1. Population ecology
The branch of ecology & environmental science that deals with characterizing the makeup, growth, and impact of populations of organisms on the environment

2. What is a community?
A community is a group of interacting populations living in the same area

3. Population
Species may consist of multiple populations that are geographically isolated from one another
A group of the same species living in the same place at the same time
Ex. Earthworms living in a garden or maple trees that live in a particular forest

4. How many individuals make up a population?
Actual size
The total # of individuals in the population
Direct count or estimation
Population density
The # of individuals to a given unit of area
Ex. Dandelion population in a field many be the # of dandelion plants per square meter

5. 3 methods for measuring population size…
1. Direct count method (census)
Just as it says…
Count all individuals in population
Done every 10 years in U.S.
Not exact due to immigration, emigration, births & deaths

6. 2. QUADRAT METHOD
Construct a grid of sample squares, each of known area, within the larger area where population lives
Individuals counted in a fraction of those sample squares & then total population is estimated
Works best for counting organisms that don’t move (trees)

7. 3. CAPTURE-RECAPTURE Used to estimate size of a mobile population
Count & mark a sample of individuals in an area on a given day & then return them to the habitat.
Next day, go back and mark another sample of individuals
Continue over the course of several days
Ex. Japanese beetles in a field.

8. Population density problem
Population density= The # of individuals to a given unit of area
Equation:
number of individuals divided by given unit of area
1,270 deer are living on an island that is 830km2 in size. What is the population density of the deer per square kilometer?

9. Population density problem
1,270 deer are living on an island that is 830km2 in size. What is the population density of the deer per square kilometer?
1,270/830= deer/km2

10. The ability to predict growth or decline is useful in monitoring and managing threatened or endangered species

11. The Passenger Pigeon Used to be most abundant bird in North America
Early 1800s, an ornithologist watched 2 billion birds that took 5 hours to fly over him
What happened?
We started cutting down the forests & the birds became easy targets for hunters
The last passenger pigeon died in 1914 in the Cincinnati Zoo

12. Population density
In general, larger organisms have lower population densities because they require more resources– and thus more area– to survive

13. High vs Low Population Density
High density
Easy to find mates
Conflict over space, food
Vulnerable to predators
Increase transmission of disease
Low density
Hard time finding mate
Less competition for space, food

14. Population Distribution
1. Random Distribution
individuals are not grouped in any particular pattern across an area.
2. Uniform Distribution
Individuals are equally spaced across a given area
3. Clumped Distribution
individuals associate in small groups or clusters that are unequally spaced across a given area
Most populations
live in clumps although other patterns occur based on resource distribution

15. Random Distribution Most unusual
Occurs when resources are found throughout an area and other organisms do not strongly influence where members of a population settle
Windblown seeds may settle and establish themselves in an area in this manner
Some spider species

17. Uniform Distribution Can occur due to… Territoriality
Limited resources
Space or Water
Plants that exhibit allelopathy

19. Clumped Distribution
Most common because resources are usually concentrated in specific areas
Protection (zebra herd)
Social species (bees/ants)

21. Calculating birth and death rates
To calculate the birth or death rate of a population, just take the number of births/deaths and then divide by the total population
Ex. If a population has 29 births a year and the original population size is 1,000, what is the birth rate for this population?
29/1,000= .029= 2.9%

22. How do populations grow?
1. Population with no immigration or emigration occurs
dN/dt(r)= (b-d)/N
N= population size
b= births
d= deaths
dN/dt (r)= growth rate of the population

23. populations grow with immigration & emigration
dN/dt (r)= (b + i) –(d + e)/N
N= population size
b= births
d= deaths
i= immigration
E= emigration
dN/dt (r)= growth rate of the population

24. Population doubling time
To calculate the time it takes for a population to double- we use the Rule of 70 70 r
How long would it take a population with a growth rate of 2% to double in size?
70 = years 2

25. Exponential Growth J curve “Malthusian Growth”
Exponential Growth Curve of a Hypothetical, Ideal Population
This usually occurs with
small populations & when
a lot of resources are available
Population
Size (N)
J curve
Time (t)
“Malthusian Growth”

27. 05_T03.JPG
Table 05-T03
Title:
Exponential growth in a savings account with 5% annual compound interest.
Caption:
Notes:
Keywords:
populations, growth rates, exponential

