1. Ch. 46 - Part 1 - Ecology of Populations
Biology, 9th ed, Sylvia Mader
Chapter 46
Ch Part 1 - Ecology of Populations
Ecology of Populations

2. Biology, 9th ed, Sylvia Mader
Scope of Ecology
Chapter 46
Ecology of Populations
Ecology
The study of the interactions of organisms with
other organisms, and
the physical environment
Levels of Study in Ecology
Individual organism live in habitats - Place where an organism lives
Population - All the individuals of a species within a particular area
Community – All the populations in a particular area interacting with each other
Ecosystem - Living community interacting with the abiotic (non-living) environment

3. Biology, 9th ed, Sylvia Mader
Ecologists studying individual organisms might study how they are adapted to their environment
Ecologists studying populations might study the factors that affect the growth and regulation of population size
Ecologists studying communities want to know how interactions such as predation and competition affect the organization of a community
Chapter 46
Ecology of Populations

4. Biology, 9th ed, Sylvia Mader
Chapter 46
Ecological Levels
Ecology of Populations

5. Density and Distribution of Populations
Biology, 9th ed, Sylvia Mader
Density and Distribution of Populations
Chapter 46
Ecology of Populations
Demography is the statistical study of a population & includes its density, distribution & rate of growth.
Population Density - Number of individuals per unit area or volume
Population Distribution - Pattern of dispersal of individuals within a space of interest
Ecologists analyze what causes the spatial and temporal “patchiness” of organisms
Limiting factors are factors that predominantly determine whether a species lives in a habitat

6. Biology, 9th ed, Sylvia Mader
Determining Density
Chapter 46
Ecology of Populations
Knowing the number of individuals in a species is often important; especially endangered species.
It is possible to get exact counts sometimes but in most cases this is impractical or impossible. Estimates are usually devised.

7. Estimating Density of Population
Biology, 9th ed, Sylvia Mader
Estimating Density of Population
Chapter 46
Ecology of Populations
Quadrat sampling
Count a limited number of sampling stations (quadrats) & estimate number for whole area
Example:
If there are 6 trees in 5 quadrats, how many should be in 20 quadrats?
Answer: 24

8. 2. Mark & Recapture Technique
Biology, 9th ed, Sylvia Mader
2. Mark & Recapture Technique
Chapter 46
Ecology of Populations
• Capture a limited number of individuals at random (Example = 25)
Mark them somehow (tag, band, dye, paint, toe clipping, ear punch, etc.)
Release back into population
At later date, randomly capture a second group of individuals (Capture 20; 2 already marked)
Determine percentage marked
2 out of 20 marked = 10%
Thus original 25 should be 10% of total = 250

9. Patterns of Dispersion
Biology, 9th ed, Sylvia Mader
Patterns of Dispersion
Chapter 46
Ecology of Populations
Environmental & social factors influence the spacing of individuals in a population
Three types of dispersion found in nature:
Clumped
Random
Uniform

10. Distribution Patterns of the Creosote Bush
Biology, 9th ed, Sylvia Mader
Distribution Patterns of the Creosote Bush
Chapter 46
Ecology of Populations

11. Biology, 9th ed, Sylvia Mader
Chapter 46
A clumped dispersion
Is one in which individuals aggregate in patches
May be influenced by resource availability and behavior
Ecology of Populations
Figure 52.3a
(a) Clumped. For many animals, such as these wolves, living in groups increases the effectiveness of hunting, spreads the work of protecting and caring for young, and helps exclude other individuals from their territory.
Most common in nature

12. Biology, 9th ed, Sylvia Mader
A uniform dispersion
Is one in which individuals are evenly distributed
May be influenced by social interactions such as territoriality
Biology, 9th ed, Sylvia Mader
Chapter 46
Ecology of Populations
Figure 52.3b
(b) Uniform. Birds nesting on small islands, such as these king penguins on South Georgia Island in the South Atlantic Ocean, often exhibit uniform spacing, maintained by aggressive interactions between neighbors.

13. Biology, 9th ed, Sylvia Mader
A random dispersion
Is one in which the position of each individual is independent of other individuals
Biology, 9th ed, Sylvia Mader
Chapter 46
Ecology of Populations
(c) Random. Dandelions grow from windblown seeds that land at random and later germinate.
Most rare in nature; used as a basis of comparison for statistical comparisons usually

14. Biology, 9th ed, Sylvia Mader
Population Growth
Chapter 46
Ecology of Populations
Rate of Natural Increase (r)
Growth rate (r) is dependent on:
1. Number of individuals born each year (b)
2. Number of individuals that die each year (d)
3. Numbers of individuals that immigrate into a population each year (i)
4. Numbers of individuals that emigrate out of the population each year (e)
Thus population growth can shown by:
Growth = (b + i) - (d + e)

15. Dynamics of Population Growth
Biology, 9th ed, Sylvia Mader
Chapter 46
Dynamics of Population Growth
Ecology of Populations
Births and immigration add individuals to a population.
Births
Immigration
PopuIation size
Emigration
Deaths
Deaths and emigration remove individuals from a population.

