There’s a lot of ways you could be a keystone species, produce a lot of food for instance, or produce food in a season where everything else doesn’t. Maybe all the energy in the system goes through this species at some point, and if you remove it there are two separate entities with no flow between them...producers one end, eaters the other. This is called a wasp waist system; the keystone species would be the one at the waist.
Fig trees are thought of as a keystone species. And sometime you can see why. They produce a LOT of food and often different trees will bloom and fruit at asynchronously, keeping food available to a system. There are usually a huge number of animals that will come to the smells of ripening fig fruits. Some of them will be young boys and girls on their way from school, off course!
We rarely notice figs when they’re not ripe however, which is kind of funny because a lot of other creatures do and they are attracted to them. Figs have another story going, one of co-evolution. The fig is actually a structure called a syconium and its flowers are enclosed inside it. For these flowers to be pollinated, a pollinator must get inside the fig. Here’s where the fig wasps come into the story. A female wasp finds a receptive fig digs into it, she then pollinates some flowers (in some species seemingly intentionally, in others not), after or along with this she lays her eggs in some of the flowers. And then dies. Several wasps may lay in a single fig. Once the next generation of wasps is born, the females mate with the males, the males dig an exit and the females fly off looking for the next fig.
(Dont have a pic of the pollinator yet, coming soon)
But that isnt it, there are others in the system, other wasps the gallers. These guys are in some ways the cheats of the system. They lay their eggs from the outside inducing galls for their larvae to eat. The larvae of some even eat the larvae of those that came before. Thats a galler laying eggs.
Off course the gallers arent all shiny happy people, because right behind that lovely fig ripe for the laying lurks the big bad.........ANT. Red weaver ants, those big bad evil creatures that will shy from attacking nothing, wait for these wasps (pollinators and gallers) to eat them.
They get them too sometime, these little flitty things. Heres two ants fighting over who gets to keep the wasp.
So thats the fig wasp story, gleaned from the comprehensive presentation of Mahua and Yuvraj at CES, IISc.