Direct relationship (between keystone species and other organisms):

Keystones species are very functional in the ecosystem in which there removal or absence as predators can lead to explosion of prey populations and decrease diversity. Keystone species help define an ecosystem and without they ecosystem can cease to exist.

Explanation:

Keystone species are predators species that help regulate the populations of other species through its activities or effects on the ecosystem. Keystone species exert both direct or indirect activities on the ecosystem. An indirect interaction occurs when species influence one another through their interactions with other species. Which can be inform of competition, interaction modifications e.t.c

relative dating involves things like higher layers are most recent than rocks lower in the sequence. this can be extended to the known sequence of fossils. rocks containing rabbit fossils are later than those containing dinosaur fossils.  

absolute dating methods mainly use radioactive elements that have known rates of decay and produce recognizable products. for example potassium 40 decays to produce argon. once a rock has solidified the argon is trapped. by measuring the argon and potassium0 you can get an accurate number for the age.  

some other methods are good for archaeological ages. dendrochronology involves recognizing the sequence of tree rings. the orientation of magnetized particles in baked clay can be used to date a fire.

hope this .. .