1. Ch 5 Evolution, Biodiversity, and Population Ecology
Part 1: Foundations of Environmental Science

2. This lecture will help you understand:
Natural selection
How evolution influences biodiversity
Reasons for species extinction
Ecological organization
Population characteristics
Population ecology
Conservation biology

3. Striking gold in Costa Rica
Golden toads were discovered in 1964, in Monteverde, Chile
The mountainous cloud forest has a perfect climate for amphibians
Unfortunately, they became extinct within 25 years
Due to global warming’s drying effect on the forest

4. Striking gold in Costa Rica
“I must confess that my initial response when I saw them was one of disbelief and suspicion that someone had dipped the examples in enamel paint.”
-Dr. Jay M. Savage,
Describing the Golden Toad in 1966
“What a terrible feeling to realize that within my own lifetime, a species of such unusual beauty, one that I had discovered, should disappear from our planet.”
-Dr. Jay M. Savage,
Describing the Golden Toad in 1998

5. Evolution: the source of Earth’s biodiversity
Biological evolution  genetic change in populations of organisms across generations (change over time)
May be random or directed by natural selection
Natural Selection  the process by which traits that enhance survival and reproduction are passed on more frequently to future generations than those that do not

6. Understanding evolution is vital
WHY should we understand / learn about evolution?
It alters the genetic makeup of a population
It is important for understanding antibiotic and pesticide resistance, agricultural issues, production, medicines, etc.
Organisms adapt to their environment and change over time

7. Natural selection shapes organisms
In 1858, Darwin and Wallace both proposed natural selection as the mechanism of evolution
Organisms face a constant struggle to survive and reproduce (Struggle for Existence)
Individuals of a species vary in their characteristics due to genes and the environment
Some individuals are better suited to their environment and will survive and pass their genes on in their offspring (Survival of the Fittest)
Organisms evolved from common ancestor with changes over time (Descent with Modification)

8. What’s with those tail feathers?

9. Genetic variation
Adaptive Trait (Adaptation)  a trait that promotes reproductive success
Mutations  accidental changes in DNA that may be passed on to the next generation
Non-lethal mutations provide the genetic variation on which natural selection acts
Sexual reproduction also leads to variation

10. Natural selection acts on genetic variation
Directional selection drives a feature in one direction
Stabilizing selection produces intermediate traits, preserving the status quo
Disruptive selection traits diverge in two or more directions
If the environment changes, a trait may no longer be adaptive!!

11. Natural selection acts on genetic variation

12. Evidence of natural selection is everywhere
It is evident in every adaptation of every organism
Evident in bacteria and fruit flies in laboratories
Selective breeding of animals

13. Artificial selection
Artificial Selection  the process of selection conducted under human direction
For example, artificial selection has led to the great variety of dog breeds

14. Artificial selection

15. Evolution generates biodiversity
Biological Diversity  An area’s sum total of all organisms
Diversity of species, their genes, populations, and communities
Species  a population or group of populations whose members share characteristics and can freely breed with one another and produce fertile offspring
Population  a group of individuals of a species that live in the same area

16. Speciation produces new organisms
Speciation  process of generating new species
A single species can generate multiple species
Allopatric speciation  species formation due to physical separation of populations
Can be separated by glaciers, rivers, mountains
The main mode of species creation
DARWIN’S FINCHES

17. Allopatric speciation

18. Another type of speciation
Sympatric speciation  species form from populations that become reproductively isolated within the same area
Feed in different areas, mate in different seasons
Mutations

19. Speciation results in diverse life forms
Speciation generates complex patterns of diversity above the species level
Phylogenetic trees (Cladograms)  Represents the history of species divergence
Scientists can trace when certain traits evolved
Show relationships between species

20. Extinction the disappearance of a species from Earth
Occurs when a species cannot adapt quickly enough to a changing environment
Speciation and extinction affect species numbers

21. Extinction is a natural process
Extinction is irreversible: once a species is lost, it is lost forever!!!!!
HUMANS profoundly affect rates of extinction (overhunting, destroy habitats, etc.)

