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Environmental heterogeneity of Belize and southern Mexico savannahs as well as their geographical location suggest that these plant communities share floristic elements, making them conducive to a phytogeographical analysis. The aim of this study was to analyse the floristic affinities of nine savannahs of Belize and southern Mexico and to explain the similarities and differences amongst them. A binary data matrix containing 915 species was built based on the authors' own collections and on nine floristic lists already published. A second data matrix, consisting of 113 species representing trees, was also used since most literature on neotropical savannahs has focused on this life form. In addition, the ten most species-rich families as well as the characteristic species present in more than five savannahs were analysed. Floristic similarities were calculated using the Jaccard index. Dendrograms obtained in both types of analysis showed clusters with low similarity values, corresponding to geographic locations formed by the savannahs of Belize-Tabasco and the Yucatan Peninsula. The floristic affinities of the savannahs may be explained in terms of heterogeneity in climate and physiography. The Yucatan Peninsula and Belize-Tabasco groups have differences in climate type and the amount of rainfall. In addition, the Yucatan Peninsula savannahs are established at the bottom of karstic valleys, while the Belize and Tabasco savannahs develop on extensive flatlands. The savannahs of Oaxaca have the same climate type and amount of rainfall as those of the Yucatan Peninsula but they are distributed along peaks and the slopes of shale hills. Fabaceae and Poaceae mainly dominated the local floras with 121 and 116 species each; remarkably, Melastomataceae was absent in the Yucatan Peninsula and Oaxaca. Nine species occurred in five to seven savannahs, confirming that they are widespread in both Belize and southern Mexico, and the Neotropics. Geographic location and floristic affinities of the nine savannahs support, to some extent, three different biogeographic provinces. [ABSTRACT FROM AUTHOR]

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An area of endemism is defined by the spatial congruence among two or more species with distributions that are limited by barriers. In this study, we explored and discussed the use of the network analysis method (NAM) and neighbor-joining (NJ) to analyze the areas of endemism of Quercus sect. Lobatae (red oak species) in Mexico and Central America. We compared the NAM and NJ with other methods commonly used in biogeographic studies to show the advantages of these new approaches and to identify the shortcomings of other approaches. The NAM used in this study is based on notions of centrality measures, such as betweenness. We incorporated the strength of the ties within the internal networks through p-cores and aggregate constraints in iterative analyses. The NAM based on betweenness is ideal for recognizing completely allopatric areas of endemism. The iterative NAMs increase the number of possible areas of endemism because they minimize the effect of minimal overlap, and the p-core is efficient at identifying the closest relationships among species in the cases in which betweenness is not informative. The number of areas of endemism increases when the sympatry matrix minimizes the dispersal effect and the sample effort is maximized, allowing the identification of the greatest number of these areas. The NJ method supports the idea that areas diverge among themselves in a differential way; the long branches correspond to zones with high speciation rates and complex histories (biotic and tectonic), and the short branches correspond to zones with low speciation rates and simple histories. In a classification scheme, NJ was capable of identifying the areas that are considered biotically complex because of their high speciation rates. The results obtained with the NAM and NJ showed that the physiographic regions of Mexico are not natural units and that many of them are composed of at least two different biotic components. [ABSTRACT FROM AUTHOR]

Among the many explanations for the large biological diversity of Mexico is that it is the result of the contact between the Nearctic and Neotropical biotas; however, this contact-related explanation is not fully satisfactory and needs further examination in the light of historical biogeography. We offer newer insights into this issue by examining the history of the flora and the vegetation heterogeneity of the seasonally dry tropics of this country. Several environmental criteria can be used to define the seasonally dry tropical regions, but setting their precise geographical boundaries is not always straightforward. This is largely due to the large vegetation heterogeneity of this region, within which the tropical dry forest (TDF) is prominent. The origin of the TDF flora can be traced back at least as far as 20 million years before present and seems to be associated with the Tertiary North American flora. Available evidence does not support a South American origin of the TDF flora. Similarly, the separation of the TDF and the hot North American desert floras into two different bio-geographical realms is not warranted. The history of the seasonally dry tropical flora of Mexico strongly suggests that this bio-geographical dichotomy should be replaced by the recognition of the existence of a Pan-American Realm. [ABSTRACT FROM AUTHOR]

