query: SELECT DISTINCT ?role ?roleLabel (COUNT(?roleLabel) AS ?countOfRoleLabel) WHERE {
    ?item p:P225/ps:P225 ?taxonName .
    ?item p:P225 ?taxonNameStatement .
    ?taxonNameStatement prov:wasDerivedFrom ?ref .
    ?ref pr:P6184 ?role 
    SERVICE wikibase:label { bd:serviceParam wikibase:language "[AUTO_LANGUAGE], en". }
  }
  GROUP BY ?role ?roleLabel ?countOfRoleLabel
  ORDER BY DESC(?countOfRoleLabel)