1. Section 1 How Populations Grow
Chapter 15
Section 1
How Populations Grow

2. Objectives
Distinguish among the 3 patterns of dispersion in a population
Contrast exponential growth and logistic growth
Differentiate R-strategists from K-strategists

3. Population
Consists of all the individuals of a species that live together in one place at one time
Populations tend to grow: multiple offspring
Limits resources limit population
Ex. Population of walleye in Maple Lake

4. Population

5. Demography Statistical study of all populations
Study the composition of a population and try to predict how the size will change
Ex. Growth of the population of Canada in the next 10 years

7. Population Size Number of individuals in a population
Can affect the populations ability to survive
Ex. 40 moose in Glacier National Park

8. Population Density Number of individuals that live in a given area
If individuals of a population are few and spaced widely apart, they may seldom encounter one another, making reproduction rare
Ex. If 20 walleye live by the dock of my cottage

9. Population
Density
Population Density

10. Dispersion
The way the individuals of the population are arranged in space
3 patterns:
Random Distribution: location of each individual is self determined or determined by chance
Even Distribution: located at regular intervals
Clumped Distribution: individuals are bunched together in clusters

11. Dispersion

12. Population Model
Hypothetical population that attempts to exhibit the key characteristics of a real population
By making a change and observing the outcomes, demographers can predict what might occur in a real population

13. Growth Rate Population grows when more individuals are born than die
A simple population model describes the rate of population growth as the difference between the birth and death rates
Ex. Find the rate of population growth where there are 360 births and 250 deaths in a year
= 110 (population is increasing by 110 individuals/year)

14. Exponential Growth Curve
Curve in which the rate of population growth stays the same, as a result the population size increases steadily
Population size vs. time, J shaped

15. Exponential Growth Curve
N = size of the current population
r = rate of growth
K = carrying capacity, population size that an environment can sustain

16. Density Dependent Factors
Resources are density dependent factors
The rate at which they become depleted depends upon the population density of the population that uses them
Ex. Population of 200 seagulls on lake Erie vs. Population of 50 seagulls on lake Erie
Which will use up resources more quickly?

17. Logistic Model
Population model that takes into account the declining resources available to a population
Exponential growth is limited by a density dependent factor
Assumes birth and death rates vary

18. Logistic Model

19. Logistic Model
When population is below carrying capacity, growth rate is rapid
As population approaches carrying capacity death rates rise, birth rates slow
Result: rate of growth slows
Population stops growing when birth and death rates are equal
If population exceeds carrying capacity, deaths will increase and outnumber births until population falls to carrying capacity

21. Population Growth Models
Simple model (part one): calculating the population growth rate
r (rate of growth) = birthrate - death rate
The rate of population growth equals the rate of births minus the rate of deaths

22. Population Growth Models
Simple model (part 2): exponential growth curve
Delta N (change in population) = rN
Once r has been determined for a population (part 1) the number of individuals that will be added to a population as it grows is equal to the rate of growth multiplied by the number of individuals in the current population (N)

23. Population Growth Models
More realistic model: logistic model
Delta N = rN (K-N)/K
Population size calculations often need to be adjusted by the number of members of the population at carrying capacity (K)

24. Density Independent Factors
Environmental conditions
Weather and climate
Ex. Mosquito populations increase in the summer while the weather is warm, but decrease in the winter

25. R-strategist Strategy means pattern of living
R-strategist: grow exponentially when environmental conditions allow them to reproduce
Results in temporarily large populations
When environmental conditions worsen population size drops quickly
Usually have short life span, reproduce early, and have many offspring, offspring are small and mature rapidly on their own

26. R-strategist & K-strategist

27. K-Stategists
K-strategists: population density is usually near carrying capacity
Characterized by long life span, few young, slow maturing process, reproduction late in life, provide care of young, live in stable environments

28. R vs. K Strategist Ex. R-strategist Ex. K-strategist
Insects like mosquitoes
Ex. K-strategist
Whales, tigers

29. Review
Identify the pattern of dispersion of fans attending a basketball game as random, even, or clumped. Explain your answer.
Differentiate a logistic growth pattern from an exponential growth pattern.
Describe why an R-strategist might be better suited for an unpredictable environment than a K-strategist.

30. Answers
The pattern of dispersion of fans at a basketball game could be described as clumped. This could be because usually friends and family sit together, making a clumped pattern.
A logistic growth pattern is a population model that takes into account the declining resources available to a population. Whereas a exponential growth pattern is a curve in which the rate of population growth stays the same, as a result the population size increases steadily.

31. Answers
3. An R- strategist may be better suited for an unpredictable environment because they are able to reproduce exponentially when environmental conditions are favorable. They would be able to build up a large population and be able to handle an unpredictable environment when their population size would drop.