Introduction to Ecology and Ecosystem PDF

**Introduction to** **Ecology and Ecosystem** **Meaning of** **Ecology** With the growing environmental movement of the late 1960s and early 1970s, Ecology was not known only to a relatively small number of academic and applied biologists. Even now, people confuse it with terms such as environment...

**Introduction to** **Ecology and Ecosystem** **Meaning of** **Ecology** With the growing environmental movement of the late 1960s and early 1970s, Ecology was not known only to a relatively small number of academic and applied biologists. Even now, people confuse it with terms such as environment and environmentalism. Environmentalism is activism with the stated aim of protecting the natural environment. While environment represents everything that makes up our surroundings and affects our ability to live on the earth the air we breathe, the water that covers most of the earth\'s surface, the plants and animals around us, and much more. So what is ecology? Ecology is a science. According to one accepted definition, ecology is the scientific study of the relationships between organisms and their environment. The environment includes the physical and chemical conditions. However, the term ecology comes from the Greek words oikos, meaning home or place to live, or habitation and logy, meaning "the study of". The German zoologist Ernst Haeckel, originally coined the term ecology in 1866 to refer to the interrelationships of living organisms and their environment. **Ecology has complex roots.** The genealogy of most sciences is direct. Tracing the roots of chemistry and physics is relatively easy. The science of ecology is different: its roots are complex. You can argue that ecology goes back to the ancient Greek scholar Theophrastus, a friend of Aristotle, who wrote about the relations between organisms and the environment. On the other hand, ecology as we know it today has vital roots in natural history (Natural history provides a descriptive account of organisms and their environment). Early plant ecologists were concerned mostly with terrestrial vegetation and using the terms producers and consumers marked the beginning of ecosystem ecology, the study of whole living systems. Mendel's work on inheritance and Darwin's work on natural selection provided the foundation for studying evolution and adaptation and emerging population genetics. Focusing on adaptations led to a science of physiological ecology, this science is concerned with the responses of individual organisms to temperature, moisture, light, and other environmental conditions. Closely associated with physiological ecology is community ecology, which deals with the physical and biological structure of communities and community development. It began with 19th-century behavioral studies including insects, birds, and fish, which gave rise to ethology. Other observations led to investigations of chemical substances in the natural world. Scientists began to explore the use and nature of chemicals in plant and animal defense. Such studies make up the specialized field of chemical ecology. Recent years have seen the development of the use of mathematical models to relate the interaction of parameters and predict effects (ecological modeling). Finally, the development of our understanding of radiation gave rise to radiation ecology which deals with the study of the effect of radiation on the environment and living organisms. Ecology has so many roots that it probably will always remain many-faceted---as the ecological historian Robert McIntosh calls it, "a polymorphic science." Insights from these many specialized areas of ecology will continue to enrich the science as it moves forward into the 21st century. **Ecology has strong ties to other sciences.** The complex interactions taking place within ecological systems involve all kinds of physical, chemical, and biological processes. To study these interactions, ecologists must draw on other sciences. The study of how plants take up carbon dioxide and lose water, for example, belongs to plant physiology. Ecology looks at how these processes respond to variations in rainfall and temperature. This information is vital to understanding the distribution and abundance of plant populations and the structure and function of ecosystems on land. Likewise, other physical sciences, such as geology, hydrology, and meteorology. They will help us chart other ways organisms and environments interact. For instance, as plants take up water, they influence soil moisture and the patterns of surface water flow. As they lose water to the atmosphere, they increase atmospheric water content. The geology of an area influences the availability of nutrients and water for plant growth. In the 21st century, ecology is entering a new frontier, one that requires expanding our view of ecology to include the dominant role of humans in nature. Among the many environmental problems facing humanity, three of them are very important: human population growth, biological diversity, and global climate change. As the human population increased from approximately 500 million to more than 6.7 billion in the past two centuries, dramatic changes in land use have altered Earth's surface. The removal of forests for agriculture has