Biodiversity

• How did biological diversity come about?

• What are the principles of natural selection?

• What affects biodiversity?

What is biological diversity?

1. genetic diversity

2. species diversity

3. higher taxonomic diversity (taxonomy)

4. habitat diversity

How many species exist in the world?• No one knows!• Taxonomists have named and

described 1.4-1.7 million species– 56% insects– 14% plants– 3% vertebrates– 15% are in oceans

• Highly biased sample– Vertebrates much more

widely studied– What about microbes?

• 4000 different bacteria species per gram of Norwegian soil!

– Also, mostly done in Europe and N. America while most of the biodiversity is in tropical countries and in oceans

250,000

500,000

750,000

1,000,000

insects other animals

higher plants fungi

protists virusesbacteria

So how many species are there?

0

5,000,000

10,000,000

15,000,000

number of

species

total identified

total estimated to exist

however, this number could be as

high as 100,000,000

14 mil

1.7 mil

Global biodiversity seems to be at its peak

Where are these species?• Oceans

– 1 to 10 million in oceans– diverse in phyla

• 32 in oceans but only 12 phyla on land

• Tropics– 7% of land mass– 50% of species

How do species evolve?Evolution is the change in the genetic

characteristics of a population over time.

This change may happen by:1. genetic mutations2. natural selection3. geographic isolation and migration4. genetic drift (most likely in small, isolated

populations)

Views of Species Change: Evolution

• Lamarck (1809)– Use and disuse– Inheritance of acquired

characteristics• Charles Darwin (1859) • Alfred Wallace

Organisms today descended by gradual changes from ancient ancestors.

Age of the Earth: 238Uranium half-life of 4.5 billion years, current amount present suggests earth is ~ 4.6 billion years old (…so what?)

Principles of Natural Selection

• Genetic variation exists among organisms in a population, these variations are inheritable.

• Populations produce more offspring than environment can support and therefore only a fraction survive (struggle for existence)

• Individuals best adapted to environment (more “fit”) will survive and leave more offspring

• …..“Survival of the fittest”

Examples of natural selection• Moths: “industrial melanism”• DDT and mosquitos

What is “fit” changes with a changing environment

Galapagos finches• Variety of finches filling many ecological niches

• Ground feeders, flower and fruit feeders, insectivores, woodpecker finch, warbler finch

• Evolutionary divergence in < 3 million years

Island speciation in Galapagos finches• Some islands have only one

species– No competition for seeds– beak sizes have a larger range

of variation– “Generalists”

• Other islands have > 1 species– Competition for seeds– Leads to character displacement to

reduce competition– “Specialists”

Character displacement and biodiversity

• Helps explain how so many species are able to coexist

• Competitive exclusion principle: Two species that have exactly the same requirements (niches) cannot coexist in the same habitat.

• However, species that require the same resources can coexist by utilizing those resources under different environmental conditions (or niches)

• Also called “resource partitioning” or “niche partitioning”

Speciation

• Speciation = origin of new species– Central phenomenon of evolution– Evolution ≠ speciation

• When is a subpopulation defined as a new species?

• How do genes usually flow through a population?

• Reproductive isolation prevents gene flow and allows 2 populations to become distinct.

Geographic isolation and migration

Eastern Redbud Cercis canadensis L.

California redbud Cercis occidentalis Torr. ex Gray

If two populations are geographically isolated from each other for a long time, they may change so much that they cannot reproduce

Genetic drift

• Changes in the frequency of a gene in a population due to chance (not mutation, natural selection, or migration).

• Mostly an issue in small populations (endangered species)

• Genetic variability is low in small populations, so their ability to adapt to future changes in the environment is low.

Where can expect to find high biodiversity or low biodiversity?

Higher diversity in complex environments• Larger number of niches in heterogeneous environments

• Also, high diversity at a supporting trophic level leads to high diversity.

“Paradox of the Plankton”

• seemingly simple environment, many species, no competitive exclusion

• environmental complexity can still account for significant portion of diversity

• need just two limiting resources

Environments can be complex when spatial component added

Highest diversity at intermediate disturbance levels

• Intermediate Disturbance Hypothesis– low disturbance, competitors dominate– high disturbance, only a few stress-tolerators

Highest Diversity in Low Nutrient Environments

What leads to low diversity?

• Environmental stress, extreme environments, extreme disturbance, or limitation of an essential resource

• Geographic isolation (real or ecological islands)

• Recent introductions of exotic species