BIO140 Finches

What are the different types of habitats on the Galapagos Islands?

_________: diverse across the islands, which differ in size, topography, and height.

• Higher elevations: where larger trees grow

• Low islands: which have mostly cactus, grasses, and shrubs

Why do the different finches have different ways of surviving in the different habitats?

___________: evolved different ways to survive because the environment has diverse conditions

• All 13 species are related, having evolved from a single common ancestor that arrived on the archipelago and diversified

• As isolated populations adapted to surroundings and faced new conditions on different islands their traits changes. The finches evolved to suit a different lifestyle. Rosemary Grant emphasizes that the beaks are tools, and you need the right tool for the right job

• The more diverse the environment, the more opportunities for evolutionary change to produce new species. Changes in beak size demonstrate that when birds encounter different environments, they will change over a very short amount of time

How do we know that only one species of finch arrived on the Galapagos Islands and then diversified into the 13 different species?

_________: based on DNA evidence

• All of the finches currently found are more related to each other than any one of them is to a species on the mainland. This indicates only one species arrived on the archipelago and subsequently divided into 13. They all have a single common ancestor

How did the research from 1976-78 support the hypothesis that food availability was the environmental factor that forced the evolution of the finch species?

• Variation : The medium ground finch population initially showed variation in beak size and shape. Peter Grant showed the distribution of beak depths in the population in 1976

•  Limited resources: In 1977, a drought began lasting 18 months, during which almost no rain fell. The medium ground finches were forced to compete for scarce food. The populations large food supply of small, medium, and large seeds diminished and small seeds became very scarce. The birds had to turn increasingly to the large and hard seeds.

 

Adaptation - Who survived and reproduced and why?

__________:Only birds with large beaks could crack open the woody spiny fruits.

• The Grants inventoried the surviving finches and discovered larger beaks associated with higher likelihood of surviving through the drought.

• Birds with the smallest beaks had the most trouble, scraping about amongst the rocks until their plumage was so worn they could barely fly.

• Over 80% of the medium ground finches died during the drought

What happened to other species? - What was the distribution of species (beak sizes) in the next generation?

___________: When the Grants looked at the offspring of survivors they found the average beak depth was more than four percent larger than the previous generation.

• Natural selection had changed the average beak size over a very short time. The trait allowing survival and reproduction in the changed environment was passed on altering the genetic makeup of the population

What is a typical mechanism that allows one species become two species?

________:(speciation) is that two populations become separated geographically. Then these populations undergo enough change in their respective habitats that if or when they come into contact again, they do not mate.

Currently, the populations of finches are not always geographically separated, so what keeps the populations from mating?

_________: through differences in song and appearance.

• The different species sing very different songs. When researchers played back songs specific to one species males of that species responded, while the medium ground finch completely ignored it.

• Researchers found that males only courted females that had a similar size and similar beak. When presented with stuffed female specimens, the male vigorously courted a female of his own species but completely ignored the other one

What is the generally accepted explanation for the evolution of the finches on the Galapagos?

• Arrival: a single finch population arrived from the mainland, likely around 2 million years ago

• Isolation and new conditions: Descendants of this original population reached another island and faced new conditions

• as these isolated populations adapted to their surroundings their traits changed

• Speciation: if changes included traits involved in mating and the populations later came into contact again they no longer mated, at this point, they had become distinct species

How does a diversity of environments lead to evolution of different species?

_____________: the more diverse the environment the more opportunities for evolutionary change to produce those new species.

• When isolated populations encounter varied conditions they are subjected to different selective pressures. These pressures drive the accumulation of different advantageous traits