Chapter 5

Evolution, Biodiversity, Population Ecology

Evolution

• Biological evolution consists of genetic change in organisms across generations.• May proceed randomly or be

directed by natural selection.

Natural Selection

• Process by which traits that enhance survival and reproduction are passed on more frequently to future generations, altering the genetic makeup of populations through time.

Natural Selection

• Charles Darwin • Alfred Russell Wallace • Both naturalists – studied plants/animals• Proposed natural selection as a

mechanism for evolution and as a way to explain the great variety of living things.

Logic of Natural Selection

• a. Individuals of the same species vary in their characteristics.• b. Organisms produce more

offspring than can possibly survive.• c. Some offspring may be more

likely to survive and reproduce.

Logic (continued)• d. Characteristics that give individuals an

advantage in surviving and reproducing might be inherited by their offspring.

• e. These characteristics would tend to become more prevalent in the population in future generations.

*A trait that promotes success is called an adaptation.

Natural Selection• Acts on genetic variation:1.Accidental changes in DNA are called

mutations2.Most mutations have little effect; some

are deadly; a few are beneficial.3.Sexual reproduction generates variation

– genes from both parents

Natural Selection• 3 ways that genetic variation alters

organisms’ characteristics:1. Directional selection2. Stabilizing selection3. Disruptive selection*draw each graph (a, b, c) from page 115

in your notes at this time

Artificial Selection

• Process of selection conducted under human direction

*With a partner, come up with at least 2 examples of artificial selection – you have 3 minutes

Book Work

• With a partner you have not worked with:–Page 137 • Testing Your Comprehension – 1 &2• Seeking Solutions – 1• Keep this paper, you will be adding to it

daily during this chapter (answers will be checked periodically)

Evolution generates biodiversity

• Biological diversity, or biodiversity, is the sum total of all organisms in an area, taking into account the diversity of species, the diversity of populations within a community, and the diversity of communities within an ecosystem.

What is a species?

• A species is a population whose members share certain characteristics and can freely breed with one another and produce fertile offspring.

What is a population?

• A group of individuals of a particular species that live in the same area.

Speciation• Speciation produces new types of

organisms.• 1. When populations of the same

species are kept separate, their individuals no longer come in contact, so their genes no longer mix.• Called allopatric speciation

Speciation

2. If there is no contact, the mutations that occur in one population cannot spread to the other. • Called sympatric speciation

Read through the section “Populations can be separated in many ways” and list the mechanisms that can cause allopatric speciation

Vocab Study Time

• With a partner, use your flash cards to study your vocabulary words. • We will have a vocab competition at

the end of class today!

“Mapping” the History of Diversity

• Phylogenetic trees –Show relationships among groups

of organisms–Used to study how traits have

evolved over time–Page 119 – arrows used to indicate

when traits orginated

Speciation and Extinction Contribute to Biodiversity

• Extinction – the disappearance of a species from Earth

• Number of species in existence =Number added through speciation – Number removed by extinction

• Extinction brought on by humans is biggest environmental problem we are facing

Some Species more Vulnerable than Others

• Generally, extinction occurs when environmental conditions change rapidly or severely enough that a species cannot genetically adapt to the change.• Some species are vulnerable because

they are endemic, occurring in only a single place on the planet.

Episodes of Mass Extinction

• There have been five mass extinction events at widely spaced intervals in Earth’s history that have wiped out anywhere from 50 to 95% of Earth’s species each time.• Best known – 65 million years ago – end

to dinosaurs (“Science Behind the Story 122-123)

6th Mass Extinction – Is it near?

• Biologist conclude that Earth is entering its 6 mass extinction

• Caused by– Population growth– Development– Resource depletion– Destruction of natural habitats– Harvesting/Hunting– Non-native species introductions

Book Work

• Add this to your previous assignment and turn in when finished – due Wednesday morning!• Page 137–Testing Your Comprehension

#s 3, 4, and 5

Levels of Ecological Organization• Organisms Population

Community Ecosystem Biosphere

• Biosphere is the cumulative total of living things on Earth and the areas they inhabit

Levels of Organization• A group of organisms of the same species that

live in the same area is a population• Species are often composed of multiple

populations• Communities are made up of multiple

interacting species that live in the same area.• Ecosystems encompass communities and the

abiotic (nonliving) material and forces with which their members interact.

