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Biology 40S Unit 5: Ecosystems. Developed by Trevor Boehm Hutterian Interactive TV Prairie Rose School Division. Major Topics in Unit 5. Definition of ecosystem and ecology. Interaction between species (competition, predation and the food chain). Important cycles in the biosphere:
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Biology 40SUnit 5: Ecosystems Developed by Trevor Boehm Hutterian Interactive TV Prairie Rose School Division
Major Topics in Unit 5 • Definition of ecosystem and ecology. • Interaction between species (competition, predation and the food chain). • Important cycles in the biosphere: • Nitrogen cycle • Phosphorus cycle • Carbon cycle • Hydrologic (water) cycle. • Change in a community over time (succession, migration, extinction, adaptation).
Ecology and EcosystemsSome Definitions • We know that one individual “living thing” is referred to as an organism. An organism is made up of organ systems, which are made up of tissues, etc., etc. • A group of organisms of the same species is referred to as a population. • A community is all populations (all members of all species) that inhabit a certain area. • An ecosystem is all the organisms living in an area (the community of living organisms) along with their environment. • Ecology is the study of ecosystems. • The location of a community is referred to as its habitat (where that species lives).
Food Chains and Food Webs • A food chain indicates who eats whom in an Ecosystem. • A food web may contain several interrelated food chains.
Food Chain Terms:Producers and Consumers • Plants are called producers because they are able to use light energy from the sun to produce food (sugar) from carbon dioxide and water. • Animals cannot make their own food. They are consumers because they must eat plants and/or other animals. There are three groups of consumers: • Animals that eat only plants are called herbivores (or primary consumers). • Animals that eat other animals are called carnivores. • carnivores that eat herbivores are called secondary consumers • carnivores that eat other carnivores are called tertiary consumers • carnivores that consume dead animals rather than actively hunting are called scavengers • Animals and people who eat both animals and plants are called omnivores. • Decomposers feed on decaying matter. These decomposers (bacteria and fungi) speed up the return of nutrients to the environment.
Energy and Trophic Levels • Energy is lost or used at each step in a food chain or web. • Producers (plants) absorb energy from the sun, but only about half of the energy capture from the sun becomes part of the plant. The other half is used by the plant to carry out life processes, or is lost as heat. • Each level in a food web or chain is called a trophic level. • At each trophic level, the energy stored in an organism is about 1/10 that of the level below it. (10%). • Because energy diminishes at each successive trophic level, few ecosystems can contain more than 4 or 5 levels. • Organisms at higher trophic levels tend to be fewer in number than those at lower trophic levels. It takes many producers to support one carnivore.
Energy and Trophic Levels Diagram Energy lost as head at each step in the food chain.
Pyramid of Energy • The further along the food chain you go, the less food (and hence energy) remains available. • The energy present at each trophic level in a food chain can be shown using a pyramid diagram.
Pyramids ofBiomass and Numbers • Pyramids can also be used to show the number of organisms and the overall biomass present in an ecosystem. • Biomass is the mass of living matter. • The 10% rule may or may not hold true for the number of organisms present in an ecosystem, depending on the size of the organisms.
Ecological Niche • The ecological niche of an organism depends not only on where it lives but also on what it does. By analogy, it may be said that the habitat is the organism's "address", and the niche is its "profession", biologically speaking.– Odum, Fundamentals of Ecology, W B Saunders 1959 • Oak trees live in forests; that's common sense. The forest is the habitat. So if Odum was writing a letter to an oak tree he would address the letter to: Mr. Deciduous Oak Tree The Oak Forest Manitoba, Canada • What do oak trees do? If you can answer that question you know the oak tree’s "profession" or its ecological niche. • Perhaps you think that oak trees just stand there looking pretty and not doing very much, but think about it. Oak trees: • absorb sunlight by photosynthesis; • absorb water and mineral salts from the soil; • provide shelter for many animals and other plants; • act as a support for creeping plants; • serve as a source of food for animals; • cover the ground with their dead leaves in the autumn. • These six things are the "profession" or ecological niche of the oak tree. You can think of it as being a kind of job description. If the oak trees were cut down or destroyed by fire or storms they would no longer be doing their job and this would have a disastrous effect on all the other organisms living in the same habitat.
