( ( Since ( herbivores ( ( feed directly ) ( on ( producers ( -LRB- ( plants -RRB- ) ) ) ) ) ) ) ( they ( ( ( ( are ( first-order consumers ) ) and ) ( are ( at ( ( the ( second ( energy level ) ) ) ( in ( a ( food chain ) ) ) ) ) ) ) . ) ) )
(ROOT (S (SBAR (IN Since) (S (NP (NNS herbivores)) (VP (VBP feed) (ADVP (RB directly)) (PP (IN on) (NP (NP (NNS producers)) (PRN (-LRB- -LRB-) (NP (NNS plants)) (-RRB- -RRB-))))))) (NP (PRP they)) (VP (VP (VBP are) (NP (JJ first-order) (NNS consumers))) (CC and) (VP (VBP are) (PP (IN at) (NP (NP (DT the) (JJ second) (NN energy) (NN level)) (PP (IN in) (NP (DT a) (NN food) (NN chain))))))) (. .)))
Since herbivores feed directly on producers (plants) they are first-order consumers and are at the second energy level in a food chain.
(ROOT (S (NP (NNP Food) (NNS chains)) (VP (VBP carry) (NP (NN energy)) (PP (IN from) (NP (NP (NNS producers)) (PP (TO to) (NP (NNS consumers)))))) (. .)))