Large Body Mass (large + body_mass)

Distribution by Scientific Domains

Selected Abstracts

Energy density patterns of nectar resources permit coexistence within a guild of Neotropical flower-visiting bats

Marco Tschapka
Abstract Neotropical rainforests support guilds of nectar feeding bats (Phyllostomidae: Glossophaginae) with up to six coexisting species. To analyse guild structure and mechanisms of coexistence in a Costa Rican tropical lowland rainforest, the resource use and morphology of bats were compared to the energetic characteristics of preferred nectar resources and their spatio-temporal distribution. The relative abundance of nectar-feeding bats was determined from mistnet captures over 26 months. Food items were identified by analysis of pollen loads and faecal samples. Phenology, flower density and nectar sugar content of resource plants permitted quantitative estimations of resource availability expressed as energy density (kJ ha,1 day,1) throughout the annual cycle. Four glossophagine bat species co-occurred at La Selva: two permanent residents (Glossophaga commissarisi, Hylonycteris underwoodi) and two seasonal species (Lichonycteris obscura, Lonchophylla robusta) that were found in small numbers during a period of high nectar availability. The two resident species differed in their abundance and in their temporal feeding strategies. After the main flowering peak, the common G. commissarisi shifted to a more frugivorous diet, while the rarer H. underwoodi fed on the few remaining bat-flowers. Resource plant species differed in their energy density by up to two orders of magnitude. Hylonycteris underwoodi visited more often plant species with a low energy yield than G. commissarisi. Because of its smaller body size and a wing morphology that promotes fast flight, H. underwoodi appears to be better adapted to low and scattered nectar resource levels. The two seasonal species differed greatly in body mass, which suggests different strategies for high-quality resource tracking. Large body mass in Lonchophylla robusta provides an energy buffer that permits daily commuting flights between a permanent roost and profitable foraging areas, while the small Lichonycteris obscura seems to track resources nomadically. It is proposed that energy density may be a major niche dimension that restricts access of species to certain habitats and that may profoundly influence the structure of nectar-feeding bat guilds. [source]

Tandem dialyzers with dual monitors to meet Kt/V targets

N. Sridhar
Objective:,A large body mass and/or a poorly functioning vascular access predispose to inadequate Kt/V. Double dialyzers in parallel and tandem have been shown to enhance Kt/V to levels recommended by K/DOQI. We experienced difficulties with unintended excessive ultrafitration (UF), positive transmembrane pressure (TMP)-triggered pump stoppage, need for large volume saline infusion (inflating Kt/V), and a high incidence of clotting of the second dialyzer in tandem. Since blood and dialysate flow rates are higher in the tandem configuration, Kt/V should be theoretically higher. We developed a technique of using the tandem configuration with two monitors in which all the UF could be limited to the second dialyzer, the TMP of the two dialyzers independently controlled, TMP reversal eliminated, and saline infusion and unintended UF minimized. Methods:,3 large male patients with AV grafts (AVG) and 2 with tunneled catheters (TC) had 7 treatments (with Kt/V and URR calculated using the stop-flow technique in the last 5) sessions of each of single, double parallel, and tandem configurations. Blood (Qb) and dialysate-flow (Qd) were halved with Y-connectors in the parallel configuration. Qb through both dialyzers and Qd through the second were controlled with the first monitor and Qd (TMP set to near zero) through the first dialyzer controlled with the second monitor using recirculating saline through its blood pump (with the "venous" pressure adjusted using an air-filled syringe) in the tandem configuration. The patient's blood did not circulate through the blood-pump of the first machine. Qd was 500 ml/min through each dialyzer in the single and tandem and 250 ml/min in the parallel configurations. Processed blood volume (dialysis time) was exactly 85 L with AVG and 60 L with TC. Heparin dosage was constant. ANOVA, 2 k tables, and Neuman-Keuls test were used in analyzing data. Results:,Mean Kt/V (%URR) increased from 1.15 (62) with single to 1.35 (68) with parallel (p < 0.02) and 1.48 (71) with tandem (p < 0.001) dialyzers in patients with AVG but not TC [1.05 (58), 1.02 (55), and 1.25 (64) with single, parallel, and tandem, respectively]. Tandem dialyzers met targets for URR (p < 0.001) and Kt/V ( p < 0.05) more frequently than parallel with AVG but not TC. Conclusions:,Tandem dialyzers with 2 monitors are more successful than parallel dialyzers in delivering target Kt/V and URR when Qb is not compromised. [source]

