3.1 Community Ecology
Vocabulary List
community
limiting factor
tolerance
ecological succession
primary succession
climax community
secondary succession
BIOLOGICAL COMMUNITY is a group of interacting populations that occupy
the same area at the same time.
There are many factors restrict the growth of a population in
communities
What factors limit populations in communities?
Any abiotic factor or biotic factor that restricts the numbers, reproduction,
or distribution of organisms
 Factors that limit one species might enable another to thrive.
(Water is a limiting factor and organisms that need less water can survive in a
desert community.
Organisms have a range of tolerance for each limiting factor
that they encounter
For any factor, there is an upper limit and a lower limit that defines the
conditions in which an organism can live.
Tolerance is the ability of any organism to survive when exposed to abiotic or
biotic factors
Organisms have a range of tolerance for each limiting factor
that they encounter

Steelhead trout live in cool, clear coastal rivers and streams with the ideal
range of water temperature for steelhead trout is between 13˚C and 21˚C
Organisms have a range of tolerance for each limiting factor
that they encounter


However, steelhead trout can also survive water temperatures lower than
13˚C (9˚C) and more than 21˚C (up to 25˚C)
At these temperatures, steelhead trout experience physiological stress =
inability to grow or reproduce, but they still survive
Organisms have a range of tolerance for each limiting factor
that they encounter


Beyond the upper tolerance limit of 25˚C and the lower tolerance limit of
9˚C, there are no steelhead trout, as they would die living there
Therefore, water temperature is a limiting factor for steelhead when
water temperature is outside the range of tolerance
Ecological Succession


Ecosystems constantly change (a tree falling, a fire…)
The process of one community replacing another as a result of changing
abiotic and biotic factors is called Ecological Succession
Primary Succession


Is the establishment of a community in an area of bare rock that does not
have topsoil
For example, retreating glacier or volcanic eruptions can alter an ecosystem
Primary Succession
ONLY ORGANISMS PRESENT:
• Bacteria
• Fungal spores or
• Pollen grains
FIRST TO GROW (The first organisms to appear = pioneer species):
• Lichens begin to grow on the rock first
• Mosses
• Algae
Pioneer Species Help Create Soil


Pioneer species physically and chemically break down rocks.
As pioneer species die, their decaying organic materials mix with small
pieces of rock  the first stage of soil development
Pioneer Species Help Create Soil


Small weedy plants begin to grow in the soil, and as they die, they add to
the soil
Seeds brought by animals, water, and wind begin to grow.
Pioneer Species Help Create Soil

Eventually, enough soil forms to support trees and shrubs.
Pioneer Species Help Create Soil

It might take hundreds of years for the ecosystem to become balanced
and achieve equilibrium (the number of species remain relatively
constant)
Pioneer Species Help Create Soil

This is a climax community  a stable, mature community in which there
is little change in the number of species.
Secondary Succession

Disturbances such as fire or flood can disrupt a community
Secondary Succession
 Is the orderly and predictable change that takes place after a
community of organisms has been removed by such disturbances but the soil
remains.
Secondary Succession

New species of plants and animals might occupy the habitat and also the
species belonging to the climax community are likely to return.
o Pioneer species begin the process of restoring a habitat after a
disruption.
Secondary Succession

New species of plants and animals might occupy the habitat and also the
species belonging to the climax community are likely to return.
o Pioneer species begin the process of restoring a habitat after a
disruption.
o Leading again to a mature climax community
Classwork/Homework
 3.1 Reading Notes
 3.1 Study Guide
 3.1 Quick Check
 Answer both Questions
 Graph the following data to determine the range of
tolerance for catfish.
 The first number in each pair of data is temperature in
degrees Celsius, and the second number is the number
of catfish found in the stream: (0, 0); (5, 0); (10, 2); (15,
15); (20, 13); (25, 3); (30, 0); (35, 0)
 describe the stages a population goes through as it
increases in size, with reference to terms such as
exponential growth, logistic growth, cyclic growth,
carrying capacity, steady state
 describe density-dependent and density-independent
factors that limit and control population growth