THINGS TO KNOW FROM CHAPTER 54: ECOSYSTEMS Introduction Ecosystem: all organisms living in a community and the abiotic factors they interact with Ecosystems dynamics: o Energy flow: sunlight, autotrophs, heterotrophs, heat cannot be recycled energy flows through ecosystems o Chemical cycling: carbon, nitrogen, etc. matter cycles within the ecosystem 54.1: Energy Flow and Chemical Cycling Ecosystems are transformers of energy and processors of matter Ecosystems and Physical Laws o Energy cannot be created or destroyed; just transformed o Energy conversion is not completely efficient; heat is lost Trophic Relationships o Primary producers support all others (autotrophs mainly photosynthetic plants, algae and prokaryotes; also chemosynthetic autotrophs) o Heterotrophs: primary consumers: herbivores secondary consumers: carnivores that eat herbivores tertiary consumers: carnivores that eat carnivores o Detritivores or decomposers Decomposition o Prokaryotes, fungi and animals o Link primary producers and consumers in ecosystem o Make chemical elements available and bring back to soil, air, water o Mainly prokaryotes and fungi 54.2: Primary Production is Limited by Physical and Chemical Factors Primary Production: amount of light energy converted to chemical energy by autotrophs in a given time period Ecosystem Energy Budgets: o Photosynthetic production sets energy budget for ecosystem o Global Energy Budget: Only a small fraction of radiation strikes autotrophs and only small amount is usable for photosynthesis (1%) o Gross and Net Primary Productivity: GPP: Gross Primary Production; total primary production in an ecosystem; light energy converted into chemical energy by photosynthesis per unit time; some molecules are used by the plant NPP: Net Primary Production: GPP – energy used by primary producers for respiration; available energy in the ecosystem NPP is not total biomass of photosynthetic autotrophs (standing crop); NPP = new biomass at any given time Tropical rainforests are the most productive terrestrial ecosystems; estuaries and coral reefs are productive but cover a small area; oceans are large but NPP per unit area is low What limits primary production in aquatic ecosystems (marine and freshwater) o Light Limitation: only reach photic zone; not just light limits or there would be gradient along equator o Nutrient Limitation: Limiting nutrient must be added for production in a particular area; Nitrogen or Phosphorus N or P is low in photic zone and more abundant in deeper water where it is too dark for photosynthesis Iron also is a limiting nutrient Upwelling areas: nutrient rich deep waters circulate to ocean surface have high primary production Also common in freshwater lakes: eutrophication (cyanobacteria dominate); lead to loss of fishes (phosphorus) Primary Production in Terrestrial & Wetland Ecosystems o Temperature and moisture are key factors in controlling primary production in wetland and terrestrial ecosystems o Tropical: warm and wet o Actual evapotranspiration o Locally: minerals in soil can be limiting factors: N and P 54.3: Energy Transfer between Trophic Levels is Usually < 20% Secondary production: amount of chemical energy in consumer’s food that is converted to own biomass during a given time period Much of primary production is not used: don’t eat all; don’t digest all Production Efficiency: o Caterpillar uses 1/6 for secondary production (growth) also uses energy for cellular respiration (lost as heat), feces (detritivores) o Only chemical energy stored as biomass is available for secondary consumers o Net Secondary Production/Assimilation of Primary Production NSP: energy stored as biomass Assimilation: energy taken in and used for growth, respiration, and reproduction o Production Efficiency: Not used for respiration o Birds & Mammals are 1- 3 % (endotherms); Insects are 40% Trophic Efficiency and Ecological Pyramids o Percentage of production transferred from one trophic level to the next o Less than production efficiencies (energy lost in respiration, contained in feces, energy not consumed by trophic level) o Range 5 – 20%; 80 – 95% energy is not transferred to next trophic level o Pyramids of production o Pyramids of biomass (phytoplankton: usually decreases but sometimes standing crop supports larger group of consumers; production would be bottom heavy) o Pyramids of numbers: loss of energy limits biomass of top level carnivores; 4 – 5 trophic levels are maximum; predators are usually larger o Eating meat is inefficient use of energy flow; could feed more with only plant material Green World Hypothesis: o Terrestrial herbivores are held in check and consume little plant biomass o Herbivores consumer 17% of NPP of plants o Things that keep herbivores in check: Plants have defenses against herbivores Nutrients limit herbivores; not energy supply Abiotic factors limit herbivores Intraspecific competition can limit herbivore numbers Interspecific interactions keep densities in check 54.4: Biological and Geochemical Processes move Nutrients between Organic and Inorganic Parts of the Ecosystem Chemical Elements are limited; need to be recycled Biogeochemical cycles: nutrients circuit in biotic and abiotic General Model of Chemical Cycling: o Global and Local o Study Picture 54.16 on page 1195 Organic or inorganic materials Are materials directly available for use by organisms Biogeochemical Cycles (study pages 1196 – 1197) o Water Cycle o Carbon Cycle o Nitrogen Cycle: Nitrogen fixation: conversion of Nitrogen gas by bacteria to forms that can be used Ammonification: decomposes organic nitrogen to ammonium Nitrification: Ammonium is converted to nitrate by nitrifying bacteria Denitrification: anaerobic conditions; denitrifying bacteria use nitrate instead of oxygen and release Nitrogen gas o Phosphorus Cycle Decomposition and Nutrient Cycling Rates: relates to evapotranspiration Vegetation and Nutrient Cycling 54.5: Human Population is Disrupting Chemical Cycles Nutrient Enrichment: o Agriculture and Nitrogen Cycling o Contamination of Aquatic Ecosystems: cultural eutrophication Acid Precipitation: Toxins: Biological Magnification (Mercury in Big Fishes) Atmospheric Carbon Dioxide: Greenhouse Effect and Global Warming Depleting Atmospheric Ozone o