Resumen. En especies de amplia distribución, como Didelphis marsupialis y Didelphis virginiana, se predicen tamaños poblacionales grandes, alta diversidad y poca diferenciación genética. En este estudio se estimó la abundancia relativa de D. marsupialis y D. virginiana mediante la captura de

Knowledge of the genetic diversity of species in a biological community is useful for assessing the ecological and evolutionary processes that define the structure and dynamics of that community. We investigated the potential relationship between the trans-specific genetic diversity (or genetic diversity across tree species) and the diversity of tree species in a tropical subdeciduous forest. The nucleotide variation of the concatenated regions ITS 1 and ITS 3 (ITS1-3) was used to determine the trans-specific genetic diversity of 19 species of trees in five local communities at El Ocote Biosphere Reserve (REBISO), Chiapas, Mexico. Tree diversity was obtained by counting individual trees within 0.1 ha circular plots in each locality. The relationship between trans-specific genetic diversity and species diversity was established through simple linear regressions between genetic diversity parameters and community diversity. A correlation matrix was built with genetic distances (Kimura’s two-parameter model) and differences in species diversity between communities. A significant relationship was observed between nucleotide diversity (π) and species richness ( Sp), and a negative association between haplotype diversity and gamma diversity (γ). Our results show species-rich and genetically diverse tree communities and a weak association between trans-specific genetic variation and species diversity in tree communities at REBISO. This research suggests a possible ecological and genetic relationship within each community. Genetic diversity values may provide an important degree of variation upon which environmental selection pressures could operate, which may be helpful to face the current environmental modifications associated with climatic change.

Changes in the landscape due to habitat loss and fragmentation interact with ecological processes of populations, and define the local population abundance. We evaluated the relationship between the abundance of two common marsupials, Didelphis marsupialis (common opossum) and Didelphis virginiana (Virginia opossum), and landscape features in different levels of disturbance at Chiapas, the Highlands and the Central Depression. The goal was to identify effects of changes in the landscape in their populations. Based on the biological characteristics of D. marsupialis and D. virginiana our expectation was to observe higher abundance of opossums in areas with intermediate disturbance. At the same time, establish a relationship between the landscape composition and the abundance of both species. We placed 48 Tomahawk traps in three disturbance levels of the landscape. Within each disturbance level we obtained the structure and composition of the landscape. The abundance of each species was considered as the number of individuals captured. A relative abundance index was estimated from individuals captured by night traps. The influence of the disturbance levels, the landscape, structure, and composition in the abundance of each species was evaluated using multiple regression and generalized lineal model. The average abundance of Didelphis spp. was higher in the Central Depression (5.56 individuals, SD = 4.82). Didelphis marsupialis was captured only in low disturbance with an average of 0.56 individuals (SD = 1.04; Figure 2a), while D. virginiana was captured in the three levels of disturbance with an average of 3.56 individuals (SD = 3.88; Figure 2b). The presence of D. marsupialis was influenced by the number of patches (NP; P = 0.003), while for D. virginiana landscape index was not associated with its presence (Table 2). Our results suggest that the abundance of D. marsupialis and D. virginiana was not influenced by level of disturbance. However, D. marsupialis was related to the number of patches and conserved areas; while D. virginiana was not affected by the landscape attributes evaluated, i. e. composition and configuration, indicating that Virginia opossum can established relatively abundant populations in landscapes highly disturbed. This study contributes to the understanding of the effects of changes in the landscape in common species in Mexico due to human activities.Los cambios en el paisaje debido a la pérdida y fragmentación del hábitat interactúan con procesos ecológicos poblacionales y definen la abundancia poblacional local. Se evaluaron las relaciones entre la abundancia de dos marsupiales comunes, Didelphis marsupialis (tlacuache común) y Didelphis virginiana (tlacuache de Virginia), y los atributos del paisaje en diferentes niveles de disturbio en Chiapas, Los Altos y la Depresión Central. El objetivo fue identificar efectos de cambios del paisaje sobre sus poblaciones. Con base en las características biológicas de D. marsupialis y D. virginiana, nuestra hipótesis fue observar una mayor abundancia ...

Abstract:The Virginia opossum (Didelphis virginiana) is considered highly adaptable to anthropogenic disturbances; however, the genetic effects of disturbance on this marsupial have not been studied in wild populations in Mexico. Here we evaluated the genetic diversity of D. virginiana at sites with different levels of disturbance within the Highlands and Central Depression regions of Chiapas in southern Mexico. Twelve microsatellite loci were used and the results demonstrated moderate mean heterozygosity (He = 0.60; Ho = 0.50). No significant differences in heterozygosity were found among sites with different levels of disturbance in both regions (range Ho = 0.42–0.57). We observed low but significant levels of genetic differentiation according to disturbance level. The inbreeding coefficient did not differ significantly from zero, suggesting that low genetic differentiation in these environments may be associated with sufficient random mating and gene flow, a result associated with the high dispersal and tolerance characteristics of this marsupial. Our results for D. virginiana in this particular area of Mexico provide a foundation for exploring the impact of human disturbance on the genetic diversity of a common and generalist species.

We studied the population viability of two common marsupials, Didelphis marsupialis and Didelphis virginiana, based on field data and published ecological and genetic information. Using the VORTEX v. 10. 2.6 program, a 100-year simulation was performed with 1000 iterations for five populations of D. marsupialis and six of D. virginiana. A low probability of extinction was observed in both species, particularly for D. virginiana (0.000–0.007). Population size is higher considering a metapopulation dynamics approach versus individual populations for the two marsupials: 498.25 individuals for D. marsupialis and 367.41 individuals for D. virginiana. The estimated mean genetic diversity was high for both D. marsupialis (He = 0.77–0.78) and D. virginiana (He = 0.79–0.82). The survival of both species over time could be expected to increase if a metapopulation dynamics is favored over the coming decades, despite a 1.3% loss rate of forest cover. The monitoring of population size and genetic diversity is highly recommended to validate the trends suggested by the model; this is especially true for D. marsupialis, a species associated with conserved areas that are becoming progressively less abundant. This research provides information on the responses of common mammalian species to environmental changes such as deforestation.