BIOLOGICAL DIVERSITY

• Microevolution-- changes within a population over generations
• Macroevolutin-- changes that merit a new branch in the tree of life

HOW TO DEFINE A SPECIES

• Taxonomy
• Biological species concept
• Reproductive isolation
• Morphological species concept
• Ecological species concept

HOW TO DEFINE A SPECIES CONT...

• Phylogenetic species concept

Taxonomy
Branch of biology that names and classifies species and groups them into broader categories using a binomial system of naming organisms.

Created by Swedish physician and botanist Carolus Linnaeus in the 18th century.

He named over 11,000 species based on this system.

Biological Species Concept

A species is a group of populations with the ability to interbreed and produce fertile offspring.

Created in 1942 by biologist Ernst Mayr.

Organisms of different species typically do not mate with each other.

Morphological Species Concept

Has identified most species named to date. It can also be applied to asexual organisms and fossils.

Unfortunately, it relies on subjective criteria and scientists may disagree on what defines a species.

Ecological Species Concept

A species is defined by their ecological niches and adaptations to their environment.

Phylogenetic Species Concept

A species is the smallest group of individuals that share a common ancestor and form one branch on the tree of life.

It traces the ancestor by comparing common characteristics.

Agreeing on the amount of differentiation needed to define a new species is conflictional.

Reproductive barriers prevent closely related species from mating with each other.

Habitat isolation: two closely related species live in different types of habitats.

Behavioral isolation: courtship rituals vary among species.

Mechanical isolation: due to placement of genitalia, it is impossible for two different species to mate.

Gametic isolation: gametes are unable to fuse between sperm and egg.

Reduced hybrid fertility: breeding between different species typically result in sterile offspring.

Sometimes a group from a population are separated from the main group geographically. Due to the lose of certain genes on both sides, new species emerge over generations. This is called allopatric speciation. Happens most often with small and isolated populations.

A new species can also arise from the same geographic area as the parent species. This is called sympatric speciation.
This occurs when mating. Some of the resulting gene flow is reduced by different factors.
Many plant species have evolved from this accident during cell division, where an extra pair of chromosomes is present. These are called polyploid, meaning they have two complete sets of chromosomes.

The evolution of many species with a common ancestor is called adaptive radiation. The adaptations they undergo better suit their environments and their rolls in that community.

Speciation can occur rapidly or slowly.
Stephen Jay Gould and Niles Eldridge are both paelientologists. Together they created the term punctuated equilibria. This describes the long periods in which little change among a species happens, punctuated by abrupt episodes of speciation.