Population Dynamics
Populations are characterized by: size, density, distribution, age structure and birth and death rate
- these factors allow us to predict the future of the population
a) size - number of individuals
b) density- larger organisms tend to have lower density, due to competition for resources
- high density can make it easier to find mates, fend off predators, but can also lead to competition for food, space and mates also increase spread of disease
c) distribution-
- clumped- individuals grouped together over an area, suggests habitat selection; seasonal breeding, migrating to plentiful resources, flocking/herding to avoid
predators, packing to hunt
- uniform- individuals are evenly spaced, suggests resources are found throughout an area, but also suggests competition for resources
- random- individuals are located haphazardly, no pattern, suggests resources are
found throughout an area
d) age structure- a populations age directly correlates to its future growth or decline
- prereproductive, reproductive, postreproductive
- an individual within a population is either reproducing, or its too young or its too old
- age structure diagrams
e) birth and death rate- are effected by all of the above factors, individuals of different ages have different probabilities of being born and dying
- survivorship curves- show the likelihood of death varying with age
* curve closely relates to reproductive strategy
Immigration and emigration, as well as birth and death rate determine how a population will grow and decline.
Growth Rate = (crude birth rate + immigration rate) - (crude death rate + emigration rate)
*unregulated populations increase by exponential growth = J Shaped Curve
Populations unrestrained by limiting factors will undergo exponential growth until they meet environmental resistance.
- density dependent limiting factors- available food, space, water, disease, predators
- density independent factors- floods, fires, landslides, natural disasters (have nothing to do with population density; they just limit population growth)
- limiting factors help to stabilize a population to its carrying capacity =
S Shaped Curve or Logistic Growth Curve
Limiting factors from the environment along with biotic potential account for population regulation
- biotic potential- an organisms ability to produce offspring
r-selected vs k-selected
many offspring few offspring
no parental care high parental care
generalist specialist
low ability to compete high ability
* Organisms want to reproduce, they have strategies to do so, limiting factors want to kill them off
Human Population
Scope of human population growth - demography is the study of human population
1) Size- 7 billion people inhabit this planet
2) Density-
- high densities
- in temperate, subtropical and tropical climates
- China, Europe, Mexico, India
- along seacoasts, rivers
- cities and suburbs
- low densities
-in extreme climate biomes
- desert, tundra
- areas far from water
- rural areas
* uneven distribution means certain areas bear more environmental impact than others
3) Distribution- globally clumped distribution
4) Age Structure- valuable in predicting future populations
- shifts in age structure like China from young to old, challenge economy, health care systems, military forces etc.
- sex ratios- for every 100 female infants born, 106 male infants are born
- males are slightly more prone to death than women,
- China! Ratios as high as 138 boys to 100 girls
5) Birth and Death Rate
- growth rate is 1.2 %, that’s 80 million people per year
- The Rule of 70- used to estimate doubling time
70 / growth rate = # of years it takes pop. to double
- immigration and emigration are playing larger roles
- refugees fleeing due to war, civil unrest, environmental degradation, tend to cause intense resource depletion due to such high densities
- fertility is declining (total fertility rate TFR)
- not enough to stabilize pop. growth, only slows the increase
- why its declining
- women’s empowerment- many women still lack the personal
freedom of choice about when and how many children to have
- education
- changing roles of women- turn toward urban areas and the work force
- family-planning- government agencies sponsor reproductive
health care,
-United Nations met in Cairo in 1994 and called for
universal access to reproductive health care -focused on related issues like education and alleviating poverty, disease and sexism rather than pushing birth control
- incentives- India has free education to families with three or less children
Lowered birth rates and lowered death rates within a nation indicate Demographic Transition
- concept that nations move from a pre-industrial state of high births and high deaths to a stable post-industrial state of low births and low deaths
- parents choose to invest in quality of life rather than quantity of children
1) Pre-Industrial- birth rates high to compensate for infant mortality (child workers)
-death rates high due to disease, unreliable food sources
2) Transitional- declining death rates due to improved medical care, food supplies
-birth rates are still high due to cultural resistance,
-population growth surges
3) Industrial- birth rates fall closing the gap with death rates and reducing population growth
4) Post-Industrial- birth and death rates low, populations stabilize
*Is it healthy for all nations to become industrialized? Remember that most of our planet is pre-industrial/developing Causes and effects of our pop. on the environment
- causes include tool making, agricultural revolution, and industrial revolution, medical advances/sanitation;
- lead to decline in death rates = births outpace deaths
- effects include land, water and air degradation, pollution, resource depletion
-IPAT model I = P x A x T x S
- Environmental impact results from population, affluence, technology and sensitivity (how fragile and ecosystem is to disturbance)
- arid climates are more sensitive than wet climates
- China- demonstrates what happens when large numbers of poor people rapidly become
more affluent
- rapid growth has lead to intense agriculture, overpumped aquifers, urban air
pollution from coal fired power and rapidly increasing numbers of cars
* some nations experience declining pops. (many in Europe, offer incentives to
have more children)
- BRIC – countries experiencing the highest growth rates
- Brazil, India and China
age structure - Percentage of the population (or number of people of each sex) at each age level in a population.
