Ecosystems

Chapter 25

Ecology

• The study of the interaction of organism with one another and with their physical environment

• Understanding the relationship of organisms to their homes

• An individual organism belongs to:

• Population – interbreeding group of the same species in the same area

• Community – an interacting group of many species that inhabit an area

• Ecosystem – community of organisms together (biotic) with the non-living parts of the environment (abiotic).

Organism Ecosystem

Obtains energy Obtains energy

Transforms chemicalsTransforms Chem.

Changes over time Changes over time

Responds to change Responds to change

Reproduces

Recycles

• The boundaries of ecosystems run together

• Biosphere – fixed boundaries– Extends over the whole Earth, from 2 miles

below the surface to the end of the atmosphere

• Ecosystems have three kinds of organisms:– Producers– Consumers– Decomposers

• Producers are autotrophs: organisms that capture energy and produce their own organic molecules.

• Consumers and decomposers are heterotrophs: organisms that consume molecules made by other organisms.

Food chain:

Carnivore (insectivore)

Herbivore

Producer

Trophic levels

• Omnivores eat from several levels of the food chain, and from several food chains – Food web

• Saprophytes - bacteria, fungi and plants that consume dead material

• Scavengers – animals that eat carcasses or large pieces of dead plants

Pyramid of Biomass

Pyramid of Biomass

• The only ecological pyramid that is always upright is the pyramid of energy.

• Each level passes on only about 10% of its energy to the next level – the rest is lost as heat. “Ten Percent Law”

Pyramid of Energy

Biogeochemical cycles

• Ecosystems lose energy, but recycle materials.

• Water cycle:– 97% in oceans– Through evaporation and transpiration of plants

water enters the atmosphere– Condenses and falls as rain – more on

continents that oceans– Excess returns to oceans by rivers and streams

Carbon Cycle• Most of the carbon is in the form of

bicarbonate ion (HCO3-)

• Living organisms• Carbon dioxide in the air• Carbonates → sediments → rock • 12% of carbon dioxide → organic molecules• Decomposers return CO2 to the atmosphere• Fossil fuels – coal, oil, natural gas → CO2

• “Greenhouse effect” → global warming

What can we do with excess carbon dioxide?

• Reduce output!

• Hide it in trees

• Bury it

• Fertilize the ocean

Nitrogen cycle• Nitrogen makes up 78 % of the atmosphere,

but this is molecular nitrogen, bound together with a triple bond which most organisms can’t break

• Plants need fixed nitrogen, in the form of ammonia or nitrates

• Lightening (5-10%), and nitrifying bacteria

• Rhizobium sp. in root nodules

• Other bacteria convert it to molecular nitrogen – denitrification.

Human effects on the nitrogen cycle

• Increasing the amount of fixed nitrogen and its movement through ecosystems.

• Greenhouse gases

• Acid soil and acid rain

• Loss of soil fertility

• “dead zones” in oceans

Phosphorus cycle

• DNA, RNA, ATP and cell membranes

• Rare in nature

• Sink to bottoms of lakes and oceans

• Terrestrial ecosystems are good recyclers of phosphorus

• Limiting nutrient for many organisms – excess causes “blooms”