1. Evolution, Biodiversity, & Population Ecology
Chapter 3

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

4. Evolution: The Source of Earth’s Biodiversity
Species = a population or group of populations whose members share characteristics
They can breed with one another and produce fertile offspring
Population = individuals of the same species that live in an area
Evolution = change over time
Biological evolution = change in populations of organisms over generations
Genetic changes lead to changes in appearance, functioning, or behavior

5. Evolution: The Source of Earth’s Biodiversity
Natural selection = process in which traits that enhance survival and reproduction are passed on more frequently to future generations than those that do not

7. Evolution: The Source of Earth’s Biodiversity
Why environmental scientists need to understand evolution:
Evolutionary processes influence pesticide resistance, agriculture, medicine, health, etc.

8. Natural selection shapes organisms and diversity
In 1858, both Darwin and Wallace proposed natural selection as the mechanism of evolution
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
Organisms with better adapted traits will produce more offspring

9. Natural selection shapes organisms and diversity
Adaptation = (traits) that lead to better reproductive success become more common 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

10. Directional selection =
drives a feature in one direction

11. Selective pressures from the environment influence adaptation
Divergent evolution = Related species in different environments experience different pressures and evolve different traits
Convergent evolution = unrelated species may acquire similar traits because they live in similar environments

13. Evidence of natural selection is all around us
It is evident in every adaptation of every organism
Artificial selection = the process of selection conducted under human direction
Produced the great variety of dog breeds and food crops

15. Evolution generates biodiversity
Biological diversity (biodiversity) = the variety of life across all levels of biological organization
Species
Genes
Populations
Communities
Scientists have described 1.8 million species
Estimates of the total number of species that exist range from 3 million to 100 million
Biodiversity exists nearly everywhere

16. 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
Natural selection can speed the process

18. We can infer the history of life’s diversification by comparing organisms
How did the major groups of organisms come to be?
Phylogenetic trees = diagrams that show relationships among species, groups, genes, etc.
Scientists can trace how certain traits evolved
Some traits evolved and were passed on
Other traits evolved more than once (e.g., the ability to fly)

20. We can infer the history of life’s diversification by comparing organisms
Knowing how organisms are related to one another helps scientists organize and name them
Categories reflect evolutionary relationships
Scientists use physical and genetic characteristics to organize
Each species gets a two-part Latinized scientific name

22. The fossil record teaches us about life’s long history
Fossil = an imprint in stone of a dead organism
Fossil record = the cumulative body of fossils worldwide

23. 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

24. Speciation and extinction together determine Earth’s biodiversity
Extinction = the disappearance of a species from Earth
Species last 1–10 million years
Extinction has historically been a natural occurrence (background extinction)

25. Speciation and extinction together determine Earth’s biodiversity
Human activity profoundly affects rates of extinction
Biodiversity loss affects people directly
Food, fiber, medicine, ecosystem services

26. Some species are especially vulnerable to extinction
Many factors cause extinction:
Severe weather, climate change, changing sea levels
Arrival of new species
Being a small population or specialized species

27. Some species are especially vulnerable to extinction
Endemic species = a species that only exists in a certain, specialized area
Very susceptible to extinction
Usually have small populations
Island species are often endemic and thus at risk

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

30. Earth has seen several episodes of mass extinctions
Background extinction rate = a constant, slow rate of extinction that occurs as a part of evolution
Mass extinction events = episodes that killed off massive numbers of species at once
Occurred five times in Earth’s history
50–95% of all species go extinct at one time
Cretaceous–Tertiary (K–T) event: 65 m.y.a
Dinosaurs went extinct
End-Permian event: 250 m.y.a
75–95% of all species went extinct “Great Dying”

31. 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
Today’s extinction rate is 100–1000 times higher than the background rate and rising
It will take millions of years for life to recover

33. We study ecology at several levels
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

34. We study ecology at several levels
Ecology & evolution are closely intertwined

35. Each organism has habitat needs
Habitat = the environment where an organism lives
It includes living and nonliving elements
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

36. Each organism has habitat needs
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

37. Niche and specialization are key concepts in ecology
Niche = summary of everything an organism does
Use of resources
Functional role in a community: habitat use, food selection, role in energy and nutrient flow, interactions with other individuals

