Submitted to: Northwest Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/16/2003
Publication Date: 5/16/2004
Citation: Arneson, L.C., Tepedino, V.J., Smith, S.L. 2004. Reproductive success of a rare fire-follower (Iliamna bakeri: Malvaceae), and its association with a native specialist bee (Diadasia nitidifrons: Apidae), in northeastern California. Northwest Science.78(2):141-149. Interpretive Summary: Iliamna bakeri, Baker¿s Globe mallow, is a showy rare plant of northeastern California and extreme southern Oregon whose seeds germinate primarily in response to fire. Plants are among the first species to appear after forest fires. Flowers are large and appear adapted for insect-pollination. We found that flowers need to be visited by pollinators to produce seeds. We found no relation between fruits produced per flower or seeds produced per fruit and distance to nearest conspecific plant, nor was there an association between plant size and reproductive success. There was no difference in the likelihood of producing fruits or seeds according to the time of flowering. We found no relation between fruits produced per flower or seeds produced per fruit and age or size of burn. The only significant result was between fruits per flower and distance to the next nearest burn. The primary pollinator of Baker¿s Globe mallow was the native solitary bee Diadasia nitidifrons which was present in large numbers in all plant populations. Thus, conservation measures taken to preserve Baker¿s Globe mallow populations, such as management of grazing animals, must also include provision for conserving Diadasia nitidifrons populations.
Technical Abstract: Iliamna bakeri, a fire-following mallow endemic to the Modoc Plateau of northeast California and southern Oregon, has recently been designated a sensitive species. Management conservation decisions for such rare species are strengthened by information on natural history, but little is known about I. bakeri. Our objectives here are to describe aspects of the reproductive success of I. bakeri in several populations of different burn age and size, to determine its need for pollinators in sexual reproduction, and to identify important flower-visitors. Reproductive success (fruits/flower, seeds/fruit) varied significantly across populations but was not associated with age or size of burn. We uncovered a significant, but enigmatic, positive association between fruits/flower and distance to nearest burn. There was no phenological pattern to fruit or seed production, nor were clumped plants more likely to produce fruits or seeds than isolated plants. Flowers did not set fruit or produce seeds without pollinator visitation. The most abundant flower-visitor in most populations was Diadasia nitidifrons, a native solitary bee that visits only flowers of plants in the mallow family (Malvaceae). Diadasia nitidifrons was present in all I. bakeri populations monitored, including those most isolated. The plant¿s need for pollinators, its association with D. nitidifrons, and the tendency for plants in populations with the highest visitation to set the highest proportion of fruits per flower, suggests that this ground-nesting bee is vital to I. bakeri¿s reproductive success. Precautions to encourage D. nitidifrons populations where I. bakeri occurs could aid in successful management.