1. You have learned that both biotic and abiotic factors affect ecosystems. Give some examples of each and explain how biotic and abiotic factors could have affected the tortoises that Darwin observed on the Galapagos Islands

CH 16 DARWIN’S THEORY OF EVOLUTION16.1 Darwin’s Voyage of Discovery

Evolution

The process of change over time Change in allele frequency in a population over

time.

Geologists were suggesting that Earth was ancient and had changed over time

Biologists were suggesting that life on Earth had also changed.

Darwin’s Epic Journey

Darwin was invited to sail on the HMS Beagle’s five-year voyage mapping the coastline of South America in 1831

Darwin planned to collect specimens of plants and animals on the voyage.

Observations Aboard the Beagle

1. Species vary around the world2. Species vary locally3. Species vary over time

Darwin wanted to explain the biological diversity he observed in a scientific way

He looked for larger patterns into which his observations might fit.

Species vary Globally Darwin found flightless, ground-

dwelling birds called rheas living in South America

Rheas look and act a lot like ostriches (live in Africa).

Species vary Locally

These islands are close to one another, yet they have different ecological conditions

Different islands had distinct tortoises, mockingbirds, and finches.

Isabela Island has high peaks, is rainy, and has abundant vegetation that is close to the ground Tortoise has a dome-shaped shell and short neck

Hood Island is flat, dry, and has sparse vegetation Long neck and a shell that is curved and open around

the neck and legs allow them to reach sparse, high vegetation.

Darwin also observed that different islands had different varieties of mockingbirds All were similar to those in South America

Darwin noticed several types of small brown birds on the islands with beaks of different shapes He didn’t think they were important.

Species Vary Over Time

Darwin collected fossils Preserved remains or traces of

ancient organisms Some fossils of extinct

animals were similar to living species.

Darwin collected MANY specimens He actually kept poor records Darwin sent plant and animal specimens to

experts for identification Mockingbirds turned out to belong to three

separate species unique to the Galapagos The little brown birds were actually all species of

finches.

Some specimens he took back to England were living.

Putting the Pieces Together

Darwin began to wonder if different Galápagos species evolved from South American ancestors

He spent years researching and filling notebooks with ideas on species and evolution

Evidence suggested that species are not fixed and that they could change by some natural process.

1. Using a world map and page 381, count the number of lines of 10° latitude the Beagle crossed

2. Using the biome map from Ch 4 as a reference, identify three different biomes Darwin visited on his voyage

3. How did the geography of Darwin’s voyage give him far greater exposure to species variability than his fellow scientists back home had?