( ( The ( competitive ( exclusion principle ) ) ) ( ( states ( that ( ( two species ) ( ( can not ) ( ( occupy ( the ( exact ( same niche ) ) ) ) ( for ( very long ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (JJ competitive) (NN exclusion) (NN principle)) (VP (VBZ states) (SBAR (IN that) (S (NP (CD two) (NNS species)) (VP (MD can) (RB not) (VP (VB occupy) (NP (DT the) (JJ exact) (JJ same) (NN niche)) (PP (IN for) (ADJP (RB very) (JJ long)))))))) (. .)))
The competitive exclusion principle  states that two species cannot occupy the exact same niche for very long.
(ROOT (S (NP (JJ Competive) (NN exclusion) (NN princple)) (VP (VBZ explains) (SBAR (WHADVP (WRB why)) (S (NP (CD two) (JJ different) (NNS species)) (VP (MD can) (RB not) (VP (VB occupy) (NP (NP (DT the) (JJ same) (NN niche)) (PP (IN in) (NP (DT the) (JJ same) (NN place)))) (PP (IN for) (ADJP (RB very) (JJ long)))))))) (. .)))