Portal de Periódicos da CAPES

The Role of Nectar Robbers and Pollinators in the Reproduction of Erythrina leptorhiza

1979; Missouri Botanical Garden; Volume: 66; Issue: 3 Linguagem: Inglês

10.2307/2398843

2162-4372

Héctor M. Hernández, Víctor M. Toledo,

Plant and Fungal Species Descriptions

The pollination ecology of Erythrina leptorhiza is discussed. Flowering takes place synchronously during rainy season. The species is self-incompatible and produces some flowers with short styles. The flowers are adapted for hummingbird pollination in their morphology and high nectar production early in day. Of four bird visitors, three were nectar robbers (89% of total foraging visits) and one was a legitimate, traplining pollinator (11% of foraging visits). All species of genus Erythrina are bird pollinated (Raven, 1974, 1977; Toledo, 1974). Although most American species are pollinated by hummingbirds (Toledo, 1974), there are reports of nonspecialized passerine birds visiting Erythrina on this continent (Skutch, 1954; Timkin, 1970; Snow & Snow, 1971; Leck, 1974; Raven, 1974; Cruden & Toledo, 1977; Toledo & Hernandez, this symposium). Although there are numerous observations about hummingbirds visiting species of Erythrina (see Toledo, 1974: table 1), detailed studies of pollination by hummingbirds in this genus have been initiated only recently (Toledo, 1974; and many others). The present study of E. leptorhiza A. DC. was made because of our ignorance of its pollination ecology, and because it shares characteristics of both perchingand hummingbird-pollinated species. As pointed out by Krukoff & Barneby (1974: 362), it shows affinity with sympatric E. breviflora A. DC. (perching bird-pollinated, Cruden & Toledo, 1977) in habitat, pod and seeds. Furthermore, the very high amounts of amino acids in many samples of seeds of E. leptorhiza suggest affinities with species of sect. Breviflorae and Edules (Romeo, 1973: 65; quoted by Krukoff & Barneby, 1974: 363). In this paper an account is given of pollination ecology of E. leptorhiza, and role played by its visitors is discussed in light of flowering phenology, flower characteristics, and breeding system. STUDY AREA AND METHODS Erythrina leptorhiza is endemic to temperate elevations (+1,800-2,700 m) in southcentral Mexico, ranging from southern edge of Central Plateau through Transverse Volcanic Range to Puebla (Krukoff & Barneby, 1974: 362). It is characterized by its herbaceous habit of growth and is usually found in a secondary succession in oak and pine-oak forest. This perennial herb 1 We are grateful to Alfonso Delgado for reading manuscript. We also want to thank Luis Herrera for illustrations and Alina Chacon for her work with us in field. We are especially grateful to Dr. P. H. Raven for encouraging us to study Erythrina species and to Dr. Rupert Barneby for critically reading manuscript. The vouchers for E. leptorhiza A. DC. (Grupo Etn. 192) are deposited at MEXU and NY. The collection has been checked by B. A. Krukoff. 2 Departamento de Botanica, Instituto de Biologia, Universidad Nacional Autonoma de Mexico, Apdo. 70-233, Mexico 20, D. F., Mexico. ANN. MissoURI BOT. CARD. 66: 512-520. 1979. 0026-6493/79/0512-0520/$1.05/0 This content downloaded from 157.55.39.105 on Fri, 07 Oct 2016 04:47:07 UTC All use subject to http://about.jstor.org/terms 1979] HERNANDEZ & TOLEDO-ERYTHRINA LEPTORHIZA 513 has ability to reproduce itself vegetatively by rhizomes. The individual plants die back to soil level each year before dry winter season and grow in following wet season to become reproductive by seed again. Our field observations were made primarily in a deciduous forest situated 51 km SE of Mexico City, Morelos, on road between Xochimilco and Oaxtepec, during June and July 1978. The site is noted for high number of Erythrina leptorhiza plants, probably as a result of fire in this part of forest. For a quantitative evaluation of flowering and setting of fruit, we made some counts on 25 randomly selected plants at regular intervals. Nectar volumes were measured with calibrated micropipets (10 pl) from freshly opened flowers, before nectar had time to become more concentrated by evaporation and before it could be removed by floral visitors. At same time, we measured sugar concentration with an Erma Hand Refractometer, model A. Presence of floral dimorphism was determined by style and stamen measurements for several individual plants. Measurements were made in laboratory on previously fixed flowers in anthesis. The size of ovules and pollen grains was determined by microscopic examination and measurements. Controlled artificial pollination experiments employing techniques of Bawa (1974) were carried out to test for self-compatibility. FLOWERING PHENOLOGY AND FRUIT SET Like Erythrina breviflora (Cruden & Toledo, 1977), E. leptorhiza flowers during rainy season and is leafy at anthesis, in contrast to flowering strategy of many other Mexican species of Erythrina. Field observations indicates that almost all individuals begin to flower synchronously as early as mid-May, ending in second half of August. This is in accordance with data on herbarium sheets. Figure 1 shows a partial account of flowering dynamics. The solid line indicates number of opened flowers, and broken line indicates fruit set (percent of flowers that develop into fruit). It is important to mention that fruit set was calculated independently for three different periods of time (see Fig. 1). Thus, fruit production begins almost at final phase of flowering. Then, its rate of production increases. In other words, fruit set is increasing while number of available flowers decreases. INFLORESCENCE, FLORAL MORPHOLOGY, AND NECTAR PRODUCTION Contrasted with species which flower during dry season and have compact racemes, inflorescence of Erythrina leptorhiza is an elongated raceme (Fig. 2A). The flower stalks usually grow singly and each has an accompanying branch of leaves. Each inflorescence has from 24 to 60 or more flowers. Its floral structure is quite similar to that of all hummingbird-pollinated species of Erythrina. The narrow standard is orange and encloses sexual organs. The stamens are in four levels as they are of different lengths, thus enlarging contact's surface with visitor. The anthers face upwards facilitating deposition of pollen This content downloaded from 157.55.39.105 on Fri, 07 Oct 2016 04:47:07 UTC All use subject to http://about.jstor.org/terms 514 ANNALS OF THE MISSOURI BOTANICAL GARDEN [VOL. 66