Vertebrates are currently going extinct at an alarming rate, largely because of habitat loss, global warming, infectious diseases, and human introductions. Island ecosystems are particularly vulnerable to invasive species and other ecological disturbances. Properly documenting historic and current species distributions is critical for quantifying extinction events. Museum specimens, field notes, and other archived materials from historical expeditions are essential for documenting recent changes in biodiversity. The Islas Revillagigedo are a remote group of four islands, 700–1100 km off the western coast of mainland México. The islands are home to many endemic plants and animals recognized at the specific- and subspecific-levels, several of which are currently threatened or have already gone extinct. Here, we recount the initial discovery of an endemic snake Hypsiglena ochrorhyncha unaocularus Tanner on Isla Clarión, the later dismissal of its existence, its absence from decades of field surveys, our recent rediscovery, and recognition of it as a distinct species. We collected two novel complete mitochondrial (mt) DNA genomes and up to 2800 base-pairs of mtDNA from several other individuals, aligned these with previously published mt-genome data from samples throughout the range of Hypsiglena, and conducted phylogenetic analyses to infer the biogeographic origin and taxonomic status of this population. We found the Isla Clarión population to be most closely related to populations in the Sonora–Sinaloa state border area of mainland México and Isla Santa Catalina, in the Gulf of California. Based on genetics, morphology, and geographic distributions, we also recognize these two other lineages as distinct species. Our study shows the importance of museum specimens, field notes, and careful surveys to accurately document biodiversity and brings these island endemics (Clarión and Santa Catalina nightsnakes) and mainland population near the Sonora–Sinaloa state border to the attention of conservation biologists currently monitoring biodiversity in these fragile subtropical ecosystems.
SummaryWe present the first study of the spatial and temporal dynamics of raptors and large soaring birds from the Isthmus of Tehuantepec, Mexico. Using systematic migration counts from multiple localities in the southern states of Oaxaca and Chiapas, as well as observations of their flight trajectories during eight consecutive years (2007–2014), we describe the magnitude of these movements, their geographic extent, and the phenology of the most abundant species in both spring and fall seasons. The most abundant species were Turkey VultureCathartes aura, Swainson’s HawkButeo swainsoni, Broad-winged HawkButeo platypterus, Wood StorkMycteria americana, American White PelicanPelecanus erythrothynchos, Franklin’s GullLeucophaeus pipixcan, and American KestrelFalco sparverius. In spring, the seasonal average magnitude of migration was over 28,000 birds, while in autumn the average was over one million. The aggregated seasonal phenologies recorded illustrate a variety of migration patterns. The inter-annual variation is lower in autumn than in spring. Migrating raptors and other soaring birds did not seem to use any topographical feature as a leading line for their movements in spring, while in autumn they did. We estimated the main axis of spring flights to run along a SE–NW vector, while autumn migration follows a WNW–ESE general trajectory. Our results place the isthmus as one of the five most important sites in the world for raptors and soaring migrants. Sustaining annual migration counts at these sites is of high importance to track substantial portions (> 90%) of the global population of Turkey Vulture and Swainson’s Hawk, as well as over 10% of the global population of Broad-winged Hawk. Autumn migration counts have the potential for long-term population monitoring.
In the fragmented landscape of Los Tuxtlas, adult fig trees are found in rainforest remnants and in pastures. Syconium (fig) development is known to vary between and within Ficus species, but it is not known whether it differs between rainforest and pasture trees. We describe syconium development for two Ficus species with different life forms (free-standing vs. hemi-epiphytic) in two contrasting, adjacent habitats: undisturbed rainforest and active pastures. Over three months, we monitored 15 reproductive events in Ficus yoponensis and F. colubrinae, collecting and dissecting syconia every 3-4 days (1 291 and 815 syconia per species, respectively). External and internal structural changes in the syconia are described, including foundress occurrence and the maximum duration of the receptive phase while waiting for pollinators. The duration of both the reproductive events (< 8 weeks) and the developmental phases in the two species did not differ between rainforest and pasture trees, and are within the lower range of time reported for other Ficus species. After pollinator exclusion, the receptive phase lasted up to four times its normal duration. Syconia were slightly larger in rainforest than in pasture trees, and the infestation of F. yoponensis syconia by non-pollinating insects was higher in rainforest trees.
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