2.8: Biotic and Abiotic Influences on Ecosystems
pg. 54
Limiting Factor: is any factor that restricts the size of a
population, or the area where it can live.
Tolerance Range: the range of abiotic conditions within
which a species can survive.
Carrying Capacity: is the maximum population size of a
species that a given ecosystem can sustain.
Limiting Factors
Biotic (plant and animal food sources) and abiotic (water,
oxygen, and soil) factors are factors which may determine
which different types of organisms and how many of each
species are able to survive within an ecosystem. Humans
and their impact on ecosystems can also be a limiting factor.
Abiotic Limiting Factors
Temperature and precipitation are two factors that can
influence where a species lives. Dry arid ecosystems, such
as a desert or plains may have cacti, while wet humid
ecosystems may have rain forests. Neither of the two
organisms can survive in the others ecosystem. Every
species has a tolerance level, or range in which of an
abiotic factor in which the species could survive.
Table 1: Key Abiotic Factors in Ecosystems and Effects of Human Actions.
Biotic Limiting Factors
The biotic factors determine how easily a species can
survive in an ecosystem. A specific food and the quantity
will have an impact on a species’ ability to survive. Biotic
factors also include the relationships among organisms in
the ecosystem. There are many different types of
relationship, predator – prey for example.
Competition
When organisms compete for limited resources; such as,
space, food, water, light and the ability to reproduce, it is
known as competition. Individuals that are better equipped
to survive (Survival of the Fittest) will obtain the new
resources while the others will not and possibly parish or
have to move to another ecosystem. Plants and animals will
compete for survival.
Bear feeding on a common prey (moose)
Predation
Predation is another biotic factor which determines the
success of a species. The predator is an organism that feeds
on other organisms (food chain/web) to survive. Prey are
the organism that are eaten by the predator (lynx eats the
Hare).
One individual feeds on another
Other Interactions
Mutualism – is the interaction between two organisms
where both will benefit.
African water buffalo provides protection for a small bird, while the bird eats mites and
bugs from the buffalo’s coat, protecting it from parasites. Both organisms benefit, and
neither is harmed
Commensalism – is the interaction between two organisms
where one benefits and the other is unharmed.
Barnacles live on the humpback whale and feed on other organisms in the water.
Parasitism – is the interaction between two organisms
where one organism benefits and the other is harmed over
time (host).
A parasite is feeding on a tomato hornworm
All three interactions make up what is known as symbiotic
(symbiosis) relations.
Table 2: Key Types and Examples of Species Interactions
Carrying Capacity
The carrying capacity of an ecosystem is the ecosystems
ability to support all organisms with water, food, and
shelter (space) for survival. At sometime the population
reaches the maximum number that the ecosystem can
support, this limit is the carrying capacity.
The carrying capacity of an ecosystem can change as the
biotic and abiotic factors fluctuate over time.
How do Human Actions Affect Carrying Capacity?
Human activity can cause changes to the carrying capacity
of an ecosystem. As human actions can increase the
productivity and fertility of land for growing crops, but the
increase for one organism can lead to a decrease in carrying
capacity for another organism. Nature maintains a balance
through competition.
Check Your Learning:
Questions 1- 6, pg. 59
Wrap Up:
- Limiting factors determine the types of organisms in
an ecosystem.
- Limiting factors can be abiotic or biotic.
- Tolerance ranges describe the ranges of physical
conditions under which a species can survive.
- Species interactions include competition, predation,
mutualism, parasitism, and commensalism.
- Carrying capacity is the maximum population size that
an ecosystem can support.
- Human activities can affect the limiting factors for a
species and the carrying capacity of an ecosystem.
Try This Activity: Moose and Wolf Populations
pg. 58
Graphing a Predator – prey relationship.