Eduardo Mendoza

Experimental defaunation of terrestrial mammalian herbivores alters tropical rainforest understorey diversity

It has been suggested that tropical defaunation may unleash community-wide cascading effects, leading to reductions in plant diversity. However, experimental evidence establishing cause–effect relationships thereof is poor. Through a 5 year exclosure experiment, we tested the hypothesis that mammalian defaunation affects tree seedling/sapling community dynamics leading to reductions in understorey plant diversity. We established plot triplets (n = 25) representing three defaunation contexts: terrestrial-mammal exclosure (TE), medium/large mammal exclosure (PE) and open access controls (C). Seedlings/saplings 30–100 cm tall were marked and identified within each of these plots and re-censused three times to record survival and recruitment. In the periods 2010–2011 and 2011–2013, survival was greater in PE than in C plots and recruitment was higher in TE plots than in C plots. Overall, seedling density increased by 61% in TE plots and 23% in PE plots, whereas it decreased by 5% in C plots. Common species highly consumed by mammals (e.g. Brosimum alicastrum and Ampelocera hottlei) increased in their abundance in TE plots. Rarefaction curves showed that species diversity decreased in TE plots from 2008 to 2013, whereas it remained similar for C plots. Given the prevalence of tropical defaunation, we posit this is an anthropogenic effect threatening the maintenance of tropical forest diversity.

Density, Abundance and Activity Patterns of the Endangered Tapirus Bairdii in One of its Last Strongholds in Southern Mexico:

Bairds tapir (Tapirus bairdii) is one of the most emblematic mammalian species from Mesoamerica. Due to its level of evolutionary distinctiveness and anthropogenic threat this species was recently ranked in 34th position, in terms of its urgency for conservation, among more than 4,000 species of mammals assessed by experts from the Zoological Society of London. Despite its evolutionary and conservation relevance there remain important gaps in knowledge of the basic ecology of this species. Based on camera-trapping data, we estimated Bairds tapir abundance and analyzed its patterns of daily activity and preference for different altitude intervals in El Triunfo Biosphere reserve, one of the last strongholds for this species in southern Mexico. We also applied a recently developed method (Random encounter model) to estimate tapir density without the need of individual identification. Tapir relative abundance was: 1.3 events/100 camera-trap days and density: 0.12 ind./km2. Tapir activity concentrated around dusk (χ2= 21.18, P<0.01) and use of mid-altitude areas was preferred (χ2 = 49, P < 0.001). This study provides data on the ecology of the species and insights on study methods that can have a direct positive impact on its management and conservation.

High Resilience of Herpetofaunal Communities in a Human-Modified Tropical Dry Forest Landscape in Western Mexico:

Secondary forests are replacing mature primary forests in the tropics because of increasing demand for agricultural land to support the growing human population. It is important to determine the potential of these secondary forests to support old-growth forest species, particularly threatened animal groups such as reptiles and amphibians. Moreover, existing studies are biased towards tropical rain forests, even though tropical dry forests (TDF) are comparatively more threatened. Here we examine how different TDF successional stages support old-growth forest species of amphibians and reptiles in the Chamela region, western Mexico. Over the course of two years we conducted seven surveys for amphibians and reptiles in 15 one-ha plots representing four different stages of the succession chronosequence of the TDF, ranging from pasture to old-growth forest. We found that anurans, lizards and snakes did not differ greatly in abundance and species richness among vegetation successional stages. Moreover, dominant species were shared among most of the vegetation stages, indicating low habitat specialization. Herpetofauna species composition did not differ among vegetation stages, and species turnover among stages was relatively low. These results differ greatly from those found in some tropical rainforest sites, where characteristics of herpetofauna communities differ markedly among vegetation successional stages. Our results suggest that secondary TDF in human-dominated landscapes might support substantial reptile and amphibian diversity.

Measuring biodiversity in the Anthropocene: a simple guide to helpful methods

Quantifying biodiversity patterns in the context of human-caused environmental degradation is a fundamental task to improve conservation strategies; yet, it can be difficult given the rapid increase of available analytical methods. To guide studies on the topic, in this brief essay we present four approaches, accompanied by empirical examples, that can be used to accurately assess the impact of human activities on different facets of biological diversity. Such approaches include: (1) measurement of alpha diversity by incorporating interpolation-extrapolation techniques, Hill numbers and rank-abundance graphs; (2) beta diversity and its components of turnover and richness differences due to nestedness; (3) functional diversity, and (4) phylogenetic diversity. We highlight that a critical assessment, understanding and appropriate application of these and other emerging concepts and methods to assess biodiversity is needed to support both theoretical and applied studies, especially in biological conservation.

