Biodiversity and Evolution: 4-4

to 4-6BBy Chris Nicolo

4-4 How Do Speciation, Extinction, and Human Activities Affect Biodiversity?4-4A: As environmental conditions change, the balance between the formation of new species and the extinction of existing species determines the earth’s biodiversity.

4-4B: Human activities are decreasing biodiversity by causing the extinction of many species and by destroying or degrading habitats needed for the development of new species.

How Do New Species Evolve?

Species evolve under certain circumstances, natural selection can lead to an entirely new species.

This is accomplished through a proses called Speciation, where one species splits into 2 or more different species.

Resulting with one population of a species evolving to a point where its members can no longer breed with members of another population that either evolved differently, or did not change.

This phenomenon can be caused by 2 types of isolation: geographic and reproductive

How Do New Species Evolve? (cont.)

Another factor is Geographic isolation when different groups of the same population of a species become physically isolated from one another for a long period of time.

This separation can happen due to the behavior of the animals themselves.

Ex.: A part of a population migrate to a different geologic location for survival and begin living their as a separate group.

Separation can also be caused by a physical barrier.

Ex.: mountain range, stream, road, volcanic eruption, tectonic plate movement, or winds and/or flowing water carrying individuals to a distant area.

How Do New Species Evolve? (cont.)

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

If this process continues long enough, the genetic code of the members within the population will become altered enough to become a new species.

These events of speciation may accrue over millions of years, but humans have started playing an increasing role in this process through artificial selection and genetic engineering

Extinction Is Forever

Another factor that affects the number and types of species is Extinction, a process in which an entire species cases to exist.

When threatened with environmental change a species has three options:

Adapt to new conditions

Move to a more favorable location

Or become extinct

Endemic species are a species found in only one area and are especially vulnerable to extinction.

Types of Extinction

Background Extinction: the disappearance of species at a low rate.

Based on the fossil record and analysis of ice cores, it is estimated that the average rate for this type of extinction has been one to five species for each million species on earth.

Mass Extinction: significant rise in extinction rates above background level.

Usually a catastrophic, wide spread, global event, where 25-95% of all species are wiped out world wide in a few million years or less.

Ex. The extinction of the dinosaurs at the end of the Cretaceous period.

4-6 What roles do Species play in an ecosystem?4-6B: Any given species may play one or more of five important roles- native, nonnative, keystone, or foundation- in a particular ecosystem.

Species can Play Five Major Roles within Ecosystems Native Species: species that normally live and

thrive in a particular ecosystem

Nonnative Species: Also known as invasive, alien, or exotic species, who migrate into, or are deliberately or accidentally introduced into an ecosystem

Indicator Species Serve as Biological Smoke Alarms

Indicator species

Provide early warning of damage to a community

Can monitor environmental quality

Trout

Birds

Butterflies

Frogs

Keystone Species Play Critical Roles in Their Ecosystems Keystone species: roles have a large effect on

the types and abundances of other species

Pollinators

Top predators

Foundation Species Help to Form the Bases of Ecosystems Create or enhance their habitats, which benefit

others

Elephants

Beavers