The question above is referring to species richness which is the total number of species found in an ecosystem. The level of environmental stress will affect the number of species in an inverse relationship. More stress causes the number of species in a habitat to decline.
The living community and its nonliving environment are what we call an ecosystem.
A coral reef is an ecosystem found in warm shallow marine environments. Millions of coral animals in Phylum Cnidaria create colonies and build the structures that these tiny organisms live in which is the coral reef. They have symbiotic partners of algae called zooxanthellae which need sunlight to carry out photosynthesis. These algae live in the tissues of the coral animals and are important producers for the food webs that operate in this ecosystem.
Coral reefs are important places for fish to live, interact, hide and carry out their niches in the shallow ocean environment. Diverse species of fish, crustaceans, mollusks, bacteria, algae all interact in intricate food webs which all rely in one way or another in the presence of the reef. The reef also protects the coastline from erosion along with its role as an important habitat. Human activities including boating and diving, runoff from farms, spread of disease and rising ocean temperatures due to global warming have caused these important ecosystems to become endangered.
In an urban ecosystem, space is usually limited. Habitat is restricted mainly to the people who live there and any organisms who can tolerate being in close proximity to each other. Stress levels are higher in urban ecosystems due to noise, overcrowding, less resources, pollution and disease. Therefore, the number of organisms is less than in the coral reef.
Besides people and their household pets, you will find scavengers like mice, roaches, rats, pigeons. You will find various birds if there are enough trees for them along with squirrels. You can find bats living under bridges which resemble caves. There will be predatory birds like hawks circling above and usually scanning the area from buildings or street lights for prey. There will be various plants from gardens as well as established trees and weeds.
However, between the two ecosystems- coral reef and urban ecosystem there will be greater species diversity in the reef.