Origin of Species - Biodiversity - Lecture Slides, Slides of Biology

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Chapter 24

The Origin of Species

Macroevolution is the origin of new taxonomic groups, as opposed to microevolution, which is genetic variation between generations within a species.

A. What is a species?

1. Biological species concept

• A species is a population or group of populations whose members have the potential to interbreed with one another and produce viable offspring, but who cannot produce viable offspring with other species.

Speciation - process by which a new species originates.

• Involves the creation of a population of organisms that are novel enough to be classified in their own group.
• Two processes by which this can occur:
• Anagenesis is the accumulation of heritable traits in a population, that transforms that population into a new species.
• Cladogenesis is branching evolution, in which a new species arises as a branch of from the evolutionary tree. The original species still exists. This process is the source of biological diversity.

Courtship ritual as a behavioral barrier between species.

c. Temporal isolation

• Two species breed at different times of the day or during different seasons.

d. Mechanical isolation

• Closely related species attempt to mate, but are anatomically incompatable. (Example: flowering plants with pollination barriers; some plants are specific with respect to the insect pollinator, often occurs with butterflies/moths)

e. Gametic isolation

• Gametes must recognize each other. (Example: fertilization of fish eggs, chemical signals between sperm and egg allows sperm to “recognize” the correct egg)

A summary of reproductive barriers between closely related species

The problem with the idea of biological species concept --> How do you get organisms to breed to see whether viable offspring are produced? There are…

3. Alternative concepts of species

a. Ecological species concept

• Species are defined by their use of environmental resources; their ecological niche (e.g. species that are defined by their food source such as butterflies with certain flowers).

B. Modes of speciation

1. Allopatric speciation

• Allopatric speciation describes speciation that takes place in populations with geographically separate ranges. Gene flow is interrupted and new species evolve.

2. Sympatric speciation

• Sympatric speciation describes speciation that takes place in geographically overlapping populations. Chromosomal changes and nonrandom mating reduce gene flow.

Remember: Species arise when individuals in a population become isolated one from the other.

Key question about allopatric species is whether they are indeed different enough that viable, fertile offspring would not be produced by mating. This can be tested sometimes as in…

Another place where adaptive radiation is apparent is on island chains. This example is illustrative of what happened on the Hawaiian islands.

Would this example be allopatric or sympatric speciation?

Remember  Once geographic isolation has occurred, there still must be changes that reproductively isolate populations of individuals. If the populations evolve so that they are now new species, they cannot interbreed to produce fertile, viable offspring.