Arrange the given taxonomic groups in increasing order of species richness: Fishes, Mammals, Insects, Reptiles

Mammals < Reptiles < Insects < Fishes

Insects< Reptiles < Mammals < Fishes

Fishes < Insects < Reptiles < Mammals

Mammals < Reptiles < Fishes < Insects

To arrange the groups in increasing order of species richness (i.e., from fewest to most species), let's look at general estimates of known species:

Mammals – ~6,400 species
Reptiles – ~11,000 species
Fishes – ~34,000 species
Insects – Over 1 million described species (possibly several million undiscovered)