ECOLOGY. Population all the members of the same species that LIVE in the same place at the same time

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1 ECOLOGY Ecology is the study of the interactions of organisms with one another and with their environment. An environment is composed of both biotic and abiotic factors which influence the survival and behaviors of organisms. Biotic factors are the living and once living parts of an environment. Abiotic factors are the nonliving parts of the environment. Organism - an individual living thing. A species is a group of organisms that can mate to produce fertile offspring. Every organism is a member of a species. Population all the members of the same species that LIVE in the same place at the same time Community a group of various species that live in the same place and interact with each other. It s only made of biotic components. Ecosystems - are all of the organisms living in an area together with their physical environment. Biomes - are large climatic region that contains a number of smaller ecosystems. Biomes may exist in more than one location and are distinguished by plants and animals. Biosphere - the thin layer of Earth and the atmosphere that supports life. HABITAT & NICHE All organisms live in particular place called habitats. Every habitat has specific biotic and abiotic factors that the organism living there needs to survive. Organisms tend to be very well suited to their natural habitats due to adaptations, inherited traits, which increase their chance of survival and reproduction. Adaptations such as: camouflage (blending in with surroundings), mimicry (looking or sounding like another organism), chemical defenses (venom, ink, sprays), body parts (claws, beaks, armor plates) and unique methods of obtaining food, defending oneself, hibernation, migration, etc.. Ecological niche refers to the unique role a species has in its environment how it meets its needs for food and shelter, how it survives, and how it reproduces. A niche includes the species habitat, the environmental factors necessary for the species survival and all the species interactions with other organisms. For example: A tree frog in a Brazilian rainforest can only survive if temperatures and humidity stay within a certain range. It also needs access to a certain amount and type of food. It must avoid becoming food for predators. The sum of these conditions is the frog s niche. POPULATION ECOLOGY Populations may be described in terms of size, density and dispersion. These properties can be used to describe populations and to predict changes within them. Population sizes can be determined by factors such as births, death, immigration and emigration. r = (b - d) + (i - e) Population density is a measurement of the number of individuals living in a specified habitat. Environmental influences can alter population density and distribution, age structure and variations in population size. 1

2 Population dispersion refers to the relative distribution of its individuals within an area. Dispersion can occur in patterns: 1. Clumped - individuals aggregate in patches; influenced by resource availability & behavior 2. Uniform - individuals are evenly distributed; influenced by social interactions such as territoriality 3. Random - the position of each individual is independent of other individuals Populations usually stay about the same size from year to year because various factors kill many individuals before they can reproduce. A species biotic potential is the fastest rate at which its population can reproduce. This rate is limited by an organism s reproductive potential which is the maximum number of offspring that each member of the population can produce. Reproductive potential increases when individuals produce more offspring at a time, reproduce more often, and reproduce earlier in life. Population Growth Patterns: Exponential growth occurs when populations have plenty of food, space and have little or no competition or predators. Populations rapidly increase due to an abundance of resources. There are UNLIMITED resources. (J-shaped curve) This growth is not sustainable short lived in nature. Natural conditions are neither ideal nor constant; populations cannot grow forever and rarely grow at their reproductive potential. Resources are used up or the environment changes. Logistic growth populations are limited by environmental factors and tend to attain equilibrium in size which is determined by available resources. (S-shaped curve) Carrying capacity of a particular species is the maximum population that the ecosystem can support indefinitely. A population may increase beyond this number, but it cannot stay at this increased size due to resource availability. Because ecosystems change, carrying capacity is difficult to calculate exactly --- it s a theoretical limit. A species reaches it carrying capacity when it consumes a natural resource at the same rate at which the ecosystem produces the resources. The limited resource determines the carrying capacity for a species at a particular time LIMITING FACTORS - Factors that prevent a population from reaching its biotic potential. Limits to population size may or may not depend on the density of the population. 1. Density-Dependent Factors - Factors that have an increasing effect as the population increase. As organisms crowd together, these factors cause more damage and spread faster in larger populations. Examples: resource availability, predation, disease, competition, parasitism, stress due to overcrowding 2. Density-Independent Factors Factors that affect any population, regardless of density; NOT influenced by population size. Examples: weather, natural disasters, human activities, adaptations & behaviors of organisms 2