Population Ecology• Investigates how individuals

within a species interact with one another.• Why do some populations

increase?• Who do some populations

decrease?

Community Ecology

• Focuses on interactions among species• From one-to-one interactions to

complex relationships involving entire communities• Roane County Park

Ecosystem Ecology

• Studies living and nonliving components of systems

• Reveals patterns, such as energy and nutrient flow

Ecology at the Organism Level

• Habitat, niche, and degree of specialization are important in organismal ecology• The specific environment in which an

organism lives is its habitat.• Each organism has patterns of

habitat use. (p.124)

Organism Level (continued)• A species’ niche reflects its use of

resources and its functional role in a community.

• Species with very specific requirements are said to be specialists.

• Those with broad tolerances, able to use a wide array of habitats or resources, are generalists.

• Pros/Cons page 125

Population Ecology:Population Characteristics

• Populations exhibit characteristics that help predict their dynamics.• 1. Population size is the number of

individual organisms present at a given time.• 2. Population density is the number of

individuals in a population per unit area.

Characteristics (contd.)• 3. Population distribution is the spatial

arrangement of organisms within an area.• 4. Sex ratio -proportion of males to females.• 5. Age structure, describes the relative

numbers of organisms of each age within a population.

• 6. Birth and death rates measure the number of births and deaths per 1,000 individuals for a given time period.

Population Distribution• 3 Types:–Random – individuals are not located in

any particular pattern; resources are found throughout an area–Uniform – individuals are evenly spaced;

desert need equal space for their roots to gather water–Clumped – (most common) individuals

are arranged around resources

Age Structure• Population of mostly individuals past

reproductive age will decline• Population of mostly individuals pre-

productive age will increase• Population with even age

distribution will remain stable• Page 128, figure 5.13

Survivorship Curves• Based on birth and death rates• Page 128, figure 5.14• Type I – survival rates for young are high

and decrease at an old age (humans)• Type II – survival rates equal among age

(birds)• Type III – highest death rate at young

ages (amphibians – tadpoles)

Populations may grow, shrink, stablilize

• Population growth or decline is determined by births, deaths, immigration, and emigration.• Immigration – into• Emigration – away *E for Exit

Unregulated Populations• No external limits• Mold growing on bread, bacteria on

dead animal, trees in a new area• When a population increases by a fixed

percentage each year, it is said to undergo exponential growth.

• Relate this type to a savings account, page 129, Table 5.3

Book Work

• Page 137, Testing Your Comprehension • #s 6-8

Limiting Factors Restrain Population Growth

• Populations are contained by limiting factors - physical, chemical, and biological characteristics of the environment

• The interaction of the limiting factors determines the carrying capacity.

• Carrying capacity – max population size of a species that an environment can sustain

Logistic Growth Curve

• Populations increase sharply at first and then level off due to limiting factors• Known as environmental resistance• Page 130, Fig. 5.16 L.G.C.• Look at page 131, Fig. 5.17 for other

types of growth models

What are examples of limiting factors?

Carrying Capacities Can Change

• Some organisms can alter their environment to reduce environmental resistance and increase carrying capacity.

• Humans have used immense proportions of the planet’s resources to increase our carrying capacity, but have reduced the carrying capacities for many other organisms

Affects on Limiting Factors• Density-dependent factors -based on

population density- Increased pop., increased chance for mating- Increased pop., increased competition and disease

• Density-independent factors -not affected by population density– Temperature extremes– Catastrophic events (floods, fires, landslides, etc.)– Can eliminate large #s no matter the density

Biotic Potential

• Ability to produce offspring• Fish – high biotic potential, lay 1000s of

eggs in a short time• Whale – low biotic potential, birth to one

calf after a long gestation (pregnancy) period

• Low biotic potential organisms protect their offspring

K-Selected Species

• Low biotic potential• Populations stabilize over time at or

near carrying capacity • K stands for carrying capacity• Competition is high between

organisms

R-Selected Species

• High biotic potential• Devote energy to produce large amounts

of offspring• R stands for rate• Rate at which species increase/decline

varies and number at or near carrying capacity can be very high or very low