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).

OrganismEcosystemObtains energy Transforms chemicalsTransforms Chem.Changes over timeResponds 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

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 (HCO 3 - ) Living organisms Carbon dioxide in the air Carbonates → sediments → rock 12% of carbon dioxide → organic molecules Decomposers return CO 2 to the atmosphere Fossil fuels – coal, oil, natural gas → CO 2 “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”