1. Populations
Chapter 19

2. 19-1 Understanding Populations
The human population size has increases from just under 2 billion in 1900 to over 7.3 billion in May 3, 2015
www. Worldometer.info/world-population

3. I. Properties of Populations
Population – all of the organisms of the same species living together within the same given area.

4. A. POPULATION SIZE
The number of individuals that the population contains.
Changes based on the following:
Immigration (increases)
Births (increases)
Emigration (decreases)
Deaths (decreases)

5. Often a population size is often estimated.
This is done by taking a SAMPLE (take a count of all of the individuals of the population in a much smaller area). The sample is used to estimate the population of the entire area. So if there are 100 individuals in 1 km2, we can assume there will also be this number in every 1km2. So, in 100 km2 we can estimate there are 10,000 individuals.
Key to remember here is this is an estimate and there is potential for error.
What if we used the population of rats in NYC to estimate the population of rats in NYS. Would this work? Why/why not?

7. B. POPULATION DENSITY
Population density is the number of individuals in a population per unit area or volume. (could be water)
People per mile2
See table 19-1 on p382
Based on the information in the chart –
Which country is the most densely populated?
Which country is the least densely populated?
What is the mean population density for the countries listed?

8. C. DISPERSION
describes how the individuals of a population are spread out in the given area
Clumped – individuals are clustered together (like a flock of geese or a pack of wolves)
Uniform – the individuals of the population are spread out evenly (the same distance apart from each other) think of nesting penguins – close together but out of pecking range.
Random – individuals of the population are spread out over the area without regard to one another.

10. II. POPULATION DYNAMICS
Populations are constantly changing in size.
Factors that impact population size:
Birth rate (BR) – the number of births per year
Death rate (DR) – the number of deaths per year
Life Expectancy – is how long an organism lives (survives)

11. A. AGE STRUCTURE
usually a depiction, a chart or graph that shows the relative number of individuals of a population at specific age ranges.
Age structure of a population is important in determining a populations potential for growth or decrease over time.
Populations that have more individuals in their reproductive years have greater potential for population growth than a population with very few younger individuals.

13. B. PATTERNS OF MORTALITY
Mortality = state of being alive
A survivorship curve is a line on a graph that shows the mortality of individuals of a population over time. The mortality of different species tend to match one of the three following survivorship curves:

14. Survivorship Curves: Type I Type II Type III
there is a low mortality rate relative to the number of individuals.
Individuals tend have a strong chance to survive to old age.
Type II
There is a steady death rate regardless of age
Half of the population dies by mid life expectancy for random reasons.
Type III
Many more are born than can survive
Many die very early in life
Most die before reproducing

15. 19-2 Measuring Populations

16. I. POPULATION GROWTH RATE
an indication of change in population size over time
Calculated using the following equation:
(# births + # immingrants) – (#deaths + # emigrations) = change in population
If the number is positive the population is growing
If the number is negative the population is decreasing
If the number is zero, there is no change.

17. B. POPULATION SIZE
because populations, especially human population tends to be so large, we divide the population size by 1000 ( to make the numbers easier to deal with) we indicate we have done this by using term “per capita”.
Example: for a population of 1000 there are 20 births – so 20/1000 = .02 (births/percapita/year) this is our birth rate per capita. If within that same population there are 35 deaths, the death rate would be 35/1000 = .035 (deaths/per capita/ year) death rate per capita.

18. What is the population growth rate?
Example: for a population of 1000 there are 20 births – so 20/1000 = .02 (births/percapita/year) this is our birth rate per capita. If within that same population there are 35 deaths, the death rate would be 35/1000 = .035 (deaths/per capita/ year) death rate per capita
What is the population growth rate?
( ) = (a negative number so the population is decreasing). If the number were positive, the population would be growing.
So the population is decreasing by 1.5 % per capita per year.

19. II. EXPONENTIAL MODEL
Describes a population in rapid population growth.
Even in the number is small, overtime the population grows rapidly as more and more individuals reproduce.
The exponential model for growth is represented on a graph as a “J” curve.
Rapid population growth means that resources plentiful and there is no competition.

21. Applying the exponential model
rapid population growth until resources become scarce.
At this point the population may overshoot the carrying capacity (maximum number of individuals the ecosystem can provide for)
population size will level off and fluctuate very little after that.
Exponential growth cannot continue indefinetly, just until carrying capacity is reached.

22. III. Logistic Model
Describes a population that grows rapidly until resources become limited (Carrying Capacity is reached). This leads to competition and struggle for resources and survival. This causes population growth to slow and eventually level out.
Logistic model is sometimes called an “S” curve.

24. IV. Population Regulation
Population size is controlled in two mechanisms:
Density Dependent Factors - these are factors that are caused by the size of the population :
Disease due to proximity and sanitation, overcrowding.
Competition for limited resources –
Food
Shelter
Nesting materials and sites
Density Independent Factors – these are factors that decrease population size that are not related to the size of the population:
Natural disasters
Flood
Drought
Fire
Volcanic eruption

25. B. Population Fluctuations
Often population size is related to natural cycles in the ecosystem
A plentiful summer may lead to more food supply for herbivores. Herbivores as a result have more offspring. More herbivores means more food for predators, which means higher birth rate for predators. Now, more predators, eat more herbivores which means higher death rate, decline in population of herbivores. This eventually leads to less food and starvation for predators without prey. So cyclic, trends in populations effect trends of other populations within the community.

27. (Skip Perils of small populations – bottlenecking ) we did this in chapter 17.