Energy Flows in Ecological Systems Producers and Consumers Green pigments in plants, chlorophylls, absorb light energy from the sun Plants combine carbon dioxide and water, using energy from the sun, into high-energy carbohydrates such as starches, cellulose, and sugars, during photosynthesis Photosynthesis produces oxygen

Energy Flows in Ecological Systems Producers and Consumers Organisms with the ability to capture energy and manufacture matter are known as autotrophs, or producers All other organisms are known as heterotrophs, or consumers There are two kinds of autotrophs: phototrophs and chemoautotrophs Phototrophs get their energy from light, while chemoautotrophs obtain their energy from chemicals in the environment

Energy Flows in Ecological Systems Producers and Consumers Both phototrophs (plants algae, and bacteria) and chemoautotrophs (mainly bacteria, play a critical role in Earth’s biogeochemical cycles – nitrogen cycle, carbon cycle, phosphorous cycle, sulfur cycle, hydrologic cycle, rock cycle) The process of photosynthesis produces billions of tons of biomass (living matter) throughout the world, despite energy degradation and loss

Energy Flow in Ecological Systems Energy and Material Transformations Energy continually flows through systems. Almost all ecosystems are driven by energy from the sun. Energy is converted from a higher form to a lower form as it is utilized Matter (organic and inorganic materials) are cycled and recycled within ecosystems. Matter can be stored for long or short terms.

Energy Flows in Ecological Systems Remember Energy Flows Matter Cycles

Energy Flows in Ecological Systems Producers and Consumers Besides photosynthesis, cellular respiration is another essential energy pathway in organisms carbohydrates are broken down into inorganic molecules, carbon dioxide, and water energy is released and can be used for many purposes by the organism Aerobic organisms must have access to oxygen for cellular respiration to take place, or they will die

Energy Flows in Ecological Systems Food Chains Some of the energy captured by autotrophs is passed on to other organisms, the consumers, through a food chain Each level of the food chain is called a trophic level Herbivores eat producers and are the energy source for higher-level consumers, or carnivores Omnivores, such as humans, raccoons, sea anemones, and cockroaches, can get their energy from multiple trophic levels

Energy Flows in Ecological Systems Food Chains Primary Consumers: eating plants Secondary Consumers: eating herbivores Tertiary Consumers: eating animals that are secondary consumers or higher

A Food Chain

Energy Flows in Ecological Systems Food Chains Decomposer food chains are just as important as grazing food chains These chains are based on dead organic material called detritus, which is high in potential energy but difficult for typical consumer organisms to digest Decomposer food chains play a key role in breaking down plant and animal material into products such as carbon dioxide, water, and inorganic forms of phosphorus and nitrogen and other elements

A Decomposing Food Chain

Energy Flows in Ecological Systems Food Chains Detrital food chains tend to dominate in forest ecosystems, and freshwater ecosystems Grazing food chains dominate in marine ecosystems Producers are photosynthetic phytoplankton Zooplankton graze on the phytoplankton The more species in an ecosystem, the more resilient it is to stress because there are more alternative energy pathways Ecological redundancy, or functional compensation

Energy Flows in Ecological Systems Food Chains Food chains tend to exist as part of complex food webs in which many alternative routes exist for energy to flow through the ecosystem The most complex food webs tend to exist under most favourable conditions for life Ecologists debate whether ecosystems are mostly controlled by predators (top-down control) or by prey populations (bottom-up control)

Food Web

Energy Flows in Ecological Systems Biotic Pyramids The second law of thermodynamics explains how energy flows from trophic level to trophic level, with a loss of usable energy at each transformation Energy efficiency: portion of energy entering system that is transformed into useful form of energy or work In natural food chains may be as low as 1%; 90% lost at each trophic level Some ecosystems have an inverted biomass pyramid (natural grasslands, oceans)

Pyramid of Energy Flow

Energy Flows in Ecological Systems Biotic Pyramids Natural food chains are inefficient because Only 10–20% of biomass is converted to food for next level Assimilated food energy is often low (not all food is digested) Energy is released as heat during cellular respiration The longer the food chain, the less efficient The energy pyramid has important implications for humans In terms of energy efficiency, it would be better to operate as low on the food chain as possible—as primary consumers or vegetarians

Energy Flows in Ecological Systems Productivity The rate at which energy is changed into biomass; usually expressed in kilocalories per square metre /year Gross primary productivity (GPP) is the overall rate of biomass production Cellular respiration (R), must be subtracted from the GPP to reveal the net primary productivity (NPP); the amount of energy available to heterotrophs The most productive ecosystems are wetlands and tropical rainforests; the least are deserts, the Arctic and open Ocean Humans use 40% of all terrestrial NPP for their own use and human population is expected to increase by 40% in the next 50 years

Photosynthetic Efficiency = 3.7 x 104 ------------ x 100 172 x 104 = 2.15% Gross Primary Production is the total energy fixed by producers (autotrophs) during photosynthesis Net Primary Production is the energy stored as biomass (gross production – energy lost as heat in respiration)

NPP = 800 kJ m-2year-1 Photosynthetic efficiency = 1.3% GPP = 24 x106 kJ m-2year-1 NPP = 69.7 x 103 kJ m-2year-1 NPP = 200 kJ m-2year-1 114 x 103 kJ m-2year-1

NPP in Ecologcial Systems

Energy Flows in Ecological Systems Productivity Measurements can also be made of net community productivity (NCP), including heterotrophic and autotrophic respiration Over time, natural systems mature towards maximization of NCP Auxiliary energy flows allow some ecosystems and sites to be very productive For example, tidal energy in an estuary brings in nutrients and helps dissipate wastes

Net Community Productivity

Discussion Questions To Be Answered on your Blog Page Throughout the last hundred years, humans have exerted increasing influence over the environment. How do humans influence the flow of energy through ecosystems, and what are some of the impacts of this? Given what you have learned about the transformation of energy, how might a vegetarian diet reduce the pressures on ecosystems? Why are some of the most productive ecosystems at greatest risk from human disturbances? What are the kinds of human activities that lead to these disturbances?