Inter-relationship of species
“The number of bumblebees in any district depends in a great measure upon the number of field-mice, which destroy their combs and nests”. “[Because] the number of mice is largely dependent, as everyone knows, on the number of cats . . . It is quite credible that the presence of a feline animal in large numbers in a district might determine, through the intervention first of mice and then of bees, the frequency of certain flowers in that district!” - Charles Darwin, On the Origin of Species