Download Biology Chapter 29

Origin and Distribution of Communities
29.1 Ecological Succession
 A 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 Causes
 Succession 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 Causes
 Examples:
 Soil erosion and runoff into a pond
 Volcanic eruption
 Clearing of land by humans
 Changes in climate and precipitation.
 In any succession, the resulting plant life will determine
what new species will inhabit the area.
Succession and its Causes
 Different 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 Succession
 This 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 Forest
 Lichens 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 Succession
 While 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 Community
 Are 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 Forest
 Ponds 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 Succession
 Occurs 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 Succession
 As it occurs, small plants with shorter life cycles are
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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 Biomes
 Different biomes determined by environmental
factors:
 Temperature
 Humidity
 Precipitation
Factors determined by: altitude, latitude, wind patterns,
and topography (surface characteristics).
World’s Biome Distribution
Biomes Precip cm/year
 Tundra – 12 cm
 Taiga – 35-40 cm
 Temperate Forest – 100 cm
 Tropical Rain Forest - >200 cm
 Grassland – 25-75 cm
 Desert - <10 cm
Ocean
 Surface 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 continued
 Temperature – 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.
Organisms
 Ecologists 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
Zones
 Neritic Zone – area above the continental shelf
 Oceanic Zone – region of deeper waters of the ocean
basin
 Littoral Zone – portion of the neritic zone closest to
shore – most likely to change

Influenced by tides, temperature changes, runoff, salinity
changes
Zones
Circulation of Water
 In 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 Communities
 Deep-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 Biosphere
 Important 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.