3 COMMUNITY ECOLOGY Species interactions are based on whether each species causes benefit or harm to the other species in a given relationship. Each interaction affects evolution, persistence of a species and the overall diversity of life. Organisms have evolved together and therefore adjusted to one another. An organism s niche and habitat are important factors in these interactions. Competition A relationship in which different individuals attempt to use the same limited resources. Each individual has less access to the resource & is harmed by the competition. Members of the same species must compete with each other because they require the same resource they occupy the same niche. When members of different species compete, their niches overlap, which means that both species use some of the same resources in a habitat. Competitive Exclusive Principle - Two species that have exactly the same requirements cannot coexist in exactly the same habitat. Otherwise, competition will occur. Indirect competition Species compete even if they never come into direct contact with each other. (i.e. Insects feeding on same plant at different times.) Predation The act of one organism (predator) feeding on another organism (prey). Most organisms are vulnerable to predation, so there are strong selective pressures for adaptations that serve as defenses against predators. Adaptations that can enhance survival of prey include camouflage, warning coloration, mimicry and protective covering. Some predators eat only specific types of prey. In this close relationship, the sizes of each population tend to increase and decrease in linked patterns. However, many predators will feed on whichever prey is easiest to capture. Symbiosis A relationship in which two species live in close association. These species may evolve adaptations that reduce the harm or improve the benefit of the relationship. Parasitism An organism that lives in or on another organism (host) and feeds on it. Parasites usually do not kill their hosts, but weakens or develops a disease. Mutualism Two species provide a benefit and depend on each other for survival. Commensalism A relationship in which one species benefits and the other species is neither harmed nor helped. ECOSYSTEMS Changes in Ecosystems - Ecological succession is a gradual process of change and replacement of some or all of the species in a community. Ecological succession may take hundreds or thousands of years. Each new community that arises makes it harder for the previous community to survive, because of competition for resources. Succession provides opportunities for new resources and niches to become available for the next community. Primary Succession The initial establishment and development of an ecosystem. Begins in a place without any soil and no previous life exists. Starts with the arrival of living things such as lichen, moss or bacteria that do not need soil to survive these first organisms are called pioneer species. Soil starts to form as pioneer species and the forces of weather and erosion help break down rocks into smaller pieces. Pioneer species decompose and add small amounts of organic matter to the rock to make soil. Simple plants like mosses and ferns grow in the new soil. When 3

4 these plants decompose, it adds more organic material. The soil layer thickens and other plants begin to take over. These plants die, and they add more nutrients to the soil. Shrubs and trees can survive now. Insects, small birds, and mammals have begun to move in. What was once bare rock now supports a variety of life. Primary succession can occur on new islands created by volcanic eruptions, in areas exposed when a glacier retreats, sand dunes or any other surface that has not previously supported life. Slow process because it begins with no soil. Climax Community is composed of species best adapted to conditions in an area and has reached equilibrium. The ecosystem is established and changes are slow. Secondary Succession The reestablishment of an ecosystem that contains soil and vegetation of a previous biological community ---- ecosystems have been disturbed or disrupted by humans or animals, or by natural processes such as storms, floods, fires, earthquakes, etc. These disturbances open up opportunities for new niches to be established during the rebuilding of the area. The soil remains and the process is faster than primary succession. Energy Flow in Ecosystems - The primary source of energy for an ecosystem is the sun. Photosynthetic organisms change light energy from the sun into carbohydrates. As organisms consume food and use energy from carbohydrates, the energy travels from one organism to another. When an animal eats a plant, some energy is transferred from the plant to the animal. Organisms use this energy to move, grow and reproduce. Because plants make their own food, they are called autotrophs or producers. A producer is an organism that can make carbohydrates (organic compounds) from the sun s energy or inorganic compounds. (i.e. Bacteria in deep-ocean vents use hydrogen sulfide, an inorganic compound, as the energy source to perform chemosynthesis). A heterotroph or consumer is an organism that eats other organisms or organic matter instead of producing its own nutrients. Consumers get their energy indirectly by eating producers or other consumers. 4

