Download Environment and Organisms

S7L4 Students will examine the dependence of
organisms on one another and their environments.
c. Recognize that changes in environmental conditions
can affect the survival of both individuals and entire species.
Population
Dynamics
 Population is a group of organisms of the same species
living in the same geographic area.
 Growth rate is how much the population as a whole
grows, rather than its individuals.
 Density is how many organisms per unit of space.
 Population Dynamics is the study of these dynamics
Growth
 Growth rate is its change in population size per unit of
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time.
Immigration is when organisms move into a population.
Emigration is when organisms move out of a population.
Growth rate can be positive (more in the population than
before), negative (less in the population than before) or
zero (no change).
Density of a population is the number of organisms per
unit area; the more organisms living in a given amount of
space, the denser the population in that space.
Carrying Capacity
 Carrying capacity is the number of individuals that a
given environment can support.
Population Size and Limiting
Factors
 Populations cannot continue to grow without reaching
some environmental limits, such as lack of nutrients,
energy, disease, living space and other resources.
 These are called limiting factors because they limit
how many members of a population can be sustained
in an area. There are two main categories of
limiting factors: density-dependent factors and
density-independent factors.
Density Dependent Factors
 Issues like competition, disease and predation that
only become limiting when a population in a given
area reaches a certain size.
 When a city grows too fast or has a huge population
increase, adequate health care may be difficult to
obtain, and so the death rate increases.
Density Independent Factor
 Issues like unusual weather, natural disasters and
seasonal cycles.
 These factors affect all individuals within an area,
regardless of population, size or density.
 Human modifications to the environment, like
damming a river, can affect organisms.
Changed
Environmental
Conditions
that allow them to survive and reproduce when conditions
 Some species can make adaptations or have characteristics
change.
 If conditions change faster than a species can adapt, the
species might become extinct.
 The more individuals of a species there are, the greater the
mathematical possibility that individuals exist that are better
suited to survive.
 The faster the reproductive cycle, the more quickly the
adaptation will become a dominant characteristic.