( ( Invasion ( of ( Exotic Species ) ) ) . )
(ROOT (NP (NP (NNP Invasion)) (PP (IN of) (NP (NNP Exotic) (NNPS Species))) (. .)))
Invasion of Exotic Species .
(ROOT (S (NP (JJ Exotic) (NNS species)) (VP (VBP are) (ADVP (RB also)) (VP (VBN called) (NP (JJ invasive) (NNS species)) (SBAR (IN because) (S (NP (PRP they)) (VP (VBP threaten) (NP (JJ other) (NNS species))))))) (. .)))