Ecology and Evolution

Chapter 14 (with some of ch.35 and 36)

Charles Darwin

• His idea changed the way we look at the world.

• His contribution was developing a scientific theory of biological evolution that explains how modern organisms evolved over time.

Remember What a “Theory” is

• In science, the term theory is used to represent ideas and explanations that have been confirmed through tests and observations

• The theory of evolution remains one of the most useful theories in biology because it explains many questions and observations

Some questions that can be answered by evolution.

• Why do so many different animals have the same structures, the arm bones in a human are the same bones as a flipper in a whale?

• Why do organisms have structures they no longer use, like the appendix in a human? Non functioning wings in penguins

• Why are there bones and fossil evidence of creatures that no longer exist? What happened to these creatures?

• Why do so many organisms' morphology and anatomy follow the same plan?

• Why is the sequence of DNA very similar in some groups of organisms but not in others?

• Why do the embryos of animals look very similar at an early stage?

Darwin’s Theory of Evolution

• The Theory of Evolution is considered a Unifying Theory of Biology, because it answers many of these questions and offers and explanation for the data.

Darwin’s Epic Journey

• He was the naturalist aboard the HMS Beagle, a ship that traveled on a 5 year voyage beginning in 1831.

• He collected samples and took notes in a journal.

Darwin’s Observations

He noticed three patterns of Biodiversity1. Different, yet ecologically similar animals

inhabited separate but ecologically similar habitats.• Example: different flightless birds live in similar

grasslands across South America, Australia, and Africa.

2. Different, yet related animals occupied different habitats within a local area.• Same type of tortoise on different islands of the

Galapagos.

3. Some fossils of extinct animals were similar to living species.

Example: The extinct Glyptodont very similar to the armadillo

Ideas That Shaped Darwin’s Thinking

• Darwin was not only influenced by his own notes, observations and animal specimens he collected, he was influenced by the work of other scientist.

• Three works in particular, the work of:– Hutton and Lyell– Lamarck– Malthus

Hutton and Lyell

• Concluded that the Earth is extremely old and that the process that changed the Earth in the past are the same processes that operate in the present. – Effect it had on Darwin's thinking: if the earth

could slowly change over time, could life change too?

Lamarck’s evolutionary hypothesis

• Lamarck suggested that organisms could change during their lifetimes by using or not using various parts of their bodies. He also suggested that these acquired traits could be passed on to their offspring.

Malthus

• Malthus reasoned that if the human population grew unchecked, there wouldn’t be enough living space and food for everyone.– Effect it had on Darwin's thinking: if there was not

enough food and space for organisms it would lead to a fight for survival. When Darwin realized that most organisms don’t survive and reproduce he wondered which individuals survive…and why.

Artificial Selection

• One more thing that influenced Darwin’s thinking….artificial selection.

• He studied change produced by plant and animal breeders.

• Breeders knew that some plants produced larger fruits than others, some cows produce more milk than others. They chose those specific individuals to breed, thereby passing on the desired trait to the next generation.

16.3 Darwin Presents His Case

• In 1858, 20 years AFTER he developed his theory he published On the Origin of Species

Evolution by Natural Selection

• His theory incorporates three main ideas:– Struggle for Existence

• members of each species compete regularly for resources.

– Variation and Adaptation• Some variation of traits are better suited to life in their

environment that others.• Adaptation- characteristics that increases an organisms

fitness

– Survival of the Fittest• those organisms best suited to their environment will

survive and reproduce.• Fitness- is measured by an organisms ability to survive and

reproduce.

Evolution by Natural Selection

• Natural Selection is the process by which organisms with variation most suited to their local environment survive and leave more offspring.

Natural Selection occurs only when:1. More individuals are born than can survive

(struggle for existence).2. There is natural heritable variation (variation and

adaptation)3. There is variable fitness among individuals (survival

of the fittest)

Evidence of Evolution

• Fossil Record• Geographic Distribution• Homologous Body Structures• Embryonic Development• Molecular Divergence

Fossil Record• Fossil- preserved

remains of ancient organisms.

• Many recently discovered fossils form series that trace the evolution of modern species from extinct ancestors

Geographic Distribution• Organisms may descend with modification from a

common ancestor• Similar animals in different locations are products of

different lines of evolutionary decent that have common environmental pressures

Homologous Structures• Homologous Structure-

structures that have different mature forms but develop from the same embryonic tissue (similar structure/ different function)

• Vestigial structure- structure/organ that is reduced in size an has no apparent function.

Embryonic Development

• Many animals with backbones are very similar in the early stages of development.

• Evidence that organisms have descended from a common ancestor.

The Evidence for Evolution

• Traces of our evolutionary past are also evident at the molecular level– organisms that are more distantly

related should have accumulated a greater number of evolutionary differences than two species that are more closely related

– the same pattern of divergence can be seen at the protein level

Figure 17.7 Molecules reflect evolutionary divergence

Evolution of Populations

Charles Darwin

• Darwin’s Theory of Evolution– Organisms evolve by Natural Selection– Fitness- an organisms ability to survive and reproduce– Survival of the fittest- organisms that are better adapted to their environment will live

long enough to reproduce

• Darwin did not have an understanding of heredity (the passing of traits from parent to offspring)– Darwin was unable to explain:

1. the source of variation2. how inheritable traits were passed from one generation to the next

Gene Pool• You can gain an

understanding of evolution by studying individuals of a population.