destroyed many natural habitats, resulting in a rate of species extinction (loss of biodiversity) that is unique in Earth's history. Due to the growing demand for energy from fossil fuels, the chemistry of the atmosphere is changing in ways that are altering Earth's climate (global climate change). These environmental problems are ecological in nature, and the science of ecology is essential to understanding their causes and identifying ways to mitigate their impacts. In general, there are many branches of science with a high relation to ecology as explained in the following diagram:  **Figure:** The relationship between ecology and other sciences **Ecosystems** You know that Earth is perhaps the only planet in the solar system that supports life. The portion of the earth that sustains life is called the biosphere. The biosphere is very huge and cannot be studied as a single entity. It is divided into many distinct functional units called ecosystems. All the living and nonliving things that interact in a particular area make up an ecosystem. The term 'ecosystem' was coined by Sir Arthur George Tansley in 1935. An ecosystem is a functional unit of nature encompassing complex interaction between its biotic (living) and abiotic (non-living) components. **Components of an ecosystem** They are broadly grouped into:- **(A) Abiotic components (Nonliving): The abiotic component can be grouped into the following:-** \(1) Physical factors: Such as sunlight, temperature, rainfall, humidity, and pressure. They sustain and limit the growth of organisms in an ecosystem. \(2) Inorganic substances: Carbon dioxide, nitrogen, oxygen, phosphorus, sulfur, water, rock, soil, and other minerals. \(3) Organic compounds: such as carbohydrates, proteins, and lipids. They are the building blocks of living systems and therefore, make a link between the biotic and abiotic components. **(B) Biotic components (Living):** \(1) Producers (autotrophs, i.e. self-feeders): The green plants manufacture food for the entire ecosystem through the process of photosynthesis. Green plants are called autotrophs, as they absorb water and nutrients from the soil, and carbon dioxide from the air, and capture solar energy for this process. \(2) Consumers (heterotrophs, i.e. other feeders): They are called heterotrophs and they consume food synthesized by the autotrophs. Consumers, depending on their food habits, can be further classified into three types : \(A) Herbivores (Primary consumers),e.g. deer, rabbits, cattle, etc., are plant eaters and they feed directly on producers. In a food chain, they are referred to as the primary consumers. \(B) Carnivores (Secondary consumers) are meat eaters and they feed on herbivores (primary consumers). They are thus known as secondary consumers. They are animal eaters, e.g. lions, and tigers. ( C) Omnivores (Third- and higher-level consumers) eat both plants and animals, e.g. pigs, rats, and humans. \(3) Decomposers: Also called saprotrophs. These are mostly bacteria and fungi that feed on dead decomposed and dead organic matter of plants and animals by secreting enzymes outside their body on the decaying matter. They play a very important role in the recycling of nutrients. They are also called detrivores or detritus feeders. Below, a diagram explains the components of an ecosystem: **Figure**: The main components of an ecosystem **Functions of ecosystem** Ecosystems are complex dynamic systems. They perform certain functions. These are:- \(1) Energy flow through food chain \(2) Nutrient cycling (biogeochemical cycles) \(3) Homeostasis (the tendency of an ecosystem to resist the changes) **Types of ecosystems** Ellenberg, (1973) has classified the world into a hierarchy of ecosystems. The biosphere is the largest. Next lower level is mega-ecosystems such as marine ecosystems, limnic ecosystems (ecosystems of fresh water), and terrestrial ecosystems. The lower level is the macro-ecosystem (forests, etc.) within each mega-ecosystem. Macro-ecosystems which divided into microecosystems ( such as mountains and valleys ). We can also divide ecosystems according to the diversity of these systems, such as freshwater systems, estuaries ecosystems, marine ecosystems, and terrestrial ecosystems. Also, we can divide the ecosystems depending on the presence of the major components ( abiotic substances, producers, consumers, and decomposers) to complete ecosystems and incomplete ecosystems. The ecosystems that do not contain all the four basic components of an ecosystem and may lack one or more are called incomplete ecosystems. For example, depths of the sea and caves lack producers but contain only consumers and decomposers. **Ecosystem structure: Abiotic environmental factors** It is well known that ecology includes a broad area of investigation --- from the individual organism to the biosphere. We begin with the individual organism, examining the processes it uses and constraints it faces in maintaining life under varying environmental conditions. The individual organism forms the basic unit in ecology. The individual senses and responds to the physical environment. But before embarking on our study of other aspects of ecological systems, we examine characteristics of the abiotic (physical and chemical) environment that function to sustain