Chapter 55 Ecosystems and Restoration Ecology An ecosystem is the sum of all the organisms living in a given area and the abiotic factors with which they interact Energy enters most ecosystems as sunlight which is converted into chemical energy by autotrophs passed onto heterotrophs in the form of organic molecules and dissipated as heat Energy can return via metabolism of plants and animals and decomposition 55 1 PHYSICAL LAWS GOVERN ENERGY FLOW CONSERVATION OF ENERGY The first law of thermodynamics states that energy cannot be created or destroyed but only transferred or transformed Plants and photosynthetic organisms convert solar energy into chemical energy but the amount does not change The Second law of thermodynamics states that every exchange of energy increases the entropy of the universe and that energy are inefficient energy lost as heat CONSERVATION OF MASS Matter can also not be created or destroyed Therefore we can measure chemical element use in ecosystems Chemical elements are continually recycled in a community Elements can be lost or gained in a particular ecosystem but not on a global scale A high consumption of elements will limit resources and limit production in that ecosystem ENERGY MASS AND TROPHIC LEVELS Primary Producers form the trophic level that support all other trophic levels Most use photosynthesis to generate chemical energy sugars and organic compounds for consumers Heterotrophs form the level above the primary producers Carnivores that eat herbivores are SECONDARY CONSUMERS while carnivores that eat other carnivores are TERTIAIARY CONSUMERS DETRITIVORES decomposers recycle detritus organic material that is nonliving and are very important in returning organic materials from all trophic levels into inorganic compounds for primary producers 55 2 ENERGY AND OTHER LIMITING FACTORS CONTROL PRIMARY PRODUCTION IN ECOSYSTEMS ECOSYSTEM ENERGY BUDGETS In most ecosystems primary producers use light energy to synthesize energy rich organic molecules and consumers acquire their organic molecules later via food webs Therefore the amount of photosynthetic production sets the spending limit for the ecosystems entire energy budget The Global Energy Budget Although he sun producers a lot of energy only a few amount gets used because only a small fraction of sunlight that reaches the Earth s surface is actually used in photosynthesis because radiation mostly strikes objects that don t photosynthesize Furthermore only a few wavelengths are absorbed by the photosynthetic pigments Therefore only about 1 of sunlight gets converted into chemical energy Gross and Net Production GROSS PRIMARY PRODUCTION GPP is known as the amount of energy from light or chemicals in chemoautotrophs that gets converted to the chemical energy of organic molecules per unit time NET PRIMARY PRODUCTION NPP is the amount of primary production generated minus the energy used by the primary producers Usually NPP is about of GPP Net primary production can be expresses as energy per unit area per unit time J m 2 yr or as biomass mass of vegetation added per unit area per unit time NPP should not be confused with total biomass STANDING CROP NET ECOSYSTEM PRODUCTION NEP is a measure of the total biomass accumulation during time and is calculated using primary production minus total respiration of all organisms in an ecosystem NEP is useful because it tracks the flow of CO2 or O2 into and out of the ecosystem PRIMARY PRODUCTION IN AQUATIC ECOSYSTEMS Light and nutrients are very important in controlling primary production Light Limitation Because solar radiation drives photosynthesis light would be a key variable in controlling primary production in oceans Furthermore because the suns rays is more direct at the equator one would expect the case that production should increase from the poles down to the equator However that is not the case due to Nutrient limitation Nutrient Limitation Nutrients limit primary production in most oceans and lakes more than light Nitrogen or Phosphorus is usually the limiting nutrients in most environments Concentrations of these nutrients are low in the trophic zone because they are rapidly taken up by the phytoplankton and because detritus sink Not areas that are nutrient rich have numerous phytoplanktons The Sargasso Sea has on of the highest nutrient levels but iron blown from the land limits primary production Areas of upwelling have high levels of primary production because it brings nutrients from the bottom of the sea to the top EUTROTROPHICATION occurs when an added nutrient fertilizer runoff stimulates the growth of primary producers When the primary producers die and the detritivores decompose them depleting the water of oxygen PRIMARY PRODUCTION IN TERRESTRIAL ECOSYSTEMS At regional and global scales temperature and moisture are the main factors controlling primary production Climate variables of moisture and temperature are very useful for predicting NPP in terrestrial eco systems EVOTRANSPIRATION the amount of water that evaporates shows how much water an environment has is very useful in predicting primary production as well Nutrient Limitations and Adaptations That Reduce Them Nitrogen limits plant growth on a global scale Phosphorus is also very important and is low in soils of deserts or basic soils where some phosphate precipitates and becomes unavailable to plants Adding a non limiting nutrient will have no effect on growth Adaptions have evolved to increase nutrient uptake and one of them is the symbiosis between plant roots and fixing bacteria Mycorrhizal association between plant roots and fungi are very important in supplying limiting elements Plant roots also have root hairs and some release enzymes to increase availability of elements 55 3 ENERGY TRANSFER BETWEEN TROPHIC LEVELS IS TYPICALLY ONLY 10 EFFICIENT Secondary Production Growth of the ecosystem is the amount of chemical energy in consumers food that is converted to their own new biomass during a given period Herbivores only eat a small fraction of plant material and can digest only a small portion of it PRODUCTION EFFICIENCY When a caterpillar feeds on a leaf only about 33J of the 200J is used for growth The Caterpillar stores some the energy for cellular respiration and passes the rest in feces Energy in the feces is given off as heat as it is decomposed and the energy used for the caterpillar s respiration is lost from the ecosystem as heat THEREFORE ENERGY FLOWS THROUGH AN ECOSYTEM