Competition • Competition is the interaction between two or more organisms, or groups of organisms, that use a common resource in short supply. • There can be competition between members of the same species and competition between members of different species. • Competition results in a reduction in the numbers of one or both competitors. • Over time, one or both competitors may adapt (diverge) to rely on resources where competition is least or absent. • The resources in short supply for which organisms compete may be obvious things, such as nutrients and light for plants, or sources of food for animals. However, there are less obvious resources. For example, competition for suitable nesting sites is important in some species of birds.
Prolonged Competition Can Lead to Developing Exclusive Niches
Predation • A predator is any animal which eats another animal. • For example: spiders eating flies, lions eating zebras. • Providing the prey species reproduces as fast as it is predated, its population will stay at a constant size. If the rabbits in a grassland ecosystem reproduce faster than the foxes predate them, the rabbit population will increase. • Predators are one main type of consumers. The other type is scavengers, which feed off of dead organisms.
Predator-Prey Cycle • Species can control each other to some extent. • In the example below, the snowshoe hare is the prey and the lynx is the predator. • Notice that an increase in prey population leads to an increase in predator population. The increased hunting of the prey will reduce its population, and the lack of food will cause the predator population to decrease. • The example below appears to cycle about every 10 years.
Ecological Succession • Ecological succession is the long-term process of natural vegetation communities changing. • The community of plants in an area largely determines what animal life will be part of that community. • Two types of succession: • Primary succession is the development of plant life where none existed previously. • Secondary succession takes place where land has been scarred by fire or disturbance such as plowing. Secondary succession is much faster than primary succession. Soil, nutrients, and seeds are already present.
Primary andSecondary Succession Both secondary and primary succession are seen in this pond scene. In the background we see secondary succession: trees taking over a former ploughed field. The pond itself shows the shrinkage and shallowing caused by plant growth: this is primary succession.
Pioneer Species andClimax Communities • The first population to move into a geographical area is referred to as a pioneer species. • If this pioneer population is successful in its new location, it will change the environment in such a way that new populations can move in. • As populations are replaced, changing plant forms bring with them different types of animals. • As a community moves through the stages of succession, total biomass increases, more nutrients are maintained within the system, species diversity increases, and and size and life spans of organisms increases. • Eventually, the community will reach a point where the mixture of populations creates no new changes in the environment. At this point, the specific populations in the stable community are said to make up a climax community. While individuals within a climax community will come and go, the essential makeup of the populations within the climax community will stay constant.
Factors Which Affect Success of an Organism • Both living and nonliving factors. • The nonliving factors, called abiotic factors, include: • solar energy (amount of sunlight) • oxygen, CO2, and water levels • temperature and humidity • pH • availability of nitrogen • type of soil and soil nutrients • The living factors, called biotic factors, are the other living organisms in the ecosystem – producers, consumers, and decomposers.
Responses of Organisms to Change in their Environment • Three, and only three, possible responses to a major change: • Adapt – adjust to the new situation. • Migrate – move to a location where the situation is more favourable. • Die
Extinction andEndangered Species • When the last living member of a species dies, the species becomes extinct. • Extinction is the result of some change in the ecosystem which makes it difficult for the species to survive. • A species with only a small number of living members is called an endangered species because it is at risk of becoming extinct.
Causes of Species Extinction and Endangerment • The main causes of species extinction or endangerment are: • habitat destruction • commercial exploitation (such as plant collecting, hunting, and trade in animal parts) • damage caused by non-native plants and animals introduced into an area • pollution. • Of these causes, direct habitat destruction threatens the greatest number of species.
