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51.
Summary Since the successful control of prickly pear cactus by Cactoblastis cactorum in Australia, populations of plants and moths have persisted at low densities in open woodland sites. A contagious egg distribution causes overcrowding of larvae on some plants but insures low levels or no attack of other plants. This prevents extinction of plants and insects. Cactoblastis moths choose plants with characteristics which may increase the success of their larvae. Field observations and cage experiments indicate that large, green cactuses near previously attacked cactuses receive more eggs. Plants which are actively photosynthesizing are also more attractive as oviposition sites. These oviposition preferences contribute to the observed contagious egg distribution.While open woodland Opuntia and Cactoblastis populations fluctuate around an equilibrium, pasture populations may better be described by the hide and seek model, with the woodland populations serving as refuges. Average plant quality and variation in quality are suggested as important components in the dynamics of this system.This paper is dedicated to the memory of our friend Mike Sabath. 相似文献
52.
Within-individual strategies of variation (e.g., phenotypic plasticity) are particularly relevant to modular organisms, in
which ramets of the same genetic individual may encounter diverse environments imposing diverse patterns of selection. Hence,
measuring selection in heterogeneous environments is essential to understanding whether environment-dependent phenotypic change
enhances the fitness of modular individuals. In sublittoral marine habitats, competition for light and space among modular
taxa generates extreme patchiness in resource availability. Little is known, however, of the potential for plasticity within
individuals to arise from spatially-variable selection in such systems. We tested whether plasticity enhances genet-level
fitness in Asparagopsis armata, a clonal seaweed in which correlated traits mediate morphological responses to variation in light. Using the capacity for
rapid, clonal growth to measure fitness, we identified aspects of ramet morphology targeted by selection in two contrasting
light environments and compared patterns of selection across environments. We found that directional selection on single traits,
coupled with linear and nonlinear selection on multi-trait interactions, shape ramet morphology within environments and favor
different phenotypes in each. Evidence of environment-dependent, multivariate selection on correlated traits is novel for
any marine modular organism and demonstrates that seaweeds, such as A. armata, may potentially adapt to environmental heterogeneity via plasticity in clonal morphology. 相似文献
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A competitive inhibitor of the GTP reaction in protein synthesis 总被引:15,自引:0,他引:15
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Induced tolerance of stored-product beetles to methyl bromide 总被引:2,自引:0,他引:2
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This paper describes a new vegetation classification for the Greater Maya Mountains of Belize, focusing primarily on the Chiquibul Forest Reserve. Extensive use is made of GIS, remote sensing, botanical collections and field visits to provide a macro‐ and meso‐scale overview of the vegetation of this region. A total of 32 vegetation classes have been defined, both geographically and structurally, including 11 new classes. Where possible, classes have been compared with earlier classifications. A dominant scaling technique has been used to enable direct comparison between ground truthing data and a supervised Maximum Likelihood Classifier image‐based vegetation classification. The merits of such classifications and the effect of scale are discussed. 相似文献
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