You study an isolated population of a snail that lives along the coast. you have documented that there is natural, heritable variation in the thickness of the snails’ shells. an invasive crab (one not found in this particular area before) is introduced from asia. the crab is really good at crushing thin snail shells. based on this information, answer the following questions: what do you predict will happen to the average shell thickness of snails in this population over time?

The average of the snails having less thick shell will disappear.

Explanation:

When a population of snails consists of both less thick and more thick snails. When an invasive species of crab enters this population.

This crab is capable of eating the snails having thin shell. Sooner or later the crabs having thin shells will disappear and the snails having thick shells will survive more.

Over a period of time there will be no snails left with thin shells only the shells having thick shells will be naturally selected and will reproduce to have a population.  

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i think its the first one