( ( An increase ) ( in ( ( the number ) ( of predators ) ) ) )
(ROOT (NP (NP (DT An) (NN increase)) (PP (IN in) (NP (NP (DT the) (NN number)) (PP (IN of) (NP (NNS predators)))))))
An increase in the number of predators
(ROOT (S (NP (DT A) (JJR fewer) (NNS predators)) (VP (VBZ is) (ADJP (RBS most) (JJ likely) (S (VP (TO to) (VP (VB cause) (NP (NP (DT the) (NN number)) (PP (IN of) (NP (NP (NNS rabbits)) (VP (VBG living) (PP (IN in) (NP (DT an) (NN area))) (S (VP (TO to) (VP (VB increase))))))))))))) (. .)))
A fewer predators is most likely to cause the number of rabbits living in an area to increase.