1. Ecology and evolution: Populations, communities, and biodiversity4
Ecology and evolution: Populations, communities, and biodiversity

2. This lecture will help you understand:
How evolution generates biodiversity
Speciation, extinction, and the “biodiversity crisis”
Population ecology
Community ecology
Species interactions
Conservation challenges
Evolution by natural selection

3. Central Case: Striking Gold in a Costa Rican Cloud Forest
The golden toad of Monteverde, discovered in 1964, had disappeared 25 years later.
Researchers determined that warming and drying of the forest was most likely responsible for its extinction.
As the global climate changes, more such events can be expected.

4. Biodiversity
Biodiversity, or biological diversity, is the sum of an area’s organisms, considering the diversity of species, their genes, their populations, and their communities.
A species is a particular type of organism; a population or group of populations whose members share certain characteristics and can freely breed with one another and produce fertile offspring.

5. Biodiversity
Costa Rica’s Monteverde cloud forest is home to many species and possesses great biodiversity.
Figure 5.1

6. Natural selection Natural selection rests on three indisputable facts:
• Organisms produce more offspring than can survive.
• Individuals vary in their characteristics.
• Many characteristics are inherited by offspring from parents.

7. Natural selection THEREFORE, logically…
• Some individuals will be better suited to their environment; they will survive and reproduce more successfully.
• These individuals will transmit more genes to future generations.
• Future generations will thus contain more genes from better-suited individuals.
• Thus, characteristics will evolve over time to resemble those of the better-suited ancestors.

8. Natural selection
Fitness = the likelihood that an individual will reproduce
and/or
the number of offspring an individual produces over its lifetime
Adaptive trait,
or adaptation = a trait that increases an individual’s fitness

9. Natural selection Evidence of natural selection is all around us:
In nature …
Diverse bills have evolved among species of Hawaiian honeycreepers.
Figure 4.23a

10. Beak Types Resulting From Natural Selection
Unknown finch ancestor
Insect and nectar eaters
Fruit and seed eaters
Greater Koa-finch
Kona Grosbeak
Akiapolaau
Maui Parrotbill
Kuai Akialoa
Amakihi
Crested Honeycreeper
Apapane

11. Natural selection Evidence of natural selection is all around us:
… and in our domesticated organisms.
Dog breeds, types of cattle, improved crop plants—all result from artificial selection (natural selection conducted by human breeders).
Figure 4.23b

12. Speciation The process by which new species come into being
Speciation is an evolutionary process that has given Earth its current species richness—more than 1.5 million described species and likely many million more not yet described by science.
Allopatric speciation is considered the dominant mode of speciation, and sympatric speciation also occurs.

13. Allopatric speciation
1. Single interbreeding population
2. Population divided by a barrier; subpopulations isolated
Figure 5.2

14. Allopatric speciation
3. The two populations evolve independently, diverge in their traits.
4. Populations reunited when barrier removed, but are now different enough that they don’t interbreed.
Figure 5.2

15. Allopatric speciation
Many geological and climatic events can serve as barriers separating populations and causing speciation.
on.

16. Formation
of the
earth’s
early
crust and
atmosphere
Small
organic
molecules
form in
the seas
Large
(biopolymers)
First
protocells
Single-cell
prokaryotes
eukaryotes
Variety of
multicellular
organisms
form, first
in the seas
and later
on land
Chemical Evolution
(1 billion years)
Biological Evolution
(3.7 billion years)

17. Geographic Separation
Early fox
population
Spreads
northward
and
southward
separates
Adapted to heat
through lightweight
fur and long ears,
legs, and nose, which
give off more heat.
Adapted to cold through heavier fur, short ears,
short legs, short nose. White fur matches snow for camouflage.
Gray Fox
Arctic Fox
Different environmental
conditions lead to different
selective pressures and evolution
into two different species.
Northern population
Southern population

18. Mimicry Span worm Bombardier beetle Viceroy butterfly mimics
monarch butterfly
Foul-tasting monarch
butterfly
Poison dart frog
When touched, the
snake caterpillar
changes shape to look
like the head of a snake
Wandering leaf insect
Hind wings of io moth
resemble eyes of a
much larger animal

19. Phylogenetic trees
Life’s diversification results from countless speciation events over vast spans of time.
Evolutionary history of divergence is shown with diagrams called phylogenetic trees.
Similar to family genealogies, these show relationships among organisms.

20. Phylogenetic trees
These trees are constructed by analyzing patterns of similarity among present-day organisms.
This tree shows all of life’s major groups.
Figure 5.4

21. Phylogenetic trees
Within the group Animals in the previous slide, one can infer a tree of the major animal groups.
Figure 5.4

22. Phylogenetic trees
And within the group Vertebrates in the previous slide, one can infer relationships of the major vertebrate groups, and so on…
Figure 5.4

23. Extinction
Extinction is the disappearance of an entire species from the face of the Earth.
Average time for a species on Earth is ~1–10 million years. Species currently on Earth = the number formed by speciation minus the number removed by extinction.

24. Extinction Some species are more vulnerable to extinction than others:
• Species in small populations
• Species adapted to a narrowly specialized resource or way of life
Monteverde’s golden toad was apparently such a specialist, and lived in small numbers in a small area.

25. Extinction Some species are more vulnerable to extinction than others:
• Species in small populations
• Species adapted to a narrowly specialized resource or way of life
Monteverde’s golden toad was apparently such a specialist, and lived in small numbers in a small area.

26. Life’s hierarchy of levels
Life occurs in levels:
from the atom up to
the molecule to
the cell to
the tissues to
the organs to
the organism…
Figure 5.7

27. Life’s hierarchy of levels
… and from the organism to the population to
the community to
the ecosystem to
the biosphere.
Ecology deals with these levels, from the organism up to the biosphere.
Figure 5.7

28. Ecology The study of: the distribution and abundance of organisms,
the interactions among them,
and the interactions between organisms and their abiotic environments
Ecology is NOT environmental advocacy!
(= a common MISUSE of the term)

29. Habitat and niche
Habitat = the specific environment where an organism lives (including living and nonliving elements: rocks, soil, plants, etc.)
Habitat selection = the process by which organisms choose habitats among the options encountered
Niche = an organism’s functional role in a community (feeding, flow of energy and matter, interactions with other organisms, etc.)

30. Population ecology
Population = a group of individuals of a species that live in a particular area
Several attributes help predict population dynamics (changes in population):
• Population size
• Population density
• Population distribution
• Age structure
• Sex ratio

31. Population size
Number of individuals present at a given time Population size for the golden toad was 1,500+ in 1987, and zero a few years later.

32. Population density Number of individuals per unit area or,
Number of individuals per unit volume
Population density for the harlequin frog increased locally as streams dried and frogs clustered in splash zones.

33. Population distribution
Spatial arrangement of individuals
Clumped
Random
Uniform
Figure 5.8

34. Age structure
Or age distribution = relative numbers of individuals of each age or age class in a population
Age structure diagrams, or age pyramids, show this information.
Figure 5.9

35. Age structure Pyramid weighted toward young: population growing
Pyramid weighted toward old: population declining
Figure 5.9

36. Sex ratio Ratio of males to females in a population
Even ratios (near 50/50) are most common.
Fewer females causes slower population growth.
Note human sex ratio biased toward females at oldest ages.

37. Population growth
Populations grow, shrink, or remain stable, depending on rates of birth, death, immigration, and emigration.
(birth rate + immigration rate) –
(death rate + emigration rate)
= population growth rate

38. Exponential growth
Unregulated populations increase by exponential growth:
Growth by a fixed percentage, rather than a fixed amount.
Similar to growth of money in a savings account

39. Exponential growth in a growth curve
Population growth curves show change in population size over time.
Scots pine shows exponential growth
Figure 5.10

40. Limits on growth
Limiting factors restrain exponential population growth, slowing the growth rate down.
Population growth levels off at a carrying capacity—the maximum population size of a given species an environment can sustain.
Initial exponential growth, slowing, and stabilizing at carrying capacity is shown by a logistic growth curve.

41. Logistic growth curve
Figure 5.11

42. Population growth: Logistic growth
Logistic growth (shown here in yeast from the lab) is only one type of growth curve, however.
Figure 5.12a

43. Population growth: Oscillations
Some populations fluctuate continually above and below carrying capacity, as with this mite.
Figure 5.12b

44. Population growth: Dampening oscillations
In some populations, oscillations dampen, as population size settles toward carrying capacity, as with this beetle.
Figure 5.12c

45. Population growth: Crashes
Some populations that rise too fast and deplete resources may then crash, as with reindeer on St. Paul Island.
Figure 5.12d

46. Density dependence
Often, survival or reproduction lessens as populations become more dense.
Density-dependent factors (disease, predation, etc.) account for the logistic growth curve.

47. Biotic potential and reproductive strategies
Species differ in strategies for producing young.
Species producing lots of young (insects, fish, frogs, plants) have high biotic potential.
Others, such as mammals and birds, produce few young.
However, those with few young give them more care, resulting in better survival.

48. (environmental resistance)
POPULATION SIZE
Growth factors
(biotic potential)
Favorable light
Favorable temperature
Favorable chemical environment
(optimal level of critical nutrients)
Abiotic
Biotic
High reproductive rate
Generalized niche
Adequate food supply
Suitable habitat
Ability to compete for resources
Ability to hide from or defend
against predators
Ability to resist diseases and parasites
Ability to migrate and live in other
habitats
Ability to adapt to environmental
change
Decrease factors
(environmental resistance)
Too much or too little light
Temperature too high or too low
Unfavorable chemical environment
(too much or too little of critical
nutrients)
Low reproductive rate
Specialized niche
Inadequate food supply
Unsuitable or destroyed habitat
Too many competitors
Insufficient ability to hide from or defend
Inability to resist diseases and parasites
Inability to migrate and live in other
Inability to adapt to environmental
Biotic Potential

49. Percentage surviving (log scale)
Survivorship
Percentage surviving (log scale)
100 10 1
Age
Early loss
Constant loss
Late loss

50. K-strategists Terms come from:
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
Elephant
Saguaro
K-Selected Species
Terms come from:
K = symbol for carrying capacity. (Populations tend to stabilize near K.)

51. 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
r-Selected
r = intrinsic rate of population increase. (Populations can potentially grow fast, have high r.)

52. Community ecology
Ecologists interested in how populations or species interact with one another study community ecology.
Community = a group of populations of different species that live in the same place at the same time
e.g., Monteverde cloud forest community–golden toads, quetzals, trees, ferns, soil microbes, etc.

53. Roles in communities: Producers
By eating different foods, organisms are at different trophic levels, and play different roles, in the community
Plants and other photosynthetic organisms are producers.
Figure 5.14b

54. Primary consumers
Animals that eat plants are primary consumers, or herbivores, and are at the second trophic level.
Figure 5.14b

55. Secondary consumers
Animals that eat herbivores are secondary consumers, at the third trophic level.
Figure 5.14b

56. Detritivores and decomposers
Detritivores and decomposers eat nonliving organic matter; they recycle nutrients.
Figure 5.14b

57. Trophic levels
Together these comprise trophic levels.
Figure 5.14b

58. Food chains and webs
We can represent feeding interactions (and thus energy transfer) in a community:
Food chain: Simplified linear diagram of who eats whom
Food web: Complex network of who eats whom

59. Food web for an eastern deciduous forest
Figure 5.14a

60. A “keystone” holds an arch together.
Keystone species
Species that have especially great impacts on other community members and on the community’s identity
If keystone species are removed, communities change greatly.
A “keystone” holds an arch together.
Figure 5.15a

61. Keystone species
When the keystone sea otter is removed, sea urchins overgraze kelp and destroy the kelp forest community.
Figure 5.15b

62. Balance of Life
(a) Southern sea otter
(b) Sea Urchin
(c) Kelp bed

63. Predation
One species, the predator, hunts, kills, and consumes the other, its prey.
Figure 5.16

64. Predation drives adaptations in prey
Cryptic coloration:
Camouflage to hide from predators
Warning coloration:
Bright colors warn that prey is toxic
Mimicry:
Fool predators
(here, caterpillar mimics snake)
Figure 5.18

65. Competition When multiple species seek the same limited resource
Interspecific competition is between two or more species.
Intraspecific competition is within a species.
Usually does not involve active fighting, but subtle contests to procure resources.

66. Interspecific competition
Different outcomes:
Competitive exclusion = one species excludes the other from a resource.
Species coexistence = both species coexist at a ratio of population sizes, or stable equilibrium.

67. Competitive Exclusion Principle
Click to view animation.

68. Interspecific competition
Adjusting resource use, habitat use, or way of life over evolutionary time leads to:
Resource partitioning = species specialize in different ways of exploiting a resource.
Character displacement = physical characters evolve to become different to better differentiate resource use.

69. Resource partitioning
Tree-climbing bird species exploit insect resources in different ways.
Figure 5.20

70. Parasitism
One species, the parasite, exploits the other species, the host, gaining benefits and doing harm.
Figure 5.21

71. Mutualism Both species benefit one another.
Hummingbird pollinates flower while gaining nectar for itself.
Figure 5.22

72. Oxpeckers and black rhinoceros Clown fish and sea anemone
Mutualism
Oxpeckers and black rhinoceros
Clown fish and sea anemone
Mycorrhizae fungi on juniper
seedlings in normal soil
Lack of mycorrhizae fungi on
juniper seedlings in sterilized soil

73. Succession
A series of regular, predictable, quantifiable changes through which communities go
• Primary succession: Pioneer species colonize a newly exposed area (lava flows, glacial retreat, dried lake bed).
• Secondary succession: The community changes following a disturbance (fire, hurricane, logging).

74. Primary aquatic succession
1. Open pond
2. Plants begin to cover surface; sediment deposited
3. Pond filled by sediment; vegetation grows over site
Figure 5.24

75. Secondary terrestrial succession
Figure 5.23

76. Click to view animation.
Succession
Click to view animation.

77. Ecosystem Characteristics at Immature and Mature Stages of Ecological Succession
Ecosystem Structure
Plant size
Species diversity
Trophic structure
Ecological niches
Community organization
(number of interconnecting links)
Ecosystem Function
Biomass
Net primary productivity
Food chains and webs
Efficiency of nutrient recycling
Efficiency of energy use
Immature Ecosystem
(Early Successional Stage)
Small
Low
Mostly producers, few decomposers
Few, mostly generalized
High
Simple, mostly plant herbivore
with few decomposers
Immature Ecosystem
(Late Successional Stage)
Large
High
Mixture of producers, consumers, and decomposers
Many, mostly specialized
Low
Complex, dominated by decomposers
Table 8-1 Page 158

78. Invasive species
A species that spreads widely and rapidly becomes dominant in a community, changing the community’s normal functioning
Many invasive species are non-native, introduced from other areas.
Purple loosestrife invades a wetland.
Figure 5.25

79. Climate change and Monteverde
Monteverde’s cloud forest become drier in the 1970s–1990s.
Number of dry days rose
Stream flow fell
From The Science behind the Stories

80. Climate change and Monteverde
Cool ocean; low clouds; mountains receive moisture
Warm ocean; high clouds; mountains get less moisture
From The Science behind the Stories

81. Viewpoints: Conservation of Monteverde?
Robert Lawton
Nathaniel Wheelwright
“A few committed people can have an impact. Conservation efforts must take into account local social aspirations. Conservation can lead to economic success. But local conservation is not enough.”
“Whatever negative local impact the steady onslaught of ecotourists may have on resplendent quetzals and howler monkeys, it is more than compensated for by inspiring people to appreciate tropical forests and their own natural heritage.”
From Viewpoints

82. Conclusions: Challenges
Earth’s biodiversity faces a mass extinction event caused by human actions.
Climate change may alter communities and cause species extinctions.
Invasive species pose a new threat to community stability.
Conservation efforts need to consider local economies and social conditions in order to succeed.
Evolution and natural selection provide a strong explanation for how Earth’s life diversified.

83. Conclusions: Solutions
There is still time to avoid most species extinctions threatened by human actions.
Studies like those at Monteverde are clarifying the effects of climate change.
Ecological restoration efforts can remove invasive species and restore original communities.
Many conservation efforts today are locally run or promote local economies.

84. QUESTION: Review Allopatric speciation requires…? a. Natural selection
b. More than two populations
c. Some kind of barrier separating populations
d. Sex ratio bias in one population
Answer = c

85. QUESTION: Review Which is a K-strategist?
a. A dragonfly that lays 300 eggs and flies away
b. An oak tree that drops its acorns each year
c. A bamboo plant that flowers only once every 20 years
d. A human who raises three children
e. A fish on the second trophic level
Answer = d

86. QUESTION: Review
Which of the following lists of trophic levels is in the correct order?
a. Producer, secondary consumer, herbivore
b. Producer, herbivore, secondary consumer
c. Secondary consumer, producer, detritivore
d. Herbivore, carnivore, producer
Answer = b

87. QUESTION: Review
Primary succession would take place on all of the following EXCEPT…?
a. The slopes of a Hawaiian volcano’s new lava flow
b. A South Carolina coastal forest after a hurricane
c. Alaskan land just uncovered as a glacier melts
d. A new island formed by falling levels of a reservoir in Ohio
Answer = d

88. QUESTION: Weighing the Issues
Can we continue raising the Earth’s carrying capacity for humans by developing technology and using resources more efficiently?
a. Yes, our growth can continue indefinitely.
b. Our growth can continue some more, but will eventually be halted by limiting factors.
c. No, we cannot raise Earth’s carrying capacity for ourselves any longer.
Answer = personal opinion

89. QUESTION: Weighing the Issues
Are national parks and preserves the best way to conserve biodiversity?
a. Yes, because species depend on their habitats and intact communities being protected.
b. No, because climate change can ruin conservation efforts if it changes conditions inside preserves.
c. Ecotourism and encouraging local interest in conservation is more important than establishing parks.
Answer = personal opinion

90. QUESTION: Interpreting Graphs and Data
You would expect this population to be…?
a. Growing rapidly
b. Shrinking rapidly
c. Stable in size
d. Oscillating in size
Answer = a
Figure 5.9

91. QUESTION: Interpreting Graphs and Data
How can you tell that this population growth curve shows exponential growth?
a. Population is increasing.
b. Data points match curve closely.
c. Population is rising by the same number during each interval.
d. Population is rising by the same percentage during each interval.
Answer = d
Figure 5.10

92. QUESTION: Interpreting Graphs and Data
This shows growth ending at a(n)
a. exponential… carrying capacity
b. intrinsic… equilibrium
c. logistic… carrying capacity
d. runaway… equilibrium
e. logistic… extinction
Answer = d
Figure 5.12a

93. QUESTION: Viewpoints
What is the most important lesson we can learn from the Monteverde preserve?
a. Preserves do little good if species can become extinct inside them.
b. Climate change means that we will need more than preserves to save all species.
c. Ecotourism and local participation can make for successful conservation.
Answer = personal opinion