( ( ( ( ( reproductive isolation ) ( ( ( The inability ) ( of ( ( ( two populations ) or ) species ) ) ) ( to ( produce ( ( ( fertile offspring ) or ) ( interbreed ( as ( ( a consequence ) ( of physi ) ) ) ) ) ) ) ) ) - ) ( ( ( ological ( or ( genetic incompatibility ) ) ) or ) ( environmental barriers ) ) ) . )
(ROOT (NP (NP (NP (JJ reproductive) (NN isolation)) (SBAR (S (NP (NP (DT The) (NN inability)) (PP (IN of) (NP (NP (CD two) (NNS populations)) (CC or) (NP (NNS species))))) (VP (TO to) (VP (VB produce) (UCP (ADJP (JJ fertile) (JJ offspring)) (CC or) (VP (VBN interbreed) (PP (IN as) (NP (NP (DT a) (NN consequence)) (PP (IN of) (NP (NNS physi)))))))))))) (: -) (NP (NP (JJ ological) (CC or) (JJ genetic) (NN incompatibility)) (CC or) (NP (JJ environmental) (NNS barriers))) (. .)))
reproductive isolation The inability of two populations or species to produce fertile offspring or interbreed as a consequence of physi- ological or genetic incompatibility or environmental barriers.
(ROOT (S (SBAR (IN If) (S (NP (CD two) (NNS populations)) (VP (VBP do) (RB not) (VP (VB mate) (CC and) (VB produce) (NP (ADJP (JJ fertile)) (NN offspring)))))) (, ,) (NP (JJ separate) (NNS species)) (VP (VBP result)) (. .)))