( ( exotic species ) ( invasion . ) )
(ROOT (S (NP (JJ exotic) (NNS species)) (VP (VBZ invasion)) (. .)))
exotic species invasion.
(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))))))) (. .)))