Biodiversity

Balance

Between

Speciation and extinction

What is biodiversity?

• Type 1: Total number of species in world

• Type 2: Genetic variation within and between species.

• Type 3: Ecosystem biodiversity: huge variety of ecosystems and habitats

Total number of species

• What patterns do you see?

• How do you think scientists estimate the ``unnamed species’’?

Genetic biodiversity

•

                                      European sheep breeders protecting genetic diversity of their breeds.

These are all one species

• These are all different species

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Genetic biodiversity

• For example, humans are one species, but we have a great variety of variation in many genes, such as blood type

• Each species has thousands of genes

Ecosystem biodiversity

What is an ecosystem??

• A community of organisms, its abiotic environment, and their interactions

Levels of ecological organization

• Biosphere: all life on Earth and the life-supporting region of Earth

• Ecosystem• Community?

– Populations of different species in the same area or habitat

• Population?– Group of individuals of same species in same area or

habitat

Origin of biodiversity

• EVOLUTION

• Simple definition:

Descent with modification– Includes microevolution: changes in gene

frequency from one generation to the next• Includes macroevolution: descent of different

species from a common ancestor

Natural Selection

• Darwin’s big contribution• Inherently logical:

– Organisms produce more offspring than survive

– Individuals vary in important characteristics

– Many characteristics are inherited

– SO:

– some individuals will be better suited to the environment

• Those individuals will be more likely to survive and reproduce

• Their offspring likely to be more suited to the environment

Definition of evolution

• Descent with modification– KEY: Evolution proceeds by changes in genes

• NOT JUST: ``Change over time’’– Lots of things change over time:

• Trees change color

• Mountains erode

• Continents move– These are NOT evolution

Evolution is NOT

• Just a process of getting better

• Something that organisms TRY to do

Geneology: sharing a common ancestor

•

Evolution: sharing acommon ancestor

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Natural Selection

• Darwin’s big idea

• HOW evolution can happen

• Follows logically from some simple ideas:

Logic of natural selection

• (1) Organisms produce more offspring than can survive.– Even elephants—if all survived . . .

• Often, these differences are due to differences in the genes and therefore can be inherited

Logic of natural selection• (2) Individuals vary in their characteristics

Logic of natural selection

• Often, these differences are due to differences in the genes and therefore can be inherited

Logic of natural selection

• (3) Some of the characteristics that vary give individuals an advantage in surviving to maturity and reproducing.– Some individuals will be better suited to their

environment than others

Logic of natural selection

• (4) These better-suited individuals produce more offspring that survive

• They may survive longer to reproduce

• They may produce more offspring

• They may produce offspring of higher quality

KEY TAKE HOME POINT

• Natural selection acts on phenotypes—that is, features of organisms such as their speed, their toughness, their ability to hide.

• But, genotypes—the genes organisms have—are responsible for the phenotypes.

• SO, natural selection results in differential success of specific alleles in a population.

Natural selection doesn’t mean:

• Only the strong survive NO– Sometimes, other ways of being fit (e.g., hiding)

• Only the best-suited individuals survive NO– Many types may survive. Over long periods, the

more fit will leave more offspring.

Natural Selection

• Often MIScharacterized as ``evolution by random chance’’

• What IS random about natural selection?– The production of variation by mutation and

genetic recombination

Evidence for evolution

• Fossils

                                   

                                     

                             

                                  

                                   

                                     

Evidence for evolution

• Homology: characteristics that organisms share from a common ancestor

• Good example: limbs of tetrapods

Evidence for evolution

• Biogeography: the geographic distribution of species tells stories that geology and evolution can shed light on

• e.g.: Dinosaurs that can’t swim, but are found on several continents says those continents were once connected

Evidence for evolution

• DNA

• All life uses the same 4 DNA bases: thymine, adenine, guanine, cytosine

• Biochemical pathways trace evolutionary relationships just as fossils do

Evidence for evolution• Artificial selection

– Humans can mimic the selection process, bend evolution to our will (sometimes!!) and produce useful plants and animals.

