Feeding ecology and specialist diet of critically endangered Ridgway's Hawks

Ridgway's Hawks (Buteo ridgwayi) are critically endangered forest raptors endemic to the Caribbean island of Hispaniola, with ～100 pairs remaining in the world. The species is ecologically little known yet such studies are important for understanding critical habitat needs and population dynamics. We studied the provisioning behavior of adults at 22 nests on the northeast coast of the Dominican Republic from 2005 to 2008. Mean brood size was 1.80 ± 0.45, and the mean number of fledglings per nest was 1.10 ± 0.97. We found that 80% of the prey items delivered to nestlings were reptiles, with lizards accounting for 65% of the prey and those in the genus Celestus accounting for nearly 35% of prey. Other prey items included snakes (14%), rats (9%), and smaller proportions of birds, frogs, and centipedes. The number of prey items and amount of biomass delivered to nestlings did not vary with brood size, but adults delivered more prey to 3‐ to 5‐week‐old nestlings and more biomass to 5‐week‐old nestlings. Food delivery rates did not differ between successful or failed nests, suggesting that food availability did not influence nest outcome. Given that most prey items delivered to nestlings in our study were reptiles, conservation strategies developed for Ridgway's Hawks (e.g., translocations and habitat conservation) should take into consideration their specialist reptile diet.     

Fluorescence probes specific for the plasma membrane of intact human erythrocytes and lymphocytes

Human erythrocytes and lymphocytes were isolated from venous blood and subjected to one of two protocols. In one protocol the suspended cells were labeled with fluorophore (fluorescamine or 12(9)AS). This procedure was followed sequentially by cellular lysis, cellular fractionation, and fluorescence and absorption readings. In the other protocol the suspended cells were lysed, and then the cellular homogenate labeled with fluorophore followed by cellular fractionation and spectroscopy readings. The lymphocytes were fractionated into plasma membrane, cytosol, and nuclear-mitochondrial fractions and the erythrocytes into plasma membrane and cytosol fractions. The results demonstrate that under the given labeling conditions, both fluorescamine and 12(9)AS are highly localized to the plasma membrane of intact human erythrocytes and lymphocytes. Furthermore, by P-31 NMR analysis, fluorophore labeling did not alter cellular high energy phosphate metabolism or cellular permeability to Mn²⁺. Therefore, these fluorophores are potentially powerful probes of human erythrocyte and lymphocyte plasma membrane dynamics in inherited and acquired disease states.     

Human-Induced Trophic Cascades along the Fecal Detritus Pathway

Human presence and activity in tropical forest is thought to exert top-down regulation over the various ‘green-world’ pathways of plant-based foodwebs. However, these effects have never been explored for the ‘brown-world’ pathways of fecal-detritus webs. The strong effects of humans on tropical game mammals are likely to indirectly influence fecal detritivores (including Scarabaeine dung beetles), with subsequent indirect impacts on detrivore-mediated and plant-facilitating detrital processes. Across a 380-km gradient of human influence in the western Brazilian Amazon, we conducted the first landscape-level assessment of human-induced cascade effects on the fecal detritus pathway, by coupling data on human impact, game mammal and detritivore community structure, and rate measurements of a key detritus process (i.e. dung beetle-mediated secondary seed dispersal). We found evidence that human impact indirectly influences both the diversity and biomass of fecal detritivores, but not detritivore-mediated processes. Cascade strength varied across detritivore groups defined by species'' traits. We found smaller-bodied dung beetles were at higher risk of local decline in areas of human presence, and that body size was a better predictor of cascade structure than fecal resource manipulation strategy. Cascade strength was also stronger in upland, unflooded forests, than in seasonally flooded forests. Our results suggest that the impact of human activity in tropical forest on fecal-detritus food web structure is mediated by both species'' traits and habitat type. Further research will be required to determine the conditions under which these cascade effects influence fecal-detritus web function.