1. Environmental Science Chapter 8: Understanding Populations

2. Understanding Populations - Big Ideas
Population sizes change according to changes in the environment.
The size and growth rate of human population has changed drastically over the last 200 years. Those changes have led to profound changes to almost every place on Earth.

3. Section 8.1: How Populations Change in Size
GOALS
Describe the 3 main properties of a population
Describe exponential population growth
Relate how the reproductive behavior of individuals can affect the growth rate of their population
Explain how nature regulates population size

4. The Decline of the Passenger Pigeon
How does a species go from having billions to extinct in just one century…The Passenger Pigeon Story.
Extinct in the wild since 1900 and last died in the Cincinnati Zoo 1914.

5. Review: What is a population?
Population: all the members of the same species that live in the same place at the same time
Field mice living in a corn field, grizzly bears of Yellowstone Park area
Wolves in Yellowstone NP

6. Population Size Why care about the size of the population?
How can scientists estimate the population (say of Elephant Seals on a beach in CA)?

7. Population Size
The number of individuals in a population at a given time
Sudden and dramatic decreases in population size can indicate an unhealthy population headed toward extinction
Ecologists often use sampling techniques to estimate population size.
Did You Know? The passenger pigeon was once North America’s most abundant bird. Hunting drove them to extinction in less than 100 years.

8. Estimating Population
How can you estimate the population of trees in this valley?
WHY NOT COUNT THEM ALL?
WHY IS SAMPLING NEEDED?

9. Mark and Recapture
Common way of estimating population size

10. Population Density What is population density?
What are advantages and disadvantages of high and low density?

11. Population Density Measure of how crowded a population is
Larger organisms generally have lower population densities.
Low population density: More space, resources; finding mates can be difficult
High population density: Finding mates is easier; tends to be more competition; more infectious disease; more vulnerability to predators

12. Population Distribution
How organisms are arranged within an area:
RANDOM
CLUMPED
UNIFORM
Occurs when individuals hold territory or compete for space
Plants in a desert
Occurs where resources needed are found throughout
Wildflowers in a meadow
Most Common. Occurs where resources are together
Water hole in desert, humans in cities

13. Many bird species are territorial
Many bird species are territorial. In territorial birds species, what kind of population structure would you expect?
UNIFORM

14. Population Distribution
Random distribution: Organisms arranged in no particular pattern
Uniform distribution: Organisms evenly spaced
Clumped distribution: Organisms grouped near resources; most common distribution in nature

15. What type of distribution?
CLUMPED
WHY?

17. Population Growth?
Why are there so few whales, but so many bacteria?

18. Growth Rate
Change in the size of a population over a given time period
AND
Immigration
MINUS
Emigration

19. Factors the Determine Population Growth
A population’s relative birth and death rates (mortality and natality) affect how it grows
births > deaths = population increase
deaths > births = population decrease
Immigration
Emigration

20. Immigration/Emigration
In addition to births and deaths, population growth is affected by immigration and emigration—individuals moving into and out of a population.
Migration, seasonal movement into and out of an area, can temporarily change population size.

21. Population Calculations
Net population Change = (births + immigration) – (deaths + emigration)
There are 300 people living in a village, 50 children are born, 20 people die, 10 immigrate and 2 emigrate. What is the new population?

22. Calculating Growth Rate
Determined by the following equation: (birthrate + immigration rate) – (death rate + emigration rate)
Growing populations have a positive growth rate; shrinking populations have a negative growth rate.
Usually expressed in terms of individuals per 1000
Current human growth rate 1.25% down from 2.2% in 1963

23. Every spring, many species of bird travel north to the Arctic to breed, and in the fall travel south again for the winter. This is an example of _____
MIGRATION

24. How Populations Grow
What resources are available to the population?

25. Patterns of Growth EXPONENTIAL GROWTH
Population increases by a fixed percentage every year.
Normally occurs only when small populations are introduced to an area with ideal environmental conditions
Rarely lasts long
WHAT SHAPE DOES EXPONENTIAL GROWTH LOOK LIKE?
Starts slowly, then takes off – “J-Shaped Curve”

27. Why doesn’t exponential growth last long?

28. Limiting Factors
Limiting Factor Principle: too much or too little of any abiotic factor can limit or prevent growth of a population, even if all other factors are near or above optimum
Why are there no citrus fruit growing in NJ?
Why do trees grow toward the sky?

29. What Might Be Some Limiting Factors in the Ocean?
may include:
Salinity pH
Sunlight
Dissolved oxygen
Temperature

31. Carrying Capacity
Limiting Factors lead to Carrying Capacity: the largest population an environment can sustain
What is the maximum amount of wolves that can be sustained in Yellowstone?

32. Carrying Capacity Limiting resources – used as quickly as provided
Competition within population
Competition for territory

33. Carrying Capacity

34. Logistic Growth
Carrying Capacities are NOT fixed

35. Population (Thousands)
Exponential Growth – not controlled, occurs when there are no limiting factors, and little competition
Population (Thousands)
Black Bear Population in Northern NJ

36. Logistic Growth – controlled
Population (Thousands)
Pelican Population off the Western Coast of Florida

37. Population Growth of Wolves and Moose Living in the Isles Royale of Lake Superior

38. A population of wolves is reintroduced into Yellowstone National Park
A population of wolves is reintroduced into Yellowstone National Park. For the first decade, the wolf population grows exponentially. Then, the population growth slows. The new pattern is known as ___
LOGISTIC GROWTH
In the example above, where wolves are reintroduced to Yellowstone National Park, the number of elk and other prey species within the park are _____
Limiting Factors

39. Biotic Potential
A species’ maximum rate at which its population can grow
Many factors influence biotic potential, including gestation time and generation time
Species with high biotic potential can recover more quickly from population declines than species with low biotic potential

40. Reproductive Potential
The maximum number of offspring that each member of the population can produce in ideal conditions

41. Biotic Potential Scorpion Fish Mature 3-5 years
Release 50,000 to 100,000 eggs
Once fertilized take days to hatch
HIGH BIOTIC POTENTIAL
Orangutans
Females Mature 10 years
Birth to single babies once every eight years
LOW BIOTIC POTENTIAL

42. Population Regulation
Population size may be density dependent or density independent.

43. Density Dependent
Deaths occur more quickly in a crowded population than in a sparse population
When individuals of a population are densely packed together
Limited resources, predation and disease result in higher rates of death in dense populations than in sparse populations

44. Density Independent
Certain proportion of a population may die regardless of the population’s density
Affects all populations in a general or uniform way
Severe weather and natural disasters are often density independent causes of death

45. Section 8.1 Population Growth Review
Describe the factors that influence population’s growth rate
Explain exponential and logistic growth
Explain how limiting factors and biotic potential affect population growth
Crash Course - Ecology