– Check out corn (teosinte)

Adaptations

• Traits that are successful in their environment

• An adaptation to one environment may be NEUTRAL or UNFAVORABLE in another environment

• May be simple—heavier coat in colder climate—or complex—the mammalian eye

Again:

• Adaptations are specific to the environment.– A zebra’s coat pattern is camouflage in the

African savannah. It would not be advantageous in a North American grassland.

– Running speed is advantageous for a cheetah on the savannah. But cats in the rainforest (e.g., jaguar) are not fast. Strength and stealth are more important than speed there.

The finches on the Galapagos are thought to have evolved from a single species of ancestral finch, probably the generic sort of seed-eating finch shown in the center. When a population of finches was reproductively isolated on one of the islands, it adapted over time to feed on a new food source. After time, it was sufficiently different from its ancestor to be considered a new species.

•

Adaptation examples: mimicry

• How could such mimicry evolve?

• What is the advantage to the orchid?

• Is there a cost or benefit to the wasp?

• Some orchids (a kind of flower) mimic wasps. They look enough like a female wasp to fool males into ``mating’’ with them and thus transfer their pollen

                                                                

Adaptation examples: more mimicry

• • Katydids have evolved a body form that looks like a leaf.

• Why? What is the advantage to the katydid?

Adaptation examples: still more mimicry

•

• Non-poisonous king snakes mimic poisonous coral snakes

• Many examples of mimicry in nature

                                                                  

Speciation

• One species evolves into another OR splits into two.

• How can this happen?– Geographic isolationallopatric speciation

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Biodivrsity patterns: hotspots

Birds in South America

History of life

• As previous picture shows:– Complex creatures and structures have evolved– But simple life forms still common and

dominate in many habitats ``Earth still belongs to the bacteria’’

– Speciation generates diversity; extinction reduces it

•

Extinction

• The disappearance of a species from Earth

• Local disappearance is called extirpation

• 99% of ALL species that have ever existed are extinct

Extinction• Two kinds:1. Background: the regular, consistent,

extinction of species over millions and hundreds of millions of years

- Result of environmental change, species interactions

2. Mass: the relatively sudden extinction of a great number of species in a short period of time (few million years, or less)

This graph shows extinction rates. You can see that five times in the last 600 million years, the rate has spiked up. Those are MASS EXTINCTIONS. The last one is when the dinosaurs died. Between mass extinctions, there is a more steady extinction rate, called BACKGROUND EXTINCTION.

•

Date of extinctionmya=million years ago

% species lost Species affected

65 mya

Cretaceous

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 Triassic 44 Marine vertebrates and invertebrates.248

248 Permian 75-95 Marine vertebrates and invertebrates.380

380 Devonian 70 Marine invertebrates

450-440

Ordovician

50 Marine invertebrates

6th mass extinction?

• We are in the midst of a 6th mass extinction.

• First one caused by human activity.

Evidence for 6th mass extinction

• Birds: very well studied group, with a good fossil record

• Background extinction rate 1 species per 100 years

128 extinctions in last 500 years

103 extinctions in last 200 years

• 1,186 of about 9700 bird species are threatened

Population biology

• The study of populations (duh!)

• Individuals of the same species, inhabiting a geographic area and potentially interacting

Population characteristicsi.e., how to describe populations

• Size

• Density

• Distribution

• Sex ratio

• Age structure

• Birth and death rates – Also immigration and emigration

Size

• Count ‘em– Mark-release-recapture

• Why important??– Genetic drift– Usually: populations get small before they go

extinct (duh!)

Density

• # of individuals of a population per unit area

• Affects ability to find mates and aggressive interactions

• What do humans do that can affect density?

Distribution

• Species tend to have characteristic dispersions

Sex ratio

• Proportion of females to males

• Usually 50:50 ( or 1:1)

Age structure

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Birth, death rates

• All of the characteristics so far influence birth and death rates

• Given as #/1000 individuals– = crude birth rate or crude death rate

• Easy to calculate– B – d = r (rate of natural increase)