Scientific Reasoning Module - Act III
Final Assignment
Background
A population is a group of organisms of the same species that live in a particular
geographic location. For example, people living in the city of Phoenix are considered a
population of humans.
Biologists estimate the number of ...
Scientific Reasoning Module - Act III Final Assignment
Background
A
population
is a group of organisms of the same species
that live in a particular
geographic location. For example, people living in the city of Phoenix are considered a
population of humans.
Biologists estimate the number of organisms in a population (population size) to know
whether a species has become too rare or too abundant. Knowing a population's size
also enables biologists to manage the resources needed to sustain the population. For
example, biologists have estimated how many people will live in Phoenix during the next
40 years to know whether the current water supply will support the future population.
A
population grows when the number of organisms born exceeds the number that die.
Conversely, a population shrinks when the number of organisms that die exceeds the
number born.
If the population of humans in Phoenix
grows from one year to the next,
the number of people born must have exceeded the number of people who died.
Growth rate
is a measure of how a population’s size
changes over time. A
positive
growth rate
means that the population size increases
over time (i.e., the population
grows). A
negative growth rate
means that the population
size decreases over time (i.e.,
the population shrinks). A
growth rate of zero
means
that the population size does not
change over time (i.e., the population neither grows nor shrinks, but remains stable).
Population size increases from year to year if its growth rate is greater than 0. For
example, if the growth rate for Phoenix for the last 10 years were 0.16, the population size
would have increased by 16% (a mean of 1.6% per year). If the nearby town of Sierra Vista
experienced a growth rate of -0.05 during the same period, its population size decreased
by 5% over 10 years (a mean of -0.5% per year). The growth of a population depends on many variables, including the abundance of
food. Organisms rely on the matter and energy in food to survive and reproduce.
Predators, such owls (see figure above), consume other organisms as food, referred to as
prey.
Prey density
is the number of prey living in
an area. The greater the prey density,
the more prey exist in an area. A population of predators requires a sufficient prey
density to persist over time.
Scenario
The National Park Service has monitored two populations of locally endangered owls for
50 years. Biologists for the park service measured the growth rate and prey density of
each population from 1971 to 2021. Their goal was to ensure that the owl populations
persist for many years to come.
Recently, the National Park Service was allocated funds by Congress to protect this
species of owls. Unfortunately, the new budget is sufficient to protect only one of the two
populations. The biologists read studies about interventions to save similar species of
birds and concluded that increasing the prey density would be a simple yet effective
strategy to protect these owls.
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