1. Ch 5 Population Ecology Part 1: Foundations of Environmental Science
PowerPoint® Slides prepared by
Jay Withgott and Heidi Marcum
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

2. This lecture will help you understand:
Population characteristics
Population ecology
Conservation biology

3. Ecology is studied at several levels
Ecology and evolution are tightly intertwined
Biosphere = all living things on Earth and the areas they inhabit
Ecosystem = communities and the nonliving (abiotic) material and forces they interact with
Community = interacting species that live in the same area

4. Levels of ecology science
Population ecology = investigates the quantitative dynamics of how individuals within a species interact
Community ecology = focuses on interactions among species (one-on-one to interrelationships among communities)
Ecosystem ecology = studies living and nonliving components of systems to reveal patterns
nutrient and energy flow

5. Organismal ecology: habitat
Habitat = the environment in which an organism lives
includes living and nonliving elements
scale-dependent: from square meters to square km
Habitat use = each organism thrives in certain habitats, but not in others (non-random patterns)
Habitat selection = the process by which organisms actively select habitats in which to live
availability and quality of habitat are crucial to an organism’s well-being
human development conflicts with this process

6. Organismal ecology: niche
Niche = an organism’s use of resources and its functional role in a community
habitat use, food selection, role in energy and nutrient flow
interactions with other individuals
Specialists = species with narrow niches and very specific requirements
extremely good at what they do, but vulnerable to change
Generalists = species with broad niches that can use a wide array of habitats and resources
able to weather variable conditions, may not thrive

7. Gause’s Principle
No two species can fill the same niche at the same time
The weaker species will fill the smaller niche, relocate or die.

8. Population ecology
All populations show characteristics that help scientists predict their future dynamics
Understanding human population dynamics is central to environmental science
Population size = the number of individual organisms present at a given time
numbers can increase, decrease, cycle, or remain the same

9. Population ecology
Population density = the number of individuals within a population per unit area
high densities make it easier to find mates, but increases competition, and vulnerability to predation & disease
low densities make it harder to find mates, but individuals benefit from more resources and space

10. Population ecology
Population distribution (dispersion) = spatial arrangement of organisms within an area
Random – individuals located haphazardly, with no pattern
Uniform – individuals are evenly spaced, can be due to territoriality
Clumped – arranged according to availability of resources needed to survive
most common in nature

11. Population ecology Sex ratio = proportion of males to females
in monogamous species, a 50/50 sex ratio maximizes population growth
Age structure (distribution) = the relative numbers of organisms of each age within a population
Age structure diagrams (pyramids) = show the age structure of populations

12. Birth and death rates
Crude birth/death rates = rates per 1000 individuals
Survivorship curves = the likelihood of death varies with age
Type I: More deaths at older ages
Type II: Equal number of deaths at all ages
Type III: More deaths at young ages

13. Four factors of population change
Natality = births within the population
Mortality = deaths within the population
Immigration = arrival of individuals from outside the population
Emigration = departure of individuals from the population
Growth rate formula =
(Crude birth rate + immigration rate) - (Crude death rate + emigration rate) = Growth rate
per 1000 individuals per year
expressed in % - better able to compare populations

14. Exponential population growth
Steady growth rates cause exponential population growth
increases by a fixed percent
Graphed as a J-shaped curve
Exponential growth cannot be sustained indefinitely
occurs in nature with a small population and ideal conditions
usually when introduced to a new environment

15. Limiting factors restrain population growth
Limiting factors = physical, chemical and biological characteristics that restrain population growth
water, space, food, mates, shelter, breeding sites, temperature, predators, and disease
interaction of these factors determines carrying capacity
may be determined by experiment
Environmental resistance = All limiting factors taken together

16. Carrying capacity
Carrying capacity = the maximum population size of a species that its environment can sustain
An S-shaped logistic growth curve
Limiting factors slow and stop exponential growth
Carrying capacity can vary
Humans have raised their carrying capacity by decreasing the carrying capacity for other species

17. Perfect logistic curves aren’t often found

18. Population density affects limiting factors
Density-dependent factors = limiting factors whose influence is affected by population density
increased chance of finding mates, but risk of predation and competition for mates occurs with increased density
Density-independent factors = limiting factors whose influence is not affected by population density
temperature extremes & catastrophic events such as floods, fires, and landslides

