Continental scale dietary patterns in a New World raptor using web-sourced photographs

Dietary studies are essential to better understand raptor ecology and resource requirements through time and space, informing species habitat use, interspecific interactions and demographic rates. Methods used to collect data on raptor diets can constrain how dietary analyses can be interpreted. Traditional approaches to study raptor diets, such as analysis of pellets or prey remains, often provide dietary data at the local population level and tend to be restricted to pairs during the breeding season. The increasing use of citizen science data has the potential to provide dietary inferences at larger spatial, demographic and temporal scales. Using web-sourced photography, we explore continental-scale demographic and latitudinal dietary patterns between adult and non-adult Crested Caracaras (Caracara plancus), throughout the species' range across the Americas. We analysed 1,555 photographs of caracaras feeding and found no age effects on the probabilities of different food groups being included in photographs. The probability of reptiles being included in photographs of caracaras from the northern population was significantly higher than those from the southern population, with the opposite pattern for birds. There were significant latitudinal effects with the probabilities of fishes and invertebrates in the diet of northern caracaras increasing towards the equator. Contrastingly, the probability of mammals in the diet increased away from the equator for both populations. Assuming the focal species is well-sampled, web-sourced photography can improve our understanding of raptor diets at large-scales and complements more traditional approaches. This approach is more accessible to raptor researchers without access to the field or expertise in physical prey identification techniques.

An updated list of the Mexican herpetofauna: with a summary of historical and contemporary studies

The growth in our knowledge of the diversity of the herpetofauna of Mexico has occurred over the period of approximately 445 years from the work of Francisco Hernández to that of a broad multinational array of present-day herpetologists. The work of this huge group of people has established Mexico as one of the most significant centers of herpetofaunal biodiversity in the world. This status is the result of a complex orography, in addition to diverse habitats and environments and the biogeographic history of Mexico. The current herpetofauna consists of 1,421 native and introduced species, allocated to 220 genera, and 61 families. This figure is comprised of 1,405 native species and 16 non-native species (as of April 2023). The non-native species include two anurans, 13 squamates, and one turtle. The level of endemism is very high, presently lying at 63%, with this level expected to increase with time. Species richness varies among the 32 federal entities in the country, from a low of 50 in Tlaxcala to a high of 492 in Oaxaca. Amphibian species richness by state-level can be envisioned as comprising three levels of low, medium, and high, with the lowest levels occurring in the Peninsula of Baja California, a group of seven states in north-central and central Mexico, and a group of three states in the Yucatan Peninsula, with the highest levels occupying the southern states of Guerrero, Puebla, Veracruz, Oaxaca, and Chiapas, and the medium level in the remaining states of the country. Reptile species richness also can be allocated to three categories, with the lowest level occupying Baja California Sur, a group of central states, and the states of the Yucatan Peninsula, and the highest level found in a cluster of the states of Veracruz, Guerrero, Oaxaca, and Chiapas. Knowledge of the Mexican herpetofauna will continue to grow with additional studies on systematics, conservation, and the construction of checklists at various levels.

Biogeography of terrestrial vertebrates and its conservation implications in a transitional region in western Mexico

Conservation biogeography, which applies principles, theories, and analyses of biodiversity distribution patterns to address conservation challenges, can provide valuable insight and guidance to policy making for protection of biodiversity at multiple scales. The temperate and tropical ecosystems of the Nearctic-Neotropical transition in the small western state of Colima, Mexico, support a mosaic of remarkably diverse fauna and flora and provide a rare opportunity to determine spatial distribution patterns of terrestrial vertebrate species, assess human-induced threats, and identify potential conservation strategies. We analyzed the spatial distribution patterns and correlated them with the current land cover and extent of the protected areas. Despite its limited geographic extension, 29% (866) of all vertebrates, and almost a quarter of both endemic and threatened species in Mexico, live in Colima. Our analysis identified clear high-richness concentration sites (i.e., “hotspots”) coincident for all groups and that elevation and both temperate and tropical ecosystems composition exert significant influence on richness patterns. Furthermore, current species´ distribution also showed significant correlation with natural and disturbed landcover. Significant hotspots for all species groups coincided poorly with the limited protected areas in the state (only 3.8%). The current state of natural land cover (less than 16%) in the state, coupled with its remarkable biological importance, highlights the need for further complementary conservation efforts including expansion and creation of new protected areas, significant restoration efforts and other conservation measures to maintain this uniquely biogeographic and biological diverse region of the country.

