Ecology is basically concerned with how many basic levels of organisation?
Three
Two
Four
Eight
Which is the correct order of ecological hierarchy?
$A$ : Population ecology is a link of ecology to population genetics and evolution.
$R$ : Natural selection operates at population level to evolve the desired traits.
Species which occupy a similar ecological niche in similar communities occupying different biogeographical regions are
The study of inter-relationship between living organisms and their environment is called
$A$ population is