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Knowledge of statistical power is essential for sampling design and data evaluation when testing for genetic differentiation. Yet, such information is typically missing in studies of conservation and evolutionary genetics, most likely because of complex interactions between the many factors that affect power. powsim is a 32‐bit Windows/DOS simulation‐based computer program that estimates power (and α error) for chi‐square and Fisher's exact tests when evaluating the hypothesis of genetic homogeneity. Optional combinations include the number of samples, sample sizes, number of loci and alleles, allele frequencies, and degree of differentiation (quantified as FST). powsim is available at http://www.zoologi.su.se/~ryman .  相似文献   
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ABSTRACT. Gynes and males of Lasius flavus Fab. were taken from the nest as they eclosed, and at intervals thereafter until the mating flight, and their respiration was measured. After the mating flight respiration was measured in gynes at various stages of colony foundation. Respiration in gynes rose rapidly to a peak as they began to accumulate food reserves for colony foundation. Subsequently, the respiratory rate declined and remained at a low level until the mating flight and during the claustral phase of colony foundation. Once the colony was well established and the queen actively laying, the respiratory rate returned to that at the beginning of maturation. Males showed smaller changes in their respiratory rates, which were generally higher than those of the gynes. The variation in respiration in males seemed to be due to increasing restlessness as the time of the mating flight approached.  相似文献   
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Nitrogen‐13 (t1/2 9.97 m), a radioactive isotope of nitrogen, offers unique opportunities to explore plant nitrogen utilization over short time periods. Here we describe a method for administering 13N as gaseous 13NH3 to intact leaves of Nicotiana tabacum L. (cv Samsun), and measuring the labelled amino acids using radio high‐performance liquid chromatography (HPLC) on tissue extract. We used this method to study the effects of defence induction on plant nitrogen utilization by applying treatments of methyl jasmonate (MeJA), a potent defence elicitor. MeJA caused a significant increase relative to controls in key [13N]amino acids, including serine, glycine and alanine by 4 h post‐treatment, yet had no effect on 13NH3 incorporation, a process that is primarily under the control of the glutamine synthatase/glutamate synthase pathway (GS/GOGAT) in cellular photorespiration. We suggest that the reconfiguration of nitrogen metabolism may reflect induction of non‐photorespiratory sources of nitrogen to better serve the plant's defences.  相似文献   
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chifish is a 32‐bit Windows/DOS program evaluating divergence at multiple gene loci. It tests the hypothesis of no difference at any locus both by means of Pearson's traditional chi‐square and by using Fisher's method of combining P values obtained by Fisher's exact test. Input data are read from a file formatted for genepop . Commonly used population genetics software do not perform chi‐square tests, and the simultaneous application of both techniques aids in situations where poor power of the ‘exact approach’ may prevent detection of true differentiation (e.g. few populations and few alleles per locus).  相似文献   
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Tree planting in the tropics is conducted for a number of reasons including carbon sequestration, but often competes with increasingly scarce water resources. The basics of forest and water relations are frequently said to be well understood but there is a pressing need to better understand and predict the hydrological effects of land‐use and climate change in the complex and dynamic landscapes of the tropics. This will remain elusive without the empirical data required to feed hydrological process models. It is argued that the current state of knowledge is confused by too broad a use of the terms ‘forest’ and ‘(af)forestation’, as well as by a bias towards using data generated mostly outside the tropics and for nondegraded soil conditions. Definitions of forest, afforestation and reforestation as used in the climate change community and their application by land and water managers need to be reconciled.  相似文献   
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1. The invasive golden apple snail (Pomacea canaliculata), native to South America, is a serious pest on rice seedlings in south‐east Asia and has also been shown to consume large amounts of macrophytes in natural wetlands, with large effects on ecosystem functioning. Earlier studies suggest that the snail undergoes an ontogenetic diet shift, feeding on algae and detritus as juveniles and shifting to aquatic macrophytes as adults. 2. Here, we study the effects of snail populations with a size‐structure typical of either populations at an invasive front or the size‐structure of established populations. In an enclosure experiment performed in a wetland in Laos, we compared treatments with small snails only (3 mm; invasive treatment) to treatments with small, medium sized (10 mm) and adult (>25 mm) snails (established treatment). The effects of snail grazing on three aquatic macrophyte species and periphytic algae were quantified. 3. We found that snails of all sizes had a strong negative effect on the biomass of all macrophyte species and periphytic algae. There was no evidence of an ontogenetic diet change, i.e. snails in both the invasive and established treatments affected macrophyte biomass. Foraging was size‐dependent in that small snails had higher relative foraging capacity (g plant consumed per g of snail) compared with medium and adult snails. Small snails, therefore, depressed growth of medium snails at increasing densities through exploitative competition for preferred resources, while adult snails did not grow at all in the presence of small snails. 4. Density dependence is common in freshwater invertebrates, including gastropod populations, but differences in size dependent foraging‐ and competitive‐ability have rarely been demonstrated in this group of organisms. Knowledge about intra‐specific differences in ecological performance may, however, both deepen our understanding of the processes that underlie population dynamics in invertebrates such as gastropods, and help develop control strategies for invasive golden apple snails.  相似文献   
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Thawing permafrost in the sub‐Arctic has implications for the physical stability and biological dynamics of peatland ecosystems. This study provides an analysis of how permafrost thawing and subsequent vegetation changes in a sub‐Arctic Swedish mire have changed the net exchange of greenhouse gases, carbon dioxide (CO2) and CH4 over the past three decades. Images of the mire (ca. 17 ha) and surroundings taken with film sensitive in the visible and the near infrared portion of the spectrum, [i.e. colour infrared (CIR) aerial photographs from 1970 and 2000] were used. The results show that during this period the area covered by hummock vegetation decreased by more than 11% and became replaced by wet‐growing plant communities. The overall net uptake of C in the vegetation and the release of C by heterotrophic respiration might have increased resulting in increases in both the growing season atmospheric CO2 sink function with about 16% and the CH4 emissions with 22%. Calculating the flux as CO2 equivalents show that the mire in 2000 has a 47% greater radiative forcing on the atmosphere using a 100‐year time horizon. Northern peatlands in areas with thawing sporadic or discontinuous permafrost are likely to act as larger greenhouse gas sources over the growing season today than a few decades ago because of increased CH4 emissions.  相似文献   
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