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1.
Does size matter?   总被引:1,自引:0,他引:1  
For 40 years, the debate has raged. Do mammalian cells monitor cell size when deciding whether to divide? More recent models suggest an indirect solution, but the field is far from reaching a final verdict.  相似文献   

2.
This study examined the relationship between otolith size and growth in juvenile cod (Gadus morhua L.). Two groups of juvenile cod were reared under different food ration and temperature regimes to obtain fish of similar somatic size but with different sized otoliths. The two groups were subjected to alternating temperature regimes and intermediate ration levels. Large otoliths grew significantly faster than the small ones and variation between individuals was extensive. The ratio of otolith growth during cold and warm temperature exposure did not differ between groups, and the observed growth pattern is therefore not attributable to differential growth within individual temperature periods. The ratio decreased with otolith size, presumably as a result of ontogenetic decrease in otolith protein composition. These results suggest that processes coupled to the metabolic rate of the endolymphatic epithelium are the key driver behind otolith growth.  相似文献   

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Although intrasexual contests generally favor bigger or stronger individuals, the relevance of body size to war of attrition-typedisputes between weaponless animals such as butterflies isunclear. In this study I aimed to investigate the significanceof size in this context by studying territorial contests inHypolimnas bolina (L.), a species that exhibits consistentseasonal plasticity in body size. In this species adult ageis positively correlated with large size in spring but withsmall size in autumn. This shift allowed independent evaluationof the relevance of each variable (size and age) to intrasexualcontest success. Observation of a population of marked individualsindicated that only age appeared important, with the winnersof pair-wise contests significantly older than losers in both seasons, and with contests lasting longer when the age differencebetween the combatants was small. Age was also linked to residency;residents won 99% of all contests. This study suggests thatsize does not matter in these aerial disputes, but age andresidency do. It is not yet possible to determine whether olderbutterflies are intrinsically better competitors, or whether they simply have greater opportunity to find a vacant territory.  相似文献   

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Fish cover a large size range, from milligrams to tonnes, and many of them are regularly exposed to large variations in ambient oxygen levels. For more than half a century, there have been various, often divergent, claims regarding the effect of body size on hypoxia tolerance in fish. Here, we attempt to link old and new empirical data with the current understanding of the physiological mechanisms behind hypoxia tolerance. Three main conclusions are drawn: (1) body size per se has little or no impact on the ability to take up oxygen during hypoxic conditions, primarily because the respiratory surface area matches metabolic rate over a wide size range. If size-related differences are seen in the ability for oxygen uptake in a species, these are likely to reflect adaptation to different life-styles or habitat choice. (2) During severe hypoxia and anoxia, where fish have to rely on anaerobic ATP production (glycolysis) for survival, large individuals have a clear advantage over smaller ones, because small fish will run out of glycogen or reach lethal levels of anaerobic end-products (lactate and H(+)) much faster due to their higher mass-specific metabolic rate. (3) Those fish species that have evolved extreme adaptations to hypoxia, including haemoglobins with exceptionally high oxygen affinities and an alternative anaerobic end-product (ethanol), reveal that natural selection can be a much more powerful determinant of hypoxia tolerance than scaling of physiological functions.  相似文献   

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Previous studies of the vocalization frequencies of mammals have suggested that it is either body mass or environment that drives these frequencies. Using 193 species across the globe from the terrestrial and aquatic environments and a model selection approach, we identified that the best‐supported model for minimum and maximum frequencies for vocalization included both body mass and environment. The minimum frequencies of vocalizations of species from all environments retained the influence of body mass. For maximum frequency however, aquatic species are released from such a trend with body mass having little constraint on frequencies. Surprisingly, phylogeny did not have a strong impact on the evolution of the maximum frequency of mammal vocalizations, largely due to the pinniped species divergence of frequency from their carnivoran relatives. We demonstrate that the divergence of signal frequencies in mammals has arisen from the need to adapt to their environment.  相似文献   

9.
Abstract Introduced birds are a pervasive and dominant element of urban ecosystems. We examined the richness and relative abundance of introduced bird species in small (1–5 ha) medium (6–15 ha) and large (>15 ha) remnants of native vegetation within an urban matrix. Transects were surveyed during breeding and non‐breeding seasons. There was a significant relationship between introduced species richness and remnant size with larger remnants supporting more introduced species. There was no significant difference in relative abundance of introduced species in remnants of different sizes. Introduced species, as a proportion of the relative abundance of the total avifauna (native and introduced species), did not vary significantly between remnants of differing sizes. There were significant differences in the composition of introduced bird species between the different remnant sizes, with large remnants supporting significantly different assemblages than medium and small remnants. Other variables also have substantial effects on the abundance of introduced bird species. The lack of significant differences in abundance between remnant sizes suggests they were all equally susceptible to invasion. No patches in the urban matrix are likely to be unaffected by introduced species. The effective long‐term control of introduced bird species is difficult and resources may be better spent managing habitat in a way which renders it less suitable for introduced species (e.g. reducing areas of disturbed ground and weed dominated areas).  相似文献   

10.
Gamboa  Miguel A.  Laureano  Sugei  Bayman  Paul 《Mycopathologia》2003,156(1):41-45
Endophytic fungi inhabit living plant tissues without causing disease symptoms. Although abundant, the extent of their contribution to fungal biodiversity remains unclear. Since endophytic fungi are poorly known, especially in the tropics, current estimates of fungal species are probably conservative. Here we tested strategies for sampling endophytic fungi in tropical plants. We compared the number of fungi isolated from 400 mm2 leaf pieces that were divided into increasingly small fragments. Leaf pieces were surface-sterilized, cut into fragments and plated on culture media. For a given area, cutting leaf pieces into smaller fragments significantly increased the number of fungal morphospecies recovered. There was a strong linear relationship between size of fragments and number of fungi isolated. By extrapolation, an estimated 16 ± 3 fungi could be recovered from a 2 × 2 cm leaf piece, using infinitely small fragments. This represents a large part of the fungal diversity estimated to exist in leaf endophytes in a population. We conclude that reducing the size and increasing the number of leaf fragments will increase the number of fungal species isolated. This strategy will help to estimate real values of endophytic fungal diversity.This revised version was published online in October 2005 with corrections to the Cover Date.  相似文献   

