( ( ( The character ) ( used ( to ( ( measure displacement ) ( in ( Hydrobia species ) ) ) ) ) ) ( ( is ( difference ( in ( shell size ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN character)) (VP (VBN used) (S (VP (TO to) (VP (VB measure) (NP (NN displacement)) (PP (IN in) (NP (NNP Hydrobia) (NNS species)))))))) (VP (VBZ is) (NP (NP (NN difference)) (PP (IN in) (NP (NN shell) (NN size))))) (. .)))
The character used to measure displacement in Hydrobia species is difference in shell size.
(ROOT (S (NP (NNP Character) (NNP displacement)) (VP (VBZ is) (NP (NP (DT the) (NN concept)) (PP (IN by) (SBAR (WHNP (WHNP (WDT which) (CD two) (NNS species)) (PP (IN within) (NP (DT the) (JJ same) (NN area)))) (S (VP (TO to) (VP (VB coexist) (PP (IN by) (S (VP (VBG adapting) (PP (IN by) (S (VP (VBG developing) (NP (JJ different) (NNS specializations))))))))))))))) (. .)))