22. Some species are more vulnerable to extinction
Extinction occurs when the environment changes too rapidly for natural selection to keep up
Endemic species  a species only exists in a certain, specialized area (EXAMPLE??)
Very susceptible to extinction … WHY???
These species usually have small populations
Many other factors also cause extinction
Severe weather
New species
Specialized species

23. Earth has had several mass extinctions
Background extinction rate  extinction usually occurs one species at a time
Mass extinction events  five events in Earth’s history that killed off massive numbers of species at once (MOST COMMON?)
50-95% of all species went extinct at one time
Humans are causing the sixth mass extinction event
Resource depletion
Population growth
Development

24. Species’ ranges can be severely restricted
Some U.S. salamander species live on top of single mountains … VULNERABLE TO EXTINCTION!

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

26. Levels of ecological organization
Population ecology = investigates the quantitative dynamics of how individuals within a species interact
Community ecology = focuses on interactions among species
Ecosystem ecology = studies living and nonliving components of systems to reveal patterns
Nutrient and energy flows

27. Organismal ecology: habitat
Habitat  the environment in which an organism lives
Includes living and nonliving elements
Habitat use  each organism thrives in certain habitats, but not in others
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 developments conflict with this process

28. 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 live in many different places

29. Population characteristics
All populations show characteristics that help scientists predict their future dynamics
Population size  the number of individual organisms present at a given time
Numbers can increase, decrease, cycle or remain the same

30. Population characteristics
Population density  the number of individuals within a population per unit area
High densities make it easier to find mates, but increase competition, and vulnerability to predation
Low densities make it harder to find mates, but individuals enjoy plentiful resources and space

31. Population characteristics
Population distribution (dispersion)  spatial arrangement of organisms within an area
Random: haphazardly located individuals, with no pattern
Uniform: individuals are evenly spaced due to territoriality
Clumped : arranged according to availability of resources
Most common in nature

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

33. Birth and death rates
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

34. 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
Why would individuals move in or out of an area?

35. Exponential population growth
Steady growth rates cause exponential population growth
Graphed as a J-shaped curve
Exponential growth cannot be sustained indefinitely
It occurs in nature with a small population and IDEAL conditions

36. Exponential population growth
UNLIMITED RESOURCES!!!
Exponential Growth

37. Logistic population growth
Growth that is limited and levels off is logistic population growth
Graphed as a S-shaped curve
More likely to occur in nature but not often
Takes into account that resources are limited in nature

38. Carrying capacity
Carrying capacity  the maximum population size of a species that its environment can sustain
Certain factors slow and stop exponential growth
Carrying capacity changes
Humans have raised their carrying capacity by decreasing the carrying capacity for other species

39. Perfect logistic curves aren’t often found

40. Limiting factors restrain growth
Limiting factors  physical, chemical and biological characteristics that restrain population growth (cause decline)
Competition for resources, predation, parasitism, disease, weather, and human disturbances

41. Population density affects limiting factors
Density-dependent factors  limiting factors whose influence is affected by population density
Increased risk of predation and competition for mates occurs with increased density
Density-independent factors  limiting factors whose influence is NOT affected by population density
Events such as floods, fires, and landslides

42. Population density affects limiting factors

43. Biotic potential and reproductive strategies vary
Biotic potential  the ability of an organism to produce offspring
K-selected species  animals with long gestation periods and few offspring
Have a low biotic potential
Stabilize at or near carrying capacity
Good competitors
r-selected species  animals which reproduce quickly
Have a high biotic potential
Little parental care

44. K-selected vs. r-selected species

45. 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

46. 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 source of resources
Human population growth pressures biodiversity

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

48. 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

49. 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

50. 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

51. 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

52. 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

53. 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

54. 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

55. 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

56. 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)

57. 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

58. 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