Understanding how species use and persist in agricultural areas is useful for planning conservation efforts at the landscape scale. Information at the population level is scarce, even for organisms, such as dung beetles, that are traditionally used in biodiversity studies to evaluate the effects of anthropic disturbance. Based on multiple mark-recapture events, the description of movement patterns and three population parameters (population size, survival and recruitment) were compared for two dung beetle species (Dichotomius cf. alyattes and Oxysternon conspicillatum) in a fragmented Andean landscape dominated by sun-grown coffee crops. Interspecific differences were detected in movement patterns and in the minimum distance moved across the landscape, with the latter associated with wing loading and species habitat preferences. D. cf. alyattes was captured in both the forest and in sungrown coffee plots, but tended to limit its movement to patches of forest, while O. conspicillatum covered large distances in short periods of time across the sun-grown coffee crops (ca. 1.7 km/24 h). The population of each species increased during the months of greatest precipitation, prior to the recruitment of new beetles. Given their great capacity for movement, habitat preference and their differential use of the landscape, the species studied can be used as models to evaluate the functional connectivity of Andean landscapes under high anthropic demand. Our results support the idea of the differential response of species to land-use changes, an aspect that should be considered for effective biodiversity conservation and ecosystem functioning in human-dominated landscapes.

To evaluate the response of the ant assemblages to different management practices in the tropical dry forests of southwestern Colombia, 10 sites that conserve forest fragments surrounded by pastures and sugarcane crops were sampled. Tuna-fish baits placed on the ground in the three habitats captured 100 ant species (41 genera). The greatest number of species was found in the forests in contrast with a significant loss of richness and diversity in the productive habitats, the pastures being richer than the cane fields. Species richness was negatively correlated with the abundance of the little fire ant Wasmannia auropunctata. Ant species composition was related to soil temperature and percent ground cover, as well as being partially determined by location and the abundance of W. auropunctata. The forests had a significantly different species composition from the other two habitats, but there were no consistent differences between the pastures and the cane fields.

Fig trees (Ficus spp.) and Agaonine fig-wasps participate in an obligate mutualism. Fig wasps can only develop within fig inflorescences (syconia) and they are the only organisms capable of pollinating fig flowers.Other non-pollinating wasps that lay eggs by inserting their ovipositors from the outside can also develop in syconia. These parasitic wasps may be parasitoids of either pollinating or other nonpollinating wasps, or form galls in fig flowers or other tissues. Depending on this interaction, parasitic wasps may have various effects on the production of pollinating wasps and seeds. Wasps in the genus Idarnes, which parasitize New World figs (subgenus Urostigma), have an effect on wasp production but not on seed production. Heterandrium spp., which have short ovipositors and lay on external flowers, are infrequent and no effect on seed production has been documented. In the Colombian Andes, Idarnes spp. and Heterandrium spp. are the most frequent parasites of the Ficus andicola -Pegoscapus sp. mutualism, affecting 62 and 43 percent of syconia, respectively. Controlling for other factors that influence wasp and seed production, such as number of foundresses, syconium size and tree, we found that Idarnes reduced pollinator production by almost half but did not reduce seed production, whereas Heterandrium reduced seed production by 40 percent, and marginally affected pollinator production. Our results provide the first clear documentation of Heterandrium spp. impact on fig seed production. Whether the relative abundance of this genus is a generalized phenomenon in montane forest remains to be determined.Abstract in Spanish is available in the online version of this article.

Se determinó la proporción de zonas verdes con presencia de nidos y el nivel de infestación de la hormiga arriera, Atta cephalotes, en tres comunas del municipio de Cali. Entre marzo y abril de 2002, se evaluaron 143 zonas verdes entre parques, separadores de calle, jarillones y polideportivos, cubriendo un área de 1.276.131 m2. La mayor proporción (89%) de las zonas verdes tuvo una intensidad de infestación baja-media; es decir que la mitad ó menos de su área total estaba ocupada por nidos de hormigas. El restante (11%) presentó infestación alta, en la cual más de la mitad del área fue colonizada por arriera. El 68% de los nidos se ubicó en terrenos planos naturales, seguido de zonas planas inclinadas como jarillones (27%) y algunos nidos localizados cercanos a estructuras construidas por el hombre. El área de los nidos varió entre 1 y 211 m2. Se encontró una correlación positiva entre el número de cuadrantes que permitieron conocer el 50% de las bocas y el área del nido (r= 0, 70). Basados en esta metodología, es posible realizar una estimación rápida y confiable del grado de infestación de las áreas afectadas por la hormiga arriera, como medida previa para su manejo o control.

1. Interspecific competition is a major structuring principle in ecological communities. Despite their prevalence, the outcome of competitive interactions is hard to predict, highly context-dependent, and multiple factors can modulate such interactions. 2. We tested predictions concerning how competitive interactions are modified by anthropogenic habitat disturbance in ground-foraging ant assemblages inhabiting fragmented Inter-Andean tropical dry forests in southwestern Colombia, and investigated ant assemblages recruiting to baits in 10 forest fragments exposed to varying level of human disturbance. 3. Specifically, we evaluated how different components of competitive interactions (patterns of species co-occurrence, resource partitioning, numerical dominance, and interspecific trade-offs between discovery and dominance competition) varied with level of habitat disturbance in a human-dominated ecosystem. 4. Multiple lines of evidence suggest that the role of competitive interactions in structuring ground-foraging ant communities at baits varied with respect to habitat disturbance. As disturbance increased, community structure was more likely to exhibit random co-occurrence patterns, higher levels of monopolization of food resources by dominant ants, and disproportionate dominance of a single species, the little fire ant (Wasmannia auropunctata). At a regional scale, we found evidence for a trade-off between dominance and discovery abilities of the 15 most common species at baits. 5. Together, these results suggest that human disturbance modifies the outcome of competitive interactions in ground-foraging ant assemblages and may promote dominant species that reduce diversity and coexistence in tropical ecosystems.