( Therefore ( , ( producers ( always ( ( ( belong ( to ( ( ( the ( first ( trophic level ) ) ) and ) decomposers ) ) ) ( to ( ( ( the ( last ( trophic level ) ) ) ; ) ( consumers ( that ( directly ( eat ( ( the producers ) ( ( belong ( to ( the ( second ( trophic level ) ) ) ) ) ( and ( so on ) ) ) ) ) ) ) ) ) ) ) . ) ) ) ) )
(ROOT (S (ADVP (RB Therefore)) (, ,) (NP (NNS producers)) (ADVP (RB always)) (VP (VBP belong) (PP (TO to) (NP (NP (DT the) (JJ first) (JJ trophic) (NN level)) (CC and) (NP (NNS decomposers)))) (PP (TO to) (NP (NP (DT the) (JJ last) (JJ trophic) (NN level)) (: ;) (NP (NP (NNS consumers)) (SBAR (WHNP (WDT that)) (S (ADVP (RB directly)) (VP (VBP eat) (SBAR (S (NP (DT the) (NNS producers)) (VP (VBP belong) (PP (TO to) (NP (DT the) (JJ second) (JJ trophic) (NN level))) (ADVP (CC and) (RB so) (IN on)))))))))))) (. .)))
Therefore, producers always belong to the first trophic level and decomposers to the last trophic level; consumers that directly eat the producers belong to the second trophic level and so on.
(ROOT (S (NP (NP (JJ Secondary) (NNS consumers)) (PRN (-LRB- -LRB-) (SBAR (WHNP (WDT which)) (S (VP (VBP eat) (NP (JJ primary) (NNS consumers))))) (-RRB- -RRB-))) (VP (VBP are) (VP (VBN considered) (S (VP (TO to) (VP (VB be) (ADJP (JJ trophic) (NP (NN level) (CD 3)))))))) (. .)))