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Performance Trade-offs (performance + trade-off)
Selected AbstractsPerformance Trade-offs Driven by Morphological Plasticity Contribute to Habitat Specialization of Bornean Tree SpeciesBIOTROPICA, Issue 4 2009Daisy H. Dent ABSTRACT Growth-survival trade-offs play an important role in niche differentiation of tropical tree species in relation to light-gradient partitioning. However, the mechanisms that determine differential species performance in response to light and soil resource availability are poorly understood. To examine responses to light and soil nutrient availability, we grew seedlings of five tropical tree species for 12 mo at < 2 and 18 percent full sunlight and in two soil types representing natural contrasts in nutrient availability within a lowland dipterocarp forest in North Borneo. We chose two specialists of nutrient-rich and nutrient-poor soils, respectively, and one habitat generalist. Across all species, growth was higher in high than low light and on more nutrient rich soil. Although species differed in growth rates, the ranking of species, in terms of growth, was consistent across the four treatments. Nutrient-rich soils improved seedling survival and increased growth of three species even under low light. Slower-growing species increased root allocation and reduced specific leaf area (SLA) and leaf area ratio (LAR) in response to decreased nutrient supply. All species increased LAR in response to low light. Maximum growth rates were negatively correlated with survival in the most resource-limited environment. Nutrient-poor soil specialists had low maximum growth rates but high survival at low resource availability. Specialists of nutrient-rich soils, plus the habitat generalist, had the opposite suite of traits. Fitness component trade-offs may be driven by both light and belowground resource availability. These trade-offs contribute to differentiation of tropical tree species among habitats defined by edaphic variation. [source] DIFFERENTIAL PERFORMANCE AMONG LDH-B GENOTYPES IN RANA LESSONAE TADPOLESEVOLUTION, Issue 5 2000Hansjürg Hotz Abstract The European pool frog, Rana lessonae, is widely polymorphic for two common alleles (b, e) at the lactate dehydrogenase-B (LDH-B) locus. We compared fitness-related larval life-history traits among LDH-B genotypes, which originated from segregation in heterozygous parents, in an artificial pond experiment where tadpoles of R. lessonae from a Swiss population were raised together with tadpoles of the hemiclonal hybrid R. esculenta at two densities. In R. lessonae, LDH-B e/e homozygotes at each density had a higher proportion of metamorphs among survivors, reached metamorphosis earlier, and were heavier at metamorphosis than b/b homozygotes; b/e heterozygotes had intermediate values. That e/e individuals were superior to b/b in both time to and mass at metamorphosis is surprising because these two life-history traits are thought to reflect a performance trade-off; e/e genotypes apparently compensated for shorter time to metamorphosis by a higher growth rate. The two alleles showed the same performance ranking when combined in hybrids with a R. ridibunda allele: When R. esculenta from Swiss populations reared in the same ponds had received the e allele rather than the b allele from their R. lessonae parent, they reached metamorphosis earlier, but did not differ in mass at metamorphosis. The degree of linkage disequilibrium in the source population of the eight R. lessonae used as parents of the R. lessonae tadpoles is unknown, so we cannot exclude the possibility that the performance differences are caused by some anonymous tightly linked gene, rather than the LDH-B locus, that constitutes the genomically localized target of natural selection. A causal involvement of LDH-B is plausible, nevertheless, because this enzyme takes part in the central energy-metabolizing processes and has been reported to underlie fitness differences in other animals; also, differential performance of LDH-B genotypes has been observed in R. lessonae larvae from another population. The present results suggest strong directional selection for allele e; the sum of available data, including an independent laboratory experiment, suggests that partial environment-dependent overdominance combined with balancing selection favoring e/e homozygotes under some and b/b homozygotes under other conditions may be partially responsible for the broad maintenance of the LDH-B polymorphism in R. lessonae. [source] Adaptive resource allocation in OFDMA systems with fairness and QoS constraints,EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 6 2007Liang Chen This paper describes several practical and efficient adaptive subchannel, power and bit allocation algorithms for orthogonal frequency-division multiple-access (OFDMA) systems. Assuming perfect knowledge of channel state information (CSI) at the transmitter, we look at the problem of minimising the total power consumption while maintaining individual rate requirements and QoS constraints. An average signal-to-noise ratio (SNR) approximation is used to determine the allocation while substantially reducing the computational complexity. The proposed algorithms guarantee improvement through each iteration and converge quickly to stable suboptimal solutions. Numerical results and complexity analysis show that the proposed algorithms offer beneficial cost versus performance trade-offs compared to existing approaches. Copyright © 2007 John Wiley & Sons, Ltd. [source] Resource specialization in a phytophagous insect: no evidence for genetically based performance trade-offs across hosts in the field or laboratoryJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 4 2009S. J. AGOSTA Abstract We present a field test of the genetically based performance trade-off hypothesis for resource specialization in a population of the moth Rothschildia lebeau whose larvae primarily feed on three host plant species. Pairwise correlations between growth vs. growth, survival vs. survival and growth vs. survival across the different hosts were calculated, using families (sibships) as the units of analysis. Of 15 pairwise correlations, 14 were positive, 5 significantly so and none were negative. The same pattern was found using complementary growth and survival data from the laboratory. Overall, we found no evidence of negative genetic correlations in cross-host performance that would be indicative of performance trade-offs in this population. Rather, variation among families in performance appears to reflect ,general vigour' whereby families that perform well on one host perform well across multiple hosts. We discuss the implications of positive genetic correlations in cross-host performance in terms of the ecology and evolution of host range. We argue that this genetic architecture facilitates colonization of novel hosts and recolonization of historical hosts, therefore contributing to host shifts, host range expansions, biological invasions and introductions, and host ranges that are regionally broad but locally narrow. [source] An analysis of capital expenses and performance trade-offs among IMS CSCF deployment optionsBELL LABS TECHNICAL JOURNAL, Issue 4 2008Anne Lee Service providers around the world are deploying or planning to deploy the IP Multimedia Subsystem (IMS) in their core networks. IMS allows the delivery of new multimedia applications that can enhance the user's experience and bring in new revenue for the operators. These operators are now faced with deciding how to best deploy the various IMS functional elements in their networks. In this paper, the authors provide a survey of the various options available to the operators and present an analysis of some of those deployment options. In particular, the paper addresses questions around the advantages and disadvantages of centralizing or distributing control functions such as the call session control function (CSCF) in terms of capital expenditure (CAPEX) costs and latency trade-offs. Without the proper deployment strategy, there can be major differences in the overall cost of the network and therefore it is important to perform such an analysis. Initial recommendations and general observations are given that can assist network planners and operators to more efficiently develop an IMS deployment strategy. Further analysis and study that includes operational expenditure (OPEX) costs should also be factored into the final decision. © 2008 Alcatel-Lucent. [source] | ||||||||||