def METHOD_NAME(zone_example_grid):
    mg = zone_example_grid
    se = SpeciesEvolver(mg)
    expected_field = np.zeros(mg.number_of_nodes)
    np.testing.assert_array_equal(mg.at_node["taxa__richness"], expected_field)
    introduced_taxa = [TestTaxon(), TestTaxon()]
    se.track_taxa(introduced_taxa)
    se.run_one_step(10)
    expected_field = np.array([0, 0, 0, 2, 2, 2, 0, 0, 0])
    np.testing.assert_array_equal(mg.at_node["taxa__richness"], expected_field)