( ( Primary producers ) ( ( comprise ( ( ( ( ( ( the ( bottom ( trophic level ) ) ) , ) ( followed ( by ( ( ( ( ( primary consumers ) ( -LRB- ( herbivores -RRB- ) ) ) , ) then ) ( ( secondary consumers ) ( -LRB- ( ( ( carnivores feeding ) ( on herbivores ) ) -RRB- ) ) ) ) ) ) ) , ) and ) ( so on ) ) ) . ) )
(ROOT (S (NP (JJ Primary) (NNS producers)) (VP (VBP comprise) (NP (NP (DT the) (JJ bottom) (JJ trophic) (NN level)) (, ,) (VP (VBN followed) (PP (IN by) (NP (NP (NP (JJ primary) (NNS consumers)) (PRN (-LRB- -LRB-) (VP (VBZ herbivores)) (-RRB- -RRB-))) (, ,) (RB then) (NP (NP (JJ secondary) (NNS consumers)) (PRN (-LRB- -LRB-) (NP (NP (NNS carnivores) (VBG feeding)) (PP (IN on) (NP (NNS herbivores)))) (-RRB- -RRB-)))))) (, ,) (CC and) (ADVP (RB so) (RB on)))) (. .)))
Primary producers comprise the bottom trophic level, followed by primary consumers (herbivores), then secondary consumers (carnivores feeding on herbivores), 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)))))))) (. .)))