Ecology and Ecosystems Basics

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What is Ecology? The scientific study of the interactions between organisms and their environment. Derived from Greek words: oikos (house/dwelling place) and logos (study). Focuses on the distribution and abundance of living organisms and their interactions with each other and their physical surroundings. Who Coined the Term? German zoologist Ernst Haeckel in 1866. Components of Environment Abiotic Components: Non-living physical and chemical factors. Climatic factors: Light, temperature, precipitation, humidity, wind. Edaphic factors: Soil composition, pH, minerals, water content. Topographic factors: Altitude, slope, exposure. Biotic Components: Living organisms. Producers (Autotrophs) Consumers (Heterotrophs) Decomposers (Detritivores) Ecosystem A community of living organisms (biotic components) interacting with their non-living environment (abiotic components) as a functional unit. Term coined by A.G. Tansley in 1935. Can be natural (forest, pond) or artificial (aquarium, crop field). Components of Ecosystem Abiotic Components Inorganic Substances: Water, carbon dioxide, oxygen, nitrogen, calcium, phosphorus, etc. Organic Substances: Proteins, carbohydrates, lipids, humic substances (link biotic and abiotic). Climatic Factors: Temperature, light, rainfall, humidity. Biotic Components Producers (Autotrophs): Organisms that produce their own food, primarily through photosynthesis (e.g., plants, algae). Consumers (Heterotrophs): Organisms that obtain energy by feeding on other organisms. Primary Consumers (Herbivores): Feed on producers (e.g., deer, rabbit). Secondary Consumers (Carnivores/Omnivores): Feed on primary consumers (e.g., snake, fox). Tertiary Consumers (Top Carnivores): Feed on secondary consumers (e.g., eagle, lion). Decomposers (Detritivores): Organisms that break down dead organic matter, returning nutrients to the environment (e.g., bacteria, fungi). Ecological Pyramids Graphical representation of the relationship between different trophic levels in an ecosystem. Pyramid of Numbers Represents the number of individual organisms at each trophic level. Can be upright (grassland), inverted (tree ecosystem), or spindle-shaped (parasitic food chain). Example (Upright): Grass $\rightarrow$ Grasshopper $\rightarrow$ Frog $\rightarrow$ Snake Pyramid of Biomass Represents the total dry weight or biomass of organisms at each trophic level. Usually upright (terrestrial ecosystems), but can be inverted (aquatic ecosystems, where producers like phytoplankton have short lifespans and less biomass than zooplankton). Pyramid of Energy Represents the total amount of energy at each trophic level. Always upright because energy is lost as heat at each transfer to a higher trophic level (10% law). Cannot be inverted. Energy flows unidirectionally from producers to consumers. Nutrient Cycling in Ecosystem The movement of nutrients (elements) through the biotic and abiotic components of an ecosystem. Also known as Biogeochemical Cycles . What are Biogeochemical Cycles? Natural pathways by which essential elements of living matter are circulated. Elements flow between non-living (abiotic) and living (biotic) components. Each cycle has: Reservoir (Nutrient) Pool: Larger, slow-moving, usually abiotic portion (e.g., atmosphere for nitrogen, rocks for phosphorus). Exchange (Cycling) Pool: Smaller, more active portion, rapid exchange between biotic and abiotic. Classified as: Gaseous Cycles: Reservoir is the atmosphere or hydrosphere (e.g., Nitrogen, Oxygen, Carbon, Water). Sedimentary Cycles: Reservoir is Earth's crust (e.g., Iron, Calcium, Phosphorus, Sulfur). Nitrogen Cycle Atmospheric nitrogen ($N_2$) is converted into usable forms by organisms. Key processes: Nitrogen Fixation: $N_2$ to ammonia ($NH_3$) or ammonium ($NH_4^+$) by bacteria (e.g., Rhizobium ), lightning, or industrial processes. Nitrification: Ammonia to nitrites ($NO_2^-$) and then to nitrates ($NO_3^-$) by nitrifying bacteria (e.g., Nitrosomonas , Nitrobacter ). Assimilation: Plants absorb nitrates/ammonia; animals obtain nitrogen by eating plants/other animals. Ammonification: Decomposers convert organic nitrogen from dead organisms and waste products back into ammonia. Denitrification: Nitrates back to atmospheric $N_2$ by denitrifying bacteria (e.g., Pseudomonas ). Simplified Carbon Cycle Carbon moves between the atmosphere, oceans, land, and living organisms. Processes: Photosynthesis: Plants absorb $CO_2$ from atmosphere/water to produce organic compounds. Respiration: Organisms release $CO_2$ into atmosphere/water. Decomposition: Decomposers break down dead organic matter, releasing $CO_2$. Combustion: Burning of fossil fuels and biomass releases $CO_2$. Ocean Absorption/Release: Oceans absorb atmospheric $CO_2$ and release it. Energy Flow Models Single Channel Energy Flow Model / Universal Energy Flow Model Describes energy flow as a simple, linear path from producers to consumers. Energy moves unidirectionally, with significant loss at each trophic level (10% law). Typically depicted as a food chain. Example: Sun $\rightarrow$ Producer $\rightarrow$ Primary Consumer $\rightarrow$ Secondary Consumer $\rightarrow$ Tertiary Consumer. Double Channel Energy Flow Model / Y-Shaped Energy Flow Model Proposed by Odum, this model recognizes two main channels of energy flow within an ecosystem: Grazing Food Chain: Starts with living green plants (producers) and moves to herbivores and then carnivores. Detritus Food Chain: Starts with dead organic matter (detritus) and moves to decomposers (bacteria, fungi) and detritivores. These two chains are interconnected, as waste products and dead organisms from the grazing food chain become part of the detritus food chain. Provides a more realistic representation of energy flow in most ecosystems. Ecological Succession The gradual process of change and development in species composition and community structure over time in an ecosystem. Stages of Secondary Succession Occurs in areas where a pre-existing community has been removed or disturbed, but soil or substrate remains intact (e.g., abandoned farm fields, areas after a forest fire). Faster than primary succession due to existing soil and seeds. Pioneer Species: Often fast-growing, opportunistic species colonize the disturbed area (e.g., annual weeds, grasses). Intermediate Stages: Gradually replaced by perennial herbs, shrubs, and then fast-growing trees (e.g., pines). Climax Community: A stable, mature community that is in equilibrium with its environment. The species composition remains relatively stable until a new disturbance occurs. (e.g., oak-hickory forest).