38. Niche and specialization are key concepts in ecology
Specialists = species that have narrow niches and specific needs
Extremely good at what they do
But vulnerable when conditions change
Generalists = species with broad niches
Use a wide array of habitats and resources
Can live in many different places

40. Population Ecology
Population = individuals of a particular species that inhabit an area
Species may have different arrangements of their populations

41. Populations show characteristics that help predict their dynamics
Certain characteristics of a population help scientists predict what will happen to them in the future
Helps in managing threatened species
Population size = number of individuals present at a given time
Populations generally grow when resources are abundant and predators are few
Decline in response to loss of resources, other species, disasters

42. Population density
Population density = the number of individuals in a population per unit area
High densities have advantages and disadvantages
+Easier to find mates
-Increased competition and vulnerability to predation
-Increased transmission of diseases
-Sometimes causes organisms to leave an area if too dense
Low densities provide access to plentiful resources and space but make it harder to find mates

43. Population distribution
Population distribution (dispersion) = spatial arrangement of organisms
Random = haphazardly located individuals, with no pattern
Uniform = individuals are evenly spaced
Territoriality, competition
Clumped = organisms found close to other members of population
Most common in nature
Clustering around resources
Mutual defense

45. Sex ratio and age structure
Sex ratio = proportion of males to females
In monogamous species, a 1:1 sex ratio maximizes population growth
Most species are not monogamous, so ratios vary

46. Birth and death rates
Survivorship curves = graphs that show that the likelihood of death varies with age
Type I: higher death rate at older ages
Larger animals (e.g., humans)
Type II: same death rate at all ages
Medium-sized animals (e.g., birds)
Type III: higher death rate at young ages
Small animals, plants

48. Populations may grow, shrink, or remain stable
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

49. Populations may grow, shrink, or remain stable
Natural rate of population increase =
B (crude birth rate)  D (crude death rate)
Population change due to internal factors
Crude rate (per 1000 indv per year)
Population growth rate =
(B immigration rate)  (D  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

50. Unregulated populations increase by exponential growth
Exponential growth = when a population increases by a fixed percent
Graphed as a J-shaped curve
Exponential growth cannot be sustained indefinitely
It occurs in nature with:
Small population
Low competition
Ideal conditions
Occurs often with introduced
species

51. Limiting factors restrain population growth
physical, chemical, and biological attributes of the environment
Ex. Space, food, water, mates, shelter, suitable breeding sites, temperature, disease, predators
Carrying capacity (K) = 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

53. The influence of some factors depends on population density
Density-dependent factors = limiting factors whose influence is affected by population density
Increased density increases the risk of predation, disease, and competition
Results in the logistic growth curve
Larger populations have stronger effects of limiting factors
Density-independent factors = limiting factors whose influence is not affected by population density
Events such as floods, fires, and landslides

55. Carrying capacities can change
Environments are complex and ever-changing
Limiting factors can change, altering the carrying capacity
Humans lower environmental resistance for themselves
Increases our carrying capacity
Technologies overcome limiting factors
In increasing carrying capacity for humans, we now use immense portions of the planet’s resources
We have reduced the carrying capacity for countless other organisms

56. Reproductive strategies vary among species
Biotic potential = an organism’s capacity to produce offspring
K-selected species = species with long gestation periods, few offspring, and strong parental care
Have a low biotic potential
Stabilize at or near carrying capacity; good competitors
r-selected species = species that reproduce quickly and offer little or no care for offspring
Have a high biotic potential
Populations fluctuate greatly
These are the two extremes—most species fall somewhere in between

57. Protecting Species
Scientists, land managers, and private citizens are protecting the native species and habitats of Hawaii
Invasive species are being removed
Native species (like the nēnē) are being protected, and new populations are being started
Ranch land is being restored to forest
Coral reef communities are part of the largest federally protected marine reserve in the world
This restored and protected land has resulted in ecotourism = the phenomenon of people visiting the islands to experience the natural areas

58. Climate change now poses an extra challenge
Climate change is altering how we protect species and habitats
Land is typically protected to conserve the species that live there
As the climate changes, the protected land may no longer support the same species

60. 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