Notes: Speciation
Name____ KEY _____ Date_________ Per___
Warm-up – use the glossary in the back of the classroom set of Biology text books to define species and population:
A species is _____ a group of organisms that are able to interbreed and produce young _____
A population is __ a group of the same type of organism living together in the same area______
Speciation is _the formation of new species__
When two populations can no longer mate and produce offspring, reproductive isolation
has occurred.
Three causes of reproductive isolation (which leads to speciation) are:
1. Geographic isolation: populations are separated by a barrier (river, mountain or ocean).
2. Behavioral isolation: two interbreeding populations develop different behaviors (mating dances).
3. Temporal isolation: populations that live in the same habitat reproduce at different times.
Fill in the following while watching the video Galapagos Finch Evolution
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Our planet has millions_ of species; over 300,000 beetles alone.
Scientists are discovering new insights into the “mystery of mysteries”: how new species form (speciation).
The famed Galapagos finches were first brought to scientists’ attention by Charles Darwin.
The 13 species of finches live in diverse habitats. The islands differ in size, topography and height.
In these diverse habitats, the finches have evolved many ways to survive.
What is the important difference between these birds?beaks
Now we know from __ __ __ evidence that all of the finches are more related to each other than any one is to a
species on the mainland.
That tells us only one species arrived and diversified into the 13 species we see today. They’ve all come from a
common ancestor
How many finches did Biologists Peter and Rosemary Grant track at times? Over 1,000
What happened in 1977?_drought
The birds with the _smallest_ beaks had the most trouble. That year over 80_% of the medium ground finches died.
When they looked at the survivor’s offspring, they found the average beak depth was more than 4__% larger than the
previous generation. Natural Selection had changed the average beak size.
Five years later, in 1983, it rained ten times more than normal. The rain changed the vegetation such that two years
later, when drought struck, larger seeds became scarce.
That year many more finches with small beaks survived and their offspring inherited smaller beaks.
Natural Selection had swung in the opposite direction and evolution had occurred as a result.
In an amazingly short period of time, the Grants had measured evolution of beak size, not once but twice,
demonstrating that when birds encounter different environments they will change over a very short amount of time.
How did finches with different beaks become distinct species? Species are defines as populations whose members
don’t interbreed.
The males only responded to songs of their own species.
The males only courted females that had a similar size and similar beak.
The most likely scenario is that, two million years ago, a single finch population arrived from the mainland. When
their descendants reached another island, they faced new conditions. As those isolated populations adapted to their
surroundings, their traits changed, and they no longer mated. They had become distinct species.
The more diverse the environment, the more opportunities for evolutionary change to produce those new species.