1. Ch 5 Evolution, Biodiversity, and Population Ecology
Part 1: Foundations of Environmental Science
PowerPoint® Slides prepared by
Jay Withgott and Heidi Marcum
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

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

3. Striking gold in Costa Rica
Golden toads were discovered in 1964, in Monteverde, Chile
The mountainous cloud forest has a perfect climate for amphibians
Unfortunately, they became extinct within 25 years
Due to global warming’s drying effect on the forest

4. Early Earth was a very different place Theory- dispersed bits of material whirling through space around our sun were drawn together by gravity
4.5 billion years ago, Earth was a hostile place
Severe volcanic and tectonic activity
Intense ultraviolet energy from the sun
No oxygen existed in the atmosphere, until photosynthesis developed in microbes
No life existed

5. Several hypotheses explain life’s origin
Primordial soup (the heterotrophic hypothesis) - life originated from a “primordial soup” of simple inorganic chemicals in the oceans
First life forms used organic compounds for energy
“Seeds” from space (the panspermia hypothesis) - microbes from space traveled on meteorites to Earth
Life from the depths (the chemoautotrophic hypothesis) - life originated in deep-sea hydrothermal vents, with abundant sulfur
First organisms were chemoautrotrophs

6. The fossil record teaches about life’s history
Single-celled bacteria occurred on Earth 3 billion years ago
Fossil - an imprint in stone of a dead organism
Fossil record - gives information about the history of past life

7. Present-day organisms help decipher history
Biologists use present-day organisms to get information about evolution
Archea - single-celled prokaryotes very different from bacteria
The tree of life now consists of 3 prongs: bacteria, archaea, eukaryotes
Prokaryote- a typically unicellular organism that lacks organelles and nucleus

8. Evolution: the source of Earth’s biodiversity
Biological evolution - genetic change in populations of organisms across generations
May be random or directed by natural selection
Natural Selection – the process by which traits that enhance survival and reproduction are passed on more frequently to future generations than those that do not

9. Understanding evolution is vital
It alters the genetic makeup of a population
It is important for understanding antibiotic and pesticide resistance, agricultural issues, production, medicines, etc.
Organisms adapt to their environment and change over time

10. Natural selection shapes organisms
In 1858, Darwin and Wallace both proposed natural selection as the mechanism of evolution
Organisms face a constant struggle to survive and reproduce
Organisms tend to 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 will survive and pass their genes on in their offspring

11. Genetic variation
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

12. Natural selection acts on genetic variation
Directional selection - drives a feature in one direction (a-thick shell protects snail)
Stabilizing selection - produces intermediate traits, preserving the status quo (b-preserves extra resources for feeding and reproduction an favors an int. shell)
Disruptive selection - traits diverge in two or more directions (c- two traits are favored. Thin shells conserve resources and out reproduce and thick shells are well protected)
If the environment changes, a trait may no longer be adaptive

13. Evidence of natural selection is everywhere
It is evident in every adaptation of every organism
Evident in bacteria and fruit flies in laboratories
Selective breeding of animals

14. 1.5 to 1.8 million species have been discovered
Natural selection
Selective breeding has produced tremendous diversity among organisms
Adaptive radiation- burst of species formation due to natural selection
Statistics
1.5 to 1.8 million species have been discovered
Estimated 100 million species mat exist

15. Artificial selection
Artificial Selection - the process of selection conducted under human direction
For example, artificial selection has led to the great variety of dog breeds, and agricultural crops

16. Evolution generates biodiversity
Biological Diversity - An area’s sum total of all organisms
The diversity of species
Their genes
Their populations
Their communities
Species - a population or group of populations whose members share characteristics and can freely breed with one another and produce fertile offspring
Population - a group of individuals of a species that live in the same area

17. Speciation produces new types of organisms
The process of generating new species
A single species can generate multiple species
Allopatric speciation - species formation due to physical separation of populations over some geographic distance
DNA mutation arises in the isolated population
Can be separated by glaciers, rivers, mountains, migration
The main mode of species creation

18. Founder Effect (allopatric)
Genetic Drift occurs when changes in the frequency of a gene in a population are due not to mutation, selection or migration but simply to chance
Founder Effect (allopatric)
occurs when a small number of individuals are isolated from a larger population
They may have a smaller genetic variation than the original species
Both genetic drift and founder effect may not be better adapted to their environment

19. 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

20. The fossil record shows that…
Earlier organisms evolved into later ones
The vast majority of species are extinct
Numbers of species increase over time
Earlier organisms were smaller and simpler
Several mass extinctions have occurred
Large, complex organisms occurred 600 million years ago
Plants, animals, fungi

21. Speciation results in diverse life forms
Speciation generates complex patterns of diversity above the species level
Phylogenetic trees (Cladograms) - Represents the history of species divergence
Scientists can trace when certain traits evolved
Show relationships between species

22. Extinction
Species generally evolve from simple to complex and small to big, but the opposite can occur, and some even disappear
Extinction - the disappearance of a species from Earth
Occurs when a species cannot adapt quickly enough to a changing environment
Speciation and extinction affect species numbers

23. Extinction is a natural process
Extinction is irreversible: once a species is lost, it is lost forever
Humans profoundly affect rates of extinction

24. Some species are more vulnerable to extinction
Extinction occurs when the environment changes too rapidly for natural selection to keep up
Endemic species - a species only exists in a certain, specialized area (golden toad to the Monteverde cloud forest)
Very susceptible to extinction
These species usually have small populations
Many other factors also cause extinction
Severe weather
New species
Specialized species