asexual reproduction - Reproduction in which a mother cell divides to produce two identical daughter cells that are clones of the mother cell. This type of reproduction is common in single-celled organisms.
biotic potential - Maximum rate at which the population of a given species can increase when there are no limits on its rate of growth.
carrying capacity (K) - Maximum population of a particular species that a given habitat can support over a given period.
dieback - Sharp reduction in the population of a species when its numbers exceed the carrying capacity of its habitat.
environmental resistance - All the limiting factors that act together to limit the growth of a population.
exponential growth - Growth in which some quantity, such as population size or economic output, increases at a constant rate per unit of time. An example is the growth sequence 2, 4, 8, 16, 32, 64 and soon; when the increase in quantity over time is plotted, this type of growth yields a curve shaped like the letter J.
intrinsic rate of increase (r) - Rate at which a population could grow if it had unlimited resources.
J-shaped curve - curve with a shape similar to that of the letter J; can represent prolonged exponential growth.
K-selected species - Species that produce a few, often fairly large offspring but invest a great deal of time and energy to ensure that most of those offspring reach reproductive age.
linear growth - Growth in which a quantity increases by some fixed amount during each unit of time. An example is growth that increases in the sequence 2, 4, 6, 8, 10, and so on.
logistic growth - Pattern in which exponential population growth occurs when the population is small, and population growth decreases steadily with time as the population approaches the carrying capacity.
population density - Number of organisms in a particular population found in a specified area or volume.
population dispersion - General pattern in which the members of a population are arranged throughout its habitat.
population distribution - Variation of population density over a particular geographic area. For example, a country has a high population density in its urban areas and a much lower population density in rural areas.
population dynamics - Major abiotic and biotic factors that tend to increase or decrease the population size and age and sex composition of a species.
population size - Number of individuals making up a population’s gene pool.
r-selected species - Species that reproduce early in their life span and produce large numbers of usually small and short-lived offspring in a short period.
reproduction - Production of offspring by one or more parents.
S-shaped Leveling off of an exponential, J-shaped curve when a rapidly growing population exceeds
curve - the carrying capacity of its environment and ceases to grow.
sexual reproduction - Reproduction in organisms that produce offspring by combining sex cells or gametes (such as ovum and sperm) from both parents. This produces offspring that have combinations of traits from their parents. Compare asexual reproduction.
survivorship curve Graph - showing the number of survivors in different age groups for a particular species.
crude birth rate - Annual number of live births per 1,000 people in the population of a geographic area at the midpoint of a given year.
crude death rate - Annual number of deaths per 1,000 people in the population of a geographic area at the midpoint of a given year.
demographic transition - Hypothesis that countries, as they become industrialized, have declines in death rates followed by declines in birth rates.
emigration - Movement of people out of a specific geographic area. See migration. Compare immigration.
family planning - Providing information, clinical services, and contraceptives to help people choose the number and spacing of children they want to have.
fertility - The number of births that occur to an individual woman or in a population.
immigration - Migration of people into a country or area to take up permanent residence.
infant mortality rate - Number of babies out of every 1,000 born each year that die before their first birthday.
life expectancy - Average number of years a newborn infant can be expected to live.
migration - Movement of people into and out of a specific geographic area. See immigration, emigration.
population change - An increase or decrease in the size of a population. It is equal to (Births + Immigration) [[minus]] (Deaths + Emigration).
replacement-level fertility - Number of children a couple must have to replace them. The average for a country or the world usually is slightly higher than 2 children per couple (2.1 in the United States and 2.5 in some developing countries) because some children die before reaching their reproductive years.
total fertility rate (TFR) - Estimate of the average number of children who will be born alive to a woman during her lifetime if she passes through all her childbearing years (ages 15-44) conforming to age-specific fertility rates of a given year. In simpler terms, it is an estimate of the average number of children a woman will have during her childbearing years.