Alfredo Ortega-Rubio

Bio: Alfredo Ortega-Rubio is an academic researcher from Spanish National Research Council. The author has contributed to research in topics: Population & Vegetation. The author has an hindex of 14, co-authored 130 publications receiving 841 citations.

The human footprint in Mexico: physical geography and historical legacies.

Abstract: Using publicly available data on land use and transportation corridors we calculated the human footprint index for the whole of Mexico to identify large-scale spatial patterns in the anthropogenic transformation of the land surface. We developed a map of the human footprint for the whole country and identified the ecological regions that have most transformed by human action. Additionally, we analyzed the extent to which (a) physical geography, expressed spatially in the form of biomes and ecoregions, compared to (b) historical geography, expressed as the spatial distribution of past human settlements, have driven the patterns of human modification of the land. Overall Mexico still has 56% of its land surface with low impact from human activities, but these areas are not evenly distributed. The lowest values are on the arid north and northwest, and the tropical southeast, while the highest values run along the coast of the Gulf of Mexico and from there inland along an east-to-west corridor that follows the Mexican transversal volcanic ranges and the associated upland plateau. The distribution of low- and high footprint areas within ecoregions forms a complex mosaic: the generally well-conserved Mexican deserts have some highly transformed agro-industrial areas, while many well-conserved, low footprint areas still persist in the highly-transformed ecoregions of central Mexico. We conclude that the spatial spread of the human footprint in Mexico is both the result of the limitations imposed by physical geography to human development at the biome level, and, within different biomes, of a complex history of past civilizations and technologies, including the 20th Century demographic explosion but also the spatial pattern of ancient settlements that were occupied by the Spanish Colony.

Predation by Cats on the Unique Endemic Lizard of Socorro Island (Urosaurus auriculatus), Revillagigedo, Mexico

Abstract: During 1990 the distributions of the endemic lizard (Urosaurus auriculatus^ and the feral cat (Felts catus) of Socorro Island were observed and scats of the last species were collected. A total of 46 cat scats were analyzed, showing that lizards were an important prey item, varying in frequency from 33.33% in February to 66.66% in November. Because of the impact of sheep (Ovis aries) on the natural vegetation and because of the impact of cat predation, we recommend that a plan be developed for the removal of exotic species and the restoration of natural vegetation to Socorro Island. OHIO J. SCI. 93 (4): 101-104, 1993 INTRODUCTION The Revillagigedo Archipelago of Mexico, with the incidence of endemic species reaching almost 30%, is an important spot for consideration by world diversity conservation programs (Ortega et al. 1992). For instance 90% of terrestrial avian fauna are unique at the level of subspecies, species, or genus. Considering the entire Archipelago there exist only two species of endemic lizards: Urosaurus clarionensis from Clarion Island, and Urosaurus auriculatus (Cope 1871), populations of which are restricted to Socorro Island. At present, U. auriculatus lizard reaches high densities in the remanents of natural ecosystems of the island, but in the areas where the natural vegetation has been deforested by the feral sheep {Ovis aries) no lizards are present (Ortega-Rubio et al. 1991). The effects of feral sheep are more moderate on other islands (Dilks and Wilson 1979, Hercus 1964, Howard 1964), but on Socorro their impact is severe, causing erosion damage, shifts in abundance of plant species, and impaired forest regeneration (Ortega et al. 1992). Approximately 3O%o of the original natural vegetation and soil of the island have been destroyed and eroded through overgrazing by introduced sheep (Ortega et al. 1992). The problem is alarming because the rate of soil erosion has been estimated at 30 to 90 tons per hectare annually in the deforested zones (Ortega et al. 1992). There exists little work concerning the impact by cats on lizard island populations, mainly because of the availability and abundance of other prey items for the cats in these islands (Karl and Best 1982, Nogales et al. 1988, Santana et al. 1986). In Socorro Island, most of the previous work concerning U. auriculatus is devoted to taxonomic aspects, while only secondarily considering ecological relationships (Brattstrom 1955, 1982, 1990; Cope 1871; Mittleman 1942; Slevin 1926). Particularly there is no previous work considering the impact on endemic lizards by exotic species introduced to this oceanic island; such is the case of the domestic cat (Felis catus), responsible for the decline in population density 'Manuscript received 26 January 1993 and in revised form 22 June 1993 (#93-03). and the extinction of many other species, especially birds (Karl and Best 1982, Moore and Atkinson 1980, Veitch 1980), in insular ecosystems (Ebenhard 1988). MATERIALS AND METHODS Study Site Socorro Island is a volcanic cone whose highest point is Mount Everman (1,040 m), which is located at the Revillagigedo Archipelago (18°20' and 19°20' N; 110°45' and 114°5O' W) along with three other oceanic islands: San Benedicto, Clarion, and Roca Partida. Socorro Island is the biggest of the four with a surface area of 140 km (Fig. 1). It is also the more biologically important as evidenced by the incidence of endemic species. The climate of Socorro Island is arid tropical with an average annual temperature of 24.8° C and an average annual precipitation of 327.7 mm. The hurricane season extends from July to October. Remanent natural vegetation of Socorro includes nine associations (Fig. 1), varying from coastal halophytes at the seashore to several kinds of shrubs and forest along an elevation gradient reaching 1,040 m. Methods During 1990 we spent 13 consecutive days in February, 6 consecutive days in May and 8 consecutive days in November searching for scats, tracks, and other evidences of feral cats, and also looking for lizards. The feral cat is the unique mammal predator in Socorro Island. For each fecal sample collected, the vegetal association in which the sample was found and the altitude were recorded. Each fecal sample was analyzed for remnants of U. auriculatus, using a stereoscopic microscope (Zeiss Stemi SR) and comparing the residuum of scales, bones, feathers, and hairs with those of the collection of the Centro de Investigaciones Biologicas, previously established. RESULTS U. auriculatus was observed in all vegetal associations of the island, from sea level to the top of the Everman volcano. However, no lizards were observed in the eroded zones. Despite the difficulty in accurately estimating their number, the evidence of feral cat activity indicated that 102 CAT PREDATION ON LIZARDS VOL. 93

