▁by ▁J use pe ▁de ▁R iber a ▁( 1 5 9 1 - 1 6 5 2 ), ▁a ▁Spanish ▁artist ▁working ▁in ▁Nap les . ▁ ▁Notes ▁ ▁External ▁links ▁ ▁Category : F lem ish ▁eng ra vers ▁Category : F lem ish ▁Bar o que ▁pain ters ▁Category : Pe ople ▁from ▁Ant werp ▁Category : 1 6 1 4 ▁birth s ▁Category : 1 6 7 9 ▁death s ▁Category : 1 7 th - century ▁eng ra vers ▁Category : 1 7 th - century ▁publish ers ▁( people ) ▁Category : M embers ▁of ▁the ▁Ant werp ▁Gu ild ▁of ▁Saint ▁Luke <0x0A> </s> ▁In ▁the ▁evolution ary ▁bi ology ▁of ▁sexual ▁reprodu ction , ▁oper ational ▁sex ▁ratio ▁( OS R ) ▁is ▁the ▁ratio ▁of ▁sex ually ▁compet ing ▁males ▁that ▁are ▁ready ▁to ▁mate ▁to ▁sex ually ▁compet ing ▁females ▁that ▁are ▁ready ▁to ▁mate , ▁or ▁altern atively ▁the ▁local ▁ratio ▁of ▁fert il izable ▁females ▁to ▁sex ually ▁active ▁males ▁at ▁any ▁given ▁time . ▁This ▁diff ers ▁from ▁physical ▁sex ▁ratio ▁which ▁simply ▁includes ▁all ▁individuals , ▁including ▁those ▁that ▁are ▁sex ually ▁in active ▁or ▁do ▁not ▁comp ete ▁for ▁m ates . ▁ ▁The ▁theory ▁of ▁OS R ▁hypoth es izes ▁that ▁the ▁oper ational ▁sex ▁ratio ▁affect s ▁the ▁m ating ▁competition ▁of ▁males ▁and ▁females ▁in ▁a ▁population . ▁This ▁concept ▁is ▁especially ▁useful ▁in ▁the ▁study ▁of ▁sexual ▁selection ▁since ▁it ▁is ▁a ▁measure ▁of