Efectos de la Extracción de Maderas sobre la Diversidad de Mamiferos Pequeños en Bosques de Tierras Bajas de la Guayana Venezolana1

The responses of small mammal communities to forest disturbance by logging were evaluated. The study area was located in the Imataca Forest Reserve (Venezuelan Guayana Region), where vegetation was predominantly lowland rain forest. Field analyses were based on a comparative inventory of species inhabiting primary forests and areas disturbed by selective logging. The taxonomic groups used as indicators of die ecological impact of logging belonged to the orders Didelphimorphia, Chiroptera, and Rodentia (families Sciuridae, Muridae, and Echimyidae). The following sampling methods were used: (1) mist nets; (2) traps in 2.4 ha grids (each with 120 stations: 60 at ground level and 60 in trees); and (3) diurnal and nocturnal sight surveys. Total sampling effort consisted of 1904 net‐hours, 10,320 trap‐nights, and 567 h of direct observations. At least 83 mammalian species inhabited die evaluated forests (74.7 percent corresponding to Chiroptera), of which 15.3 percent were restricted to primary forest. In logged areas, small mammal communities were characterized by: (1) higher abundances of individuals; (2) lower proportions of carnivorous and gleaning insectivorous bats; (3) increases in the relative abundance of frugivorous bat species that eat the fruits of colonizing plants; (4) higher proportions of aerial insectivores (Molossidae) at die lowest levels of die forest; (5) simplification in trophic structure of non‐volant species, widi semiarboreal predator‐omnivores being die dominant guild (followed by terrestrial frugivore‐omnivores); and (6) reduction in the relative abundance of mainly canopy‐associated species. These results are explained by: (1) lower availability of key resources associated with primary forest (e.g., roosts in hollow trunks of mature trees, canopy fruits, and tree‐crown continuity); (2) higher relative abundance of some food resources, such as terrestrial invertebrates and saprophytic plants, principally in areas where primary production is limited by low‐fertility soils; (3) increase of roosting sites under fallen trunks; (4) modification of microclimatic conditions at die understory level as a consequence of a greater incident sunlight after canopy opening; and (5) increase in density of early successional plants. The implications of these results to the conservation of biodiversity in forests managed for timber extraction in die Venezuelan Guayana Region are discussed.     

Changes in Elephant Abundance Affect Forest Composition or Regeneration?

While overall numbers of African elephant have declined dramatically in recent times, some populations are now confined to protected areas and are locally overabundant—an undesirable situation for both biodiversity conservation and elephants. In forested protected areas, options to manage elephants are limited because it is difficult to safely approach animals, yet it is vital that these populations are managed because browsing by elephants can dramatically alter forest ecosystems. Using data collected over 50 yr in Kibale National Park, Uganda, we examine the prediction that increasing elephant numbers and associated changes in their foraging behavior have caused a shift in tree community composition. Although the relative abundance of elephants increased significantly between 1996 and 2010, the population structure of their preferred tree food species did not change, nor did tree community composition change in favor of species able to re‐sprout after elephant damage. Furthermore, over the last 50 yr Kibale elephants have not become more selective foragers, as would be expected if more nutritious tree species were declining. However, elephants are more abundant in disturbed areas dominated by shrubs and grasses and appear to have arrested forest succession in these areas. At their current abundance, elephants have not selectively altered the composition of intact old growth forest, but they do inhibit the regeneration of disturbed areas.     

Landscape‐scale Variation in Pathogen‐suppressive Bacteria in Tropical Dry Forest Soils of Costa Rica

Bacteria in the genus Streptomyces are ubiquitous in soil and are well‐known for their production of diverse secondary metabolites, including antibiotics that can inhibit soil‐borne plant pathogens and suppress disease. Pathogen‐suppressive soil bacteria have the potential to influence plant community composition and diversity, but remain relatively unexplored in tropical forest soils. To estimate the potential for disease suppression among Streptomyces communities in tropical dry forests, we cultured soil‐borne Streptomyces from plots in two forests in northwestern Costa Rica (Santa Rosa and Palo Verde) and quantified antibiotic‐mediated pathogen inhibition against three plant pathogens. The potential for pathogen inhibition and disease suppression by Streptomyces was highly variable across the landscape. Densities of pathogen‐suppressive Streptomyces varied by over ten‐fold and were correlated with soil nutrients across the plots. In particular, Streptomyces communities became more pathogen‐suppressive as labile soil P decreased. Inhibitor densities were significantly higher in Santa Rosa than Palo Verde, which may be related to differences in soil texture and/or plant community composition between the two forests. Our findings suggest potential differences in the degree and specificity of antibiotic‐mediated disease suppression in tropical dry forest soils of Costa Rica, and highlight the need for further studies on the drivers of pathogen‐suppressive phenotypes as well as the consequences of spatially variable pathogen inhibition for plant community composition in tropical forest ecosystems.