The Theory of Island Biogeography

Abstract: Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

Improving crop salt tolerance

Abstract: Salinity is an ever-present threat to crop yields, especially in countries where irrigation is an essential aid to agriculture. Although the tolerance of saline conditions by plants is variable, crop species are generally intolerant of one-third of the concentration of salts found in seawater. Attempts to improve the salt tolerance of crops through conventional breeding programmes have met with very limited success, due to the complexity of the trait: salt tolerance is complex genetically and physiologically. Tolerance often shows the characteristics of a multigenic trait, with quantitative trait loci (QTLs) associated with tolerance identified in barley, citrus, rice, and tomato and with ion transport under saline conditions in barley, citrus and rice. Physiologically salt tolerance is also complex, with halophytes and less tolerant plants showing a wide range of adaptations. Attempts to enhance tolerance have involved conventional breeding programmes, the use of in vitro selection, pooling physiological traits, interspecific hybridization, using halophytes as alternative crops, the use of marker-aided selection, and the use of transgenic plants. It is surprising that, in spite of the complexity of salt tolerance, there are commonly claims in the literature that the transfer of a single or a few genes can increase the tolerance of plants to saline conditions. Evaluation of such claims reveals that, of the 68 papers produced between 1993 and early 2003, only 19 report quantitative estimates of plant growth. Of these, four papers contain quantitative data on the response of transformants and wild-type of six species without and with salinity applied in an appropriate manner. About half of all the papers report data on experiments conducted under conditions where there is little or no transpiration: such experiments may provide insights into components of tolerance, but are not grounds for claims of enhanced tolerance at the whole plant level. Whether enhanced tolerance, where properly established, is due to the chance alteration of a factor that is limiting in a complex chain or an effect on signalling remains to be elucidated. After ten years of research using transgenic plants to alter salt tolerance, the value of this approach has yet to be established in the field.

Mangrove Production and Carbon sinks: A revision of global budget estimates

Abstract: results in a conservative estimate of 218 ± 72 Tg C a 1 . When using the best available estimates of various carbon sinks (organic carbon export, sediment burial, and mineralization), it appears that >50% of the carbon fixed by mangrove vegetation is unaccounted for. This unaccounted carbon sink is conservatively estimated at 112 ± 85 Tg C a 1 , equivalent in magnitude to 30–40% of the global riverine organic carbon input to the coastal zone. Our analysis suggests that mineralization is severely underestimated, and that the majority of carbon export from mangroves to adjacent waters occurs as dissolved inorganic carbon (DIC). CO2 efflux from sediments and creek waters and tidal export of DIC appear to be the major sinks. These processes are quantitatively comparable in magnitude to the unaccounted carbon sink in current budgets, but are not yet adequately constrained with the limited published data available so far.