Hypothetically, the alpine and high elevation moss flora reached central Mexico by migration from northern latitudes following the western mountain ranges. Study of 774 specimens belonging to eighteen species of Grimmia identified four patterns of distribution in Mexico: species restricted to the Neovolcanic Belt, those mainly distributed in the northwestern states, widely distributed taxa, and endemic species. Track analysis showed that the generic distribution indeed followed the western mountains. Modeling was introduced to determine the potential ranges for most Mexican species of Grimmia and review the migration hypothesis. The resulting potential distribution maps using maximum entropy show that several species have discontinuous ranges in the northwestern states. Other taxa are restricted to the Neovolcanic Belt, and still others extend their potential distribution to stations in southern Mexico and Guatemala. Although the original hypothesis proposed that the high altitude moss flora was derived from temperate North America may still be acceptable, the South American distribution of various Species indicate that migration may have also proceeded from the south. [ABSTRACT FROM AUTHOR]

The circumscription and distribution of Tillandsia dasyliriifolia are here clarified, as well as the differences with other species in what we refer to as the Tillandsia utriculata (L.) L. complex in Mexico. Aspects of reproductive biology, including pollinators of natural populations of Tillandsia dasyliriifolia in northern Yucatan State, indicate that the populations of the species in the study site are not presently in danger due to the large reproductive capacity of the species through sexual reproduction and vegetative growth. [ABSTRACT FROM AUTHOR]

This paper presents a complete list of hermatypic coral species, analyzes the biodiversity levels and describes the biogeographic patterns of the group in the Mexican Pacific. The coral fauna of the MexicanPacific consists of 23 species, which makes this region one of the highest in terms of specific richness within the tropical eastern Pacific. In general, the species are grouped in faunistic units that correspond to the traditional zoogeographic provinces recognized in the region. There is no evidence of effective biogeographic barriers throughout the Mexican Pacific region. Local extinction events, likely caused by the narrow distribution of some species, and perhaps due to the type and frequency of transpacific colonizations, modify the normalprocesses of community succession, causing the Mexican Pacific to bea highly dynamic zone in terms of its coral fauna. [ABSTRACT FROM AUTHOR]

The phenologies of trees with temperate and tropical historical phytogeographical affinities were recorded during 60 months (1990-- 1994)in a lower montane forest (1300 m a.s.l.) in Veracruz, Mexico. The objective was to determine phenological patterns and their relation toclimate for both deciduous and broadleaved-evergreen species. Leaf fall, leaf flush, flowering, and fruiting were recorded for 107 individuals belonging to twelve deciduous and twelve broadleaved-evergreen species. Phenological stages were scaled from 0 to 4 (referring to the proportion of each tree in a phenophase), and averaged monthly as aphenological index. Phenological periodicity was analysed as a nonmetric time-series using measures of predictability, constancy, and contingency. The climate is mild with a dry-cool season (November-- March), a dry-warm season (April--May), and a wet-warm season (June--October). Foliar phenological patterns differed between deciduous and evergreen species. Deciduous species dropped leaves during the dry-cool season and leaf drop was negatively correlated with minimum temperature; leaf flushing occurred during the dry-cool and dry-warm seasons and was positively correlated with maximum temperature. In general, broadleaved--evergreen species continually dropped and flushed leaves throughout the year. Flowering and fruiting patterns did not differ between leaf habits. Mean flowering peaks occurred between February andMay, but each individual species had a different annual peak. Fruiting occurred in the dry-warm and wet-warm seasons. Three species were distinct in their fruiting phenologies, Styrax and Meliosma exhibitedsupra-annual patterns, and Hedyosmum fruited most of the year. For several species, fruiting and minimum temperature were positively correlated. Factors other than abiotic ones (e.g. biotic interactions andphylogenetic relationships) may be involved in the phenological patterns observed and they should be investigated. [ABSTRACT FROM AUTHOR]