In an area with an ecological gradient, the relative abundance of plants and animals changes according to
a. human population
b. elevation
c. biome type
d. number of species

The answer would be : C. Biome type. In an area with an ecological gradient, the relative abundance of plants and animals change according to their biome type. They change it in order to survive and adapt to the environmental factors that exist around them

The best answer to the question above would be letter d. In an area with an ecological gradient, the relative abundance of plants and animals changes according to the number of species. Ecological gradients concern with the population distribution of species based on environmental tolerances.