An ignored role of sartenejas to mitigate water shortage hazards for tropical forest vertebrates

Water availability is a key limiting resource for vertebrates (Hayward and Hayward 2012). Even in tropical ecosystems supporting lush vegetation, water exists in forms not easily exploited by the local fauna (Kr€ ugel and Richter 1995; Ferrari and Hil ario 2012). For example, tropical seasonal forests growing on karst landscapes in the Yucatan Peninsula of Mexico lack flowing rivers or extensive water bodies on the surface (Garc ıa-Gil et al. 2002). However, it supports an extremely rich and abundant terrestrial vertebrate fauna (Calm e et al. 2015; Reyna-Hurtado et al. 2015). The capacity of this fauna to withstand the harsh environmental conditions imposed by water scarcity, particularly during the dry season, has traditionally been associated with natural waterholes, locally known as “aguadas” (O’Farrill et al. 2014). These aguadas form when rainfall accumulates in topographic depressions under sparse canopy cover (Torrecano-Valle and Folan 2015). There are approximately one aguada per 10.5 km in the region. Although their size may range from less than a few square meters to several hectares, most of them occupy less than a half hectare (Reyna-Hurtado et al. 2012; O’Farrill et al. 2014). The majority of the aguadas dry out during the dry season that occurs between November and April (O’Farrill et al. 2014). The likelihood of the aguadas to dry out is determined, to a large extent, by their size and depth, which also affect their thermal and chemical stratification and primary productivity (Hodell et al. 2005). While conducting field surveys to monitor wildlife in the 128,390-ha Bala’an K’aax Protected Area in the central region of the Yucatan Peninsula, Mexico (Appendix S2: Fig. S1), we set up camera-traps in nearby aguadas as well as in the vicinity of water accumulated in small crevices opened in the rocky floor. These crevices of small water deposits are known locally as sartenejas (Millspaugh 1896; Appendix S2: Fig. S2). Unexpectedly, we recorded a highly diverse faunal ensemble using water in the sartenejas. These sartenejas occurred beneath full canopy cover. There is not an estimate of the density of the sartenejas. Their estimated volume, calculated based on their length, width, six depth measurements, and the application of the half-ellipsoid formula, ranged between 11 and 79 L (SD 28; personal observation). The ecological

Use of remote cameras to evaluate ocelot (Leopardus pardalis) population parameters in seasonal tropical dry forests of central-western Mexico

Abstract The ocelot is one of the most studied felid species in the neotropics yet most of our current knowledge comes from tropical rain forests and protected areas. Therefore, we lack a comprehensive understanding on how the species abundance varies in terms of ecological parameters across its full distribution range. This is particularly true for the species population in the Northern Hemisphere, as data of ocelot populations occurring in tropical dry forests are scarce. In this study, we focused on: a) generating population data (density and sex ratios), based on camera-trapping, for ocelot occurring in the vast and understudied tropical dry forest of the western Pacific of Mexico. b) Comparing the variation in species abundance and density across its distribution range, including a larger set of studies from the Northern Hemisphere, contrasting parameters between rain forests and tropical seasonal ecosystems and re-examining the assumed relationship between precipitation and ocelot abundance. Overall, we identified 17 ocelots in our study sites and estimated an average density of 23.7 individuals (ind) per 100 km2 with a female to male ratio >1. No significant differences in ocelot density was found between seasonal tropical forests and rain forests studies (Wilcoxon test, W=71, p=0.7675). Moreover, we found no support for the relation between ocelot density and precipitation (only when restricting our analysis to rain forest data the fit of the regression model was close to be significant, R2=0.2463, p=0.07107). Our results indicate that tropical seasonal ecosystems and dry forest in particular, may present ocelot population with similar levels of abundance than tropical rain forests. We observed that precipitation is a poor predictor of ocelot abundance. In our study, we observed that overall local ecological factors (e.g. prey abundance and interspecific interactions) influenced the spatial and temporal abundance of ocelots.