Ecology – Energy flow through Ecosystems Flow of energy Almost all activities of life are powered by energy from the sun Energy moves through the communities of ecosystems in a continuous one-way flow Nutrients constantly cycle and recycle in a circular flow within ecosystems Energy enters ecosystem through photosynthesis Autotrophs or producers – convert solar energy into organic molecules (food); become the basis of the food chain Heterotrophs or consumers – acquire energy by eating other organisms

Amount of life an ecosystem can support depends on how much solar energy the producers are able to convert into food – primary productivity  Gross primary productivity – total amount of energy converted into the products of photosynthesis  Plants use 10 – 70% of their gross productivity for their own energy needs  Net primary productivity – amount of energy stored (what is left after the plant’s own cellular respiration) that is available to consumers  Measured in units of energy (calories) stored per unit area in a given period  Also measured in biomass – dry weight of organic material  Productivity of an ecosystem is influenced by many factors (amount of sun and water, temperature)

Trophic Levels Ecological niche – each species occupies it’s own unique niche which encompasses all aspects of it’s way of life – includes: Organism’s physical home or habitat Physical environmental factors necessary for survival (range of temp it can withstand, pH of soil, amount of moisture it needs, etc) What it eats and what it is eaten by – trophic level Organism’s role in ecosystem – it’s “occupation”

Trophic levels represent the levels through which energy flows as it passes from the producers to the consumers in an ecosystem “feeding level” Relationship between what an organism eats and what it is eaten by 1.Producers – autotrophic organisms that make food 2.Consumers – heterotrophs – from several trophic levels: a.Primary consumers – herbivores – eat producers b.Secondary consumers – eat primary consumers (carnivores) eat other consumers c.Top carnivore – top of food chain d.Consumers may eat at different levels e.Omnivores – eat producers and consumers f.Scavengers – consumers that eat organisms recently killed by other consumers (crows and hyenas)

3.Detritus feeders and decomposers – help decompose and return nutrients to atmosphere, soil and water  Detritus feeders – small animals and protists that break down molted exoskeletons, fallen leaves, dead bodies (ex. Earthworms, mites, nematodes, pillbugs)  Decomposers (saprophytes) – fungi and bacteria

Trophic levels can be studied by looking at food chains – each step in a food chain represents a trophic level

Natural communities have food webs rather than simple food chains – all of the possible food chains intertwined

Transfer of energy through trophic levels is inefficient Each level only passes approx 10% of the energy on to the next level (10% Law) – Why?  Some of the energy is used for growth and maintenance of organism itself  Some of the energy is lost as heat during metabolic processes  Some of the energy is locked in chemical bonds that consumer cannot break (cellulose) Less and less energy is available to subsequent levels

Transfer between trophic levels can be studied through ecological pyramids 1.Pyramid of energy – shows maximum energy (productivity) at the base and steadily diminishing amounts at higher levels

2.Pyramid of Numbers – number of individuals at each trophic level  Generally decreases as energy decreases moving up each level

Pyramid of Biomass – shows amount of biomass at each trophic level

Ecology – Human Impact Biological magnification – process by which toxic substances accumulate in increasingly high concentrations in progressively higher trophic levels – ex. DDT is dangerous because:  Decomposers cannot readily break it down into harmless substances (not biodegradable)  It is fat soluble (not water soluble) and tends to accumulate in the fatty tissues of animals  Because of inefficient energy transfer between trophic levels, herbivores eat large quantities of plant material, carnivores eat larger amounts of herbivores, etc. leading to biological magnification  Higher trophic levels (top carnivores) have highest concentrations in their tissues  DDT continues to accumulate in predator’s body through out it’s life

As humans have moved toward using fossil fuels for energy, acid rain and global warming have become major global issues Acid rain – the US discharges 30 million tons of sulfur dioxide into the atmosphere each year 90% of sulfur dioxide in atmosphere comes from human industrial activities Nitrogen oxide is also released from vehicles, power plants and industry

Acid rain or acid deposition (deposition of both wet or dry acid) Sulfur dioxide and nitrogen oxide combines with water vapor in the atmosphere to form sulfuric acid and nitric acid Acid often falls hundreds or thousands of miles away (pollutants carried by the wind) dissolved in rain (snow, fog) or as microscopic dry particles Acid eats away statues, buildings, damages trees and crops, kills life in lakes Lakes become too acid to support life Acid rain washes away essential nutrients and kills microbes that recycle nutrients Toxic metals (aluminum, lead, mercury, cadmium) dissolve easier in acid rain and run into lakes and streams – accumulates in fish leading to biological magnification

Global Warming As we burn fossil fuels, we release increasing amounts of CO 2 into the atmosphere – since 1850, CO 2 in the atmosphere has increased more than 25%  Deforestation (cutting of tens of millions of acres of forest each year) also increases CO 2 in atmosphere  Most in tropics, rain forests are burned adding CO 2 to atmosphere

Carbon Cycle

CO 2 has the ability to trap heat – acts very similar to the glass in a greenhouse – allows solar energy in and absorbs and holds the energy as heat – greenhouse effect Effect is compounded by other greenhouse gases (methane, chlorofluorocarbons or CFCs, water vapor and nitrous oxide) Greenhouse effect is a natural process, allows life on earth

Human activities have amplified the greenhouse effect leading to global warming each decade is showing record high average temps that parallel the rise in atmospheric CO 2 and methane levels

Scientists predict a rise of 1.5 o to 4.5 o C in average world air temps by end of 21 st century Last ice age was only 5 o C lower than present but that increase led to ocean levels rising and moving inland by about 100 miles and great changes in species composition

Consequences of Global Warming Sea levels will rise as polar ice caps and glaciers melt – flood coastal cities and wetlands (breeding grounds for many species of bird, fish, shrimp, crabs – may become extinct) Shift in global distribution of temps and rainfall – possibly leading to disruption of agriculture May have profound affect on distribution of tree species – may wipe out hardwood forests of eastern US May increase tropical disease-carrying organisms like mosquitoes Global warming video

The Precautionary Principle Says that preventative action should be taken now to reduce carbon emissions and greenhouse gas production before it is too late Those who wish to continue producing excess greenhouse gases should prove that there are no harmful effects before continuing Some people argue against measures to combat global warming because there is no absolute proof that the greenhouse effect is harmful Counter argument is that by the time there is proof, there will have already been catastrophic consequences to the environment