Name: ____________________
Created by Ms. Foglia adapted by Ms. Rhodes with text from Campbell and Reece
biology
Chapter 52: POPULATION ECOLOGY
The continuing growth of the human population in the face of limited resources
is a critical biological phenomenon. Population ecology is the study of the influence of
the environment on fluctuations in population size and composition.
A population is a group of individuals of the same species that occupy the same area,
use the same resources, and have a high probability of interacting and breeding with
each other.
Density and Dispersion Every population has geographic boundaries; ecologists
define boundaries based upon the type of organism and the research question being
asked. The number of individuals per unit area or volume is a population’s density; the
pattern of spacing of those individuals within the population is referred to as
dispersion.
Demography The study of the vital statistics of a population, such as birth and
death rates, is called demography. A life table presents age-specific survival data for
a population. It can be constructed by following a cohort of organisms from birth to
death, calculating the proportion of the cohort surviving at each age group.
A survivorship curve shows the number of proportion of members of a cohort still
alive at each age. Survivorship curves are often based on a beginning cohort of 1000
individuals, with the y-axis on a relative scale, so species with different life spans can
be compared on the same graph.
The life history of an organism from birth through reproduction to death
reflects evolutionary trade-offs between survival and reproduction. Life history
traits include the age at first reproduction, how often an organism breeds, and the
number of offspring produced during each reproductive episode.
Life History Diversity Some species put all their productive resources into a
single reproductive effort often called big-bang reproduction, or semelparity. Other
species follow the strategy of iteroparity, making repeated reproductive efforts over
a span of time. A key favor in the selection for and evolution of big-bang versus
repeated reproduction is the survival rate of young offspring. Big-bang reproduction
may be favored when chances of offspring survival are low in unpredictable habits. IN
more predictable environments with high competition for resources, fewer, betterprovisioned offspring may have a better chance of surviving to reproduce.
Because organisms have a finite energy budget, they cannot maximize all life
history traits simultaneously. Reproductive costs often include a reduction in survival.
The production of large numbers of offspring is related to the selective pressures of
high mortality rates of offspring in uncertain environments or from intense predation.
Parental investments in the size of offspring, incubation or gestation, and parental
care increase survival chances of offspring.
Growth of a small population in a very favorable environment will be restricted
only by the biological limitations of their life history traits. Ignoring immigration and
emigration, the change in population size during a specific time period is equal to the
number of birth minus deaths.
A population may grow exponentially for only a short time before its increased
density limits the resources available for its members. The carrying capacity (K) is
the maximum sustainable population size that a particular environment can support at
a particular time. Crowding and resources limitation may lead to decreased per capita
birth rates and increased per capita death rates.
Natural selection will favor different life history traits depending on population
densities and environmental conditions.
The ecological questions of what eventually stops population growth and what
determines population fluctuations or stability have practical applications for
conservation and agriculture.
All populations show some fluctuations in numbers. Population dynamics studies
these variations in population size and the factors that cause them.
Estimates of Earth’s carrying capacity have varied greatly and average around
10-15 billion. These estimates may use different assumptions, such as the logistic
equation, the amount of inhabitable land, or food as the limiting factor.
The concept of an ecological footprint takes into account multiple human needs
in estimating carrying capacity.
Word Roots
co- = together (cohort: a group of individuals of the same age, from birth until all are dead)
demo- = people; -graphy = writing (demography: the study of statistics relating to births and deaths
in populations)
itero- = to repeat (iteroparity: a life history in which adults produce large numbers of offspring over
many years; also known as repeated reproduction)
semel- = once; -parity = to beget (semelparity: a life history in which adults have but a single
reproductive opportunity to produce large numbers of offspring, such as the life history of the Pacific
salmon; also known as "big-bang reproduction")
1.
How can an ecologist estimate the numbers of individuals in a population?
2.
What are some possible difficulties in counting populations?
3.
Describe three patterns of dispersal.
4.
Compare the survival strategies of species and give an example of each type.
5.
Write the formula for population growth without limits. Define the terms.
6.
Define carrying capacity.
7.
Write the formula for population growth with limits. Define the terms.
8. What happens to a population when the number of individuals
approaches carrying capacity?
9. Identify factors that regulate population size.
10. Look at the growth curve of the human population. How does it compare to
the growth curves earlier in the chapter?
11. Have humans reached K? What factors are significant when explaining our
growth curve?
12. Look at the age structure diagrams of different countries. How might
the age structure influence policy?
13. Explain why the life history of an organism can’t be reproduced early, often,
have large numbers of offspring, and live long?
14. Indicate whether the following would be considered to be r-selected or Kselected life history traits.
a) early age at first reproduction; many small offspring produced
b) few, relatively large offspring produced every year
15. List some density-dependent factors that may limit population growth.
Nutrients space for nests, accumulation of toxic wastes predation
16. List some abiotic factors that may cause population fluctuations.
Extremes in weather natural disasters=fires
17. What is the best collection of life history traits that would maximize
reproductive success?
18. _______ In a range with a heterogeneous distribution of suitable habitats,
the dispersion pattern of a population probably would be
A. clumped.
B. uniform.
C. random.
D. unpredictable.
E. dense.
19. _______ A Type I survivorship curve is level at first, with a rapid increase
in mortality in old age. This type of curve is
A.
Typical of many invertebrates that produce large numbers of offspring.
B.
Typical of humans and other large mammals.
C.
Found most often in r-selected populations.
D.
Almost never found in nature.
E.
Typical of all species of birds.
20. _______Which of the following would not be a density-dependent factor
limiting a population’s growth?
A.
Increased predation by a predator
B.
A limited number of available nesting sites
C.
A stress syndrome that alters hormone levels
D.
A very early fall frost
E.
Intraspecific competition
21. _______ The human population is growing at such an alarmingly fast rate
because
A.
Technology has increased our carrying capacity.
B.
The death rate has greatly decreased since the Industrial Revolution.
C.
The age structure of many countries is highly skewed toward younger ages.
D.
Fertility rates in many developing countries are about the 2.1 children per
female replacement level.
E.
All of the above are true.
22. _______ An ecological footprint is an estimate of
(c)
A.
The carrying capacity of each nation.
B.
The available ecological capacity of each nation.
C.
The amount of land needed per person to meet the current demand on
resources.
D.
The size of a population in relationship to the resources it uses.
E.
How much land is needed to produce food for a vegetarian versus a meat eater.