11.
The medical community has long regarded obesity and overweight as serious health risks, and popular culture reflects these concerns. A focus on body weight reduction motivates many contemporary exercise and diet practices, especially among women. Yet, there is significant evidence that those risks have been exaggerated, that weight loss regimens may be more detrimental to health than moderate obesity, and that pressure to be thin leads to disordered eating and unhealthy lifestyle choices. This paper examines the problematic manners in which some national health policies regard the problems of overweight and obesity. It contends that concepts of aesthetics, grounded in 19th-century beliefs about the body, guide clinicians to emphasize measurement of the body in health assessment at potential cost to individual wellness.  相似文献   

12.
Recent studies and analyses have confirmed that baseline prostate volume is related to progression of benign prostatic hyperplasia (BPH) as well as to negative outcomes related to BPH, such as acute urinary retention (AUR) and need for surgery, and can also predict response to therapy. Other investigations have determined that prostate-specific antigen (PSA) level has good predictive value for assessing prostate volume. Strong evidence exists that baseline serum PSA level, like baseline prostate volume, predicts future prostate growth. Randomized placebo-controlled finasteride trials have shown that men with larger prostate volumes and higher PSA levels experience a clinically significant response to therapy compared with those with smaller prostate volumes and lower PSA levels. It has also been demonstrated that men with larger prostate glands and higher PSA levels are at increased risk for AUR and BPH-related surgery but that finasteride reduces these risks. Moreover, doxazosin and finasteride, alone and in combination, have been shown to significantly reduce BPH clinical progression.  相似文献   

13.
Aim To describe species–area relationships in human settlements and compare them with those from a non‐urban habitat. Location West‐central Mexico. Methods We surveyed breeding birds in 13 human settlements and five shrubland patches. We estimated bird species richness using an abundance‐based coverage estimator with equal sample sizes to eliminate biases related to sampling effort differences. To assess species–area relationships, we performed log–log linear regressions between the size of the studied patches and their estimated bird richness. We also used a logarithmic approach to determine how the species–area relationship asymptoted and made use of the Michaelis–Menten model to identify the size at which the studied patches reached their maximum species richness. We also investigated (1) possible relationships among the estimated bird richness and other variables known to affect urban‐dwelling birds (built cover, plant species richness, tree cover or human population density) and (2) changes in bird community composition related to the size of the studied human settlements. Results Species–area relationships exhibited different patterns among the studied habitats. The log–log regression slope was steeper in human settlements, while the intercept was higher in shrublands. The maximum number of species was more than twofold higher in shrublands. Human settlement patch size was the only variable significantly related to bird richness. Our community composition results show that two main bird groups are related to human settlement size, and that as the size of human settlements increases, bird community similarity in relation to the largest city increases. Main conclusions Human settlements act as ecological islands, with pronounced species–area relationships. Our results suggest that an important threshold for bird species richness and community composition is reached in human settlements > 10.2 km2. This threshold is unlikely to be generalizable among bio‐regions, and thus should be quantified and considered when studying, managing and/or planning urban systems.  相似文献   

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Proper growth and development of multicellular organisms require the tight regulation of cell growth, cell division and cell death. A recent study has identified a novel regulatory link between two of these processes: cell growth and cell death.  相似文献   

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The demand for additional children is influenced by the presence of sons within a family. This study is based on cross-sectional data of 9416 currently married women under age 50 from a Pakistan national survey in 1979-80. The analysis suggests that having at least one son in the family influences the demand for additional children. Urban and rural comparisons indicated a higher preference for sons in urban areas. Unless the socioeconomic milieu changes, son preference is likely to remain strong in Pakistan.  相似文献   

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In animals living in groups, the social environment is fundamental to shaping the behaviors and life histories of an individual. A mismatch between individual and group behavior patterns may have disadvantages if the individual is incapable of flexibly changing its state in response to the social environment that influences its energy gain and expenditure. We used different social groups of juvenile three‐spined sticklebacks (Gasterosteus aculeatus) with experimentally manipulated compositions of individual sociability to study the feedback between individual and group behaviors and to test how the social environment shapes behavior, metabolic rate, and growth. Experimentally created unsociable groups, containing a high proportion of less sociable fish, showed bolder collective behaviors during feeding than did corresponding sociable groups. Fish within groups where the majority of members had a level of sociability similar to their own gained more mass than did those within mismatched groups. Less sociable individuals within sociable groups tended to have a relatively low mass but a high standard metabolic rate. A mismatch between the sociability of an individual and that of the majority of the group in which it is living confers a growth disadvantage probably due to the expression of nonadaptive behaviors that increase energetic costs.  相似文献   

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The woolly flying squirrelEupetaurus cinereus! Thomas, 1888 is the longest sciurid and most massive mammalian glider in the world. Because of this, there has been some question about the squirrel’s gliding ability. I document three glide events performed by this species. These glide events, coupled with comparisons of glide ratios, ponderal ratios, and a log-log plot of head + body length versus body mass with other flying squirrels, demonstrates that the woolly flying squirrel, despite its size, is a capable glider and is no more robust than other flying squirrels. Predation attempts that were observed during glide events are discussed within an evolutionary context.  相似文献   

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