19. Biotic potential and reproductive strategies vary
Biotic potential = the ability of an organism to produce offspring
Interaction between biotic potential and environmental resistance helps determine the fate of the population

20. Biotic potential and reproductive strategies vary
K-selected species = animals with long gestation periods and few offspring
Have a low biotic potential
Invest in offspring
Stabilize at or near carrying capacity (K)
Good competitors
Regulated by density-dependent factors
r-selected species = animals which reproduce quickly & in quantity
Have a high biotic potential
Produce as many off spring as possible/little parental care
At or below carrying capacity
Regulated by density-independent factors

21. K-selected vs. r-selected species

22. Population changes affect communities
As population in one species declines, other species may appear
Human development now displaces other species and threatens biodiversity
As Monteverde dried out, species from lower, drier habitats appeared
But, species from the cloud-forest habitats disappeared

23. Challenges to protecting biodiversity
Social and economic factors affect species and communities
Nature is viewed as an obstacle to development
Nature is viewed as only a natural resource
Human population growth pressures biodiversity

24. Preserving biodiversity
Natural parks and protected areas help preserve biodiversity
Often, they are underprotected & underfunded
Ecotourism brings jobs and money to developing areas

25. QUESTION: Review
Which of the following is NOT a part of the process of natural selection?
a) Organisms struggle to survive
b) Organisms limit the number of young they produce
c) Individuals vary in their genetic characteristics
d) Some individuals are better suited to their environment than others
Answer: b

26. QUESTION: Review
Disruptive selection would result in which of the following?
a) Dogs with black coats evolving whiter coats in colder areas
b) Red and white flowers interbreeding, producing pink flowers
c) Fish evolving bigger eyes as the water gets muddier
d) A population of birds, some with thicker beaks that eat seeds and others with thinner beaks that eat insects
Answer: d

27. QUESTION: Review
Biological diversity includes all of the following, except:
a) Species diversity
b) Genetic diversity
c) Population diversity
d) Community diversity
e) All of these are included in the concept of biodiversity
Answer: e

28. QUESTION: Review Sympatric speciation would occur in ....
a) One population that mates in May, and another that mates in June
b) Two populations separated by the Mississippi River
c) Two populations separated by a glacier
d) Two populations separated by the Rocky Mountains
Answer: a

29. QUESTION: Review
Which of these species is least vulnerable to extinction?
a) A species with a population size of 50 individuals
b) A species distributed throughout the United States
c) A species that eats only river snails
d) A species that lives on mountaintops
Answer: b

30. QUESTION: Review An ecosystem is defined as:
a) The total living things on Earth
b) Members of the same population that can interbreed
c) Interacting species in an area
d) Species and the nonliving material they interact
with
Answer: d

31. QUESTION: Viewpoints Should we care whether a species goes extinct?
Yes, because all life is important and valuable
Yes, because we are causing this wave of extinction, so we should fix it
We should not, because it’s natural
I don’t care; it really does not affect me
Answer: any

32. QUESTION: Viewpoints
Do you think humans are subject to limiting factors and, ultimately, a fixed carrying capacity?
Yes, although we have raised the carrying capacity, there are limits to the number of humans the Earth can support
Yes, but technology will keep raising the carrying capacity, so it’s not much of a problem
No, humans are no longer constrained by environmental limits, due to our technology and ability to manipulate the environment
I don’t care; it really does not affect me
Answer: any

33. QUESTION: Interpreting Graphs and Data
Which of the following graphs shows a population that will have fewer individuals in the future?
Answer: d
(a)
(b)
(c)
(d)

34. QUESTION: Interpreting Graphs and Data
Which type of distribution is a result of individuals guarding their territory?
a) Random
b) Uniform
c) Clumped
d) None of these
Answer: b

35. QUESTION: Interpreting Graphs and Data
What does this graph show?
a) The effects of carrying capacity on population growth
b) A population that keeps growing
c) The effects of exponential growth
d) The effects of increasing carrying capacity
Answer: a