Chapter 18

Intro to Ecology

18.1 – INTRO TO ECOLOGY

What is ecology?

• the study of interactions between organisms and the living and nonliving components of their environment

What does ecology involve?

• Collecting info about organisms and their environments

• Observing/measuring interactions between organisms

• Looking for patterns among organisms and their environments and explaining

Interdependence• A key theme in biology• Refers to interconnectedness of

organisms with each other and with the nonliving parts of their environment

• Any change in the environment can affect the network of interactions and organisms seemingly far removed from the change

Levels of OrganizationFrom largest to smallest:•Biosphere•(Biomes)•Ecosystem•Community•Population•Organism

•These levels of organization are considered external as opposed to the internal levels that we learned earlier.

Recall internal levels of organization beginning with atoms:

atoms

biological molecules

cell organelles

cells

tissues

organs

organ systems

organism

Remember that these internal levels exist only in multicellular organisms!

**Internal organization for unicellular organisms stops here

Ecological levels of organization defined:

• organism – individual living thing• population – group of organisms of the

same species living in the same area• community – all of the interacting organisms

living in an area• ecosystem – living (biotic) and nonliving

(abiotic) things found in a particular area• biosphere – the thin volume of Earth

(extending below the surface and into the atmosphere) that supports life

18.2 – ECOLOGY OF ORGANISMS

Ecosystem Components:

Biotic Abiotic

Definition: Living parts Nonliving (physical and chemical) parts

Examples: All the organisms: plants, animals, bacteria, fungi, protists

Temperature, pH, oxygen, nitrogen, humidity, salinity, sunlight, precipitation, etc.

Ecosystem Components:Aquatic vs. Terrestrial

Biotic Abiotic

Aquatic ecosystem Algae and other protists, plants, animals, bacteria

Water temp., depth, turbidity, salinity, still vs. current or waves, pH, sunlight, oxygen, etc.

Terrestrial ecosystem Protists, fungi, plants, animals, bacteria

Temp., sunlight, humidity, precipitation, soil minerals, etc.

18.3 – ENERGY TRANSFER

Why do organisms need energy?

• To carry out life functions like:– growth– repair– maintenance– movement– reproduction

• Energy flows in an ecosystem.

• The amount of energy that an ecosystem receives and the amount that’s transferred from organism to organism affects the ecosystem’s structure.

Within an ecosystem there are producers and consumers

Producers Consumers

Definition Capture energy and make organic molecules

Eat other organisms or organic wastes for energy

Groups Photosynthetic: capture sunlight to make org. molecules

Chemosynthetic: use inorganic molecules to make org. molecules

Herbivores: eat producers

Carnivores: eat other consumers

Omnivores: eat producers and consumers

Detritivores: feed on wastes like dead organisms, fallen leaves, animal waste, etc.

Decomposers: detritivores that cause decay by breaking down complex molecules into simpler ones

Producers Consumers

Exp. PS: Plants, some protists, some bacteria

CS: Some bacteria

H: Antelope

C: Lions, cobras, praying mantises

O: Grizzly bear

Det.: Vulture

Dec: Bacteria and fungi

Biomass

• Organic materials produced in an ecosystem

• Producers add to the biomass by making organic molecules!

Decomposers

• “nature’s recyclers”• cause decay; make nutrients trapped

in waste available again to autotrophs

Energy Flow

• Trophic level – organism’s position in a sequence of energy transfers– 1st level = producers– 2nd level = herbivores– 3rd level = primary consumers

– 4th level = secondary consumers– 5th level = tertiary consumers

Food chains vs. food webs

• Food chains – show a single pathway of energy flow

• Single food chains are rare in nature

• Food webs – interrelated food chains in an ecosystem

Energy transferHow much energy is available for each trophic

level?

• On average, 10 percent of the total energy consumed in one trophic level is incorporated into the organisms in the next

• Why only 10%?! Organisms:– escape being eaten– die and become food for decomposers– have energy stored in places that can’t be used

(like antlers)– need/use energy themselves– some energy is also lost in metabolism (heat) –

remember that cell respiration is only 39% efficient!

Produce chemical energy from sunlight

Eat producers

Eat 1° consumers

Eat 2° consumers

Eat 3° consumers

Limitations of trophic levels

• Ecosystems rarely have more than a few trophic levels– Since only 10 percent is available to next

level, there’s not enough energy in the top level to support more levels

– Organisms at lowest level usually much more abundant; more diversity at lowest level; high levels contain less energy and can support fewer individuals

At the lowest level, there are a lot of producers, so the block is very wide.

This energy pyramid diagram represents energy flow through four trophic levels.

Only 10% of the energy is available to the next level, so there are less organisms that can exist at the level; there is less diversity. The block is smaller.

This continues up the pyramid resulting in smaller and smaller blocks – fewer organisms being supported.

Pyramids may be shaped a little differently depending on the ecosystem, but always follow this basic pattern

18.4 – ECOSYSTEM RECYCLING

3 Biogeochemical Cycles:

• Water cycle• Carbon cycle (carbon/oxygen cycle)• Nitrogen cycle

• These cycles are pathways of these materials from the environment, into living things, and back into the environment.

Water cycle includes:

• Evaporation - water enters the atmosphere from oceans, lakes, streams, etc.

• Transpiration - water enters atmosphere by evaporating out of plant leaves when stomata open

• Condensation – vapor to liquid• Precipitation – falling forms of water

• Runoff – from land into water• Percolation – water filters down through soil/rocks• Groundwater – water beneath the surface in rock

formations or spaces

Carbon cycle

• Cellular respiration – releases carbon into atmosphere (CO2)

• Photosynthesis * - uses carbon • Decomposition – releases carbon

– Fossil fuels – formed from the remains of dead organisms

• Combustion – burning of fossil fuels and other organic materials; releases carbon

Nitrogen cycle

• All organisms need nitrogen to make– Proteins (amine group in amino acids has

N)– Nucleic acids (nitrogenous bases A, T, C,

G, and U have nitrogen!)• 78% of the atmosphere is nitrogen gas

(N2) BUT plants can’t use it in that form...

• It must be converted into nitrates (NO3)

• The process of converting nitrogen gas into nitrates is nitrogen fixation

• Nitrogen-fixing bacteria convert nitrogen gas into a usable form– Live in soil – Live in nodules on roots of some plants

like beans, peas, clover, and alfalfa

Parts of the nitrogen cycle

• Nitrogen fixation – converting nitrogen gas into nitrates

• Ammonification – formation of ammonia (NH3) and ammonium (NH4) in the soil from decomposition of dead organisms

• Nitrification – performed by soil bacteria; uptake of ammonium and its oxidation into nitrites (NO2

-) and nitrates (NO3

-)– Erosion of nitrate rich rocks also releases

nitrates into the ecosystem– Plants use nitrates! Yay! They can

absorb them from the soil. Animals cannot. Boo! So how do animals get nitrogen?

• Assimilation – uptake of nitrates in soil by plants

• Denitrification – performed by anaerobic bacteria; breakdown of nitrates that releases nitrogen gas back into the atmosphere

1. Nitrogen fixing from air to soil.

2. Nitrogen in soil gets assimilated into living things.

3. Living things excrete nitrogen and die, nitrogen goes back into soil.

4. Bacteria convert soil Nitrogen back into atmosphere.

Summary of Nitrogen cycle