and constrain the patterns of life on our planet. Temperature, light, oxygen concentration, carbon dioxide, wind, speed of water flow, etc. exert profound effects on organisms living or trying to live in the ecosystem. However, because not all factors are equally important for any living organism we used the term limiting factors which we will discuss below: **Principles of Limiting Factors** Ecologists used the term \"Limiting Factors\" to refer to all environmental factors that affect an organism's ability to survive in its environment, such as food, light, water, temperature, etc. In other words, Limiting factors: are anything that tends to make it more difficult for a species to live and grow, or reproduce in its environment. **Liebig's Law of the minimum** Liebig\'s law of the minimum, often simply called Liebig\'s law or the law of the minimum, is a principle developed by Justus von Liebig. It states that the **\"Growth of a plant is dependent on the amount of foodstuff which is present in minimum quantity\".** Justus Liebig \"father of the fertilizer industry" in 1840 was a pioneer in the study of the effect of various factors on the growth of plants. He found that the yield of crops was often limited not by nutrients needed in large quantities, such as carbon dioxide and water since these were usually abundant in the environment, but by some raw material, such as boron for example, needed in minute quantities but very scarce in the soil. Extensive work since the time of Liebig has shown that two principles must be added to the concept if it is to be useful in practice.  The first: Liebig's law is strictly applicable only under steady-state conditions.  The second: important consideration is factors interaction. For explanation, Sometimes organisms can substitute, in part at least, a chemically closely related substance for one that is deficient in the environment. Thus where strontium is abundant, mollusks can substitute strontium for calcium to a partial extent in their shells. Another example of factors interaction some plants have been shown to require less zinc when growing in the shade than when growing in full sunlight, therefore, a given amount of zinc in the soil would be less limiting to plants in the shade than under the same conditions in sunlight. **Shelford\'s law of tolerance** Shelford\'s law of tolerance is a principle developed by American zoologist Victor Ernest Shelford in 1911. It states **that an organism has 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 into the law of tolerance by Shelford in 1913. Some subsidiary principles of 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 to one ecological factor, the limits of tolerance may be reduced for other ecological factors. For example, when soil nitrogen is limited, the resistance of grass to drought is reduced. In other words, that more water was required to prevent wilting at low nitrogen levels than at high levels. 4. Very frequently it is discovered that organisms in nature are not actually living at the optimum range with regard to a particular physical factor. In such cases, some other factor or factors are found to have greater importance. Certain tropical orchids, for example actually grow better in full sunlight than in shade, provided they are kept cool, in nature they grow only in the shade because they cannot tolerate the heating effect of direct sunlight. In many cases population interactions such as competition, predators, parasites, and so on prevent organisms from taking advantage of optimum physical conditions. 5. The period of reproduction is usually a critical period when environmental factors are most likely to be limiting. The limits of tolerance for reproductive individuals, seeds, eggs, embryos, and larvae are usually narrower than for non-reproducing adult plants or animals. For example, adult blue crabs and many other marine animals can tolerate brackish water (fresh water that has a high chloride continent), thus individuals are often found for some distance up rivers. The larvae, however, cannot live in such waters, there for the species can not reproduce in the river environment. To express the relative degree of tolerance, a series of terms have come into general use in ecology that utilize the prefixes steno meaning narrow, and eury meaning wide, Thus Stenothermal --eurythermal\-\--refer to temperature Stenohaline --euryhaline \--refer to salinity Stenohydric --euryhydric \-\-\-\--refer to water Stenophagic --euryphagic \-\-\-\--refer to food  **Figure:** Degree of tolerance **The physical factors as limiting factors** The broad concept of limiting factors is not restricted to physical factors, because biological interrelations are also important in controlling the actual distribution and abundance of organisms in nature. **Temperature** Temperature is one of the essential environmental factors. Compared with the range of the thousands of degrees known to occur in our universe, life, as we know it, can exist only within a tiny range of about 300 degrees centigrade-from about -- 200 to 100 ^o^C. Actually, most species and most activities are restricted to an even narrower band of temperature. Some organisms, especially in the resting stage, can exist at a very low temperature at least for brief periods, whereas