5 Herbivore Carnivore Omnivore Decomposers (fungi & bacteria) Types of Consumers eats producers eats consumers eats consumers and producers break down dead organisms and returns nutrients to the soil, water and air Remember: Energy can neither be created nor destroyed; it can only be changed from one form to another. There is always some loss of energy usually in the form of heat during the change. Each time an organism eats another organism, an energy transfer occurs. Studying the paths of energy between organisms can tell us how much energy is transferred and which organisms depend on other organisms for survival in an ecosystem. A food chain is a sequence in which energy is transferred from one organism to the next as each organism eats another organism. Energy flow in an ecosystem is more complex than energy flow in a simple chain. So a food web includes multiple food chains linked together to show many feeding relationships in an ecosystem. Each step in the transfer of energy through a food chain or food web is known as a trophic level. Energy flows from one trophic level to the next --- in ONE direction from the producer to the consumer. Find one food chain in the web --- label the trophic levels. Each time energy is transferred, some of the energy is lost as heat. Therefore, less energy is available at higher trophic levels. One way to visualize this is with an energy pyramid. When energy is used, about 90% of the energy at each trophic level is converted into heat energy and dispersed into the environment. Only about 10% of energy is stored in the animal s body as fat and is the amount of energy available to the next trophic level. Decreasing amounts of energy at each trophic level affects the number of organisms at each level and limits the number of levels in an ecosystem. Big predators are rare because a lot more energy is required to support a single predator than a single herbivore. Many ecosystems do not have enough energy to support a large population of predators. Biomass is the total amount of living tissue in each tropic level --- lower level has the greatest amount. Energy decreases Biomass decreases Population decreases 5

6 Matter Cycles in Ecosystems - Matter is recycled within and between ecosystems. Biogeochemical cycles pass the same molecules around within the biosphere. Water Cycle o Evaporation returns H 2 O back into the atmosphere which leads to condensation in the clouds. o Precipitation sends water back to Earth s surface. Most of the surface water is runoff hat returns back into a body of water, but some water seeps into the soil for groundwater or for plants to use. WATER CYCLE Carbon Cycle o Carbon is an essential component of fats, proteins and carbohydrates, which make up all organisms. o Carbon cycles between the process of photosynthesis and cellular respiration. Photosynthesis removes CO 2 and respiration releases CO 2. o Carbon is converted into carbonates which make up bones and shells. Over millions of years, carbonate deposits have produced large formations of limestone rocks resulting in one of the largest carbon reservoirs on Earth. o Some carbohydrates in organisms are converted to fats that store energy. When an organism dies and decomposition occurs, this carbon is returned to the soil and air. Over millions of years, these deposits will form coal, oil, and natural gas (fossil fuels). Burning of these fossil fuels release carbon dioxide back into the atmosphere. CARBON CYCLE How humans affect the Carbon Cycle? Cars, factories and power plants rely on fossil fuels to operate. Each year, about 6 billion metric tons of carbon is released into the atmosphere as CO 2 by the burning of fossil fuels and the burning of wood in forest fires. As a result, the amount of CO 2 levels in the atmosphere has steadily increased. Increased levels of CO 2 may contribute to global warming, which is an overall increase in temperature of the Earth. 6

