What do these words mean
"The researchers write that this “gap” in P. macrocarp recruitment could be due to extirpated rhinos (which are now relegated to Borneo, Sumatra and Java and staring down the barrel of extinction),"

- What does recruitment mean here?
- what does relegated mean here?

Thanks a lot!

Question

What do these words mean
"The researchers write that this “gap” in P. macrocarp  recruitment could be due to extirpated rhinos (which are now relegated to Borneo, Sumatra and Java and staring down the barrel of extinction),"

- What does recruitment mean here? 
- what does relegated mean here?

Thanks a lot!

Answer

recruitment = The increase in a natural population as progeny grow and new members arrive.

relegate =  to give someone or something a less important position than before. 
 Here it means that the elephants were previously found in abundance (in Thailand) but now they are found in fewer number only in places like Borneo, etc (smaller, less important places for the task at hand)