EcologyLesson 9.4

Lesson Objectives

• Outline primary and secondary succession, and define climax community.• Define biogeochemical cycles.• Describe the water cycle and its processes.• Give an overview of the carbon cycle.• Outline the steps of the nitrogen cycle.• Understand the phosphorus cycle.• Describe the ecological importance of the oxygen cycle.

ECOLOGICAL SUCCESSION• Process by which a whole community of populations changes through

time; usually occurs after a disturbance that creates unoccupied areas for colonization. Succession happens in two different ways:• Primary succession• Secondary succession

• First new colony are called the pioneer species

Primary Succession

• Occurs in an area that has never been colonized before• Lava can flow from a volcano and harden into rock• A glacier can retreat and leave behind bare rock• A landslide can uncover a large area of bare rock

Primary Succession

Secondary Succession• Occurs in formerly inhabited area that was disturbed

by fire, flood, or human action• Happens more rapidly than primary succession

Climax Communities• Fully grown stable community with much biodiversity

• Today Ecologists know that communities do not sustain climax status but are constantly going through changes

BIOGEOCHEMICAL CYCLESbio- biotic componentsgeo- geological and abiotic components

WATER CYCLE

Evaporation, Sublimation, and TranspirationSun drives the water cycle.

Heats oceans, lakes, and other bodies ofwater.Heated water evaporates. EvaporationHeats ice and snow.Heated ice and snow turns into water vapor. SublimationHeat causes plants to release water through their stomata

(pores in leaves) Transpiration

Condensation and Precipitation Rising air currents carry water from evaporation, sublimation, and transpiration into the atmosphere….eventually forming CLOUDS

Groundwater and RunoffRain falls on land and soaks into ground infiltrating and becomes groundwaterOr rain falls on land and flowsover it Runoff ends up in bodies of water

CARBON CYCLECarbon in rocks is dissolved by water and ends up in oceansOther carbon from burned fossil fuels or their by-products

ends up in the atmosphere or biosphere

Note: fossil fuels are formed from theremains of deadorganisms

Carbon in the Atmosphere

• Living organisms release carbon dioxide as a byproduct of cellular respiration. • Carbon dioxide is given off when dead organisms and other

organic materials decompose. • Burning organic material, such as fossil fuels, releases carbon

dioxide. • When volcanoes erupt, they give off carbon dioxide that is

stored in the mantle. • Carbon dioxide is released when limestone is heated during

the production of cement. • Ocean water releases dissolved carbon dioxide into the

atmosphere when water temperature rises. • From methane gases released from landfills

Carbon in the Ocean Water Most comes from atmospheric carbon dioxide that

dissolves in ocean water thus forming carbonic acid. (in cooler water)• The process is reversible in warmer water changing

carbonic acid to bicarbonate ions• Bicarbonate ions are also deposited into oceans from

runoff

Carbonic acid H2CO3

Bicarbonate ions HCO3-

Carbon in the Biosphere organic pathway• Photosynthetic algae and bacteria take up bicarbonate ions in the

ocean use it to synthesize organic compounds• Terrestrial autotrophs remove carbon dioxide from the atmosphere to

synthesize organic compounds• Both recycle it back through a process called cellular respiration• Decomposers release carbon dioxide when they consume dead

organisms• They rates of exchange are about equal

Carbon in Rocks and Sediments(geological pathway)

• Long, slow process through rock formation, subduction, and volcanism• In oceans begins as sedimentary rock; pressure of additional layers

forms the rock

NITROGEN CYCLE• Most nitrogen is stored in the atmosphere (78% nitrogen

gas)• Nitrogen moves through abiotic and biotic components of

ecosystems

Absorption of Nitrogen• Plants and producers make nitrogen-containing

organic compounds (chlorophyll, proteins, nucleic acids)• Plants absorb nitrogen from the soil through their root hairs in the from of nitrate ions• Nitrogen is changed in the soil through nitrogen fixation into nitrate ions

Nitrate ions NO3-

Nitrogen Fixation Nitrogen-fixing bacteria live in soil or in the root nodules of legumes

In aquatic system, some cyanobacteria fix nitrogen

Nitrogen gas in the atmosphere can also be fixed by lightning

Some nitrogen is converted into fertilizer by humans

Ammonification and Nitrification

• Decomposers break down organic remains and release nitrogen in the form of ammonium ions• Ammonification

• Certain soil bacteria convert the ammonium ions into nitrites. Others convert the nitrites into nitrates that

plants can absorb• Nitrification

Ammonium ions NH4-

Nitrites NO2-

Nitrates NO3

Denitrification and the Anammox Reaction

• Denitrifying bacteria in soil convert some nitrates back to nitrogen gas NO2• Denitrification

• In aquatic systems, bacteria in the water convert ammonium and

nitrite ions to water and nitrogen gas

- Anammox Reaction

Oxygen Cycle• Movement of oxygen through the atmosphere,

biosphere, and the lithosphere.

Oxygen and the Hydrosphere

• Failures in this type of movement = development of hypoxic (low oxygen) zones or dead zones• Cause: excessive nutrient pollution

from human activities that lead to depletion of oxygen required to sustain marine life

Oxygen and the Biosphere/Atmosphere • Free oxygen in the biosphere (0.01%) and atmosphere (0.36%). • The main source of atmospheric free oxygen is photosynthesis.

Photosynthesizing organisms include the plant life of the land areas as well as the oceans. • Additional source of atmospheric free oxygen comes from photolysis

Oxygen and the Lithosphere

• Largest reservoir of Earth's oxygen is within the silicate and oxide minerals of the crust and mantle (99.5%).

Lesson Summary• Ecological succession is the constant replacement of one community by another.

• Primary succession occurs in an area that has never before been colonized by plants and animals, while secondary succession occurs in an established area that was disturbed.

• Secondary succession is the type of succession that happens after something destroys the habitat, such as a flood or other natural disaster.

• Climax communities is the end result of ecological succession.

• Chemical elements and water are recycled through biogeochemical cycles. The cycles include both biotic and abiotic parts of ecosystems.

• The water cycle takes place on, above, and below Earth’s surface. In the cycle, water occurs as water vapor, liquid water, and ice. Many processes are involved as water changes state in the cycle. The atmosphere is an exchange pool for water. Ice masses, aquifers, and the deep ocean are water reservoirs.

• In the carbon cycle, carbon passes among sedimentary rocks, fossil fuel deposits, the ocean, the atmosphere, and living things. Carbon cycles quickly between organisms and the atmosphere. It cycles far more slowly through geological processes.

• The nitrogen cycle moves nitrogen back and forth between the atmosphere and organisms. Bacteria change nitrogen gas from the atmosphere to nitrogen compounds that plants can absorb. Other bacteria change nitrogen compounds back to nitrogen gas, which re-enters the atmosphere.

Lesson Summary

• The phosphorous cycle moves from inorganic sources such as rock and soil to water to terrestrial and aquatic organisms. Unlike the other biogeochemical cycles, phosphorous does not exist in the atmosphere as a gas.• In the oxygen cycle, oxygen is recycled between the atmosphere,

biosphere, and lithosphere. While 99.5% of oxygen is tied up in silicate and oxide minerals and unavailable to organisms, the primary source of oxygen in the atmosphere is photosynthesis. Respiration and decomposition in organisms removes oxygen from the atmosphere.