• Gene Pool- the combined genetic information of all the individuals in a population – Example: The gene pool of

Taft includes all of the genetic information of all the people that make up Taft’s population

Allele Frequency

• Allele Frequency- the number of times an allele occurs in a gene pool compared with the number of times other alleles occur.

• Example- Green = GG, Purple = Gg & red = gg– The allele frequency for G is 87%

(26 out of 30)– The allele frequency for g is 13% (4

out of 30)

Genetic Change Within Populations: The Hardy-Weinberg Rule

• Variation within populations puzzled many scientists– why don’t dominant alleles drive recessive alleles out of

populations?

• G.H. Hardy and W. Weinberg, in 1908, studied allele frequencies in a gene pool– in a large population in which there is random mating,

and in the absence of forces that change allele frequencies, the original genotype proportions remain constant from generation to generation

– because the proportions do not change, the genotypes are said to be in Hardy-Weinberg equilibrium

– If the allele frequencies are not changing, the population is not evolving

Genetic Change Within Populations: The Hardy-Weinberg Rule

• The Hardy-Weinberg equilibrium only works if the following five assumptions are met

1. The size of the population is very large or effectively infinite.

2. Individuals can mate with one another at random.

3. There is no mutation.

4. There is no immigration or emigration.

5. All alleles are replaced equally from generation to generation (natural selection is not occurring).

Evolution as Genetic Change in Populations

Natural Selection acts on the Phenotype not the

Genotype!!!Natural selection can change the relative frequency of alleles in a

population over time by selecting individuals with favorable phenotypes (observable

adaptations that can be physical or behavioral)

Natural Selection on Polygenic Traits

• Three Types of Natural Selection that affect polygenic traits

1. Directional Selection2. Stabilizing Selection3. Disruptive Selection

Directional Selection• When individuals at one end of the bell-shaped curve

have a higher fitness.• This causes the curve for a polygenic trait to shift to

the left or to the right.

Stabilizing Selection• Individuals near

the center of the bell-shaped curve have a higher fitness.

• The shape of the curve stays the same, but is narrowed.

Disruptive Selection

• Individuals at the upper and lower ends of the bell-shaped curve have higher fitness than individuals near the middle.

Genetic Drift

• Genetic Drift is a source of evolutionary change.

• Some alleles become more or less common by chance.

• Occurs in small populations

Speciation

• Speciation- formation of new species• When two populations cannot interbreed and

produce fertile offspring, they are reproductively isolated.

• 3Types of Reproductive Isolation:1. Behavioral Isolation2. Geographic Isolation3. Temporal Isolation

Behavioral Isolation

• Different courtship rituals

• Different ranges in mating songs

Geographic Isolation

• Two populations are separated by geographic rivers.– Ex. Rivers, mountains,

bodies of water

Temporal Isolation

• Reproduction occurs at different times– Example: Flowers

release pollen on different days

Speciation in Darwin’s Finches

• Darwin’s finches on the Galápagos are an example of adaptive radiation

– in adaptive radiation, a cluster of species changes to occupy a series of different habitats within a region

– each habitat offers different niches to occupy• a niche represents how a species interacts both

biologically and physically with its environment in order to survive

– each species evolves to become adapted to that niche

What Is Ecology?

• Levels of ecological organization

– 1. Populations– individuals of the same organism that live together are

members of a population

– 2. Species– a species consists of all the populations of a particular

organism

– 3. Communities– populations of different species that live together in the

same place constitute a community

– 4. Ecosystems– a community and the nonliving factors with which it

interacts is called an ecosystem

What is ecology?

• Levels of ecological organization

– 5. Biomes– major terrestrial assemblages of plants, animals,

and microorganisms that occur over wide geographic areas and have distinctive physical characteristics are called biomes

– 6. Biosphere– all the world’s biomes, along with its marine and

freshwater assemblages, together constitute an interactive system called the biosphere

Levels of Organization

BiosphereBiome

EcosystemCommunity

PopulationSpecies

Biosphere

Biome

Ecosystem

Community

Population

Species

Niche and Competition

• The niche concept– a niche defines an organism’s biological role

• it describes a pattern of living– a niche is the sum of all the ways an organism uses the

resources of its environment, including space, food, and many other factors

Figure 2.17 The zebras fill a niche in this African savanna community

The Niche and Competition

• Sometimes organisms cannot fully occupy their potential niche because some other organism is using it

• Competition occurs when two organisms attempt to use the same resource

– Interspecific competition – competition between members of different species

– Intraspecific competition – competition between members of the same species

Predation

• One potential and important interaction in a community involves one organism eating another—called predation

• Both predators (i.e., the eaters) and prey (i.e., the eaten) may undergo reciprocal evolutionary adjustments– this process is called coevolution

Symbiosis

• Symbiosis is an interaction in which two or more kinds of organisms interact in a close relationship

– the relationship types vary by whether or not each participant is unaffected (0), helped (+), or harmed (-)

Types of Symbiosis

+/+ Mutualism

+/0 Commensalism +/- Parasitism