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

2. Striking gold in Costa Rica
In 1964, Golden toads were discovered in Monteverde, Costa Rica
The mountainous cloud forest has a perfect climate for amphibians
They became extinct within 25 years
Climate change’s drying effect on the forest
A lethal fungus

3. Evolution generates biodiversity
Species = a population or group of populations
Whose members share characteristics
They can breed with one another and produce fertile offspring
Population = a group of individuals of a species that live in the same area
Evolution = means change over time
Biological evolution: genetic change in populations over time
Genetic changes lead to changes in appearance, functioning or behavior over generations

4. Natural selection Evolution may be random
Or directed by natural selection
Natural Selection = traits that enhance survival and reproduction
Are passed on more frequently to future generations
Than those that do not

5. Evolution by natural selection
It is one of the best-supported and most illuminating concepts in all science
It is the standpoint of modern biology
We must understand it to appreciate environmental science
Knowing ecology and learning the history of life
Evolutionary processes influence pesticide resistance, agriculture, medicine, health, etc.
In 1858, both Darwin and Wallace proposed natural selection as the mechanism of evolution

6. Natural selection shapes organisms
Premises of natural selection:
Organisms struggle to survive and reproduce
Organisms produce more offspring than can survive
Individuals of a species vary in their characteristics due to genes and the environment
Some individuals are better suited to their environment and reproduce more effectively
Natural selection acts on genetic variation

7. Genetic variation
Adaptation = the process where, over time, characteristics (traits) that lead to better reproductive success
Become more prevalent in the population
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

8. Natural selection acts on genetic variation
Natural selection changes characteristics through:
Directional selection = drives a feature in one direction
Stabilizing selection = favors intermediate traits
Preserving the status quo
Disruptive selection = traits diverge in two or more directions

9. Environmental conditions affect selection
Environmental conditions determine the pressures natural selection exerts
These pressures affect who survives and reproduces
Traits evolve that allow success in that environment
But traits that promote success at one time or place may not do so at another
Natural selection weeds out unfit individuals
It also elaborates and diversifies traits that may produce new species

10. Selective pressures influence adaptation
Related species in different environments
Experience different pressures
Evolve different traits
Convergent evolution = unrelated species may evolve similar traits
Because they live in similar environments

11. Evidence of natural selection is everywhere
It is evident in every adaptation of every organism
Artificial Selection = the process of selection conducted under human direction
Producing the great variety of dog breeds and food crops

12. Evolution generates biological diversity
Biological diversity (biodiversity) = the variety of life across all levels of biological organization
Species
Genes
Populations
Communities
Scientists have described 1.8 million species
Up to 100 million species may exist
Tropical rainforests are rich in biodiversity

13. Speciation produces new types of organisms
The process of generating new species from a single species
Allopatric speciation: species formation due to physical separation of populations
The main mode of speciation
Populations can be separated by glaciers, rivers, mountains
Each population gets its own set of mutations

14. 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
Hybridization between two species
Mutations

15. Speciation results in diverse life forms
How do major groups diverge over time?
Phylogenetic trees (cladograms) = show relationships among species, groups, genes, etc.
Scientists can trace how certain traits evolved

16. The fossil record Fossil: an imprint in stone of a dead organism
Fossil record: the cumulative body of fossils worldwide
The fossil record shows:
Life has existed on Earth for at least 3.5 billion years
Earlier types of organisms evolved into later ones
The number of species has increased over time
Most species have gone extinct
There have been several mass extinctions in the past

17. Extinction Extinction = the disappearance of a species from Earth
Species last 1-10 million years
Biological diversity is now being lost at an astounding rate
This loss of species is irreversible
Number of species = speciation - extinction

18. Extinction is a natural process, but …
Humans profoundly affect rates of extinction
Biodiversity loss affects people directly
Food, fiber, medicine, ecosystem services

19. Some species are more vulnerable to extinction
Extinction occurs when the environment changes rapidly
Natural selection can not keep up
Many factors cause extinction:
Severe weather, climate change, changing sea levels
New species, small populations
Specialized species
Endemic species = a species only exists in a certain, specialized area
Very susceptible to extinction
These species usually have small populations

20. Many U.S. amphibian species are vulnerable
Many U.S. amphibians have very small ranges
They are vulnerable to extinction
The Yosemite toad, Houston toad, Florida bog frog
40 salamander species are restricted to areas the size of a typical county
Some U.S. salamander species live on top of single mountains

21. Earth has had several mass extinctions
Background extinction rate = extinction usually occurs one species at a time
Mass extinction events = killed off massive numbers of species at once
Occurred five times in Earth’s history
50-95% of all species went extinct at one time
Cretaceous-Tertiary (K-T) event: 65 million years ago
Dinosaurs went extinct
End-Permian event: 250 million years ago
75-95% of all species went extinct

22. The sixth mass extinction is upon us
Humans are causing the sixth mass extinction event
Resource depletion, population growth, development
Destruction of natural habitats
Hunting and harvesting of species
Introduction of non-native species
It is 100-1,000 times higher than the background rate and rising
Amphibians are disappearing the fastest
170 species have already vanished
It will take millions of years for life to recover

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

24. Levels of ecological studies
Population ecology = investigates the dynamics of population change
The factors affecting the distribution and abundance of members of a population
Why some populations increase and others decrease
Community ecology = focuses on patterns of species diversity and interactions
Ecosystem ecology = studies living and nonliving components of systems to reveal patterns
Nutrient and energy flows

25. Each organism has habitat needs
Habitat = the environment where an organism lives
It includes living and nonliving elements
Habitat use = each organism thrives in certain habitats, but not in others
Results in nonrandom patterns of use
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

