POPULATION ECOLOGY

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POPULATION ECOLOGY

• the study of populations (groups of individuals
  of the same species living in a given area) and
  their relationships with their abiotic and biotic
  environments

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• Population size (N) is the number of individuals
  that make up the gene pool
• Population density is the number of individuals
  that live in a defined area or volume
• Changes in population density and number are
  affected by
• 1. Birth rate and death rate
• 2. Immigration and Emigration

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Exponential Growth

• Equation dN/dt riN
• where d the change in, N the number of
  individuals in a population, t time, and ri
  rmax the intrinsic rate of natural increase.
• Species that experience periods of exponential
  growth are called r-selected species. They tend
  to
• 1. Reproduce at a young age
• 2. Produce many small young
• 3. Offer little parental care

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Logistic growth

• takes into account the factors that regulate
  population growth and the concept of a carrying
  capacity (K) or the population size at which
  stabilization occurs

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• Equation
• dN/dt riN(K-N/K),
• where K carrying capacity, see above for other
  variables
• Species that show a stabilization of N are called
  K-selected. They tend to
• 1. Reproduce later in life
• 2. Produce fewer, larger, and more developed
  offspring.
• 3. Provide a great deal of parental care

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• Population regulation

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Density-dependent factors

• Those related to the number of individuals
  present in the population.

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Density-independent factors

• Have their effects regardless of N.

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Demography

• the study of factors that determine the size and
  structure of populations through time. It
  involves

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1. Age structure (the number of individuals of
each age) and Sex Ratio (proportions of males to
females)

• Age structure is important because fecundity (the
  number of offspring produced in a given time
  interval) and mortality rates vary for different
  age groups or classes.
• Sex ratio is important in that the number of
  births is usually more closely related to the
  number of females rather than the number of
  males.

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2. A life table

• summarizes the probability that an individual
  will survive and reproduce in any given year over
  the course of its lifetime.

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3. Survivorship Curves
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Density and Dispersion (the pattern of spacing
among individuals within the geographic
boundaries of the population
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Determination of Density

• Count individuals
• Or
• Estimate

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Mark-recapture method

• Equation m2/n2 n1/N
• where
• m2 number of marked individuals in
  the second sample
• n2 marked unmarked in second
  sample
• n1 number of individuals caught in the
  first sampling attempt
• N total population size (solve for
  N)

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Patterns of dispersion

• clumped or with individuals aggregated in
  patches
• uniform or evenly spaced
• random or where the position of one individual
  is independent of other individuals).

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Human Population Growth
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Demographics

• Growth rate formula Growth Rate (Crude birth
  rate - crude death rate). Crude birth rate is
  the number of births/1,000 people crude death
  rate is the number of deaths/1,000 people.
  Depends on age at which people get married,
  amount of education, career vs. stay at home
  women, contraceptive use, number of children
  desired by the couple, cultural values, and
  religious beliefs.
• The doubling time or the time it takes for a
  population to double is calculated as follows
  Doubling time 70/Growth Rate (). Developed
  countries in general have longer doubling times
  than developing and third world nations.
• Total Fertility Rate (TFR) is the number of
  children that women are expected to have in their
  lifetimes.
• A country reaches zero population growth when
  birth rates death rates and immigration
  emigration.
• After a country reaches replacement level
  fertility, population growth can still occur. In
  fact worldwide the population will still continue
  to grow even if all nations reach replacement
  level fertility.
• The age structure of a population also affects
  population growth.

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Factors involved in the human population increase
include but are not limited to

• Expansion into new habitats.
• Increased K. Although most living organisms
  cannot change their carrying capacities, humans
  have been able to increase theirs. There are
  many disagreements concerning the Earths
  carrying capacity for humans. Some people
  believe that we have already surpassed K, while
  others think that it may be as high as 1,000
  billion.
• 3. Side-stepping limiting factors
• a. Decreased infant mortality as a result of
  increased food supplies, the Agricultural
  Revolution, the Industrial Revolution, the
  technology, medicines, and sanitary living
  conditions.
• b. Increased life spans
• Social influences
• Religious influences

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Is this a problem?

• Some say yes
• Others say no

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But---

• It makes since that the more people we have, the
  more impact on resources and the environment.
  However, the people of developed nations tend to
  have a larger-
• The Ecological Footprint takes into account
  resources needed and wastes produced by humans.
  http//www.myfootprint.org/ .

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Should or can human population be controlled?

• Mandatory limits on number of children
• Educational programs extolling the benefits of
  smaller families
• Family planning
• But all of these are controversial

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• Another possibility is raising the standard of
  living in third world countries through
  demographic transition