the more food source available for the predator. If the predator has a good food source, they will thrive and perform at their optimum, which in turn will allow their population to grow as well. More predators mean that both the prey species are going to be hunted at a greater rate in that particular ecosystem. A decrease in one prey can also affect the population of the other prey as now they will be heavily targeted by the predator. Sometimes, the apparent competition between species and organisms can be as strong or even stronger than direct competition. This is because, though the increasing prey species is not causing direct harm to plateaued population species, the apparent competition can happen so quickly that it may even cause that species to become endangered or extinct.  Apparent competition and the effect on the Native plant Apparent competition can occur when an invasive species is introduced to an ecosystem. Take, for example, there can be apparent competition among two plant species and a set of herbivores. One plant species is native to the ecosystem while the other is an invasive species. Invasive species tend to flourish quickly in new environments and rapidly increase in population. If the invasive species increases in number then that makes more plants available for the herbivores to eat. This will increase the population of the herbivore which in turn can be harmful to the native species since there are more herbivores to prey on them. This can be seen in Fig 1 where the positives show that the herbivore is benefitting. However, we see negative, where the plants are suffering. The bolder arrows towards the native plant indicate that they suffer more in this process. Another way apparent competition takes place is when the food source of one prey species becomes more abundant. That causes the increase of the prey because there are more nutrients available for them to grow. This is how apparent competition begins as the prey population becomes larger and so the predators’ as well hence causing the detriment of the other prey species. A common case where a snake preys on both mice and a small breed of birds. There is an increase in flowers as it is spring season and so there is more nectar available for the birds to feed on. This helps the bird population to increase since their food source is more substantial. An increase in birds means more prey for the snake to feed on. Despite the bird population going up, the mice population remains the same because their source of food remained the same as well. This causes apparent competition between the species because the increase of the bird population will lead to the indirect decrease of the mice population. On the other hand, if the bird population decreases, the mice population will now be heavily hunted by the snake. This will also cause a drastic decrease in the mice population and both preys suffer once again. We see this with the introduction of an invasive grass, Ammophila arenaria, in California in the United States. The abundant increase of this grass became the largest food source for a native rodent, Peromyscus maniculatus. Thus, the rodent population became larger in number and so more rodents fed on the invasive grass and a native plant, Lupinus tidestromii. However, with the competition for nutrients and water from the invasive grass and the predation from the rodents, the Lupinus tidestromii population has become endangered as the plant species gets caught in finding ways to survive despite its competitive environment. Figure 2 below depicts the area of study, the invasive and native plant as well as the native rodent. Showing the area of study (a), invasive and native plant (b) and the rodent (c). Types of Competition There are different types of competition in ecology and these are often because of the factors that influence them. For instance, intraspecific and interspecific competition occurs between the same species and between organisms of different species, respectively. These kinds of competition depend on the taxonomical relationships or classifications between organisms. A simple example of intraspecific competition is the fact that plants are unable to grow too close to one another. Plants often release specific chemicals that prevent others from growing around them so they do not have to compete for nutrients and space. Indirect and direct competitions are determined by influential factors. Indirect competition occurs when the species in question will influence the obtainability of resources whereas direct competition occurs when the species influence resource availability in their ecosystems. Monkeys all living in the same section of the forest will influence each other directly, hence direct competition. However, monkey tribes living in different sections of the forest but using the same pond for water will indirectly compete for water. Some competition types can fall under more than one classification. They can have more than one factor influencing them. For instance, the competition that is based on mechanism can be either interference, exploitative and apparent competition. These competition types are either direct or indirect. Interference competition is a physical type of direct competition where organisms influence the survival process of others such as reproduction and foraging. Kangaroos go through interference competition when the males fight to see who will get to mate with the females. Exploitative competition happens when species are linked through a mutual limiting resource. This resource acts as a mediator between the species and is a form of indirect competition. In this case, some organisms obtain their resources before others do, leaving them with nothing to thrive on. This could happen in a case of a new litter of cats and the first set of kittens to get to the breast milk usually have a higher chance of survival than those who don’t. Apparent competition is a different kind of mechanism competition. Point to be remembered: