2. Introduction Evolution and ecology are two key concepts
Evolution: Changes that occur in organisms’ traits over time
Ecology: How organisms live in their environment
The great diversity of life on earth is the result of evolution
And evolution can be said to be the consequence of ecology over time

3. 2.1 Darwin’s Voyage on HMS Beagle
Charles Darwin ( )
Fig. 2.1
In 1831, Charles Darwin took on the role of naturalist of the ship HMS Beagle
The Beagle set sail on a five-year navigational trip around the world

4. 2.1 Darwin’s Voyage on HMS Beagle
Fig. 2.3
Most of the time was spent around South America

5. 2.1 Darwin’s Voyage on HMS Beagle
Darwin studied a wide variety of plants and animals across the globe
Particularly on the Galapagos Islands
In 1859, he published his book On the Origin of Species
In it he proposed that evolution occurs through natural selection

6. 2.2 Darwin’s Evidence
At first, Darwin was fully convinced that species were immutable
However, his observations eventually convinced him that evolution took place
Fossils of extinct species resembled living species in the same area
Galapagos finches differed slightly in appearance but resembled those on the S. American mainland

7. In all Darwin observed 14 different finch species
They differed mainly in beaks and feeding habitats
Fig Four Galapagos finches and what they eat
He believed it was “descent with modification” from a common ancestor
Or evolution

8. 2.3 The Theory of Natural Selection
Fig. 2.6
Darwin was influenced by Thomas Malthus’s Essay on the Principle of Population (1798)
Populations increase geometrically, while food supply increases only arithmetically
Thus, food supply will limit population growth

9. 2.3 The Theory of Natural Selection
Darwin was also familiar with variation in domesticated animals
Breeders use artificial selection to produce animals/plants with particular traits
Darwin proposed that such trait selection could also occur in nature
A process he termed natural selection

10. Fig. 2.7

11. 2.3 The Theory of Natural Selection
Darwin drafted a preliminary transcript in 1842
However, he shelved it for 16 years
Probably because of its controversial nature
Alfred Russel Wallace ( ) independently developed a similar theory
Correspondence between the two spurred Darwin to publish his theory in 1859

12. 2.3 The Theory of Natural Selection
Fig Darwin greets his monkey ancestor
Darwin’s Origin of Species was disturbing to many
It suggested that humans and apes have a common ancestor
Darwin presented this argument directly in a later book, The Descent of Man

13. 2.4 The Beaks of Darwin’s Finches
Darwin collected 31 finch species from the Galapagos Islands in 1835
Ornithologist John Gould determined that these finches were a closely-related group
They differed only in their bills
Darwin observed a correlation between the beaks and the food source of the birds
He concluded that the beaks had been shaped by evolution

14. 2.4 The Beaks of Darwin’s Finches
Fig A diversity of finches on a single island

15. 2.4 The Beaks of Darwin’s Finches
In 1938, David Lack set out to test Darwin’s hypothesis
Lack’s five-month observation seemed to contradict Darwin’s proposal
Lack found many different species of finch feeding together on the same seeds
So was Darwin wrong or is there something else going on?

16. 2.4 The Beaks of Darwin’s Finches
In 1973, Peter and Rosemary Grant embarked on a study of the medium ground finch
Geospiza fortis feeds preferentially on small tender seeds abundantly available in wet years
It resorts to larger, harder seeds in dry years
The Grants found out that the beak depth changed predictably year after year

17. 2.4 The Beaks of Darwin’s Finches
Fig. 2.11
Large-beaked finches increase in number
Small-beaked finches are more common
The Grants’ research supported Darwin’s hypothesis

18. 2.5 How Natural Selection Produces Diversity
Darwin believed that the Galapagos finches all evolved from a single common ancestor
The ancestor came from the South American mainland
New arrivals occupied different niches and were subject to different environmental pressures
This resulted in a cluster of species
A phenomenon termed adaptive radiation

19. 2.5 How Natural Selection Produces Diversity
The 14 finch species that Darwin studied now occupy four types of niches
1. Ground finches
2. Tree finches
3. Warbler finches
4. Vegetarian finch

20. Fig. 2.12 An evolutionary tree of Darwin’s finches

21. 2.6 What is Ecology? The term was coined by Ernst Haeckel (1866)
Gr. logos, study of
Ecology
Gr. oikos, house
Thus, ecology is the study of how organisms interact with their environment

22. 2.6 What is Ecology? There are five levels of ecological organization
1. Populations
Individuals of the same species living together
2. Communities
Populations of different species living together
3. Ecosystems
Combination of communities and associated non-living factors

23. 2.6 What is Ecology? There are five levels of ecological organization
4. Biomes
Major terrestrial assemblages of organisms that occur over wide geographical areas
5. The Biosphere
All biomes together with marine and freshwater assemblages

24. 2.7 A Closer Look at Ecosystems
Ecosystems: the fundamental units of ecology
All organisms in an ecosystem require energy
Almost all energy comes from the sun
Sun
Plants
Herbivores
Carnivores
Food chain
Energy is lost at each step of the food chain
This limits the number of steps

25. 2.7 A Closer Look at Ecosystems
Raw materials are not used up when organisms die
They are recycled back into the ecosystem for use by other organisms
Rainfall and temperature are the two most important factors limiting species distribution
These physical conditions with their sets of similar plants and animals are called biomes

26. Fig. 2.14 Biomes of North America

27. 2.8 How Species Evolve to Occupy Different Niches Within an Ecosystem
The niche of a species may be defined as its biological role in the community
It is not synonymous with habitat
Habitat  place
Niche  pattern of living

28. 2.8 How Species Evolve to Occupy Different Niches Within an Ecosystem
The principle of competitive exclusion
No two species with the same niche can coexist
Persistent competition is rare in nature
So species try to find ways to reduce competition
In resource partitioning, species avoid competition by
1. Living in different portions of the habitat
2. Using different resources

29. Same pattern has evolved independently on different Caribbean Islands
Fig Resource partitioning among sympatric lizard species
Anolis lizards
Same pattern has evolved independently on different Caribbean Islands

30. 2.8 How Species Evolve to Occupy Different Niches Within an Ecosystem
Character displacements
The changes that evolve in two species to reduce niche overlap
This is clearly seen among Darwin’s finches

31. Fig. 2.16 Character displacement in Darwin’s finches (genus Geospiza)
Bills of similar sizes when living apart
Bills of different sizes when living together

32. 2.9 Patterns of Population Growth
Innate capacity for increase
The rate at which a population grows in the absence of limits
Also termed the biotic potential
Realized rate of population increase (r)
# of individuals added minus the # lost
Thus:
r =
(birth + immigration) –
(death + emigration)

33. population growth rate = rN
Exponential Growth
To determine the population growth rate, r must be adjusted for population size
# of individuals in the population
population growth rate = rN
Realized rate of population growth
A population exhibits exponential growth at first
However, the growth rate slows down as resources become depleted

34. Fig. 2.17 Exponential growth in a population of bacteria

35. Population growth is limited by shortages of some important factor
Carrying Capacity (K)
Is the number of individuals that can be supported in a particular area indefinitely
Population growth is limited by shortages of some important factor
Space, water, nutrients
Growth of a population is approximated by the following logistic growth equation
K – N K
population growth rate = rN

36. This relationship is graphically represented as a sigmoid growth curve
Growth fluctuates around K
Fig. 2.18
Exponential growth at first

37. Life History Strategies
The particular set of adaptations that adjusts an organism’s growth rate to its environment
r-selected life history
K-selected life history
Rapid growth
Slow growth
Short lifespan
Long lifespan
Transient environments
Stable environments
Large no. of offspring
Small no. of offspring
No parental care
Parental care

38. Life History Strategies
Fig K-selected life history
Fig r-selected life history

39. 2.10 Human Populations
Throughout most of our history, human populations have been regulated by
Food availability
Disease
Predators
Two thousand years ago, the human population was ~ 130 million
It took one thousand years for it to double
And another 650 years for it to double again

40. 2.10 Human Populations
Starting in the 1700s, technological changes gave humans more control over their environment
These changes allowed humans to expand the carrying capacity of their habitats
Currently, the human population is growing at a rate of ~ 1.3% annually
Doubling time at this rate is only 54 years!

41. Fig. 2.21 History of human population size

42. Population Pyramids
Human population growth is not uniform

43. Birth rate much higher than death rate
Population Pyramids
Some countries, like Mexico, are currently growing rapidly
Fig. 2.22
Birth rate much higher than death rate

44. Population Pyramids
A population’s age structure and sex ratio can be used to assess its demographic trends
More or less rectangular pyramid
=> Stable population
Fig. 2.23
Triangular pyramid
=> Rapid future growth

45. Consumption in the Developed World
The vast majority of the world’s population is in developing countries
However, the vast majority of resource consumption is in the developed world
This disparity can be quantified by calculating the ecological footprint
The amount of productive land required to support a person throughout his or her life

46. Fig. 2.24 Ecological footprint of individuals in different countries
Resource use by humans is now 1/3 greater than the amount that nature can sustainably replace