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Similar Body Size (similar + body_size)
Selected AbstractsReproductive Investment of a Lacertid Lizard in Fragmented HabitatCONSERVATION BIOLOGY, Issue 5 2005JOSÉ A. DÍAZ calidad de hábitat; fragmentación de bosque; Psammodromus; tamaño de puesta; tamaño de huevo Abstract:,We studied the effect of habitat fragmentation on female reproductive investment in a widespread lacertid lizard ( Psammodromus algirus) in a mixed-forest archipelago of deciduous and evergreen oak woods in northern Spain. We captured gravid females in fragments (,10 ha) and forests (, 200 ha) and brought them to the laboratory, where they laid their eggs. We incubated the eggs and released the first cohort of juveniles into the wild to monitor their survival. Females from fragments produced a smaller clutch mass and laid fewer eggs (relative to mean egg mass) than females of similar body size from forests. Lizards did not trade larger clutches for larger offspring, however, because females from fragments did not lay larger eggs (relative to their number) than females from forests. Among the first cohort of juveniles, larger egg mass and body size increased the probability of recapture the next year. Thus, fragmentation decreased the relative fecundity of lizards without increasing the quality of their offspring. Reduced energy availability, increased predation risk, and demographic stochasticity could decrease the fitness of lizards in fragmented habitats, which could contribute to the regional scarcity of this species in agricultural areas sprinkled with small patches of otherwise suitable forest. Our results show that predictable reduction of reproductive output with decreasing size of habitat patches can be added to the already known processes that cause inverse density dependence at low population numbers. Resumen:,Estudiamos el efecto de la fragmentación sobre la inversión reproductiva de hembras en una lagartija lacértida ( Psammodromus algirus) ampliamente distribuida en un archipiélago mixto de bosques deciduos y siempre verdes de roble en el norte de España. Capturamos hembras grávidas en fragmentos (, 10 ha) y en bosques (, 200 ha) y las trasladamos al laboratorio, donde pusieron sus huevos. Incubamos los huevos y liberamos a la primera cohorte de juveniles para monitorear su supervivencia. Las hembras de fragmentos produjeron una puesta de menor masa y pusieron menos huevos (en relación con la masa promedio de los huevos) que hembras con talla corporal similar provenientes de bosques. Sin embargo, las lagartijas no cambiaron puestas mayores por crías más grandes porque las hembras de fragmentos no pusieron huevos más grandes (en relación con su número) que las hembras de bosques. Entre las primeras cohortes de juveniles, la mayor masa de los huevos incrementó la probabilidad de recaptura en el siguiente año. Por lo tanto, la fragmentación redujo la fecundidad relativa de las lagartijas sin aumentar la calidad de sus crías. La disponibilidad reducida de energía, el incremento en el riesgo de depredación y la estocasticidad demográfica podrían disminuir la adaptabilidad de lagartijas en hábitats fragmentados, lo que podría contribuir a la escasez regional de esta especie en áreas agrícolas salpicadas de pequeños parches de bosque por lo demás adecuado. Nuestros resultados muestran que la reducción predecible en la reproducción al disminuir el tamaño de los parches de hábitat se puede agregar a los procesos ya conocidos que causan la inversión de la denso dependencia en tamaños poblacionales pequeños. [source] Bigger is better: implications of body size for flight ability under different light conditions and the evolution of alloethism in bumblebeesFUNCTIONAL ECOLOGY, Issue 6 2007A. KAPUSTJANSKIJ Summary 1In social insects, reproductive success and survival of the colony critically depend on the colony's ability to efficiently allocate workers to the various tasks which need to be performed. In bumblebees, workers show a large variation of body size within a colony. Large workers tend to leave the nest and forage for nectar and pollen, whereas small workers stay inside the nest and fulfill nest duties. It was speculated that size-related differences of the sensory system might contribute to alloethism found in bumblebee colonies. 2In the first part, we investigated how body size determines eye morphology. We measured several eye parameters of Bombus terrestris workers and drones. In both, workers and drones, larger individuals had larger eyes with larger facet diameters, more ommatidia and larger ocelli. At similar body size, drones exhibited larger eyes and ocelli compared to workers. Due to theoretical considerations, we predict that large individuals with large eyes should be better able to operate in illumination conditions of lower intensity than small individuals, since ommatidial sensitivity is proportional to the square of facet diameter. 