6_2018_12_12!06_20_22_PM.docx

6_2018_12_12!06_20_22_PM.docx

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  ` Ecology Lecture11-10 Dr. Saba Riad Limiting factor In biology, a limiting factor is a resource or environmental condition that limits the growth, abundance, or distribution of an organism or a population of organisms in an ecosystem. . Limiting factors may be physical or biological. in The essential material available liebig s law of minimum (1840): - 1 amounts most closely approaching the minimum need to tends to be the limiting one 2- Shelford's "LAW" OF TOLERANCE Organisms have an ecological maximum and minimum, with a range in between which represents the "limits of tolerance". In this law not only may too little of something be a limiting factor , as proposed by Liebig, but also too much , as in the case of such factors as heat, light, and water ,thus organisms are constrained by both the maximum and minimum extremes of an environmental condition; these extremes represent the limits of tolerance. The concept of the limiting effect of maximum as well as minimum was incorporated in to the law of tolerance by Shelford in 1913. . V.E.Shelford in 1913 law of tolerance by E In to the Some principles to the law of tolerance may be stated as follows: 1)organisms may have a wide range of tolerance for one factor and a narrow range for another. 2)organisms with wide ranges of tolerance for all factors are likely to be most widely distributed. 3)when conditions are not optimum for a species with respect to one ecological factor the limits of tolerance may be reduced for other ecological factor the limits of nitrogen ced for other ecological factor, for example when soil tolerance may be redu is limiting the resistance of grass to drought is reduced.in other words more water was required to prevent nitrogen levels than at high levels.
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  4)organisms in natureare not actually living at the optimum range of particular physical factor. he limits of tolerance for reproductive individuals seeds eggs embryos seedlings 5)t and larvae are usually narrower than for non reproducing adult plants or animals. For the relative degree of tolerance a series of terms have come in to general use in STENO , meaning narrow that use of the prefixes ecology For the relative degree of tolerance a series of terms have come in to general use in ecology that use of the prefixes STENO , meaning narrow eury , meaning wide. Stenothermal----eurythermal refers to temperature Stenohydric ------ euryhydric refers to water Stenohaline----------euryhaline refers to salinity Stenophagic-------euryphagic refers to food Stenoeciouc-----------euryecious refers to habitat selection. Light, temperature and water(rainfall) are ecological factors on land.Light, temperature ,and salinity are the important ones in the sea and oxygen may be major importance in fresh water. Physical factors light and light penetration Photic zone: depth to which light is penetrates zone of photosynthesis and primary production. Aphotic zone: is below photic zone Most of ocean is dark Light too little for photosynthesis Dysphotic zone: is very low in Limiting factors: temperature • Temperature affects metabolic rate: the rate at which reactions proceed in an organism • Metabolic rate doubles for every 10°C increase in body temperature
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  • Most marineorganisms are ectothermic – same body temperature as the surrounding water . – clams, shrimp, most fish ... Some marine organisms are endothermic - – constant and usually higher body temperature than the surrounding water . – marine mammals, birds, some tuna and sharks Limiting factors: salinity • Normal marine salinity is 35‰ • Too high or too low is damaging – Low diversity in estuaries (low salinity) – Low diversity in areas of high evaporation (high salinity) • Maintaining salt balance is critical - organisms do this by : – Diffusion – passive movement from areas of high concentration to low concentration – Osmosis – diffusion of water through a membrane – Active transport – active removal of substances from an area of low concentration to high concentration And there are pressure , O2 , and dissolved nutrients. LIMITING FACTORS ON LAND Light: Photoperiodism is the physiological reaction of organisms to the length of day or night. It occurs in plants and animals. Photoperiodism can also be defined as the developmental responses of plants to the relative lengths of light and dark periods. Long-day plants Long-day plants flower when the night length falls below their critical photoperiod. These plants typically flower in the northern hemisphere during late spring or early summer as days are getting longer. In the northern hemisphere, the longest day of the year (summer solstice) is on or about 21 June. After that date, days
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  grow shorter (i.e.nights grow longer) until 21 December (the winter solstice). This situation is reversed in the southern hemisphere (i.e., longest day is 21 December and shortest day is 21 June). Short-day plants Short-day plants flower when the night lengths exceedtheir critical photoperiod.] They cannot flower under short nights or if a pulse of artificial light is shone on the plant for several minutes during the night; they require a continuous period of darkness before floral development can begin. Natural nighttime light, such as moonlight or lightning, is not of sufficient brightness or duration to interrupt flowering. In general, short-day (i.e.long-night) plants flower as days grow shorter (and nights grow longer) after 21 June in the northern hemisphere, which is during summer or fall. The length of the dark period required to induce flowering differs among species and varieties of a species. Photoperiodism affects flowering by inducing the shoot to produce floral buds instead of leaves and lateral buds. Day-neutral plants[] - Day-neutral plants, such as cucumbers, roses, and tomatoes, do not initiate flowering based on photoperiodism. Instead, they may initiate flowering after attaining a certain overall developmental stage or age, or in response to alternative environmental stimuli, such as vernalisation (a period of low temperature). WATER FACTOR: XEROPHYTE Plants that live in conditions where water is scare (for example in the desert) MESOPHYTE Land plants living in environment with moderate amount of moisture. HYDROPHYTE A plant adapted to grow in water.
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  TEMPERATURE FACTOR: An OLIGOTHERMAL(microthermal)is an organism that can live in an environment that offers very low levels of temperature. An POLYTHERMAL(megathermal) is an organism that can live in an environment that offers very high levels of temperature. An MESOTHERMAL is an organism that can live in an environment that offers medium levels of temperature. SOIL: Soil is the mixture of minerals, organic matter, gases, liquids, and the myriad of organisms that together support plant life. It is a natural body that exists as part of the pedosphere and which performs four important functions: it is a medium for plant growth; it is a means of water storage, supply and purification; it is a modifier of the atmosphere; and it is a habitat for organisms that take part in decomposition of organic matter and the creation of a habitat for new organisms. Soil is considered to be the "skin of the earth" with interfaces between the lithosphere, hydrosphere, atmosphere, and biosphere. Soil consists of a solid phase (minerals and organic matter) as well as a porous phase that holds gases and water.] Accordingly, soils are often treated as a three-state system. . Soil science has two main branches of study: Edaphology and Pedology. Pedology is focused on the formation, description (morphology), and classification of soils in their natural environment, whereas Edaphology is concerned with the influence of soils on organisms.