• Conservation assessment of Guaiacum sanctum and Guaiacum coulteri: Historic distribution and future trends in Mexico

      López-Toledo, Leonel; Gonzalez-Salazar, C.; Burslem, D.F.R.P.; Martinez-Ramos, M. (2011)
      Guaiacum sanctum and Guaiacum coulteri are long‐lived Mesoamerican timber tree species heavily exploited throughout their range and considered to be at risk of extinction. Both species are included on the IUCN Red List and on CITES Appendix II, but there has been no formal assessment of the conservation status of either species. We used ecological niche modeling and rapid assessments of local density and population size structure to provide such evaluations....
    • Demographic effects of legal timber harvesting on Guaiacum sanctum L., an endangered neotropical tree: implications for conservation

      López-Toledo, Leonel; Murillo-García, A.; Martínez-Ramos, M.; Pérez-Salicrup, D. (2011)
      Guaiacum sanctum is a timber tree species from the Americas, considered threatened in eleven different countries, including Mexico, and listed in CITES Appendix II. This species is currently harvested legally in the southern Mexican state of Campeche. Despite its protected status, the current condition of its populations and the effects of harvesting upon them have not been assessed. The conservation status of four unlogged populations were evaluated across Central Campeche by documenting their densities and demographic structures, and then compared the size class demographic structures of one unlogged and three logged populations at different times after harvest (3, 8 and 20 years) to evaluate the effects of timber harvesting upon population structure. Additionally, a regeneration index (proportion of seedlings within the population) was estimated for each of the seven populations. Densities of G. sanctum varied from 278 to 1732 stems/ha with ≥1cm at 1.3m·height in Campeche. Differences were found in the population structures of unlogged populations, although the density of seedlings and trees was high in all of the sites. Contrary to expectations, higher densities were found in all size classes in logged populations. Results suggest that current logging practices do not have a drastic negative effect on the density of remaining individuals. Although the results indicate that G. sanctum in Campeche is not locally endangered, it is recommend that it be maintained in CITES Appendix II.
    • Potential management of Chamaedorea seifrizii (Palmae), a non-timber forest product from the tropical forest of Calakmul, Southeast Mexico

      López-Toledo, Leonel; Horn, Christa M.; López-Cen, A.; Collí-Díaz, R.; Padilla, A. (2011)
      Leaves and seeds of Chamaedorea (xate) palms are important non-timber forest products (NTFPs). In the Calakmul region (Yucatan Peninsula) of Mexico, several communities have sporadically collected and sold seeds of C. seifrizii since 1980. However, harvesting has intensified recently, raising concerns about overexploitation....
    • Predation of nesting Thick-billed Parrots Rhychopsitta pachyrhyncha by bobcats in northwestern Mexico

      We report on what appear to be increasing predation events on nesting Thick-billed Parrots Rhychopsitta pachyrhyncha. Thick-billed Parrots are classified as ‘Endangered’ and their seasonal breeding range is restricted to increasingly fragmented and degraded high elevation mixed conifer forest habitat within the Sierra Madre Occidental region of north-western Mexico. Predation of established breeding pairs has recently contributed to the ongoing decline of Thick-billed Parrot populations by removing mature birds with high reproductive value, which has associated consequences for future recruitment. We observed increasing predation events on nesting Thick-billed Parrots by bobcats Lynx rufus accompanied by kittens throughout the 2018–2019 breeding seasons, and we speculate that recent reductions in bobcat habitat have pushed them into new ranges where they are supplementing their diet with nontraditional prey items.
    • Resilience to chronic defoliation in a dioecious understorey tropical rain forest palm

      López-Toledo, Leonel; Endress, Bryan A.; Anten, N.; Ackerly, D.; Martinez-Ramos, M. (2012)
      Chronic defoliation reduces fitness components of C. elegans palms differentially between genders. Recovery is gradual and is slower and less complete in females compared with males. The lower level of resilience to chronic defoliation shown by female plants may have profound consequences for the dynamics and genetic variability of populations of tropical understorey plants...
    • Source–sink population dynamics and sustainable leaf harvesting of the understory palm Chamaedorea radicalis

      Berry, Eric J.; Gorchov, David L.; Endress, Bryan A.; Liu, Jianguo; Hull, Vanessa; Morzillo, Anita T.; Wiens, John A. (Cambridge University PressCambridge, 2011)
      In this study we assessed the sustainability of leaf harvesting of the palm Chamaedorea radicalis by modeling the dynamics of harvested populations using stage-structured transition matrices. Within the study site, El Cielo Biosphere Reserve, palm demography and population growth is dependent on substrate type; a relationship that is due to the role of rock outcrops as a refuge from herbivory by free-ranging livestock....
    • The soil seed bank in abandoned tropical pastures: source of regeneration or invasion?

      López-Toledo, Leonel; Martínez-Ramos, Miguel (2011)
      We assessed the availability of both pioneer and non-native species in the soil seed bank of old-growth forest and recently abandoned pasture, to evaluate whether the soil seed bank in these pastures represents a source of regeneration of species from adjacent old-growth forest or of invasion by non-native species. Our study was conducted at Selva Lacandona, Chiapas, Mexico. Soil samples were randomly collected from 6 sites in old-growth forest, and 6 sites in abandoned pastures. Seedlings from soil samples were identified and classified into pioneer, non-native (weeds/graminoids), and other forest species. Pioneer species seeds were virtually absent in pastures, but represented ~30% of seeds in the forest. Non-native species comprised ~99% of the soil seed bank in pastures. In the forest, soil seed bank density of weeds and graminoids decreased with increasing distance (up to 4 km) from agricultural fields, and comprised up to 25% (Mean ± 1SE= 16 ± 7) of the seed bank. Our results show a near total elimination of pioneer species from the soil seed bank in pastures, and considerable invasion of the borders of the Montes Azules reserve by seeds of non-native species. Thus, in the region studied, the soil seed bank in abandoned pastures represents a source of invasion by non-native species into old-growth forest rather than a potential source of forest regeneration.