José Luis León de la Luz

Patterns of abundance and population structure of Pachycereus pringlei (Cactaceae), a columnar cactus of the Sonoran Desert

Understanding the mechanisms that determine the distribution and abundance of plants is a major problem in ecology. However, very few studies have explored the factors controlling the abundance of columnar cacti throughout their range of distribution. In this paper, we describe the density and size structure of 26 populations of Pachycereus pringlei throughout its distribution range in the Sonoran Desert. Major differences in abundance were detected between island and mainland and peninsular areas, with islands sustaining significantly larger densities than mainland and peninsular populations. Within peninsular populations, the abundance was negatively associated with latitude and positively associated with annual and seasonal rainfall. In contrast, the abundance in mainland populations showed neither latitudinal trend nor an association with rainfall. In peninsular populations, mean height and basal diameter of branched plants showed a negative association with population density whereas mainland populations showed no significant association. None of the populations exhibited a population structure that fitted the log-normal distribution expected for young, growing populations with constant recruitment. Insular, peninsular and␣mainland populations showed a population structure with an uneven size distribution typical of populations experiencing regeneration pulses.

Status, density and habitat relationships of the endemic terrestrial birds of Socorro Island, Revillagigedo Islands, Mexico

Abstract Socorro Island supports the highest plant and animal diversity of the Revillagigedo Islands. Eight endemic terrestrial bird species (one endemic genus and seven endemic subspecies) currently are present on the island. One endemic species is now extinct and the status of another endemic subspecies is uncertain. Forty visiting species (both seasonal and accidental) represent the non-endemic terrestrial avifauna of the island. In this work, we present quantitative data on the abundance and density of the endemic avifauna and on the degree of habitat disturbance on Socorro Island. We found that plant species richness, plant density, and number of vegetative strata in the less disturbed areas to be positively related to bird density. The simple community structure and fragile island ecosystem are now threatened by several factors including sheep overgrazing, erosion, predation by feral cats, and human disturbance. Therefore, we propose that the island be protected by means of an integratedresource management plan and be designated as a legally protected area. Five management strategies are needed immediately. Finally, we propose to work jointly with Mexican military personnel to manage, improve, and preserve the ecosystems of Socorro Island.

On the urgency of conservation on Guadalupe Island, Mexico: is it a lost paradise?

Guadalupe is an oceanic island located in the Pacific Ocean off Mexicos northwest coast. Its flora is composed of many plant species with more northern affinities and disjunctions from the California Floristic Province. Almost 16% of the native plant species are endemic, including two monospecific genera. However, the activities of feral goats released in the early 19th century have devastated most of the island. At present, at least 26 native plant species have disappeared from Guadalupe and many more seem to be on the threshold. To add to the problem, 61 exotic plant species have been documented on the island, many of which are aggressive weeds. In this paper, we propose eight types of environmental conditions for the island where different species assemblages of the pristine flora probably existed before their demise. It is of obvious urgency that the island needs a recovery plan and the first step should include the eradication of the feral goats. Only after this process can subsequent conservation measures be applied to ensure any restoration of this natural heritage. The recovery plan will need to address both spontaneous and human-induced plant repopulation processes from the main islands three southern islets, which have never been impacted by goats. Also, it may be necessary to reintroduce non-endemic, native plant taxa from the nearest Californian islands and the Mexican coast in order to reestablish some of the islands original diversity of plant species and communities. However, it should be noted that the forested communities do not have great hopes of recovering in the short term, since the ground water and soil conditions have been significantly altered. Furthermore, the eradication of an estimated 4000 goats still living on the island (year 2000) depends upon the vacillating motivation and will of Mexican authorities.

Using Endemic Plant Species to Establish Critical Habitats in the Sierra de La Laguna Biosphere Reserve, Baja California Sur, Mexico

The Sierra de La Laguna, in the southern part of the state of Baja California Sur, Mexico, was decreed a biosphere reserve in 1994. It harbors relict plant communities with a high level of endemism. Floristic research has established that the two main communities, the oak–pine woodland (OPW) and the dry tropical forest (TDF), harbor 43 and 33 endemic species, respectively. We segregate the reserve surface into seven major habitats and each endemic species were assigned a hierarchic value into an abundance-distribution scale, useful as dominance ranking. Using such scale, we found that almost half of the species are in the lowest rank (low abundance and aggregate distribution). Using GIS, we obtain the surface for each habitat, where mountainsides represent the largest in the reserve area. We obtained an index of importance from the proportion of endemic species by habitat and its surface occupied, founding that, in spite of the small and fragmented nature of the upland riparian habitats, they have the greatest index value. Consequently, for future conservation plans in the reserve, these habitats should be considered remarkable sites, meriting better attention to ensure endemic plant preservation. Also, since 86% of the endemic species appear in one, two or three habitats, a high dependency on particular environmental conditions is suggested for them.

Development and Characterization of 10 Microsatellite Loci in the Giant Cardon Cactus, Pachycereus pringlei (Cactaceae)

• Premise of the study: Microsatellite primers were developed for the cardon, a giant columnar cactus (Pachycereus pringlei) of the Sonoran Desert, to investigate intraspecific genetic patterns of diversity and population structure. • Methods and Results: Using 454 GS-FLX technology and bioinformatics tools, microsatellite primers were successfully identified on 282 reads, including di-, tri-, tetra-, penta-, and hexanucleotides. A set of 10 primers were characterized on 80 individuals collected in two areas of the Baja California peninsula, Mexico. All 10 loci were polymorphic, with a mean of 6.3 alleles per locus and overall levels of observed and expected heterozygosities ranging from 0.41 to 0.59 and from 0.40 to 0.57, respectively. Alleles per individual plant ranged from one to four, suggesting a polyploidal genome. • Conclusions: These loci should be useful for future investigations of population structure, genetic diversity, and gene flow in the cardon cactus.Premise of the study: Microsatellite primers were developed for the cardon, a giant columnar cactus (Pachycereus pringlei) of the Sonoran Desert, to investigate intraspecific genetic patterns of diversity and population structure. Methods and Results: Using 454 GS-FLX technology and bioinformatics tools, microsatellite primers were successfully identified on 282 reads, including di-, tri-, tetra-, penta-, and hexanucleotides. A set of 10 primers were characterized on 80 individuals collected in two areas of the Baja California peninsula, Mexico. All 10 loci were polymorphic, with a mean of 6.3 alleles per locus and overall levels of observed and expected heterozygosities ranging from 0.41 to 0.59 and from 0.40 to 0.57, respectively. Alleles per individual plant ranged from one to four, suggesting a polyploidal genome. Conclusions: These loci should be useful for future investigations of population structure, genetic diversity, and gene flow in the cardon cactus.

Two new Marina (Leguminosae) from the southern Baja California peninsula, Mexico

Marina victoriae andM. brevis are newly described species from the southern Baja California peninsula, Mexico. The former is a perennial herb locally abundant in the eroded hillsides at the foothills of Sierra de la Victoria, where an oak woodland and a dry tropical forest meet. The latter is an elusive ephemeral inhabiting a narrow strip of land between the mangroves and the desert scrub on an island in the Gulf of California. These two new species belong to the seriesChrysorrhizae, a group native to the Gulf of California basin.