Answer:
Photosynthetic organisms (plants and/or phytoplankton) are at the bottom of the food chain.
Explanation:
A rainforest ecosystem would have a more high species riches. There are vast resources such as trees and plants that contribute to animal life. More animals live in these ecosystems because of the environment itself.
A dessert ecosystem would have a low species riches. There is little plant life and low resources for survival. Only animals that have adapted to this environment have a high species rate.