( ( ( This loss ) ( of energy ) ) ( ( explains ( why ( there ( ( are rarely ) ( ( ( more ( than four ) ) ( trophic levels ) ) ( in ( a ( food ( ( chain or ) web ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT This) (NN loss)) (PP (IN of) (NP (NN energy)))) (VP (VBZ explains) (SBAR (WHADVP (WRB why)) (S (NP (EX there)) (VP (VBP are) (ADVP (RB rarely)) (NP (NP (QP (JJR more) (IN than) (CD four)) (JJ trophic) (NNS levels)) (PP (IN in) (NP (DT a) (NN food) (NN chain) (CC or) (NN web)))))))) (. .)))
This loss of energy explains why there are rarely more than four trophic levels in a food chain or web.
(ROOT (S (NP (NP (NN Loss)) (PP (IN of) (NP (NN energy)))) (VP (VBZ is) (NP (DT the) (NN reason)) (SBAR (IN that) (S (NP (NN food) (NN chain)) (ADVP (RB typically)) (VP (VBZ has) (NP (JJ few) (NNS levels)))))) (. .)))