How did the finch population change from before the drought to after? According to Figure 1, the average beak depth increased in size and the finch population had more finches with greater beak depths in 1978 than before the drought.
The amount of rainfall has a large impact on the abundance and types of seeds that are available to be eaten by finches. In the process of natural selection, only the finches that are best adapted to the available seed types survive and have offspring. ) after one year has passed.
Some of the finches were not able to survive and find food during the drought, therefore dying off, and the ones that did adapt had bigger beaks.
Unusually heavy rainfall increased the abundance of small soft seeds and decreased the abundance of larger seeds. This would allow more finches with smaller beak depths to survive and reproduce, decreasing the mean beak depth of the population.
Changing rainfall affects the types and amounts of seeds available to the finches. During rainy years, the production of large numbers of small seeds increases the fitness of finches with small beaks. In years with little rainfall, only large seeds will be available and small-beak populations will decrease.
Ongoing field studies have documented rapid changes in these birds' beak sizes and shapes in response to sudden environmental variations -- drought, or human disturbances, for example -- yet very few genetic changes have been found that accompany those physical differences between finch species, nor between populations ...
1: Finches of Daphne Major: A drought on the Galápagos island of Daphne Major in 1977 reduced the number of small seeds available to finches, causing many of the small-beaked finches to die. This caused an increase in the finches' average beak size between 1976 and 1978.
In other words, beaks changed as the birds developed different tastes for fruits, seeds, or insects picked from the ground or cacti. Long, pointed beaks made some of them more fit for picking seeds out of cactus fruits. Shorter, stouter beaks served best for eating seeds found on the ground.
Recently they reported a change in the beak size of the medium ground finch on Daphne Major. In 1977 a drought reduced the number of small seeds available for the birds, forcing them to rely on larger seeds requiring considerable force to open.
The tiny seeds the medium ground finches were accustomed to eating grew scarce. Medium ground finches with larger beaks could take advantage of alternate food sources because they could crack open larger seeds. The smaller-beaked birds couldn't do this, so they died of starvation.
How do you think the one species of finch evolved into many different species, each with its own advantages? They evolved through adaptive radiation. Adaptive Radiation: evolution of one original species to many separate species, each adapting to different living conditions and habitat.
depending on the size of the seeds it eats. The drought caused a mutation that led to larger beak sizes in the finch population. Birds that could eat larger, tougher seeds survived and reproduced during the drought. Beak size varies among the birds in the finch population under study.