( ( ( population ( ( A group ) ( of ( individuals ( from ( the ( same species ) ) ) ) ) ) ) ( ( that lives ) ( in ( the ( same area ) ) ) ) ) . )
(ROOT (NP (NP (NN population)) (NP (NP (DT A) (NN group)) (PP (IN of) (NP (NP (NNS individuals)) (PP (IN from) (NP (DT the) (JJ same) (NN species)))))) (NP (NP (DT that) (NNS lives)) (PP (IN in) (NP (DT the) (JJ same) (NN area)))) (. .)))
population  A group of individuals from the same species that lives in the same area.
(ROOT (S (NP (NP (PDT All) (DT the) (NNS members)) (PP (IN of) (NP (NP (DT a) (NN species)) (SBAR (WHNP (WDT that)) (S (VP (VBP live) (PP (IN in) (NP (DT the) (JJ same) (NN area))))))))) (VP (VBP form) (NP (DT a) (NN population))) (. .)))
All the members of a species that live in the same area form a population.