Chapter 2 Interactions in Ecosystems

Transcription

1 Chapter 2 Interactions in Ecosystems Key Ideas Living things are connected to each other in complex interrelationships. Biotic and abiotic factors are responsible for shaping a community of living things. Nutrients cycle within ecosystems. Energy flows through ecosystems. 2.1 Biotic and Abiotic Factors in Ecosystems Ecology is the study of how organisms interact with each other and with their physical environment. There are different levels of organization that an ecologist can study. The first, and simplest, level of organization that ecologists study, is a single living thing or organism. Ecologists study the behaviours, the functions, and the body structures that an organism has in order to survive in its habitat, or region in which it lives. Groups of organism of the same species that share a habitat (live in the same place), are called a population (second level of organization). All of the different populations in a particular area interact, forming a community (third level of organization). An ecosystem is made up of a community of organisms (biotic) and the nonliving (abiotic) environment. (fourth level of organization). The biosphere is the total area of Earth where living things are found, including the soil, atmosphere, and ocean (fifth level of organization) 1

2 Levels of Organization The living components of the ecosystem are called biotic factors, which include plants, fish, invertebrates, and single-celled organisms, living or dead, and their waste. The non-living components, or abiotic factors, include the physical and chemical components in the environment, temperature, wind, water, sunlight, and oxygen. Biotic and abiotic factors influence each other in an always changing balance called dynamic equilibrium. They may change (up or down), but there is an average. E.g. Victoria may have cooler or hotter than normal summer temperatures, but there is an average summer temperature of approximately 20 C. 2

3 Sometimes one factor, known as a limiting factor, is the most critical factor in determining the types of organisms that can exist in an ecosystem. 2.2 Ecological Roles and Relationships All organisms must take in water, food, and nutrients in order to survive. Nutrients are elements and compounds that organisms need to live and grow. Nutrients include water, gases (typically oxygen or carbon dioxide), vitamins, and minerals as well as the foods we eat that provide fats (long term energy), proteins (structural components and enzymes), and carbohydrates (short term energy). Organisms can be producers or consumers (herbivores, omnivores, carnivores and decomposers). These classifications depend on how the organisms get the nutrients they need to survive (or more simply, how do they eat?) Producers Producers or autotrophs are organisms that make their own food for energy. They are an important food source for other organisms. All food chains can be traced back to a producer at the beginning. There are 2 types of producers 1. Photoautotrophs: Organisms that use the energy from the Sun to produce food, which they then use for energy. This process is called photosynthesis. Phytoplankton is microscopic green algae that photosynthesize. 2. Chemoautrotrophs: Use the energy in chemicals, such as sulphur and methane, to produce food. This process is called chemosynthesis. These organisms live in places with no sun, like the bottom of the ocean floor near hydrothermal vents (hydrogen sulphide) or cold seeps (methane gas leaks out from below the earth s crust). 3

4 Consumers A heterotroph is an organism that consumes other organisms (living things) for energy. Organisms that are heterotrophs are called consumers. There are different types of consumers 1. Herbivores, also called primary consumers, eat producers. Zooplankton are microscopic animals that eat phytoplankton 2. Carnivores are consumers that eat other consumers. 3. Omnivores are consumers that eat both producers and other consumers. 4. Detrivores are consumers that feed on the waste material in an ecosystem, including the bodies of other organisms that have recently died (food is taken into the body digestion occurs waste is eliminated, i.e. pooped out) 5. Decomposers are a special type of consumer that breaks down the complex molecules, found in dead organisms and waste matter, into simpler molecules. They digest materials outside their bodies with enzymes and then absorb them. Decomposers make the nutrients contained in waste and dead matter available to producers (into the soil) through a process called biodegradation. 4

5 Predators Predation occurs when a consumer captures and eats another organism. E.g. When a lion runs down and kills a zebra, or when a spider catches a fly. The relationship between a predator and a prey is very complex and is illustrated in a predator-prey cycle. The cycle tends to be a cyclic rise and fall in both populations. A distinct characteristic of this cycle is the time lag of the predator population. This refers to the delay (in time) as the predator population responds to the changes in the prey population. 2.3 Symbiosis Symbiosis refers to any close relationship between two different species. There are three types of symbiotic relationships: 1. Mutualism is a relationship in which both species in which both species obtain some benefit from the interaction. The rhinoceros and the oxpecker. 2. Commensalism is an interaction in which one organism benefits while the other in unaffected. the clown fish and the sea anemone. 5

6 3. Parasitism occurs when one organism (the parasite) lives and feeds on, or in, the body of another organism (the host). The parasite benefits and the host is harmed. leeches and humans 2.4 Trophic Levels and Energy Flow Nutrients are cycled back into the ecosystem, but energy only moves in one direction through the community from producers to herbivores to carnivores. The energy used up on the processes that keep an organism alive, especially keeping it warm. Trophic level describes the position of the organism in relation to the order of nutrients and energy transfer (flow) in an ecosystem. The largest trophic level is the bottom, because there is more of the original suns energy in plants than in any other organism. Organisms that occupy the same position in a food chain, as primary consumers, secondary consumers, and tertiary consumers, are in the same trophic level. 6

7 Food chains show a single pathway taken by nutrients and energy through the trophic levels. In reality, ecosystems have more complex food webs, which show the different cross-linked food chains. 2.5 Ecological Pyramids Ecologists use three different types of Ecological pyramids to illustrate ecosystems: 1. Pyramid of Energy, which represents how much energy is available in each trophic level, within a given area. On average only 10% of the energy present in one trophic level is passed on to the next level (above it). Most of the energy at any level is used for basic life processes of the organisms at that level. Joules (J) is a measure of energy. 7

8 2. A Pyramid of Numbers represents the actual number of organisms present in each trophic level, in a given area. This pyramid has a large number of SMALL producers Inverted pyramids can exist only when there are a small number of LARGE produces 3. Pyramid of Biomass: This represents the total mass of living things in each trophic level, in a given area. 8

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