26. A specialized frog Epiphytes grow on trees for support
Obtaining water from the air
They collect pools of rainwater and pockets of leaf litter
Frogs lay their eggs in these rainwater pools

27. Habitats vary Habitats vary with the body size and needs of species
A soil mite vs. an elephant
Species have different habitat needs at different times
Migratory birds use different habitats during migration, summer and winter
Species use different criteria to select habitat
Soil, topography, vegetation, other species
Water temperature, salinity, prey
Species survival depends on having suitable habitat

28. Organismal ecology: niche
Niche = an organism’s use of resources
Along with its functional role in a community
Habitat use, food selection, role in energy and nutrient flow, interactions with other individuals
Specialists = have narrow niches and specific needs
Extremely good at what they do
But vulnerable when conditions change
Generalists = species with broad niches
They use a wide array of habitats and resources
They can 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 in a population per unit area
Large organisms usually have low densities
They need many resources and a large area to survive
High densities make it easier to find mates
But increase competition and vulnerability to predation
Increased transmission of diseases
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
Random = haphazardly located individuals, with no pattern
Uniform = individuals are evenly spaced
Territoriality, competition
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 1:1 sex ratio maximizes population growth
Age distribution (structure) = the relative numbers of organisms of each age in a population
Age structure diagrams (pyramids) = show the age structure of populations
In species that continue growing as they age
Older individuals reproduce more (i.e. a tree)
Experience makes older individuals better breeders

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
Births and immigration add individuals
Deaths and emigration remove individuals
Crude birth (death) rates: number of births (deaths) per 1000 individuals per year

35. Population growth rate
Natural rate of population growth =
(Crude birth rate) – (crude death rate)
Population change due to internal factors
Population growth rate =
(Crude birth rate + immigration rate) – (Crude death rate + emigration rate)
Net changes in a population’s size/1000/year
Growth rate as a percent =
Population growth rate * 100%
Populations of different sizes can be compared

36. Exponential population growth
Exponential growth
A population increases by a fixed percent
Graphed as a J-shaped curve
Exponential growth cannot be sustained indefinitely
It occurs in nature with a:
Small population
Low competition
Ideal conditions

37. Limiting factors restrain population growth
Limiting factors = physical, chemical and biological attributes of the environment
They restrain population growth
Environmental resistance = all limiting factors taken together
Stabilizes the population size
Space, food, water, mates, shelter, suitable breeding sites, temperature, disease, predators
Aquatic systems: salinity, sunlight, temperature, etc.

38. Carrying capacity
Carrying capacity = the maximum population size of a species that its environment can sustain
Limiting factors slow and stop exponential growth
An S-shaped logistic growth curve
Many factors contribute to environmental resistance and influence a population’s growth rate and carrying capacity

39. Population density impacts limiting factors
Density-dependent factors = limiting factors whose influence is affected by population density
Increased density increases the risk of predation and competition for mates
Results in the logistic growth curve
Larger populations have stronger environmental resistance
Density-independent factors = limiting factors whose influence is not affected by population density
Events such as floods, fires, and landslides

40. Perfect logistic curves aren’t often found

41. Carrying capacities can change
Environments are complex and ever-changing
Changing carrying capacities
Humans lower environmental resistance for themselves
Increasing our carrying capacity
Technologies overcome limiting factors
By increasing carrying capacity for humans
We have reduced the carrying capacity for countless other organisms
Calling into question our own long-term survival

42. Reproductive strategies vary among species
Biotic potential = an organism’s capacity to produce offspring
K-selected species = species with long gestation periods and few offspring
Have a low biotic potential
Stabilize at or near carrying capacity
Good competitors
r-selected species = species which reproduce quickly
Have a high biotic potential
Little parental care, populations fluctuate greatly

43. Population changes affect communities
As the population of one species declines, other species may appear
Human development displaces other species and threatens biodiversity
As Monteverde dried out, species disappeared
Golden toads, harlequin frogs and more had been pushed from their cloud-forest habitat into extinction
20 of 50 frog species, 2 lizard species went extinct
Species from lower, drier habitats appeared
15 species tolerant of drier conditions had moved in

44. Conserving biodiversity
Human development, resource extraction and population pressure are speeding changes
In populations and communities
Impacts threatening biodiversity have complex social, economic and political roots
We must understand these factors to solve problems

45. Costa Rica and its environment
Past economic and social forces still threaten Costa Rica’s species and ecological communities
Lush forests are seen as obstacles to agriculture and for timber
The country’s population grew to 3.34 million
Pasture land increased from 12% to 33%
Forests decreased from 80% to 25%
Species were declining and becoming endangered

46. Costa Rica’s species were in danger
Few people saw the need to conserve biological resources
Until it became clear they were being rapidly lost

47. Costa Rica is protecting its environment
The privately managed 10,500 ha (26,000 acre) Monteverde Cloud Forest Reserve was founded in 1972
To protect the forest, its plants and animals
Costa Rica created the country’s first national parks and protected areas in 1970
Centered on areas of spectacular scenery
Protecting valuable tropical dry forests, turtle nesting beaches, coral reef systems
Government support remains strong
Over 25% of its land is under some type of protection

48. Costa Rico’s protection is paying off
Ecotourism: tourists visit protected areas
Providing thousands of jobs and billions of dollars to local economies
But parks are still under-protected and underfunded
Restoration is a step beyond preservation 48

49. Conclusion
The fundamentals of evolution and population ecology are integral to environmental science
Natural selection, speciation and extinction help determine earth’s biodiversity
Understanding how ecological processes function at the population level is crucial to protecting biodiversity