Macroevolution

• Microevolution refers to the changes in the allele frequency within a population.

• Macroevolution refers to dramatic biological changes which include the origin of new species, the extinction of species and the evolution of major new features such as wings.

What is a species

• According to the biological species concept, a species is a population or group of populations whose members have the ability to breed with one another in nature and produce fertile offspring.

• Limitations of the definition:– Organisms that reproduce asexually are not included.– Fossils (which can no longer reproduce) cannot be

evaluated under this definition.

What leads to speciation

• Clearly a fly will not mate with a frog.

• But why will a Western Spotted Skunk not mate with an Eastern Spotted Skunk?

Reproductive Isolation

• Refers to the inability of two organisms to reproduce due to some kind of physical inability, or behavioral barrier.

Reproductive Isolation• 1) Geographic Isolation

– Landforms, water, and distance for organisms to move (or spread their reproductive cells) limits reproduction.• Geographic isolation of a portion of a species is a main feature of speciation.• Genetic drift and natural selection work together to form unique species.• For every species that forms, many more perish.

Eg. The Harris and White-tailed Antelope Squirrels living on different sides of the Grand Canyon

Reproductive Isolation

• 2) Habitat Isolation– Some species have adapted to a specific location

within an ecosystem.– Even though contact between the species is possible,

their preferences for their habitat prevents most contact.

• Eg. Three-spined stickleback fish– One species prefers to live in the lake bottom feeding

on snails– The other prefers the open water feeding on plankton.

Reproductive Isolation

Reproductive Isolation

Understanding the Evolutionary Story

• Adaptive Radiation (Divergent Evolution)– Organisms arriving in new habitats often face a wide

range of new and unique environmental conditions.– New habitats encourage speciation as species adapt

and evolve.– Founder effect + Natural selection + Reproductive

Isolation = Speciation

Understanding the Evolutionary Story

• Convergent evolution• Distantly related species that live in similar

environments in geographically isolated areas may develop analogous structures.

North American antelope (left) and African impala antelope (right) appear to be very closely related, but have actually evolved convergently to resemble each other.

Understanding the Evolutionary Story

• Co-evolution– Occurs when one or more species change over time

as the result of changes in another species.

• Predator-Prey Co-evolution– The ptarmigan changes its plumage from white to

brown, depending on the season. The golden eagle has excellent sight to find its food hidden in the landscape it flies over.

Understanding the Evolutionary Story

• Mutualistic Co-Evolution– The hawk moth has a specialized structure to

gather nectar from Darwin's orchid, pollinating the flower as a result.

• Mimicry: One species the mimic, resembles another species, the model in order to gain survival advantage.

Understanding the Evolutionary Story

• Parasite-Host Co-evolution– The plasmodium that causes malaria infects

mosquitoes, but does not kill them. If it is passed on to humans however, fatality of the host is possible.

Understanding the Evolutionary Story

• Evolution is not necessarily the appearance of something completely new, sometimes, it is small changes that increase the complexity of the form and function of a simple structure.

• Cumulative Selection: The evolution of a simple structure into a more complex structure through series of small adaptations.

The Rate of Speciation• Gradualism

– Darwin realized that geologic changes were very slow.– He believed speciation must also occur very slowly.– Small changes occur over a long period of time.

• Punctuated equilibrium is the opposite of gradualism (Eldredge and Gould).– Sometimes a new fossil may appear in the rock layer suddenly, persist a few

thousands or millions of years and then suddenly disappear.– Changes to a species can occur suddenly, and can be extensive enough to create a

new species in a short period of time (a few thousand generations).

Human Activities affect Diversity• Human activity often results in a decrease in

biodiversity.– Many island ecosystems, and their species diversity, have

been affected by human activity and the invasive species humans introduce.

– Harvesting resources often occurs at the expense of natural ecosystems and the niches of species.• Ocean net fishing has drastically reduced fish stocks, while also

decimating leatherback turtle populations.

The plight of the Leatherback Turtle:

-Tangled in abandoned fishing gear-Mistake plastic bags for jellyfish-Their Meat and Eggs are harvested for food.

• Pg 232, qs 1,2,7,10,11