[Campbell Biology P.749] Based on the experimental results and the additional information pr... | Practice Question

Based on the experimental results and the additional information provided, what can be concluded about the defensive role of the periwinkle shell?

  • A: The shell provides significant protection against crab predation, as unshelled periwinkles were consumed very rapidly.
  • B: Shell thickness is irrelevant to predation rates, as both southern and northern periwinkles were preyed upon.
  • C: Crabs prefer unshelled periwinkles over shelled ones, indicating a feeding preference rather than a defensive role of the shell.
  • D: The experiment primarily shows the effect of crab source population on predation, not the shell's defensive role.

Explanation

The text explicitly states that 'When the researchers presented the crabs with unshelled periwinkles, all the unshelled periwinkles were consumed in less than an hour.' This drastic difference in survival rate compared to shelled periwinkles as implied by the graph strongly indicates that the shell provides substantial protection against crab predation. The shell acts as a physical barrier that crabs must overcome to access the periwinkle's soft body.