28. However, populations do not grow indefinitely…
Every population is constrained by limiting factors
Physical, chemical & biological characteristics of the environment
Populations grow until they reach the Carrying capacity (k)
Carrying capacity= the maximum population size of a species that a given environment can sustain
This can vary, depending on changes in the environment

29. Exceeding Carrying Capacity: Move, Switch Habits, or Decline in Size
Members of populations which exceed their resources will die unless they adapt or move to an area with more resources.
Figure 8-6

30. Logistical Growth Curve of a
Hypothetical, Real Population
Carrying
Capacity (K)
Population
Size (N)
S- curve
Time (t)

31. Exponential and Logistic Population Growth: J-Curves and S-Curves
Populations grow rapidly with ample resources, but as resources become limited, its growth rate slows and levels off.
Figure 8-4

32. Exponential and Logistic Population Growth: J-Curves and S-Curves
As a population levels off, it often fluctuates slightly above and below the carrying capacity.
Figure 8-4

34. Biotic Potential and Environmental Resistance affect population size
Ability to
Have
offspring
Limiting
factors
The more offspring you produce
the higher your biotic potential

35. Environmental resistance: Limiting Factors
Density independent factors
Factors NOT influenced by the population density
They will affect the population the same, regardless of its size
Density dependent factors
Factors influenced by population density
They increase as population increases

36. Density Independent Factors
Temperature changes in the environment
Weather
Habitat destruction
Availability of water
Sunlight
Salinity
Soil chemistry
Suitable Breeding Sites
Dissolved Oxygen
Fire, flood, earthquake, etc.

37. Density dependent factors
Competition for food resources
Predation
Disease
Territoriality
Changes in reproductive capacity (some slow down when populations become overcrowded like mice/rats)
Behavioral changes (some species resort to cannibalism and killing their young when they become overcrowded)

38. biotic potential: organisms fall into one of the following two groups
r-strategists/r-selected species
k- strategists/k-selected species
Mortality due to density independent factors
J shaped growth curve
Insects, fish, bacteria, algae, rodents, weeds
Mortality due to density dependent factors
S shaped growth curve
Sharks, birds, some reptiles, most mammals

39. Little or no parental care and protection of offspring
r-Selected Species
Cockroach
Dandelion
Many small offspring
Little or no parental care and protection of offspring
Early reproductive age
Most offspring die before reaching reproductive age
Small adults
Adapted to unstable climate and environmental conditions
High population growth rate (r)
Population size fluctuates wildly above and below carrying capacity (K)
Generalist niche
Low ability to compete
Early successional species
Figure 8.10
Natural capital: generalized characteristics of r-selected (opportunist) species and K-selected (competitor) species. Many species have characteristics between these two extremes.
Fig. 8-10a, p. 168

40. Fewer, larger offspring High parental care and protection of offspring
K-Selected Species
Elephant
Saguaro
Fewer, larger offspring
High parental care and protection
of offspring
Later reproductive age
Most offspring survive to reproductive age
Larger adults
Adapted to stable climate and environmental conditions
Lower population growth rate (r)
Population size fairly stable and usually close to carrying capacity (K)
Specialist niche
High ability to compete
Late successional species
Figure 8.10
Natural capital: generalized characteristics of r-selected (opportunist) species and K-selected (competitor) species. Many species have characteristics between these two extremes.
Fig. 8-10b, p. 168

41. Types of Population Change Curves in Nature
Population sizes may stay the same, increase, decrease, vary in regular cycles, or change erratically.
Stable: exhibits dynamic equilibrium.
Irruptive: when populations explode and crash.
Cyclic: populations fluctuate up and down
Irregular: erratic changes.

42. Types of Population Change Curves in Nature
Population sizes often vary in regular cycles when the predator and prey populations are controlled by the scarcity of resources.

43. Survivorship curves
Proportion of individuals in a population that survive to a particular age

44. Survivorship curves Long life span
Type I:
Long life span
Young survive, death rates high among elderly
Top consumers & k-strategists
Humans
Type II:
Constant death rate at all ages
Birds, rodents, flowering plants
Type III:
High death rates among young; if live, likely to live entire life span
Fish, insects, amphibians, sea turtles, oysters, redwood trees, etc. (r-strategists)