7 Nitrogen Cycle All organisms need nitrogen to build proteins, which are used to build new cells. However, most organisms CAN NOT use atmospheric nitrogen, which makes up 78% of atmospheric gases. It must be altered or fixed before organisms can use it. Nitrogen-fixing bacteria convert atmospheric nitrogen into ammonia or nitrate, a usable form of nitrogen. o Nitrogen-fixing bacteria live in the soil or in root nodules of plants called legumes. The bacteria use sugars provided by the legumes to produce nitrates. The excess nitrogen fixed by the bacteria is released into the soil. Nitrification The process of bacteria converting ammonia (NH 3 ) (toxic to plants) to nitrites (toxic to plants) (NO 2 -) and then finally to nitrates (NO 3 -). o Animals get nitrogen by eating plants or other animals. Decomposers in the soil break down waste or decaying organisms and return the nitrogen to the soil. o Denitrification - The process of releasing fixed nitrogen back to atmospheric nitrogen gas. Denitrifying bacteria transform nitrogen in the soil back into atmospheric nitrogen gas. NITROGEN CYCLE How humans affect the Nitrogen Cycle? Humans have impacted this cycle due to agricultural fertilization, burning of fossil fuels, wastewater etc. Excessive nitrogen contributes to acid precipitation, contamination of water, removal of nitrogen from topsoil, and destruction of plant through the release of excess nitrogen. Phosphorus Cycle The phosphorus cycles fairly slowly through the earth s water, soil and living organisms. It is an essential element for life, in molecules of DNA and ATP, and often is a limiting nutrient for plant growth. Most phosphorus is stored in the Earth s rocks/soils and is released to water via erosion and weathering. Phosphorus does NOT exist as a gas!! o When rocks erode, small amounts of phosphorus dissolve in soil and water. When organisms excrete waste or decompose, phosphorus is added in soil and water. o Plants take up phosphorus in aquatic and terrestrial ecosystems and animals eat the plants; returning the phosphorus to the soil via urine, feces, and death. How humans affect the Phosphorus Cycle? Humans remove large amounts of phosphate from the earth through mining to make fertilizers, reduce phosphorus in tropical soils by clearing forests and then we add excess phosphates into aquatic systems. Phosphorus disrupts aquatic systems through runoff of animal wastes, fertilizers and discharges from sewage treatment systems. Excessive amounts of phosphorus and nitrogen in aquatic ecosystems can cause an algal bloom, overgrowth of algae. Algal blooms can deplete nutrients such as oxygen from the ecosystem. 7

8 Environmental Issue Whether a resource is "renewable" or "nonrenewable" is about how long nature takes to renew it. Renewable resources can regenerate and are replaceable. However, a renewable resource is not necessary unlimited such as freshwater. Drought and overuse could make it limited. Nonrenewable resources cannot be replenished by natural processes such as fossil fuels: coal, oil and natural gas. Fossil fuels formed over millions of years from buried organic materials. Sustainable Use is a way of using natural resources at a rate that does not deplete them. This system operates without causing long-term harm to the ecological resources on which it depends. Land Resources Soil can be permanently damaged if it is mismanaged. Soil erosion occurs when the surface soil wears away by water or wind. Plowing the land removes roots that hold the soil in place and can cause soil to erode easily. Desertification occurs in dry climates, when a combination of farming, overgrazing and drought has turned once productive areas into deserts. Deforestation occurs when forests are cut down and lead to severe erosion as soil is exposed to heavy rains. Erosion can wash away nutrients. Grazing and plowing after deforestation can change the soil and microclimates that in turn prevent the re-growth of trees. Sustainable use of resources include contour plowing -- leaving previous year s crop in place to hold the soil -- crop rotation and livestock rotation harvest mature trees. Water Resources Overfishing occurs when fish stocks are being harvested faster than they can reproduce. Depletion of this food resource can alter the ecosystem by collapsing fish populations. Pollutants such as chemicals, waste and sewage enter the water cycle and contaminate water. Pollutants can increase the growth of algae and bacteria. Sustainable use of resources includes limit fishing and use aquaculture to farm aquatic organisms. Protection of natural water systems such as wetlands to filter pollutants. Air Resources Smog mixture of chemicals that create a haze in the atmosphere. Primarily due to automobile exhaust and industrial emissions. Acid Rain - Burning of fossil fuels release acidic gases containing nitrogen and sulfur compounds into the atmosphere. These gases combine with water vapor to form nitric and sulfuric acids. Acid rain changes the chemistry of the soil. Lowering the soil ph leaches away nutrients and reduces nutrient availability. It also increases availability of toxic elements like mercury from the soil which can enter other parts of the biosphere. Acid rain changes the chemistry of the water killing aquatic organisms. Acid rain causes corrosion of metals. 8