25. Earth has had several mass extinctions
Background extinction rate –the average rate of extinction that occurred before the appearance of humans
Fossil record indicates that for both bird and mammals one species in the world typically becomes extinct every years or
One to five species per million species on earth extinction usually occurs one species at a time

26. Extinction
Mass extinction events – a catastrophic widespread event where large groups of species are wiped out in a geological period lasting up to 5 million years
five events in Earth’s history that killed off massive numbers of species at once (20-60 million years apart during the past 500 million years)
250 million years ago, 50-95% of all species went extinct at one time
Humans are causing the sixth mass extinction event
Resource depletion
Population growth
Development

27. Causes of Extinction
Risk- the chance that a species of population will become extinct owing to one of these causes
1- Population Risk- random variations in population rates (in birth rates and death rates) can cause a species low in abundance to become extinct (butterfly in Colorado mountains only lay their eggs in the buds of a lupine tree. Their was a late snow killing all the buds)
2- Environmental Risk- changes in the environment that occur. This includes variations in the physical and biological environment

28. Causes of Extinction – cont.
3- Natural Catastrophe- sudden changes in the environment that is not a result of human activities (volcano, earthquake, flood)
4- Genetic Risk- changes in genetic characteristics, not caused by external environmental changes (species lacks variety and may be vulnerable)

29. Species’ ranges can be severely restricted
Some U.S. salamander species live on top of single mountains

30. Endangered Species- Red List
The International Union for Conservation of Nature (IUCN) is the world's main authority on the conservation status of species. A series of Regional Red Lists are produced by countries or organizations, which assess the risk of extinction to species
The percentage of species in several groups which are listed as red critically endangered, orange endangered, or yellow vulnerable on the 2007 IUCN Red List

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

32. Levels of ecological organization
Population ecology - investigates the quantitative dynamics of how individuals within a species interact
Community ecology - focuses on interactions among species
Ecosystem ecology - studies living and nonliving components of systems to reveal patterns
Nutrient and energy flows

33. Organismal ecology: habitat
Habitat - the environment in which an organism lives
Includes living and nonliving elements
Scale-dependent: from square meters to miles
each organism thrives in certain habitats, but not in others (habitat 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

34. Organismal ecology: niche
Niche - an organism’s use of resources and its functional role in a community
total way of life or role of a species in an ecosystem
Habitat use, food selection, role in energy and nutrient flow
Interactions with other individuals
Specialists - species with narrow niches and very specific requirements
Extremely good at what they do, but vulnerable to change
Generalists = species with broad niches that can use a wide array of habitats and resources
Able to live in many different places

35. 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

36. Population characteristics
Population density - the number of individuals within a population per unit area
High densities make it easier to find mates, but increase competition, and vulnerability to predation
Low densities make it harder to find mates, but individuals enjoy plentiful resources and space
Population dynamics – the study of how the characteristics of the population change in response to changes in the environmental conditions

37. Population characteristics
Population distribution (dispersion) - spatial arrangement of organisms within an area
Random – haphazardly located individuals, with no pattern
Uniform – individuals are evenly spaced due to territoriality
Clumped – arranged according to availability of resources
Most common in nature

38. Population characteristics
Sex ratio - proportion of males to females
In monogamous species, a 50/50 sex ratio maximizes population growth
Age Structure - the relative numbers of organisms of each age within a population
Age structure diagrams (pyramids) - show the age structure of populations

39. Birth and death rates
Crude birth/death rates - rates per 1000 individuals
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

40. 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
Growth rate formula -
(Crude birth rate + immigration rate) - (Crude death rate + emigration rate) - Growth rate

41. Exponential population growth
Steady growth rates cause exponential population growth
Something 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 and ideal conditions

42. Limiting factors restrain growth
Intrinsic rate of increase (r) is the rate at which the population of a species would grow if it had unlimited resources
- Reproduce early in life
- Have short generation times
- can reproduce many times and have many offspring
Limiting factors - physical, chemical and biological characteristics that restrain population growth
Water, space, food, predators, and disease

43. Carrying capacity
Carrying capacity (K)- the maximum population size of a species that its environment can sustain
An S-shaped logistic growth curve
Limiting factors slow and stop exponential growth
Carrying capacity changes
Humans have raised their carrying capacity by decreasing the carrying capacity for other species

44. Perfect logistic curves aren’t often found

45. Population density affects limiting factors
Density-dependent factors - limiting factors whose influence is affected by population density
Increased risk of predation and competition for mates occurs with increased density
Density-independent factors - limiting factors whose influence is not affected by population density
Events such as floods, fires, and landslides

46. Biotic potential and reproductive strategies vary
Biotic potential - the ability of an organism to produce offspring
K-selected species - animals with long gestation periods and few offspring
Have a low biotic potential
Stabilize at or near carrying capacity
Good competitors
r-selected species - animals which reproduce quickly
Have a high biotic potential
Little parental care

47. K-selected vs. r-selected species

48. Population changes affect communities
As population in one species declines, other species may appear
Human development now displaces other species and threatens biodiversity
As Monteverde dried out, species from lower, drier habitats appeared
But, species from the cloud-forest habitats disappeared

49. Challenges to protecting biodiversity
Social and economic factors affect species and communities
Nature is viewed as an obstacle to development
Nature is viewed as only a source of resources
Human population growth pressures biodiversity

50. Preserving biodiversity
Natural parks and protected areas help preserve biodiversity
Often, they are underfunded
Ecotourism brings jobs and money to developing areas