The answers to your questions are as follows :
Herbivores feed on variety of plants because not all herbivores feed on the same type of plant therefore an area with a variety of plants or grasses will have a variety of herbivores as well.
The lowest trophic level in a food chains are the primary producers which are green algaes and green plants.
Overpopulation leads to increase competition for basic amenities such as food, shelter and water. therefore the resulting effect of the overpopulation of coyotes is an increase in competition amongst themselves.
Hence we can conclude that the answers to your questions are as listed above.
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