3In the second part, we tested this prediction. In a behavioural experiment, we first caught bumblebees of various sizes in the field and then determined the lowest light intensity level at which they are just able to fly under controlled laboratory conditions. We tested workers of B. terrestris and B. pascuorum, and workers and drones of B. lapidarius. Large bumblebees were able to fly under lower light levels compared to small bees, with light intensity thresholds ranging from 1·1 to 5·5 lux. 4Our results indicate that the increased light sensitivity of the visual system of large bumblebees allows them to fly under poor light conditions, for example, very early in the morning or late at dusk. This is of potential benefit to the survival of a bumblebee colony since flowers that open early in the morning usually have accumulated a relatively high amount of nectar and pollen throughout the night, and large bumblebees can utilize these resources earlier than most other bees. Thus, our findings have important implications for the understanding of the functional significance and evolution of alloethism in bumblebee colonies. [source] Evolution of single-chick broods in the Swallow-tailed Gull Creagrus furcatusIBIS, Issue 2 2003ANA Agreda Swallow-tailed Gulls lay single-egg clutches, and so raise single-chick broods. As they are pelagic seabirds, this small brood size is expected to relate to proximate food limitation owing to infrequent food deliveries. However, a previous brood doubling experiment detected an 82% increase in fledging success from experimentally doubled broods compared to controls. We repeated the brood doubling experiment, and found that none of 50 enlarged broods produced more than one independent offspring. Control and experimental parents produced fledglings of similar body size, which also had indistinguishable rates of fledging and subsequent survival and reproduction. A variety of parameters estimating survival and breeding costs of reproduction showed no treatment effect. Since two-chick broods yield dramatically higher fledging rates at some times, apparently without excess costs of reproduction, selection on brood size appears to favour a two-chick brood. However, selection may not favour a two-egg clutch if egg production is very costly. Additionally, our estimates of reproductive success do not incorporate the performance of experimental and control offspring as adults, which could differ, since growth of chicks differed slightly by treatment. [source] Comparative foraging and nutrition of horses and cattle in European wetlandsJOURNAL OF APPLIED ECOLOGY, Issue 1 2002Catherine Menard Summary 1Equids are generalist herbivores that co-exist with bovids of similar body size in many ecosystems. There are two major hypotheses to explain their co-existence, but few comparative data are available to test them. The first postulates that the very different functioning of their digestive tracts leads to fundamentally different patterns of use of grasses of different fibre contents. The second postulates resource partitioning through the use of different plant species. As domestic horses and cattle are used widely in Europe for the management of conservation areas, particularly in wetlands, a good knowledge of their foraging behaviour and comparative nutrition is necessary. 2In this paper we describe resource-use by horses and cattle in complementary studies in two French wetlands. Horses used marshes intensively during the warmer seasons; both species used grasslands intensively throughout the year; cattle used forbs and shrubs much more than horses. Niche breadth was similar and overlap was high (Kulczinski's index 0·58,0·77). Horses spent much more time feeding on short grass than cattle. These results from the two sites indicate strong potential for competition. 3Comparative daily food intake, measured in the field during this study for the first time, was 63% higher in horses (144 gDM kg W,0·75 day,1) than in cattle (88 gDM kg W,0·75 day,1). Digestibility of the cattle diets was a little higher, but daily intake of digestible dry matter (i.e. nutrient extraction) in all seasons was considerably higher in horses (78 gDM kg W,0·75 day,1) than in cattle (51 gDM kg W,0·75 day,1). When food is limiting, horses should outcompete cattle in habitats dominated by grasses because their functional response is steeper; under these circumstances cattle will require an ecological refuge for survival during winter, woodland or shrubland with abundant dicotyledons. 4Horses are a good tool for plant management because they remove more vegetation per unit body weight than cattle, and use the most productive plant communities and plant species (especially graminoids) to a greater extent. They feed closer to the ground, and maintain a mosaic of patches of short and tall grass that contributes to structural diversity at this scale. Cattle use broadleaved plants to a greater extent than horses, and can reduce the rate of encroachment by certain woody species. [source] Field metabolic rates of black-browed albatrosses Thalassarche melanophrys during the incubation stageJOURNAL OF AVIAN BIOLOGY, Issue 6 2004Scott A. Shaffer Field metabolic rates (FMR) and activity patterns of black-browed albatrosses Thalassarche melanophrys were measured while at sea and on nest during the incubation stage at Kerguelen Island, southwestern Indian Ocean. Activity-specific metabolic rates