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Correlates of Plant Biodiversity in Mediterranean Baja California, Mexico
No full textNorthwestern Baja California is an area of exceptionally high local endemism, nestled at the southernmost end of the California Floristic Province (CFP), one of the world's mediterranean-climate regions. The ecotonal position between the CFP and the central deserts of the Baja California Peninsula reflects the transition of the major climatic regimes. This area appears to have been more climatically stable than adjacent areas, and the local endemism along the coast is largely the result of the persistent marine layer, which buffers temperature extremes and maintains moisture during the drier months of the year. The driving hypothesis of this dissertation is that long-term climatic stability provided by the cold coastal upwelling of the California Current (driven in turn by the large-scale circulation of the seas) has buffered climatic conditions along the coast, reducing species extinctions and allowing adaptive processes leading to high levels of endemism in the local flora. The high productivity of the coastal upwelling has also had an impact on local plant diversity through the impact of prehistoric shell middens on soil heterogeneity: Ocean deposits (aragonite shells) extracted by indigenous people have added to landscape complexity and increased biological diversity along the coast. Shell middens are scattered along the coast, and idiosyncratically change soil conditions and the resultant plant communities. Shell middens consistently increase native plant diversity, but with very different species compositions, overlapping conservation priorities for archeology and biodiversity. The climate-buffering effect of the coastal currents can be evaluated in the flowering dynamics of the local plant communities: Plant phenology is predominantly controlled by season and available moisture. Fogs dampen seasonality in flowering times and plants flower for longer time periods at the coast, allowing probable mechanisms for speciation. This stability is consistent with the high levels of endemism that can be seen along the coast, and in microclimate effects on phenology along the inland-to-coast gradient. Conservation of coastal habitats in this southern edge of the California Floristic Province is of elevated importance due to the refugium effect of the marine layer, and the presence of archeological sites that increase biodiversity
Contrasting patterns in leaf traits of Mediterranean shrub communities along an elevation gradient: measurements matter
No full textWe assessed the changes in community-weighted mean (CWM) and variability of specific leaf area (SLA) and leaf area (LA) of different Mediterranean shrub communities along an elevation gradient in the island of Sardinia (Italy). Furthermore, we explored the relative contribution of species turnover and intraspecific variation to shifts in CWM values along the gradient. Forty sampling units (5 × 5 m) were selected in a probabilistic way along a 1300 m elevation gradient which crossed four thermotypes (thermometric belts). Leaf traits were measured in each sampling unit. ANOVA and a trend test for monotonic changes in variance were used to assess, respectively, CWM differences and variability in both the leaf traits across thermotypes. Variance decomposition of CWM values was used to identify the role of inter- and intraspecific variation. SLA and LA responded differently along the studied gradient in terms of abundance-weighted mean values and variability: CWM of SLA showed the lowest values in the driest thermotype, while LA in the more humid one; SLA variability showed a significant increasing trend with increased water availability, while LA variability did not show any pattern. The contribution of intraspecific trait variation was significant for both the leaf traits, but higher for SLA, where negative covariation between inter- and intraspecific variation was detected. We highlight the importance of simultaneously considering measurements of both leaf traits to understand the functional response of communities in Mediterranean environments. Moreover, neglecting intraspecific variation in leaf traits, even along steep gradients with relevant species compositional changes, can result in the underestimation of the amount of trait variation in response to environmental changes
The San Quintín Kangaroo Rat is Not Extinct
No full textThe San Quintín kangaroo rat (Dipodomys gravipes) is a medium-sized kangaroo rat restricted to a stretch of coastal habitat from San Telmo to El Rosario, Baja California, Mexico. Agriculture in the San Quintín area began in 1891 when British farmers converted parts of the landscape to agriculture. Now, much of the preferred habitat in the documented range of the species has been converted to agriculture. Dipodomys gravipes has a high affinity for flat terrain and is intolerant of cultivation. As a result of extensive and profound habitat alteration by agriculture, D. gravipes has been listed as endangered by the Mexican government. Since then, and given the lack of further captures, biologists and conservationists have feared the species could be extinct. However, Tremor and Vanderplank captured four specimens on 4 July 2017 on Mesa Agua Chiquita near San Quintín
The Flora of Greater San Quintín, Baja California, Mexico (2005–2010)
No full textThe plants of San Quintín (Baja California, Mexico) were documented through intensive fieldwork and collection of herbarium specimens to create a checklist of species. The region is located near the southernmost extent of the California Floristic Province, and the flora is influenced by the adjacent desert to the south. A total of 435 plant taxa were documented, of which 82% are native plants. Almost one in three native plant taxa in Greater San Quintín is a sensitive species, here documented as rare and/or locally endemic, and many taxa have yet to be evaluated fully for rarity and threats. Four major habitats were identified, and a checklist is presented for each. Shell middens and vernal pools represent micro-habitats with unique species that also warrant conservation consideration. All habitats in Greater San Quintín are threatened by human activity, and agricultural water use practices are unsustainable. There is a pressing need for conservation of the natural areas that remain in this unique but heavily impacted region. The El Socorro Dunes and the volcanic bay are of particular conservation value with several narrowly endemic taxa. As a transitional area in a global biodiversity hotspot, Greater San Quintín is home to many species on the edge of their ranges and may be of critical importance to biodiversity conservation in a changing climate
Plant Life of a Desert Archipelago: Flora of the Sonoran Islands in the Gulf of California by Richard Stephen Felger, Benjamin Theodore Wilder, Humberto Romero-Morales
No full textVolume: 7Start Page: 666End Page: 66
Threats to an Extreme Endemic: Chenopodium flabellifolium (Amaranthaceae) on Isla San Martin.
No full textVolume: 36Start Page: 50End Page: 5
Resources for Humans, Plants and Animals: Who Is the Ruler of the Driver? And: Can Resource Use Explain Everything?
No full text