16. Biology, 9th ed, Sylvia Mader
Biotic Potential
Chapter 46
Ecology of Populations
Biotic Potential is the highest possible rate of natural increase for a population when resources are unlimited.
Whether biotic potential will be high or low depends on demographic characteristics of the population such as:
Usual number of offspring per repro. event
Chances of survival until age of reproduction
How often each individual reproduces
Age at which reproduction begins

17. Biotic Potential affected by number of offspring
Biology, 9th ed, Sylvia Mader
Chapter 46
Ecology of Populations
Biotic Potential affected by number of offspring
HIGH:
Pigs produce many offspring that mature quickly
LOW:
Rhinos produce few offspring that mature slowly

18. Biology, 9th ed, Sylvia Mader
Mortality Patterns
Chapter 46
Ecology of Populations
Population growth patterns assume populations are made of identical individuals. In reality, the individuals are all in different stages of their life span (young, medium, old)
A cohort
Composed of all the members of a population born at the same time
Survivorship
The probability that newborn individuals of a cohort will survive to a particular age

19. Biology, 9th ed, Sylvia Mader
Survivorship Curves
Chapter 46
Ecology of Populations
A survivorship curve is a graphic way of representing the numbers of individuals alive at different ages.
There are three idealized types of survivorship curves found in nature:
Type I - Most individuals survive early life
Type II - Constant rate of survivorship throughout life
Type III - Most individuals die young

20. Biology, 9th ed, Sylvia MaderII
III 50
100 1 10
1,000
Percentage of maximum life span
Number of survivors (log scale)
Biology, 9th ed, Sylvia Mader
Chapter 46
Ecology of Populations

21. Biology, 9th ed, Sylvia Mader
Type I Curve
Chapter 46
Ecology of Populations
Shows low infant mortality
Produce few offspring
Provide offspring with high degree of parental care. Increases likelihood they will survive to maturity
Occurs in humans and other large mammals like elephants and whales
Show a low rmax (biotic potential)

22. Biology, 9th ed, Sylvia Mader
Type II Curve
Chapter 46
Ecology of Populations
Mortality is more constant over life span
Produce moderate # of offspring
Provide offspring with moderate amount of parental care.
Occurs in songbirds, lizards & small mammals

23. Biology, 9th ed, Sylvia Mader
Chapter 46
Survivorship Curve - Belding’s ground squirrels Type II - death rate is relatively constant
Ecology of Populations
Figure 52.4
1000
100 10 1
Number of survivors (log scale) 2 4 6 8
Age (years)
Males
Females

24. Biology, 9th ed, Sylvia Mader
Type III Curve
Chapter 46
Ecology of Populations
Shows high death rates for very young
Survivorship improves as individuals survive to increased ages
Produce very large numbers of offspring
Provide little or no care for offspring
Occurs in many marine invertebrates, insects, fishes & plants
Show a high rmax (biotic potential)

25. Biology, 9th ed, Sylvia Mader
Survivorship Curves
Chapter 46
Ecology of Populations

26. Biology, 9th ed, Sylvia Mader
Age Distributions
Chapter 46
Ecology of Populations
What proportion of the population falls into the 3 major age categories:
1. Prereproductive
Too young to reproduce yet
2. Reproductive
Ages at which reproduction takes place
3. Postreproductive
Too old to reproduce anymore

27. Age Structure Diagrams
Biology, 9th ed, Sylvia Mader
Age Structure Diagrams
Chapter 46
Ecology of Populations
At least three age structure diagrams are possible:
Increasing
Pyramid-shaped. Prereproductive group is largest of three groups.
Stable
Bell-shaped. Reproductive group equals prereproductive group
Decreasing
Urn-shaped. Prereproductive group is smaller than reproductive group. Postreproductive group is the largest.

28. Age Structure Diagrams
Biology, 9th ed, Sylvia Mader
Chapter 46
Ecology of Populations
Age Structure Diagrams

29. Patterns of Population Growth
Biology, 9th ed, Sylvia Mader
Patterns of Population Growth
Chapter 46
Ecology of Populations
Two patterns of population growth:
1. Discrete breeding
Members of population have only one single reproductive event in their lifetime
- Many insects, annual plants

30. Discrete Breeding in Salmon
Biology, 9th ed, Sylvia Mader
Discrete Breeding in Salmon
Chapter 46
Ecology of Populations

31. Patterns of Population Growth
Biology, 9th ed, Sylvia Mader
Patterns of Population Growth
Chapter 46
Ecology of Populations
2. Continuous breeding
Members of population experience many reproductive events throughout their lifetime
- Most vertebrates, perennial plants like shrubs & trees

32. Continuous Breeding in Birds
Biology, 9th ed, Sylvia Mader
Continuous Breeding in Birds
Chapter 46
Ecology of Populations

33. Biology, 9th ed, Sylvia Mader
Exponential Growth
Chapter 46
Ecology of Populations
Exponential Growth Model
1. Describes population growth in an idealized situation in which resources such as food, shelter, room, etc. are unlimited
2. Under these conditions the rate of reproduction (r) is at its maximum & is called the intrinsic rate of increase (rmax).

