Lesson #3: Population Dynamics Flashcards
(10 cards)
Interactions among Species in an Ecosystem
A species is defined as a group of organisms that can interbreed and produce
fertile offspring.
A group of organisms of the same species that live in a given area at the same
time are called a population.
Populations living together and interacting with each other is called a
community.
Populations interact with each other and the abiotic components of the
ecosystem. This unique combination of spatial habitat and interactions with
other species is called a niche.
Population Growth
If a population experiences ideal conditions the resulting population growth over time will be exponential. This produces
the “J” shaped curve on a graph.
This indicates exponential
growth.
However, when a population
colonizes a new area the growth curve produced is a sigmoid or “S” shaped curve. The
environment will eventually limit the growth of the population.
Carrying Capacity
The combination of the different limiting factors determine the carrying
capacity of that environment.
The carrying capacity of an ecosystem is the number ofindividuals of a
population that can survive in a given area.
Limits to Growth
Factors that influence the size of a population are known as limiting factors.
There are four main categories of limiting factors:
Materials and Energy – the availability of energy, water, carbon and other
materials
Food Chains – population size at any trophic level is limited by the
population sizes in all the levels below it.
Competition
Density – the number of individuals in an area at one time.
Explaining a Population Growth Curve
At the beginning of the curve there is little environmental resistance and the
population grows exponentially.
At this stage the birth rate (natality)is higher than the death rate
(mortality).
As population density increases the limiting factors begin to limit the growth
of the population.
In this transitional phase, the mortality rate increases. The population is
still growing.In the final part of the curve, the plateau phase, the population mortality rate
and natality rate are almost equal.
This occurs around the carrying capacity of the environment.
Variables to be considered at this point need to include immigration and
emigration. With immigration increasing the population and emigration
decreasing it.
Competition
When looking at competition it is important to distinguish between the 2 types of
competition seen in an ecosystem.
Intraspecific Competition – competition between members of the same
species
Interspecific Competition – competition between member of different
species
The Niche Concept
In order for a species to survive in a given area, suitable abiotic variables must
be within the zone of tolerance as well as all the species it needs to interact
with must be present.
Two species cannot survive indefinitely in the same habitat if their niches are
identical. This is known as the competitive exclusion principle.
Competitive Exclusion Principle
This was demonstrated in
experiments on Paramecium
by Carl Friedrich Gauss. He
cultured two species
individually under ideal
conditions to determine the
expected biomass of that
species.
Next, the two species were
cultured together under the
same conditions and both
species declined but one
declined much more than the other.
Fundamental and Realized Niche
The competitive exclusion principle led to the designation of the realized
niche.
The fundamental niche is the potential mode of existence, given the
adaptations of that species.
The realized niche is the actual mode of existence, which is the result of both
adaptations and competition.
Density
Limiting factors can be density dependent or density independent.
Density Dependent Limiting Factors
These are factors that affect populations as the population size increases.
Examples include disease, aggression, stress.
Density Independent Limiting Factors
These are factors that affect populations regardless of size. Examples
include flood, fire, tornado, hurricane.