a few microorganisms, chiefly bacteria and algae can live and reproduce in hot springs where the temperature is close to the boiling point. In general, the upper limits are more quickly critical than the lower limits and the range of temperature variation tends to be less in water than on land, and aquatic organisms generally have a narrower limit of tolerance to temperature than equivalent land animals. Temperature, therefore is universally important and is very often a limiting factor. Temperature, light, and water largely control the seasonal and daily activities of plants and animals. Temperature is often responsible for the zonation and stratification which occur in both land and water environments. **Animals fall into three groups relative to temperature regulation** To regulate temperature, some groups of animals generate heat metabolically. This internal heat production is **endothermy,** meaning "heat from within." The result is **homeothermy** (from the Greek *homeo,* "the same"), or maintenance of a fairly constant temperature independent of external temperatures. Another group of animals acquires heat primarily from the external environment. Gaining heat from the environment is **ectothermy,** meaning "heat from without." Unlike endothermy, ectothermy results in a variable body temperature. This means of maintaining body temperature is **poikilothermy** (from the Greek *poikilos*). Birds and mammals are notable **hoameotherms,** usually called warm-blooded. Fish, amphibians, reptiles, insects, and other invertebrates are **poikilotherms,** often called cold-blooded because they can be cool to the touch. A third group regulates body temperature by endothermy at some times and ectothermy at other times. These animals are **heterotherms** (from *hetero,* "different"). Heterotherms employ both endothermy and ectothermy, depending on environmental situations and metabolic needs. Bats, bees, and hummingbirds belong to this group. Environmental sources of heat control the rates of metabolism and activity among most poikilotherms. Rising temperatures increase the rate of enzymatic activity, which controls metabolism and respiration. For every 10°C rise in temperature, the rate of metabolism in poikilotherms approximately doubles. Most terrestrial poikilotherms can maintain a relatively constant daytime body temperature by behavioral means, such as seeking sunlight or shade. Homeothermic birds and mammals meet the thermal constraints of the environment by being endothermic. They maintain body temperature by oxidizing glucose and other energy-rich molecules in the process of respiration. The process of oxidation is not 100 percent efficient, and in addition to the production of chemical energy in the form of ATP, some energy is converted to heat energy. Homeotherms use some form of insulation--- a covering of fur, feathers, or body fat. For mammals, fur is a major barrier to heat flow. Mammals change the thickness of their fur with the season, a form of acclimation. Arctic and Antarctic birds such as penguins have a heavy layer of fat beneath the skin. Birds reduce heat loss by fluffing the feathers, making the feathered ball. However, some animals use unique physiological means for thermal balance. The camel, for example, stores body heat by day and dissipates it by night, especially when water is limited. Many ectothermic animals of temperate and Arctic regions withstand long periods of below-freezing temperatures in winter through supercooling and developing a resistance to freezing. **Supercooling** of body fluids takes place when the body temperature falls below the freezing point without actually freezing. The presence of certain solutes in the body that function to lower the freezing point of water influences the amount of supercooling that can take place. Some Arctic marine fish, certain insects of temperate and cold climates, and reptiles employ supercooling by increasing solutes, notably glycerol, in body fluids. Glycerol protects against freezing damage, increasing the degree of supercooling. In some species, more than 90 percent of the body fluids may freeze, and the remaining fluids contain highly concentrated solutes, muscles and organs are distorted. After thawing, they quickly regain normal shape. **The ecological rules** There are some rules that correlate organisms especially (endothermic animals) with latitudes such as: \- **Bergmann\'s rule:** It is a biological rule formulated by Christian Bergmann. This rule correlates temperature with body mass in animals. Generally, animals living in cold areas are larger than their counterparts in warmer areas The rule is often applied only to mammals and birds (endothermic). \- **Allen\'s rule:** it is an ecological rule posited by Joel Allen. It states that animals from colder climates usually have shorter appendages (such as tails, ears, nose, legs, etc) than the equivalent animals from warmer climates. In cold climates, the increase of exposed surface area leads to increasing loss of heat. Animals in cold climates need to conserve as much energy as possible. A low surface area to volume ratio helps to conserve heat. In warm climates, the opposite is true. Therefore, animals in warm climates will have high surface area-to-volume ratios to help them lose heat.