Research on helminths from Mexican amphibians: gaps, trends, and biases

We present a taxonomic, spatial, and thematic overview of the current state of knowledge on helminth parasites of Mexican amphibians. Sixty-six host species have been studied so far, representing 17.5% of the amphibian species distributed in Mexico. A total of 139 nominal species of helminths - 68 platyhelminths, 62 nematodes, three acanthocephalans, three annelids (hirudineans), and three arthropods (pentastomids) - have been recorded parasitizing these hosts. Most taxa found in larval stages have not been identified at the species level. The gastrointestinal nematode Aplectana itzocanensis exhibits the broadest host range, while the bladder fluke Gorgoderina attenuata and A. itzocanensis show the widest geographic distribution. Our analysis of helminthological studies evidenced gaps and biases on research efforts that have been devoted to relatively few host species, regions, and approaches. Most helminthological records come from two species, the cane toad Rhinella marina and the Montezuma's frog Lithobates montezumae, and most studies have focused on describing the helminth fauna of a host species in a particular location or on the description of new helminth species. The highest proportion of records corresponds to the Veracruzan biogeographic province, and helminth richness is significantly correlated with host richness and with total amphibian richness by biogeographic province. Only three provinces (Yucatan Peninsula, Pacific Lowlands, and Baja Californian) have positive, yet still low helminth species discovery effort. Based on our findings, we recommend pursuing research approaches unexplored in Mexico and we provide guidelines to improve research on helminths parasitizing amphibians.

Endemism patterns are scale dependent

Areas of endemism are important in biogeography because they capture facets of biodiversity not represented elsewhere. However, the scales at which they are relevant to research and conservation are poorly analysed. Here, we calculate weighted endemism (WE) and phylogenetic endemism (PE) separately for all birds and amphibians across the globe. We show that scale dependence is widespread for both indices and manifests across grain sizes, spatial extents and taxonomic treatments. Variations in taxonomic opinions-whether species are treated by systematic 'lumping' or 'splitting'-can profoundly affect the allocation of WE hotspots. Global patterns of PE can provide insights into complex evolutionary processes but this congruence is lost at the continental to country extents. These findings are explained by environmental heterogeneity at coarser grains, and to a far lesser extent at finer resolutions. Regardless of scale, we find widespread deficits of protection for endemism hotspots. Our study presents a framework for assessing areas for conservation that are robust to assumptions on taxonomy, spatial grain and extent.

Environmental heterogeneity explains coarse-scale β-diversity of terrestrial vertebrates in Mexico

We explored the hypothesis that high β–diversity of terrestrial vertebrates of Mexico is associated with a high environmental heterogeneity (HEH) and identify the drivers of β–diversity at different spatial scales. We used distribution range maps of 2,513 species of amphibians, reptiles, mammals, and birds occurring in Mexico. We estimated β–diversity for each taxon at four spatial scales (grid cells of 2°, 1°, 0.5° and 0.25°) using the multiplicative formula of Whittaker β_w. For each spatial scale, we derived 10 variables of environmental heterogeneity among cells based on raw data of temperature, precipitation, elevation, vegetation and soil. We applied conditional autoregressive models (CAR) to identify the drivers of β–diversity for each taxon at each spatial scale. CARs increased in explanatory power from fine–to–coarse spatial scales in amphibians, reptiles and mammals. The heterogeneity in precipitation including both, coefficient of variation (CV) and range of values (ROV), resulted in the most important drivers of β–diversity of amphibians; the heterogeneity in temperature (CV) and elevation (ROV) were the most important drivers of β–diversity for reptiles; the heterogeneity in temperature (ROV) resulted in the most important driver in β–diversity for mammals. For birds, CARs resulted significant at fine scales (grid cells of 0.5° and 0.25°), and the precipitation (ROV and CV), temperature (ROV), and vegetation (H) and soil (H) were heterogeneity variables retained in the model. We found support for the hypothesis of environmental heterogeneity (HEH) for terrestrial vertebrates at coarse scales (grid cell of 2°). Different variables of heterogeneity, mainly abiotic, were significant for each taxon, reflecting physiological differences among terrestrial vertebrate groups. Our study revealed the importance of mountain areas in the geographic patterns of β–diversity of terrestrial vertebrates in Mexico. At a coarse scale, specific variables of heterogeneity can be used as a proxy of β–diversity for amphibians and reptiles.

Functional Redundancy Instead of Species Redundancy Determines Community Stability in a Typical Steppe of Inner Mongolia

Background

The redundancy hypothesis predicts that the species redundancy in a plant community enhances community stability. However, numerous studies in recent years questioned the positive correlation between redundancy and stability.

Methodology

We explored the relationship between the species redundancy, functional redundancy and community stability in typical steppe grassland in Northern China by sampling grassland vegetation along a gradient of resource availability caused by micro-topography. We aimed to test whether community redundancy enhanced community stability, and to quantify the relative importance of species redundancy and functional redundancy in maintaining community stability.

Results

Our results showed that the spatial stability of plant community production increases with increased supply of soil resources, and the functional redundancy instead of species diversity or species redundancy is correlated with the community stability. Our results supported the redundancy hypothesis and have implications for sustainable grassland management.