# data[].attributes.body
Which mechanism of microevolution caused the beak of the medium ground finch population on Daphne Major to increase in average size from 1976 to 1978?

# data[].attributes.body
The total rainfall decreased from 130mm in 1976 to 20mm in 1977.

# data[].attributes.body
Natural selection caused the beak of the medium ground finch population on Daphne Major to increase in average size from 1976 to 1978.

# data[].attributes.body
The portulaca numbers decreased from a high of 18 in 1976 to a high of 2 in 1978, and the tribulus numbers decreased at a lower rate, with a high of 14 in 1976 to a high of 6 in 1978.

# data[].attributes.body
The average beak depth increased from 9.6mm in 1976 to 10.5mm in 1978, and the average beak length increased from 10.7mm to 11.6mm.

# data[].attributes.body
Due to the decrease in rainfall, the portulaca plants couldn't get enough water to grow and died. This caused the birds to rely on tribulus plants for food, and the ones with greater beak depth/length were able to eat.

# data[].attributes.body
Because the birds had larger and tougher beaks, they were able to open the tougher shell that tribulus plants have and get the food they needed to survive.

# data[].attributes.body
Natural selection was in favor of the traits of greater beak depth and greater beak length, and the birds that had this trait were able to reach the seeds in tribulus plants to survive.