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Aim The purpose of this study was to examine the biogeographical relationships of the tree flora of the Yucatan Peninsula (YP2). To this aim we: (1) evaluated the affinities of political entities of tropical America with the Yucatan Peninsula, considering the distribution of tree species occurring in the latter region; (2) assessed floristic affinities between political entities of the Yucatan Peninsula based on endemic species; (3) defined biogeographical districts for the Mexican portion of the Yucatan Peninsula; and (4) evaluated the conservation status of endemic species in the area. Location The Yucatan Peninsula is a biogeographical area comprising the entire territory of the Mexican states Campeche, Quintana Roo, and Yucatan, adjacent small portions of Tabasco and Chiapas, the El Peten department in Guatemala, and the northern half of Belize. Because of heterogeneous data availability some analyses were restricted to the first three above listed Mexican states (YP1), which comprise the core of the Yucatan Peninsula. Methods Distributional data of 434 tree species were obtained from three sources: inspection of 7640 herbarium specimens, specialist advice regarding the taxonomic status of the tree species, and an extensive review of taxonomic and floristic literature. We based the various analyses of phytogeographical affinities on Jaccard's Index. Information on individual species distributions was subjected to a multivariate analysis. Occurrence of endemic species in five existing protected areas in the Yucatan Peninsula was analysed by examining floristic checklists available for them. Results Affinities of the tree flora of YP1 with twenty-four political entities of tropical America generally decreased as geographical distances from this region increased. Distributional patterns of the seventy-two tree species endemic to YP2 showed the strongest affinities to exist between Campeche, Quintana Roo and Yucatan, and in turn these entities displayed a large similarity with Belize and Guatemala. Regionalization of YP1, based on the distributions of both all species and the endemic ones, led to the distinction of two districts: a smaller one in the north-western corner, and a larger one comprising the remaining areas. Although the distributions of numerous species in the two groups matched the limits of these districts, ubiquitous species of panpeninsular distribution also occurred. For YP1 we identified nineteen endemic trees, indicating a percent endemism of 4.4 for this area. Of the sixty-four species endemic to YP2 which occur in YP1, fifty-two (81.2 %) have been recorded in at least one of the five protected areas of this territory (three occurred in the five preserves and nineteen did so in a single one), whereas twelve (18.8 %) were not found in any protected area. Main conclusions The definition of the Yucatan Peninsula as a biogeographical province was confirmed. The strongest floristic affinities of YP1 were with Mesoamerican entities, whereas affinities with the Antilles were much weaker. The distinction of two biogeographical districts corresponds closely to the peninsula's climatic and vegetational zonation. This regionalization agrees partially with schemes proposed for other animal and plant groups. Further inventory work in protected areas is needed to adequately assess the conservation status of the Yucatan Peninsula's tree endemics. |
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