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ECOLOGÍA - MEXICO
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Reproductive biology of Opuntia: A review A review of the reproductive biology of fleshy-fruited species of Opuntia sensu stricto was conducted. Among Cactaceae, Opuntia is the most diverse and widely distributed genus in the Americas. The genus is strongly associated with bee pollination and coevolution with at least two bee genera is suggested. Fruits and vegetative parts, such as spiny cladodes, are closely linked with seed dispersal and highly efficient vegetative dissemination by animals. Vegetative multiplication appears to be more efficient than sexual reproduction for plant recruitment. Both sexual reproduction and plant multiplication seem to have contributed to the ecological and evolutionary success of the genus, but empirical evidence is lacking A review of the reproductive biology of fleshy-fruited species of Opuntia sensu stricto was conducted. Among Cactaceae, Opuntia is the most diverse and widely distributed genus in the Americas. The genus is strongly associated with bee pollination and coevolution with at least two bee genera is suggested. Fruits and vegetative parts, such as spiny cladodes, are closely linked with seed dispersal and highly efficient vegetative dissemination by animals. Vegetative multiplication appears to be more efficient than sexual reproduction for plant recruitment. Both sexual reproduction and plant multiplication seem to have contributed to the ecological and evolutionary success of the genus, but empirical evidence is lacking. Journal of Arid Environments. Vol. 64 No. 4, p549-585, 37p. |
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Question: Can we recognize areas of high endemism and high endemic richness, using data from collections, and what are the ecological variables that best explain these areas? Location: Peninsula of Baja California, Mexico. Methods: We analysed the distribution of 723 endemic vascular plants species along the peninsula of Baja California and neighbouring islands distributed in 218 cartographic cells 15' × 20' in size. By means of a residual analysis, we identified areas of significantly high endemic species richness, and we calculated the degree of endemicity (or rarity) in each cell by giving to each species a weight factor inversely proportional to the land area it covers. Results: Nine regions of high-endemicity and/or high endemic species richness were found. Discussion and conclusions: The analyses of rarity and endemic species richness showed two contrasting scenarios: High endemicity values in oceanic and sky islands accounts for a high number of species with a restricted distribution, promoted most likely by genetic isolation and high environmental heterogeneity. High endemic richness along the peninsular coast is related to ecotonal transition along vegetation types. After correcting for collection effort (i.e. the number of specimens collected within a cell), we found the phytogeographic region and altitudinal heterogeneity to be the variables that best predicted endemic richness. Both high endemism and high endemic richness have distinct geographic patterns within our study region. The nine endemic regions provide elements for priority definitions in future conservation programs. Journal of Vegetation Science , Vol. 18, No. 2, p327-336, 10p |
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Previous studies have shown there is a wide spectrum of incipient management practices between gathering and agriculture, that include resources commonly considered "wild." Based on the study of 20 species used as foodstuffs in the community of Santa Maria Tecomavaca (Mexico), we evaluated nonagricultural management forms such as gathering, incipient nonselective management, incipient selective management and occasional ex situ cultivation to learn if they represent a gradient in the intensity of manipulation of a resource. The way in which the intensity of manipulation of a resource can vary as a function of cultural importance and the species' biology was also analyzed. Using an index that measures the intensity of management of a resource, it has been established that the degree of intensity depends on: the specialization of the practices directed to the environment as well as to the individuals; the number of persons performing these practices; and the number of different practices taking place. The degree of management intensity is also a consequence of the joint action of cultural importance and of species' biology. Human Ecology , Vol. 35, No. 3, p303-314, 12p |
