Ecology 5th Edition by Manuel Molles

Exercise 13

Bshary studied changes in fish species richness in response to both natural and experimental removals and additions of the cleaner fish Labroides dimidiatus (see fig. 17.18). Why did he not just focus on the response of fish species richness to natural additions and removals of the cleaner fish?
Figure 17.18 Results of experimental and natural removals or additions of cleaner wrasses. Labroides dimidiatus, to reef patches in the Red Sea (data from Bshary 2003).