Chapter 5Evolution of Biodiversity

Earth is home to a tremendous diversity of

species

•Ecosystem diversity- the variety of ecosystems within a given region.

•Species diversity- the variety of species in a given ecosystem.

•Genetic diversity- the variety of genes within a given species.

Biological Diversity Biological Diversity

Number, variety and variability of Earth’s organisms- 1.9 million identified

Consists of three components:

Genetic diversity (below)

Species

richness

Ecosystem

diversity

Fig. 4-2, p. 82

Functional Diversity The biological and chemical processes such as energy flow

and matter recycling needed for the survival of species, communities, and ecosystems.

Ecological Diversity The variety of terrestrial and

aquatic ecosystems found

in an area or on the earth.

Solar energyChemical

nutrients (carbon dioxide, oxygen,

nitrogen, minerals)

Heat

Heat Heat

Decomposers (bacteria, fungi)

Producers (plants)

Consumers (plant eaters, meat eaters)Heat Heat

Genetic Diversity The variety

of genetic material within a species or a population.

Species Diversity The number and abundance of species

present in different communities.

How Do New Species Evolve?

•Speciation: one species splits into two or more species

•Geographic isolation: happens first; physical isolation of populations for a long period

•Reproductive isolation: mutations and natural selection in geographically isolated populations lead to inability to produce viable offspring when members of two different populations mate

•Species richness- the number of species in a given area.

•Species evenness- the measure of whether a particular ecosystem is numerically dominated by one species or are all represented by similar numbers of individuals.

Evolution is the mechanism underlying biodiversity

•Evolution- a change in the genetic composition of a population over time.

•Microevolution- evolution below the species level.

•Macroevolution- Evolution which gives rise to new species or new genera, family, class or phyla.

• 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

Creating Genetic Diversity

•Genes- physical locations on chromosomes within each cell of an organism.

•Genotype- the complete set of genes in an individual.

•Mutation- a random change in the genetic code.

•Phenotype- the actual set of traits expressed in an individual.

Evolution by artificial and natural selection

•Evolution by artificial selection- when humans determine which individuals breed.

•Evolution by natural selection- the environment determines which individuals are most likely to survive and reproduce.

Darwin’s theory of evolution by natural selection

• Individuals produce an excess of offspring.

•Not all offspring can survive.

• Individuals differ in their traits.

•Differences in traits can be passed on from parents to offspring.

•Differences in traits are associated with differences in the ability to survive and reproduce.

Evolution by Random Processes

•Mutation- occur randomly and can add to the genetic variation of a population.

•Genetic drift- change in the genetic composition of a population over time as a result of random mating.

•Bottleneck effect- a reduction in the genetic diversity of a population caused by a reduction in its size.

•Founder effect- a change in a population descended from a small number of colonizing individuals.

Speciation and extinction determine biodiversity

•Allopatric speciation- when new species are created by geographic or reproductive isolation.

•Sympatric speciation- the evolution of one species into two species in the absence of geographic isolation, usually through the process of polyploidy, an increase in the number of sets of chromosomes.

Sympatric 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

The pace of evolution

Evolution shapes ecological niches and determines species distributions

•Range of tolerance- all species have an optimal environment in which it performs well. The limit to the abiotic conditions they can tolerate is known as the range of tolerance.

•Fundamental niche- the ideal conditions for a species.

Niches

•Realized niche- the range of abiotic and biotic conditions under which a species lives. This determines the species distribution, or areas of the world where it lives.

•Niche generalist- species that live under a wide range of conditions.

•Niche specialist- species that live only in specific habitats.

Adaptive RadiationAdaptive RadiationEmergence of Emergence of numerous species numerous species from a common from a common ancestor introduced to ancestor introduced to new and diverse new and diverse environments-happens environments-happens when a niche opens when a niche opens due to changesdue to changes

Example::

Hawaiian Hawaiian Honeycreepers Honeycreepers

Natural selection acts on genetic variation

• Directional selection = drives a feature in one direction

• Stabilizing selection = produces intermediate traits, preserving the status quo

• Disruptive selection = traits diverge in two or more directions

If the environment changes, a trait may no longer be adaptive

Coevolution• Evolutionary change

•One species acts as a selective force on a second species

• Inducing adaptations •that act as selective force on the first

species Example:1.Wolf and Moose2.Acacia ants and Acacia trees2.Yucca Plants and Yucca moths3.Lichen

Convergent Evolution

Species from different evolutionary branches Species from different evolutionary branches may come to resemble one another if they live may come to resemble one another if they live

in very similar environmentsin very similar environments

Example:Example:

1. Ostrich (Africa) and Emu (Australia).1. Ostrich (Africa) and Emu (Australia).

2. Sidewinder (Mojave Desert) and2. Sidewinder (Mojave Desert) and

Horned Viper (Middle East Desert)Horned Viper (Middle East Desert)

Scientific Importance of Genetic Diversity

Genetic Engineering

Incorporation of genes from one organism into a different species

Provided:

New vaccines

More productive farm animals

Agricultural plants with desirable characteristics

Depends on genetic diversity (cannot create genes)

Important to protect this diversity

Why we need diversity

Example contributions to human life:

Food

Clothing

Shelter

Pollination of crops

Antibiotics and medicines

Biological processes (nitrogen fixation)

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

Evidence of Evolution

•1. Biogeography

•2. Fossil Record

•3. Taxonomy

•4. Homologous Structures

•5. Comparative Embryology

•6. Molecular Biology

The Fossil Record

•Fossils- remains of organisms that have been preserved in rock. Much of what we know about evolution comes from the fossil record.

Science Focus: Species Richness on Islands

• Species equilibrium model, theory of island biogeography

• Rate of new species immigrating should balance with the rate of species extinction

• Island size and distance from the mainland need to be considered

• Edward O. Wilson

The Five Global Mass Extinctions

•Mass extinction- when large numbers of species went extinct over a relatively short period of time.

Earth has had several mass extinctions

• Background extinction rate = extinction usually occurs one species at a time

• Mass extinction events = five events in Earth’s history that killed off massive numbers of species at once

• 50-95% of all species went extinct at one time

• Humans are causing the sixth mass extinction event

• Resource depletion

• Population growth

• Development

Adaptive Radiation-- new species evolve during recovery period following mass extinction

Mass ExtinctionsDate of the Extinction

Event

Percent Species Lost

Species Affected

65 mya

(million

years ago)

85 Dinosaurs, plants (except ferns and seed bearing plants), marine vertebrates and invertebrates. Most mammals, birds, turtles, crocodiles, lizards, snakes,

and amphibians were unaffected.

213 mya 44 Marine vertebrates and invertebrates

248 mya 75-95 Marine vertebrates and invertebrates

380 mya 70 Marine invertebrates

450 mya 50 Marine invertebrates

The Sixth Mass Extinction

•Scientists feel that we are in our sixth mass extinction, occurring in the last two decades.

•Estimates of extinction rates vary widely, from 2 % to 25% by 2020.

• In contrast to previous mass extinctions, scientists agree that this one is caused by humans.

Characteristics of Endangered Species

Extremely small (localized) range

Requiring a large territory

Living on an island

Having a low reproductive success

Small population size

Low reproductive rates

Requiring specialized breeding areas

Having specialized feeding habitats

Endangered & Extinct Species

Endangered & Extinct Species

Earth’s Biodiversity Hotspots

Causes of Loss of Biodiversity

•Habitat Loss

•Invasive species

•Climate change

•Pollution

•Overharvesting