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Invasive plant encroachments threaten biodiversity and ecosystem viability worldwide. Effects of invasives on native Sonoran Desert ecosystems are, for example, a growing concern among ecologists and land managers. Potential distributions of the exotic Brassica tournefortii and Schismus arabicus were modeled for ‘El Pinacate y Gran Desierto de Altar' Biosphere Reserve (PBR) in Sonora Mexico using genetic algorithms within a geographic information system (GIS) database. Spatial models were created using known presence points for B. tournefortii and S. arabicus, and the merged and separated influence of natural and human-related variables, respectively. Best performing models were summed to produce probability models for each species and suite of variables. Models derived from human related variables showed higher significance and accuracy values for both invasives. Combined probability models were reclassified to isolate areas of high-predicted presence, which served to identify individual variables that favor most the potential occurrence of invasives. Variables showing greatest predictive skill were isolated and recombined to produce models of merged conditions of high probability presence. Internal road networks were strongest predictors of presence, revealing the potential importance of humans as vectors of invasiveness in the PBR. Ecological Modelling, Vol. 204, No. 3/4, p457-474, 18p |
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The phylogeography of Rhabdochona lichtenfelsi, a nematode parasite specific to endemic goodeids in Mexico , is used to infer the biogeographical history of fragmentation and recent evolution of the Mesa Central drainages. Geological history of the west-central region of Mexico suggests that extant freshwater basins are the result of different vicariant events that fragmented ancient watercourses and lakes within the Mesa Central. Location Major freshwater river basins of the Mesa Central, Mexico : Ameca, Cotija, Lerma, Rio Verde, Panuco, and lakes Cuitzeo and Zacapu. Methods Haplotype diversity and phylogeographical structure of 10 populations of R. lichtenfelsi, sampled from the complete range of this species, were analysed with partial sequences of cytochrome c oxidase subunit I (456 bp). Analyses performed included phylogenetic tree estimation methods (neighbour-joining, maximum parsimony and maximum likelihood), genetic diversity, distance and structure estimates, and nested clade analysis. Results High overall haplotype diversity, unique haplotypes, and strongly structured populations were found in the basins sampled. Three phylogenetically and demographically identifiable clades were recovered. These clades fit an isolation-by-distance model. Significant population expansion was observed for two clades and for the entire population. Time of divergence was estimated as 1.0 and 0.84 Ma for the different clades. Main conclusions The distribution of R. lichtenfelsi haplotypes does not correspond to the present distribution of the basins of Mesa Central, but instead reflects the distribution of those basins during a recent geological period (Pleistocene). While our current knowledge of the evolution and geographical relationships of the Mesa Central basins comes from studies of freshwater fish encompassing a more ancient history, our results suggest that, during the past million years, old basins and connections existed where today isolated... Journal of Biogeography , May2007, Vol. 34, No. 5, p787-801, 15p |
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Oryzomys couesi cozumelae is an endemic, threatened rodent from Cozumel Island, Mexico . We estimated its genetic diversity and structure by analyzing microsatellite loci in 228 samples from 12 sampling sites widely distributed throughout the island. Unexpected high levels of genetic and allelic diversity were found: a total of 54 alleles, an average of 10. 8 alleles per locus, and high heterozygosity values (mean H <sub>O</sub> =0. 624, H <sub>E</sub> =0. 690 and H <sub>Nei</sub> =0. 689). These values are higher than those reported for small sized insular mammals, higher than that found in 37 individuals of the mainland O. Couesi from southern Mexico (H <sub>O</sub> =0. 578) that we analyzed for comparative purposes, and similar to those of other mainland small mammal populations. Despite factors that affect Cozumel's biota, such as exotic predators and competitors, hurricanes, seasonal population fluctuations and anthropogenic activities, no evidence of genetic bottlenecks was found. A significant population structure was observed and a model of isolation-by-distance was supported. Our findings render O. C. Cozumelae a high conservation value, not only for its high genetic diversity and structure, but because available data suggests that its population has declined significantly in recent years. Further habitat fragmentation and population isolation could result in a higher genetic structure and loss of genetic diversity. The protection of habitat, the maintenance of habitat connectivity and the removal of introduced competitors and predators are a conservation priority. Acknowledging that the genetic structure of populations has crucial conservation implications, the present genetic information should be taken into account in management plans for the conservation of O. C. Cozumelae. Biological Conservation, Vol. 137, No. 2, p210-222, 13p |
