What is a species?

What is a species?

Its not as straightforward a question as most believe.

Macroevolution and Speciation

Evolution creates (and destroys) new species, but …

These are members of different species - eastern (left) and western (right) meadowlark.

Thursday, September 19, 2013• Get the handouts from the front• Get an iPad if needed• You will have 5 minutes to review your

document before presenting• You will present for no more than 5 minutes• Talk about speciation after presentations• Vocab Quiz tomorrow• BONUS DUE TOMORROW

Thursday, September 19, 2013

• Pick up handouts• Get with your groups to discuss

presentation• You’ll have 5 minutes to look over rubric

and fix anything• Presentations will be 5 minutes each—

MAX• Speciation talk afterward• Vocab quiz 3 tomorrow—time for questions

after

What is a Species?

There is only one extant (existing) human species.

What is a Species?

And these are all members of a single species.

Determining What Is and What Isn’t a Distinct Species Can Have Economic Consequences

Northern spotted owl (left) and barred owl (right).

What is a Species?

The definition we’ll use is this: A species is a group of individuals capable of interbreeding to produce fertile offspring.

This is the biological species concept. Like all attempts to define a species, it has many problems.

One Problem in the Biological Species Concept

For asexually-reproducing organisms, like these bacteria, what constitutes a species?

…and another problem with the Biological Species Concept…

Where do you draw the line between different ‘species’?

What is a population?

• Members of a species that live in the same geographical area and interbreed

How Many Species Are There?

We don’t know.

About 2 million species have been described.

Estimates of existing species number range from 4 million to 100 million (with 10-15 million being a more commonly considered upper estimate).

How did this diversity of life come to be?

Species = basic unit

Speciation - rise of new species

Continuous lineage - informationpassed through genes

Two Patterns of Speciation

Branching evolution can be Adaptive radiation if many species come from one common ancestor

How Do Species Arise?

Geographic isolation is the primary extrinsic reproductive isolating mechanism.

The key to speciation is reproductive isolation of populations.

There are extrinsic and intrinsic reproductive isolating mechanisms.

Process of speciation:

Parentspecies

I. Barrier

2 separate species

III. Don’t interbreedII. Diverge

Reproductive Isolation May Occur With or Without Geographic Isolation

Allopatric speciation occurs when geographic isolation creates a reproductive barrier (an extrinsic mechanism).

Sympatric speciation occurs when a reproductive barrier is created by something other than geographic isolation (intrinsic mechanisms).

Allopatric Speciation

Two species of ground squirrel are postulated to have descended from a common ancestral population that was separated by formation of the Grand Canyon.

Harris’ antelope squirrel White-tailed antelope squirrel

Intrinsic Reproductive Isolating Mechanisms Are Always Required for Speciation

Intrinsic mechanisms involve changes to organisms that prevent interbreeding.

In allopatric speciation, intrinsic mechanisms come into play once populations are physically separated.

In sympatric speciation, intrinsic mechanisms are the only ones involved.

Harris’ antelope squirrel White-tailed antelope squirrel

Many Intrinsic Reproductive Isolating Mechanisms Drive Speciation

(different habits within an overlapping range)

Courtship rituals, like these, are critical for mating within a species, but ineffective for attracting members of other species.

Many Intrinsic Reproductive Isolating Mechanisms Drive Speciation

Courtship rituals, like these, are critical for mating within a species, but ineffective for attracting members of other species.

Behavioral Isolation Mechanisms

Many Intrinsic Reproductive Isolating Mechanisms Drive Speciation

Many Intrinsic Reproductive Isolating Mechanisms Drive Speciation

Hybrid Infertility Was the Impetus for Cloning a Mule

Speciation Occurs at Widely Differing Rates

A slow rate of speciation evidenced by a living horseshoe crab (13 extant species) and a 300 million year-old fossil species

A rapid rate of speciation evidenced by Galapagos finches which have diversified into 13 species within the last 100,000 years.

Speciation Rates

Generalists, like the horseshoe crab, tend to remain as stable species.

Specialists, like the Galapagos finch, tend to be unstable as species.

Speciation also becomes rapid when, as occurred with Galapagos finches, new niches become available.

Speciation Dynamics - Gradualism or Punctuated Equilibrium?

Punctuated equilibrium appears to be a more accurate view of speciation dynamics.

Does Evolution Create the Perfect Organism?

No, only better organisms as evolution is constrained by history and buffeted by random events.

Essentially, every organism on earth is in significant part a sum of accidents.

Species Come and Go

Best estimates from the fossil record indicate that greater than 99% of species that have exited are now extinct.

A typical “lifetime” for a species is about 1 million years.

Mass Extinctions Are a Fact of Life

90% of all species that have ever existed are now extinct …

Gary Larson