34. Exponential Growth Equation
Biology, 9th ed, Sylvia Mader
Exponential Growth Equation
Chapter 46
Ecology of Populations
If immigration & emigration are ignored a population’s growth rate (rmax) equals birth rate (b) minus death rate (d)
 rmax = b - d
Population growth equation can be expressed as:
dN/dt = change in number of individuals over a given time
N = population size  dN dt
rmaxN

35. Exponential Growth results in a J-shaped curve
Biology, 9th ed, Sylvia Mader
Chapter 46
Exponential Growth results in a J-shaped curve
Ecology of Populations
Figure 52.9 5 10 15
500
1,000
1,500
2,000
Number of generations
Population size (N) dN dt 
1.0N
0.5N

36. J-shaped curve characteristic of some populations that are rebounding
Biology, 9th ed, Sylvia Mader
Chapter 46
J-shaped curve characteristic of some populations that are rebounding
Ecology of Populations
Figure 52.10
1900
1920
1940
1960
1980
Year
2,000
4,000
6,000
8,000
Elephant population

37. Biology, 9th ed, Sylvia Mader
Logistic Growth
Chapter 46
Ecology of Populations
Environmental factors will eventually limit population growth slowing down exponential growth.
These factors are called population-limiting factors.
Lack of food, water, space, etc.
Population growth will now fit the Logistic Growth Model which produces an S-shaped curve.

38. Logistic Growth results in an S-shaped curve
Biology, 9th ed, Sylvia Mader
Chapter 46
Logistic Growth results in an S-shaped curve
Ecology of Populations

39. Biology, 9th ed, Sylvia Mader
Logistic Growth
Chapter 46
Ecology of Populations
This model includes the concept of:
1. Carrying capacity (K)
- Is the maximum number of individuals of a given species that the environment can support
•The value of K varies, depending on species and the habitat

40. Biology, 9th ed, Sylvia Mader
Logistic Growth
Chapter 46
Ecology of Populations
2. The closer the population size nears the carrying capacity, the more likely resources will become scarce & biotic factors likes competition & predation will become evident.
•Birth rate will decline & death rate will increase until population stops growing.
3. Eventually the population stabilizes at the carrying capacity

41. Logistic Growth Equation
Biology, 9th ed, Sylvia Mader
Chapter 46
Logistic Growth Equation
Ecology of Populations dN dt 
(K  N) K
rmax N
If population is well below carrying capacity:
a. Then N is very small & (K-N)/K is ~1
Population will grow exponentially.
2. If population is very close to carrying capacity:
a. Then N is very large & (K-N)/K is ~0
Population will stop growing.

42. Biology, 9th ed, Sylvia Mader
Chapter 46
Logistic & Exponential Growth Curves
Ecology of Populations dN dt 
1.0N
Exponential growth
Logistic growth
1,500  N
1,500
K  1,500 5 10 15
500
1,000
2,000
Number of generations
Population size (N)
Figure 52.12

43. The Logistic Model and Real Populations
Biology, 9th ed, Sylvia Mader
Chapter 46
The Logistic Model and Real Populations
Ecology of Populations
Figure 52.13a
800
600
400
200
Time (days) 5 10 15
(a) A Paramecium population in the lab. The growth of Paramecium aurelia in small cultures (black dots) closely approximates logistic growth (red curve) if the experimenter maintains a constant environment.
1,000
Number of Paramecium/ml

44. Biology, 9th ed, Sylvia Mader
Some populations overshoot K
Before settling down to a relatively stable density
Biology, 9th ed, Sylvia Mader
Chapter 46
Ecology of Populations
Figure 52.13b
180
150
120 90 60 30
Time (days)
160
140 80
100 40 20
Number of Daphnia/50 ml
(b) A Daphnia population in the lab. The growth of a population of Daphnia in a small laboratory culture (black dots) does not correspond well to the logistic model (red curve). This population overshoots the carrying capacity of its artificial environment and then settles down to an approximately stable population size.

45. Biology, 9th ed, Sylvia Mader
Chapter 46
Some populations
Fluctuate greatly around K
Ecology of Populations
Figure 52.13c 80 60 40 20
1975
1980
1985
1990
1995
2000
Time (years)
Number of females
(c) A song sparrow population in its natural habitat. The population of female song sparrows nesting on Mandarte Island, British Columbia, is periodically reduced by severe winter weather, and population growth is not well described by the logistic model.