It has been suggested that tropical defaunation may unleash communitywide 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 ¼ 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.

Abstract:Wildlife species population density estimation is important from both ecological and management perspectives. The pellet-group counting method has been used to evaluate density of the white-tailed deer (Odocoileus virginianus). This species is an important component of human diet in tropical habitats. The objectives of this study were to: 1) compare density estimates using four methods: counts in circular plots (FSC, Fecal Standing Crop and FAR, Fecal Accumulation Rate), and counts in transects (LT, Line Transect and ST, Strip Transect); 2) simulate the effect of increased sampling effort on density and precision, and; 3) evaluate the effort required to detect changes in population density using LT. From 2006 to 2007, we intensively sampled a 1 km 2 quadrant in a Mexican tropical dry forest. The results indicate that all four methods produce similar mean population density estimates. However, estimates of precision were dependent on sample size which in turn was associated with the particular counting method used. In descending order of estimate precision, the methods ranked as: LT, ST, FSC, and FAR. To detect population changes of < 20%, we suggest the establishment of 5 to 22 transects (LT) of 390 m during the dry season. To reduce bias in density estimation, it is important to obtain defecation and pellet decomposition rates in the study site.Key words: fecal counts; sampling methods; density; precision; Odocoileus virginianus. Resumen:Desde una perspectiva ecológica y de manejo es necesario estimar la densidad poblacional de la fauna. El método de conteo de grupos fecales es empleado frecuentemente para estimar la densidad de muchas especies incluido el venado cola blanca (Odocoileus virginianus). Este cérvido es importante en la cacería de subsistencia en regiones tropicales. Los objetivos del estudio fueron: 1) comparar las estimaciones de densidad empleando cuatro métodos: conteos en parcelas circulares (FSC, "Fecal Standing Crop" y FAR, "Fecal Accumulation Rate"), y conteos en transectos (LT, "Line Transect" y ST, "Strip Transect"); 2) simular el efecto de aumentar el esfuerzo de muestreo sobre la densidad y su precisión, y 3) evaluar el esfuerzo requerido para detectar cambios en la densidad empleando LT. De 2006 a 2007, monitoreamos intensivamente un cuadrante de 1 km 2 localizado en un bosque tropical seco del centro de México. Encontramos que los cuatro métodos proporcionan estimaciones poblacionales similares. Sin embargo, la precisión de las estimaciones dependió del tamaño de muestra, el cual a su vez fue determinado por el método de conteo utilizado. Así, LT produjo la estimación de densidad más precisa, seguido por ST, FSC y finalmente FAR. Para detectar cambios poblacionales < 20%, sugerimos poner 5-22 transectos (LT) de 390 m de longitud durante la época seca. Para reducir el sesgo de la estimación es importante obtener las tasas de defecación y de descomposición de los excrementos en el área de estudio.

No abstract

en el sureste mexicano Spatial and temporal analysis of the structure of the community of medium and large body sized mammals in the Biosphere Reserve El Ocote, southern Mexico

Resumen: Tanto desde una perspectiva ecológica como de manejo, es importante conocer la proporción de sexos y la estructura de edades de las poblaciones de venado cola blanca (Odocoileus virginianus). Sin embargo, en aquellos lugares donde no es posible ver directamente a los animales en vida libre, no es sencillo determinar su edad y sexo por lo que se han empleado métodos indirectos como el análisis morfométrico de los pellets. Con el fin de determinar si la variación entre pellets de individuos de diferentes edades y sexo permite su correcta categorización, se colectaron los grupos fecales de individuos conocidos en cautiverio en la UMA-Zoológico Flor del Bosque, Puebla. Se obtuvieron 180 muestras de las cuales 18 fueron de crías (< 1 año), 78 de juveniles (2-3 años) y 84 de adultos (> 3 años). Se comparó el promedio de todas las variables morfométricas entre grupos fecales de un mismo individuo y entre individuos de la misma clase de edad y sexo. Nuestros resultados sugieren que dada la alta variación presentada en las medidas morfométricas de los pellets de un mismo individuo en una misma época y entre épocas del año, y la baja variación mostrada entre grupos fecales de individuos de diferentes clases de edad y sexo, el análisis morfométrico de pellets es una metodología poco confiable para determinar la estructura de edad y sexo de una población de O. v. mexicanus. En consecuencia, la técnica de clasificación fuzzy no logra una categorización adecuada de la población en estudio pues sólo separa a los machos adultos de 5 y 6 años, mientras que los machos de menor edad y juveniles, así como hembras adultas y juveniles no son discriminados en clases separadas. Se sugiere realizar análisis similares a este con otras subespecies de venado que no exhiban un fuerte dimorfismo sexual como aquellas distribuidas hacia el centro y sur de México. Palabras clave: estructura de edades, método indirecto, pellets, técnica fuzzy, Odocoileus  virginianus.Abstract: Both from an ecological perspective as management, it is important to know the sex ratio and age structure of populations of white-tailed deer (Odocoileus virginianus). However, in places where you can not directly see the animals in the wild is not easy to determine their age and sex so indirect methods have been used as a morphometric analysis of the pellets. To determine whether the variation between pellets of individuals of different age and sex allows proper categorization, fecal groups were collected from known individuals in captivity in the Zoo UMA-Flor del Bosque, Puebla. We obtained 180 samples of which 18 were young (<1 year), 78 juveniles (2-3 years) and 84 adults (> 3 years). We compared the average for all morphometric variables between groups fecal same individual and between individuals of the same age class and sex. Our results suggest that given the high variation shown in the body measures of the pellets from the same individual in the same season and between seasons, and low fecal variation shown between groups of individuals of different age classes and sex, analysis morphometry of pellets is an unreliable method to determine the age and sex structure of a population of O. v. mexicanus. Consequently, the fuzzy classification technique does not achieve appropriate categorization of the study population because only separates adult males of 5 and 6 years, while younger males and juveniles and adult females and juveniles are not discriminated against in separate classes. Similar analysis suggested this to other subspecies of deer that do not exhibit strong sexual dimorphism as those distributed to the central and southern Mexico.Key words: Structure of ages, indirect method, pellets, technology fuzzy, Odocoileus  virginianus.