A Hypothesis to Explain the Reduced Distribution of the Mangrove Pelliciera rhizophorae Tr. & Pl.

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The mangrove Pelliciera rhizophorae had a wide distribution in the Caribbean area until at least the beginning of the Miocene. By the early Pliocene its distribution had been reduced drastically. This reduction in range and its present distribution appears to be related to the influence of past and present climates on soil salinity regimes within the mangrove ecosystems. Intolerance of the species to soil salinities higher than 37%oo may explain its absence in the dry areas of the eastern Pacific coast. Abundant runoff from more humid uplands and localized areas of high rainfall have allowed the survival of small P. rhizophorae populations on the Caribbean coasts of Central and South America. PELLICIERA IS A MONOTYPIC NEOTROPICAL MANGROVE GENUS which has been of great paleobotanical and phytogeographic interest because of its wide representation in the Tertiary record and current restricted distribution. The only species, Pelliciera rhizophorae Tr. & P1., grows exdusively in mangroves of tropical America (Kobuski 1951). Although the provenance of the species is unknown, Fuchs (1970) has suggested an African origin because of pelliceroid pollen found in Oligo-Miocene sediments of the Niger delta. PAST AND PRESENT DISTRIBUTION Pelliciera rhizophorae had a wide distribution in the Caribbean area during the Tertiary. Hammen and Wijmstra (1964) reported the presence of P. rhizophorae (described as Psilatricolporites crassus) in Oligocene-Miocene sediments in Guyana. The species also has been found in Oligocene-Miocene sediments of Chiapas, Mexico (Langenheim et al. 1967), in Eocene sediments of Jamaica and Panama (Graham 1977), in Eocene-Miocene sediments of Colombia (Wijmstra 1968) and in Miocene sediments of Brazil (Boer et al. 1965), Venezuela (Fuchs 1970) and Trinidad (Fuchs 1970). It is clear that P. rhizophorae was present throughout the Caribbean and northern South America until at least the beginning of the Miocene. Reduction in this range appears to have started in the early Miocene. Pelliciera rhizophorae has not been reported from the late Miocene sediments in the northern Caribbean, although it was present in isolated areas of northern South America throughout the Miocene (Graham 1977). Presently, significant stands of the species exist only from the Gulf of Nicoya, Costa Rica to the Esmeraldas River, Ecuador (Graham 1977). In addition, some isolated individuals grow dose to the tidal channels north of the Gulf of Nicoya and south of the Esmeraldas River (Horna et al. 1980, Jimenez 1981). Although the distribution of this species has been traditionally described as restricted to the Pacific coast of America, several small populations have been recently reported on the Caribbean coasts of Central and South America (Fig. 1). About 1000 individuals have been found in the Cartagena and Barbacoas bays, Colombia (Calderon 1983). Two other small populations have been reported in the estuary of the Prinzapolca River, Nicaragua (D. Neill, pers. comm.) and Chiriqui Lagoon, Panama (Ballou and Getter, in prep.). The reasons for the drastic reduction in the Tertiarian distribution of the species and for its current restricted range are still not clear. Fuchs (1970) suggested that poor propagative power and special edaphic demands of the species are responsible for its extremely restricted distribution. Graham (1977) proposed that the range reduction most likely involved the interaction of sea-level fluctuations, interspecific competition, and cooler climates by late Miocene. Gentry (1981) noted that the species seems to occur only in dimatically wetter areas and suggested that it might have been eliminated from the Caribbean by Pleistocene dry periods. A HYPOTHESIS FOR THE PRESENT DISTRIBUTION Recent observations of P. rhizophorae communities on the Pacific coast of Costa Rica (Jimenez 1981) reveal special ecological requirements that could explain its present restricted distribution. These observations suggest that Pelliciera is more sensitive to high soil salinities than other more widespread neotropical mangroves (Table 1). I Received 29 March 1983; revised 16 July 1983; accepted 1 August 1983. 304 BIOTROPICA 16(4): 304-308 1984 This content downloaded from 157.55.39.133 on Fri, 17 Jun 2016 05:37:47 UTC All use subject to http://about.jstor.org/terms