of five albatrosses at sea (FMRat-sea) were measured using doubly labeled water (DLW), and by equipping birds with wet-dry activity data loggers that determined when birds were in flight or on the water. The metabolic rates of four birds incubating their eggs (FMRon-nest) were also measured using DLW. The mean±SD FMRat-sea of albatrosses was 611±96 kJ kg,1 d,1 compared to FMRon-nest of 196±52 kJ kg,1 d,1. While at sea, albatrosses spent 52.9±8.2% (N=3) of their time in flight and they landed on the water 41.2±13.9 times per day. The FMR of black-browed albatrosses appear to be intermediate to that of three other albatross species. Based on at-sea activity, the power requirement of flight was estimated to be 8.7 W kg,1 (or 4.0×predicted BMR), which is high compared to other albatross species, but may be explained by the high activity levels of the birds when at sea. The FMRat-sea of albatrosses, when scaled with body mass, are lower than other seabirds of similar body size, which probably reflects the economical nature of their soaring flight. [source] The palaeoecology of the Vombatidae: did giant wombats burrow?MAMMAL REVIEW, Issue 1 2001Andrew P. Woolnough ABSTRACT Debate over the origins of burrowing in the Vombatidae has continued since the discovery of the remains of the largest of all wombats, Phascolonus gigas, in the nineteenth century. In this paper, we argue that the largest of the ancestors of extant wombats did not burrow due to physical and physiological limitations of burrows. Further, we suggest that the burrowing characteristics of the extant wombats were derived from an ancestor of similar body size (20,40 kg) that is presently not represented in the fossil record. [source] Gastrointestinal Morphology of the Crowned Lemur (Eulemur coronatus)ANATOMIA, HISTOLOGIA, EMBRYOLOGIA, Issue 6 2009C. Schwitzer Summary I provide measurements of the gastrointestinal tract of a captive female Eulemur coronatus, obtained at necropsy, and describe its morphology. The small intestine, caecum and colon were short when compared with those of other lemur species. The ratio of intestine length to body length was low. Distinct sacculations were present in the caecum, but not in the colon. The results suggest that E. coronatus is able to digest a certain amount of structural polysaccharides as contained in plant cell wall. The main fermentation chamber seems to be the caecum. Its digestive morphology implies that E. coronatus relies on a diet higher in energy-rich cell contents than those of other lemur species of similar body size. [source] Asymmetric coexistence: bidirectional abiotic and biotic effects between goose barnacles and musselsJOURNAL OF ANIMAL ECOLOGY, Issue 4 2006TAKASHI KAWAI Summary 1Species coexistence depends on the net effect of interacting species, representing the sum of multiple interaction components that may act simultaneously and vary independently depending on ambient environmental conditions. Consequently, for a comprehensive understanding of the compound nature of species interactions and coexistence, a mechanistic approach that allows a separate evaluation of each interaction component is required. 2Two sessile filter-feeders, the goose barnacle Capitulum mitella and the mussel Septifer virgatus, coexist on moderately wave-exposed rocky shores in south-western Japan. In the upper intertidal, Capitulum positively influenced Septifer survivorship and growth through amelioration of thermal stress and of physical disturbance. On the other hand, these species are potential competitors as they have similar body sizes and modes of resource utilization. These opposite processes, facilitation and competition, are based on abiotic characteristics and biotic functions of the two species, respectively. 3In order to quantify the bidirectional abiotic, biotic and net effects, a series of experimental manipulations was conducted involving the use of living neighbours with both abiotic and biotic effects, and artificial mimics to simulate abiotic effects without biotic effects. 4Capitulum had strong positive abiotic effects on the mussel survivorship in most experimental periods, while the biotic effect was negligible or weakly negative, suggesting that the net effect of Capitulum on mussel survival was largely attributable to the abiotic effect. In contrast, a significantly negative biotic effect on the mussel growth rate was always present, though this was cancelled out by the larger, positive abiotic effect. In the case of Septifer, its abiotic and biotic effects on the survivorship of goose barnacles were negligible, while those on the growth rate showed temporal variation. 5With respect to the relationship between species interaction and environmental conditions, the strength of abiotic facilitative effect of Capitulum on mussel survival increased with increasing abiotic stress, while the strength of biotic effect was negligible or weakly negative. As regards the effects of mussels on goose barnacles, our study indicated no obvious relationship. These results point to the importance of decomposing interaction for an accurate, mechanistic understanding of species relations and coexistence. [source] | ||||||||||