9 Biodiversity refers to the number of different species in a given area --- variation of life in the biosphere including species, ecosystem and genetic diversity. Species play an important role in an ecosystem because species are either dependent on or depended upon by at least one other species. When on species disappears from an ecosystem, a strand in a food web is removed. Keystone species are critical to the functioning of an ecosystem. These species control the population size of organisms in lower tropic levels. Threats to biodiversity include altering habitats, hunting species to extinction, introducing toxic compounds into food webs and introducing invasive species to new environments. About 65 mya, a series of changes in the Earth s climate and ecosystems caused the extinction of about half the species of Earth. It takes many years for biodiversity to rebound after a mass extinction, the extinction of many species in a short period of time. Large populations that adapt easily too many habitats are not likely to become extinct (i.e. rats & cockroaches). Species with small populations in limited areas can easily become extinct. At risk species include those that migrate, those that need special habitats and those that are exploited by humans. o Endangered species A species that is likely to become extinct if protective measures are not taken immediately. o Threatened species A species that has a declining population and that is likely to become endangered if it is not protected. 1. Habitat Destruction and Fragmentation As human populations grow, we use more land to build homes and harvest resources. Humans destroy and fragment the habitats of other species. Natural habitats are destroyed and the remaining pieces of habitat contain fewer species and less diversity. Habitat loss causes almost 75% of the extinction now occurring. 2. Invasive Species A non-indigenous species is introduced into a particular region and can threaten native species that have no natural defenses against them. 3. Excessive Hunting, Harvesting and Poaching Many countries now have laws to regulate hunting, fishing, harvesting and trade of wildlife. 4. Pollution Chemicals used by humans are making their way into food webs around the world. The long-term effects may not be clear until after many years of use (i.e. DDT & bald eagle). Biological magnification occurs when toxic substances enter the food chain. Concentrations of harmful substances increase in organisms at higher trophic levels in the chain or web. CRITICAL areas of Biodiversity Some parts of the world contain a greater diversity of species than others. An important feature is that they have a large portion of endemic species ---- species that are native to and found only within a limited area. Ecologist often use the numbers of endemic species of plants as an indicator of overall biodiversity, because plants from the bases of ecosystems on land. o Biodiversity hotspots have high numbers of endemic species and are the most threatened areas on Earth. Most hotspots have lost 70% of their original natural vegetation. The U.S. hotspots include the Florida Everglades, the Californian coastal region, Hawaii, the Midwestern prairies and the forest of Pacific Northwest. 9

10 Ozone The ozone contains a layer of ozone gas (O 3 ) in the upper atmosphere of Earth. It is naturally occurring and absorbs much of the ultraviolet (UV) radiation emitted by the sun from reaching Earth s surface. Ozone is a global sunscreen. The increase in UV radiation causes sunburn, cancer, damage plant leaves, phytoplankton and decrease organisms resistance to disease. Ozone depletion is caused by chlorofluorocarbons (CFCs). CFCs are used in aerosol cans and as coolants in refrigerators and air conditioners. In the cold of the polar atmosphere, CFCs act as catalysts that enable UV light to break apart ozone molecules. Greenhouse Effect The Greenhouse Effect is a natural process in which atmospheric gases absorb thermal radiation (heat). Some of sun s radiation is reflected back into space, but some passes through and is absorbed by Earth. Heat from the Earth is radiated outward and absorbed by greenhouse gases. Greenhouse gases regulate our climate by trapping heat and keeping Earth warm enough to sustain life. The main greenhouse gases are Carbon Dioxide (CO 2 ), Methane (CH 4 ) and Nitrous Oxide (N 2 O). Humans accelerate this natural process by creating more greenhouse gases in the atmosphere through activities such as: Burning fossil fuels deforestation -- creates more CO 2 Industrial processes and mining -- emissions from livestock and agricultural practices -- decomposition in landfills creates more CH 4 Agricultural and industrial practices combustion of fossil fuels and solid waste creates more N 2 O Ultimately, more greenhouse gases mean more infrared radiation trapped which gradually increases the temperature of the Earth s surface. This increase in average temperature of the biosphere is called Global Warming. Impacts of Global Warming: Ice sheets and glaciers are melting worldwide, especially at the Earth s poles. Ecosystems will change some species will move farther north or become more successful; others won t be able to move and could become extinct. Sea level rises. Floods and droughts will become more common. Precipitation has increased across the globe, on average. Less fresh water will be available. Hurricanes and other storms are likely to become stronger. Species that depend on one another may become out of sync. For example, plants could bloom earlier than their pollinating insects become active. 10