@staticmethod
def _get_relatedspecies(dct, rel, dst):
    """Get related species."""
    assert dst['schemaClass'] == 'Species'
    assert rel['stoichiometry'] == 1
    if 'relatedSpecies' not in dct:
        dct['relatedSpecies'] = set([int(dst['taxId'])])
    else:
        dct['relatedSpecies'].add(int(dst['taxId']))