An Incenter Nocturnal Hemodialysis Program,Three Years Experience

M. Gene Radford
We report our experience with a program of long, slow, overnight hemodialysis (HD) performed 3 times a week in an existing dialysis facility. Beginning in April 1999, 14 chairs in one bay of our facility were replaced with beds, subdued lighting was installed, and machine alarms were decreased to minimum volume. Fresenius F60 dialyzers were selected with a QB of 220,300 ml/min and a QD of 400,500 ml/min. Patients dialyze for 7,8 hrs overnight. Staffing is with 1 nurse and 1 PCT for 10 patients. Standard dialysate is used, and heparin is dosed 100 U/kg at treatment initiation and again at mid-treatment. All access types are utilized. The program is open to all patients in our area. A total of 65 patients have participated, with a current census of 20 patients. Participants have tried nocturnal dialysis for a variety of reasons including work/school schedules, excessive interdialytic weight gains, inadequate dialysis (due to poor access function or large body mass), and hemodynamic instability with standard daytime HD. Blood pressure control has improved among the participants in the program, perhaps due to more gentle ultrafiltration and improvement in maintenance of dry weight. Among 31 patients who remained on nocturnal dialysis for over 6 months, 21 started the program on an average of 2.5 antihypertensive agents (AHA). After 6 months, 9 patients no longer needed AHA while 12 patients remain on an average of 1.3 AHA. URR also improved by an average of 4.35 among 13 patients who transferred from standard incenter HD to the nocturnal program. In all, 45 patients have left the program, for reasons which include insomnia/social (15), death (9), transfer to home HD (8), renal transplantation (6), noncompliance (3), moved away (2), and other (2). In conclusion, long overnight HD can be performed in an existing dialysis facility, providing patients with another HD option. Patients who may benefit from this modality include those with daytime jobs, patients with inadequate clearance on standard HD, patients with excessive interdialytic weight gains, and those who poorly tolerate standard HD. [source]

A biomechanical constraint on body mass in terrestrial mammalian predators

LETHAIA, Issue 4 2008
Observations on extant mammals suggest that large body mass is selectively advantageous for a terrestrial predator on large herbivores. Yet, throughout the Cenozoic, some lineages of terrestrial mammalian predators attained greater maximal body masses than others. In order to explain this evolutionary pattern, the following biomechanical constraint on body mass is hypothesized. The stress, set up in the humerus by the bending moment of the peak ground reaction force at maximal running speed, increased with increasing body mass within a given lineage of terrestrial mammalian predators, resulting in a decreasing safety factor for the bone, until a predator could no longer attain the maximal running speed of its smaller relatives. The selective disadvantage of reduced maximal running speed prevented further increase of body mass within the lineage. This hypothesis is tested by examining the scaling of humeral dimensions and estimating maximal body masses in several lineages of terrestrial mammalian predators. Among lineages with otherwise similar postcranial skeletons, those with the more robust humeri at a given body mass attained the greater maximal body masses. Lineages with the longer deltoid ridges/deltopectoral crests of the humeri and/or the more distally located deltoid scars (suggesting the more distal insertions of the humeral flexors) at a given body mass also attained the greater maximal body masses. These results support the existence of the proposed biomechanical constraint, although paleoecological data suggest that some lineages of terrestrial mammalian predators failed to reach the limits, imposed by this constraint, because of the small size of available prey. [source]

Inevitable evolution: back to The Origin and beyond the 20th Century paradigm of contingent evolution by historical natural selection

Lars Witting
Abstract Since neo-Darwinism arose from the work of Darwin and Mendel evolution by natural selection has been seen as contingent and historical being defined by an a posteriori selection process with no a priori laws that explain why evolution on Earth has taken the direction of the major evolutionary trends and transitions instead of any other direction. Recently, however, major life-history trends and transitions have been explained as inevitable because of a deterministic selection that unfolds from the energetic state of the organism and the density-dependent competitive interactions that arise from self-replication in limited environments. I describe differences and similarities between the historical and deterministic selection processes, illustrate concepts using life-history models on large body masses and limited reproductive rates, review life-history evolution with a wider focus on major evolutionary transitions, and propose that biotic evolution is driven by a universal natural selection where the long-term evolution of fitness-related traits is determined mainly by deterministic selection, while contingency is important predominately for neutral traits. Given suitable environmental conditions, it is shown that selection by energetic state and density-dependent competitive interactions unfolds to higher level selection for life-history transitions from simple asexually reproducing self-replicators to large bodied organisms with senescence and sexual reproduction between males and females, and in some cases, to the fully evolved eusocial colony with thousands of offspring workers. This defines an evolutionary arrow of time for open thermodynamic systems with a constant inflow of energy, predicting similar routes for long-term evolution on similar planets. [source]