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991.
992.
Cycles in insect populations: delayed density dependence or exogenous driving variables? 总被引:2,自引:0,他引:2
Summary Delayed density dependence, and the cycles in insect populations that it can generate, are often investigated using time-series analysis. Recently, several authors have raised concerns about the validity of using time-series analysis to detect density dependence. One particular concern is the suggestion that exogenous driving variables, such as cyclic weather patterns, can lead to the spurious detection of density dependence in natural populations.
Using non-biological data (the electricity bills of one of the authors), we show how easy it is to be misled by the results of time-series analysis. We then present 16 years' data on the gall-forming sawfly, Euura lasiolepis (Hymenoptera: Tenthredinidae), and show that cycles in weather, specifically winter precipitation, lead to the spurious detection of density dependence in time-series analysis. We conclude that time-series analysis cannot stand alone as a method for inferring the action of density dependence, and urge further investigation of the effects of apparent cycles in abiotic forces on insect populations. 相似文献
Using non-biological data (the electricity bills of one of the authors), we show how easy it is to be misled by the results of time-series analysis. We then present 16 years' data on the gall-forming sawfly, Euura lasiolepis (Hymenoptera: Tenthredinidae), and show that cycles in weather, specifically winter precipitation, lead to the spurious detection of density dependence in time-series analysis. We conclude that time-series analysis cannot stand alone as a method for inferring the action of density dependence, and urge further investigation of the effects of apparent cycles in abiotic forces on insect populations. 相似文献
993.
994.
Inferring evolutionary processes from phylogenies 总被引:23,自引:0,他引:23
MARK PAGEL 《Zoologica scripta》1997,26(4):331-348
Evolutionary processes shape the regular trends of evolution and are responsible for the diversity and distribution of contemporary species. They include correlated evolutionary change and trajectories of trait evolution, convergent and parallel evolution, differential rates of evolution, speciation and extinction, the order and direction of change in characters, and the nature of the evolutionary process itself—does change accumulate gradually, episodically, or in punctuational bursts. Phylogenies, in combination with information on species, contain the imprint of these historical evolutionary processes. By applying comparative methods based upon statistical models of evolution to well resolved phylogenies, it is possible to infer the historical evolutionary processes that must have existed in the past, given the patterns of diversity seen in the present. I describe a set of maximum likelihood statistical methods for inferring such processes. The methods estimate parameters of statistical models for inferring correlated evolutionary change in continuously varying characters, for detecting correlated evolution in discrete characters, for estimating rates of evolution, and for investigating the nature of the evolutionary process itself. They also anticipate the wealth of information becoming available to biological scientists from genetic studies that pin down relationships among organisms with unprecedented accuracy. 相似文献
995.
Abstract. A method is presented for the rapid isolation of eye-colour mutants in anopheline mosquitoes based on their inability to undergo a background-stimulated morphological colour change. For application of this method, larval mosquitoes, whose grandfathers had been mutagenized, were reared in black containers and examined with the naked eye en masse during the third or fourth instar. The vast majority of larvae became dark-coloured; however, rare exceptional pale larvae were observed and examined individually microscopically. Approximately half of the pale types examined were eye-colour mutants. By this method, seven sex-linked mutations in the mosquito Anopheles gambiae s.s. were easily isolated. Additional existing anopheline eye-colour mutants in An. gambiae and An. stephensi were tested and were found to be unable to undergo colour change. Several applications of this simple technique are suggested. 相似文献
996.
GORDAN S. KARAMAN TERENCE GLEDHILL F.L.S. MARK C. HOLMES F.L.S. 《Zoological Journal of the Linnean Society》1994,112(3):309-319
The subterranean amphipod Niphargus vuexfordensis/i> sp. nov. (Amphipoda: Gammaridea: Niphargidae) is described and figured from a well at Kerloge, County Wexford in southern Ireland. The taxonomic position of this species is analysed and its relationship to the controversial genus Niphargellus Schellenberg discussed. 相似文献
997.
MARK D. HUNTER 《Ecological Entomology》1998,23(2):168-173
1. Yearly population estimates of the green oak leaf roller moth, Tortrix viridana (Lepidoptera: Tortricidae), and the winter moth, Operophtera brumata (Lepidoptera: Geometridae), were taken from the pedunculate oak, Quercus robur, from 1951 to 1966 in Wytham Woods, Oxfordshire, U.K. Larval mortality from parasitoids was recorded for both species over the same period. 2. Operophtera brumata population density fluctuated around a constant mean, whereas T. viridana population density exhibited a linear decline over the sampling period. Population counts were subjected to time-series analysis after the linear decline was removed from the T. viridana data by detrending. Multiple regression models were built so that variation in the per capita rate of increase of each population could be partitioned among (a) current and previous population density, (b) current and previous population density of the second moth species, and (c) rates of larval parasitism. 3. Multiple regression analysis suggested that variation in the per capita rate of increase of O. brumata could be explained by negative feedback from O. brumata density at T–2 (32%), a negative relationship with T. viridana density at T–1 (18%), and a positive relationship with parasitism suffered by T. viridana at T–1 (24%). 4. The T. viridana population time-series was dominated by a rapid feedback process such that per capita rate of increase at time T was negatively related to population density at time T–1, explaining 53% of variance in population growth rate. Per capita rate of increase was unrelated to larval parasitism or densities of O. brumata. 5. In light of previous life-table and experimental studies on O. brumata and T. viridana, the current analyses suggest that pupal predation (data not presented) and interspecific competition are significant determinants of O. brumata population growth rates in Wytham Woods. In contrast, T. viridana population growth rates appear to be dominated by rapid negative feedback consistent with intraspecific competition. 相似文献
998.
WILLIAM LOUIS STERN W. MARK WHITTEN 《Botanical journal of the Linnean Society. Linnean Society of London》1999,129(2):87-103
Stanhopeinae are a group of tropical American orchids characterized by euglossine bee pollination and lateral inflorescences stemming from the bases of pseudobulbs. Leaves are hypostomatal, and all stomatal configurations are tetracytic. Chlorenchyma is homogeneous and characterized by fibre bundles in adaxial/abaxial or adaxial/median/abaxial positions. Collateral vascular bundles occur in a single row and feature phloic and xylic sclerenchymatous caps and thin-walled bundle sheath cells. Fibre bundles and vascular sclerenchyma are accompanied by stegmata containing conical silica bodies. Pseudobulbs have thick-walled turbinate epidermal cells and ground tissue of smaller, living assimilatory cells and larger, dead water-storage cells. Fibre bundles are usually absent but occur in several genera. Collateral vascular bundles show phloic sclerenchyma, but xylic sclerenchyma occurs only in die larger vascular bundles. Phloic and xylic sclerenchyma are associated with stegmata containing conical silica bodies. Roots are velamentous. Velamen cell walls have fine, spiral thickenings. Exodermal cells are thin-walled. The cortex features scattered thick-walled cells and in some cases branched bars of secondary cell wall material. Endodermis is either u-or O-thickened, but pericycle is always O-thickened opposite the phloem. Vascular tissue consists of alternating strands of xylem and phloem surrounded by a matrix of thick-walled cells. Pith cells may be parenchymatous or sclerenchymatous. 相似文献