Biology Chapter 29Origin and Distribution of Communities

29.1 Ecological SuccessionA series of changes in which different species

appear, only to be replaced later by others.

Biotic and Abiotic factors change over time.

Some communities are more stable than others.

Succession and its CausesSuccession can occur where no life

previously existed or where an established community exists.

Succession is caused by the effect a particular set of organisms has on the environment.

These changes make life more or less suitable to other organisms.

Succession and its CausesExamples:

Soil erosion and runoff into a pondVolcanic eruptionClearing of land by humansChanges in climate and precipitation.

In any succession, the resulting plant life will determine what new species will inhabit the area.

Succession and its CausesDifferent stages of succession will be defined

by different sets of dominant plant species.

Mosses and grasses tend to appear first.

Trees appear and become dominant much later.

Primary SuccessionThis is succession that begins in an area

where there is no life.Begins with very hardy organisms – pioneers

– that can grow under adverse conditions – pioneer stage.

Example: New England ForestLichens produce acid that breaks down rock

into soil.As lichens die, bacteria breaks them down,

adding nutrients.Mosses may grow, then grasses, shrubs, larger

plants, then finally trees.

Primary Succession

Primary SuccessionWhile the changes are occurring in the plant

species, there is an impact on the animal species as well.

The more plant life appears, the more microenvironments will develop. Example, shady area of the forest vs. sunny area in clearing.

The appearance of forest doesn’t end succession. Pine trees give way to deciduous trees.

Climax community – the final, stable (be careful here) stage of a community.

Climax CommunityAre more stable for the most part, but

changes in climate, disease, natural disaster, or human interference can change community temporarily or permanently.

Human intervention may be so severe succession may start over again, though not from the pioneer stage.

From Pond to ForestPonds can be relatively stable, but are not

climax communities. Life span depends on its size and conditions of the environment.

Consider pond surrounded by forest:

Secondary SuccessionOccurs more rapidly than primary

succession, mainly because soil is already in place.

Succession does not always lead to the same climax community. Old abandoned farm places are an example.

Trends in SuccessionAs it occurs, small plants with shorter life

cycles are replaced with larger plants with longer life cycles.

With more producers, the amount of energy trapped by photosynthesis increases.

Diversity increases as it continues.Food chains start simple and become more

complex.More complex food webs means less energy

wasted.Recycling of materials also becomes more

efficient.

29.2 BiomesDifferent biomes determined by

environmental factors:TemperatureHumidityPrecipitation

Factors determined by: altitude, latitude, wind patterns, and topography (surface characteristics).

World’s Biome Distribution

Biomes Precip cm/yearTundra – 12 cmTaiga – 35-40 cmTemperate Forest – 100 cmTropical Rain Forest - >200 cmGrassland – 25-75 cmDesert - <10 cm

OceanSurface of the Earth more than 2/3 water.The kind and number of organisms living in

the oceans far exceeds those on land.Abiotic Factors:

Light – intensity decreases with depth (generally does not get further than 200 meters) Producers live only where there is accessible light.

Abiotic Factors continuedTemperature – it is important, but it does not

vary as much as it does on land. Why?

Example: Mid-Atlantic Ocean, temperatures vary only about 10 degrees Celsius from the top to the bottom.

OrganismsEcologists classify aquatic organisms into 3

main groups:Plankton – organisms that float in the water and

are carried by currents algae, protists, small multicellular animals

Nekton – animals that move freely through the water under their own power fish, whales, shrimp, squid

Benthos – Organisms that live attached to or crawl on the bottom. barnacles, starfish, sponges, clams – most found at

shoreline or close to it in shallow waters

ZonesNeritic Zone – area above the continental

shelfOceanic Zone – region of deeper waters of

the ocean basinLittoral Zone – portion of the neritic zone

closest to shore – most likely to change Influenced by tides, temperature changes, runoff,

salinity changes

Zones

Circulation of WaterIn cold climates, surface water becomes

colder.Cold water is more dense than warm, so it

sinks.Warmer water below rises.Also, wind pushes surface water in a

direction, and water from below fills in.Important because nutrient from decomposed

matter are returned to the surface to promote plant growth.

Circulation of Water

Unique Ocean CommunitiesDeep-sea vents – areas where the bottom

water is warmed by vents from the magma below.

Animals like 3 foot long tube worms, clams, octopus, unusual fish live here

The BiosphereImportant to point out that all land and sea

biomes interact with each other, just as micro communities interact within an ecosystem.

What happens in one region may impact another.Great example is El Nino effects.