1. Evolution, Biodiversity, and Population Ecology
Chapter 3

2. Evolution: The Source of Earth’s Biodiversity
Natural Selection Shapes Organisms and Diversity:
Darwin and Wallace proposed natural selection as mechanism of evolution
Premises of natural selection:
Organisms struggle to survive/reproduce and produce more offspring than survive
Individuals of species vary in characteristics due to genes and environment
Some individuals are better suited to their environment, reproduce more effectively
Organisms with better adapted traits produce more offspring

3. Evolution Generates Biodiversity:
Biological diversity (biodiversity) - variety of life across all levels of biological organization
Species
Genes
Populations
Communities

4. Speciation Produces New Organisms:
Allopatric speciation - species formation due to physical separation of populations
Main method of speciation
Caused when population are separated by glaciers, rivers, mountains, etc.
Each population gets own set of mutations
Natural selection can speed process

6. Speciation and Extinction Determine Earth’s Biodiversity:
Extinction - disappearance of a species from Earth
Species last 1–10 million years
Human activity greatly affects rates of extinction
Biodiversity loss affects people directly
Food, fiber, medicine, ecosystem services

7. Some species Particularly Vulnerable to Extinction:
Extinction can occur when environment changes faster than natural selection keeps up
Many factors cause extinction:
Severe weather, climate change, changing sea levels
Arrival of new species
Being a small population or specialized species

8. Endemic species - species only existing in a certain, specialized area
Very susceptible to extinction
Usually have small populations
Island species are often endemic and thus at risk

9. Earth’s Episodes of Mass Extinctions:
Mass extinction events - episodes that kill massive numbers of species at one time
Five in Earth’s history
Cretaceous–Tertiary (K–T) event: 65 million years ago
Dinosaurs extinct
End-Permian event: 250 million years ago
75–95% of species extinct

10. A Sixth Mass Extinction is Beginning:
Humans are causing sixth mass extinction event
Resource depletion, population growth, development
Destruction of natural habitats
Hunting and harvesting of species
Introduction of non-native species
It will take millions of years for life to recover

11. Population Ecology Population Characteristics Predict Dynamics:
Population size - number of individuals present at a given time
Size will fluctuate depending on a number of factors
Population density - number of individuals in a population per unit area
Population distribution (dispersion) - spatial arrangement of organisms
Random, uniform, or clumped
Age distribution (structure) = the relative numbers of organisms of each age in a population

12. Birth and Death Rates:
Survivorship curves – graphs showing the likelihood of death varying 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

14. Populations Grow, Shrink, or Remain Stable:
Natural rate of population increase is (Crude birth rate)  (crude death rate)
Population change due to internal factors
Population growth rate is (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

15. Limiting Factors:
Limiting factors - physical, chemical, and biological attributes of environment restrain population growth
Space, food, water, mates, shelter, suitable breeding sites, temperature, disease, predators

16. Factors Influencing 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
Density-independent factors - limiting factors whose influence is not affected by population density
Events such as floods, fires, and landslides

17. Reproductive Strategies:
Biotic potential - organism’s capacity to produce offspring
K-selected species - species with long gestation periods, few offspring, and strong parental care
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
high biotic potential
Populations fluctuate greatly

18. Climate Change:
Climate change alters 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