The effect of water on the ground nesting habits of the giant tropical ant, Paraponera clavata
Abstract The large predatory ant, Paraponera clavata, exerts measurable top-down effects in wet and moist Neotropical forests, and therefore its distribution has potential ecological implications. To determine how water affects the presence of this important predator, the ground nesting ecology of P. clavata was examined with respect to various habitat characteristics. Four hectares of disturbed Costa Rican lowland rain forest were surveyed for ant colonies to determine nest distribution patterns in wet and dry habitat; significantly more colonies were found in dry habitat. Seventeen of 19 nests built on slopes of > 5° inclination were positioned on the downward side of the tree, possibly using the trunk as a shield against runoff during rain showers. Moisture and pH inside nests were significantly different from adjacent soil. These results suggest that water influences the ground nesting habits of P. clavata, thus ecological differences between comparatively wet and dry portions of tropical forests may arise from the relative abundance of this ant species.
Environmental heterogeneity and seedling establishment : ant-plant-microbe interactions
1. Mounds produced by animals are important sources of disturbance in the sand shinnery oak community of western Texas. As a first step in the examination of the importance of animal-generated disturbances on the structure of the plant community we ask three questions in this study. (a) Are there differences in the abiotic or biotic characteristics of patch disturbances produced by three different species of ants? (b) Do seedling growth and survival vary when grown on soil from different species of ant mounds? (c) What is the influence of two components of the biotic environment, mycorrhizal fungi and non-mycorrhizal microbes, on seedling survival, growth rates, tissue nutrient content and patterns of biomass allocation? 2. Both the biotic and abiotic characteristics of ant mound soil differed from that of undisturbed soil and from each other. Mound soil typically had higher nutrient content than undisturbed soil and harvester ant mounds had higher nutrient content than the other species. Thus, ant mounds can generate environmental heterogeneity in this habitat. 3. Seedlings grown on unsterilized soil from harvester ant mounds were larger than seedlings grown on soil from the other two mounds, yet had lower tissue nutrient content and higher mortality rates. Seedlings grown in harvester ant soil were larger when the soil was sterilized suggesting that mycorrhizal fungi were a net energy drain in the higher nutrient content soil. Alternatively, seedlings grown without mycorrhizas in the other two mound soils were not different in size and had lower tissue nutrient concentrations than seedlings grown with mycorrhizas. 4. Thus, it appears that the fungi were beneficial in the lower nutrient content soil. In the more nutrient-rich harvester ant soil seedlings grown on sterilized soil with added non-mycorrhizal microbes were larger than seedlings grown in the absence of microbes.
Significance of passive sorption of atmospheric water vapor and feeding in water balance of the rice weevil, sitophilus oryzae
Abstract 1. 1. A water budget and kinetics for gain and loss of water was determined for Sitophilus oryzae at four water vapor activities ( a v s). Water flux was determined by using tritiated water. 2. 2. Body water content was proportional to food water content and ambient water vapor activity. The quantity of food consumed was regulated by food water content and ambient a v . 3. 3. Water imbibed with food and water passively sorbed from unsaturated ambient air constituted the major avenues of water gain. Sorption rates were proportional to a v while transpiration rates were independent of a v . 4. 4. Decrease in water gain associated with reduced feeding rates at high a v were compensated for by increased sorption rates. 5. 5. Metabolic rate was independent of a v and production of metabolic water insignificant relative to overall water exchange.