Biochemical Cycles • Recycling is not a human idea. • The earth continually cycles essential biochemical compounds to avoid “running out” and to ensure that the planet isn’t overrun with garbage. • There are four main cycles important to supporting life on earth: • The Carbon Cycle • The Hydrologic (Water) Cycle • The Nitrogen Cycle • The Phosphorus Cycle
The Carbon CyclePhotosynthesis and Cellular Respiration • Together, photosynthesis and cellular respiration form the basis of the carbon cycle. • The Earth’s atmosphere contains carbon in the form of Carbon Dioxide (CO2). • During photosynthesis, plants and other autotrophs use CO2 along with water and solar energy to build carbohydrates such as glucose. • Consumers obtain energy-rich molecules that contain carbon by eating plants and animals. • Both autotrophs and heterotrophs use oxygen to break down carbohydrates during cellular respiration. • Carbon is return to the environment through decomposers and cellular respiration (breathing releases CO2 back to the atmosphere). • These two processes are complimentary (opposites) and account for the circulation of carbon on earth.
Carbon Storage • We said that photosynthesis and cellular respiration form the basis of the carbon cycle. • However, not all carbon absorbed by living organisms is immediately returned to the atmosphere through cellular respiration. • Organic carbon forms part of the body of all living organisms. When living organisms die, they must decompose in order for this carbon to be released back into the environment. • Wood, sediments, and fossil fuels like coal and oil all store inorganic carbon. • Human activity (burning fossil fuels, deforestation) has released much of this stored carbon back into the atmosphere more quickly than natural processes.
The Hydrologic(Water) Cycle • Water continuously circulates from the oceans to the atmosphere, to the land, and back again to the oceans. • This is the hydrological cycle. • The hydrologic cycle involves the following processes: • Precipitation is liquid water from the atmosphere falling to the earth as rain, snow, etc. • Evaporation is the change from liquid water to water vapour that allows water to return to the atmosphere. • Transpiration is the loss of water vapour by plants. • Condensation is the change from water vapour to liquid water that occurs in the atmosphere. Condensation is responsible for the formation of clouds and fog. • Groundwater is water in underground aquifers beneath the surface of the earth. • Runoff is the movement of water on the earth’s surface. Most (not all) runoff will eventually find its way to the ocean or evaporate.
The Nitrogen Cycle • All organisms need nitrogen, an important nutrient, to make proteins and nucleic acids. • Most nitrogen is found in the atmosphere (80%) as N2, and most living organisms cannot use atmospheric nitrogen. • All organisms rely on the actions of bacteria that are able to transform nitrogen gas into a usable form. These bacteria have enzymes that can break the atmospheric N2 bonds. Nitrogen atoms are then free to bond with hydrogen atoms to form ammonia (NH3). • Nitrogen fixing bacteria play a key role in the nitrogen cycle. The live in the soil and in the roots of some kinds of plants, such as beans, peas, clover, and alfalfa.. Ammonia can be absorbed by plants from the soil, and is used to make proteins. • Plants can absorb nitrates and ammonia from the soil, but animals cannot. • Animals, including ourselves, obtain nitrogen in the same way we obtain energy – by eating plants and other organisms and then digesting the proteins and nucleic acids. • Decomposers return the nitrogen back to the soil from the remains of dead plants and animals. Nitrogen is also returned from animal and plant waste. • Nitrogen is returned to the Atmosphere through denitrification. Denitrification occurs when anaerobic bacteria break down nitrates and release nitrogen gas back into the atmosphere.
The Phosphorus Cycle • All organisms require phosphorus for synthesizing phospholipids, NADPH, ATP, nucleic acids, and other compounds. • Phosphorus is released from rock and soil through natural processes. • Plants absorb phosphorus from the soil. • Herbivores obtain phosphorus by eating plants, and phosrphorus moves through the food chain. • Eventually organisms will excrete phosphorus as a waste. Decomposition will release phosphorus into the soil. • Plants absorb the phosphorus from the soil and they recycle it within the ecosystem. • Much of the phosphorus from dead organic matter is washed into the water from erosion and leaching. • The phosphorus cycle has no atmospheric component, and is restricted to solid and liquid phases.