| 1. Understanding the effects of individual and population factors on variation in breeding dispersal (the movement of individuals between successive breeding sites) is key to identifying the strategies behind breeders' movements. Dispersal is often influenced by multiple factors and these can be confounded with each other. We used 13 years of data on the locations, mates, breeding success and ages of individuals to tease apart the factors influencing breeding dispersal in a colonially breeding long-lived seabird, the blue-footed booby Sula nebouxii. 2. Breeding dispersal varied among and within years. Males dispersed further in years of higher population density, and late breeding males and females dispersed further than early breeders. This temporal variation related to changes in competition for territory was taken into account in all tests of individual factors influencing breeding dispersal. 3. Individuals that retained their mates from the previous year dispersed shorter distances than those that changed their mates. 4. The effect of previous breeding success depended on mate fidelity. Unsuccessful breeding induced greater dispersal in birds that changed their mates but not in birds that retained their mates, indicating that breeders who change mates may take their own previous breeding experience into account during habitat selection. Faithful individuals may have to stay close to their previous sites to encounter their mates. 5. Male divorcees dispersed over shorter distances than their former mates, possibly because males contribute more than females to establishing territories. 6. Dispersal of males and females declined with increasing age over the first 10–11 years of life, then increased in old age, possibly due to senescent decay in the ability to compete for mates and territories. Journal of Animal Ecology, Vol. 76, No. 3, p471-479, 9p |
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The history of maize (Zea mays L.) is one of the most debated topics in New World archaeology. Molecular and genetic studies indicate that maize domestication took place in tropical southwest Mexico . Although archaeological evidence for the evolution of maize from its wild ancestor teosinte has yet to be found in that poorly studied region, other research combining paleoecology and archaeology is documenting the nature and timing of maize domestication and dispersals. Mere we report a phytolith analysis of sediments from San Andrés, Tabasco, that confirms the spread of maize cultivation to the tropical Mexican Gulf Coast >7,000 years ago (˜7,300 calendar years before present). We review the different methods used in sampling, identifying, and dating fossil maize remains and compare their strengths and weaknesses. Finally, we examine how San Andrés amplifies the present evidence for widespread maize dispersals into Central and South America. Multiple data sets from many sites indicate that maize was brought under cultivation and domesticated and had spread rapidly out of its domestication cradle in tropical southwest Mexico by the eighth millennium before the present . Proceedings of the National Academy of Sciences , Vol. 104, No. 16, p6870-6875, 6p |
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The objective of this study is to evaluate the effect of environmental (associated with the expansion of cattle ranching) and biogeographical factors on the diversity of dung beetle (Scarabaeinae) assemblages along three altitudinal gradients in the Neotropical region. One gradient is located in the Mexican Transition Zone, on the Cofre de Perote mountain, the other two are in the northern Andes (the Chiles Volcano and the Río Cusiana Basin). For the three gradients, the number of species and of individuals was similar in both forest and pasture, while species composition was different between habitats. On this mountain, species turnover in pastures was characterized by the addition of new species as altitude increased. In the northern Andes, species diversity was always greater in the forest than in the pasture, and species turnover between habitats was notably influenced by species loss with increasing altitude. As such the pasture fauna of the northern Andes was an impoverished derivative of the fauna present in the forests at the same altitude characterized by species of Neotropical affinity with a limited capacity for colonizing open, sunnier habitats. The opposite occurs in the areas used by cattle on the Cofre de Perote. This habitat has its own fauna, which is mainly comprised of Holarctic and Afrotropical species adapted to the prevailing environmental conditions of areas lacking arboreal vegetation. These results suggest that the impact on beetle communities caused by human activities can differ depending on the geographic position of each mountain and, particularly, the biogeographical history of the species assemblage that lives there. Ecography, Vol. 30, No. 2, p193-208, 16p |
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