抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

The Theory of Island Biogeography

In the early 1980s, a strategy for graphical representation of multivariate (multi-species) abundance data was introduced into marine ecology by, among others, Field, et al. (1982). A decade on, it is instructive to: (i) identify which elements of this often-quoted strategy have proved most useful in practical assessment of community change resulting from pollution impact; and (ii) ask to what extent evolution of techniques in the intervening years has added self-consistency and comprehensiveness to the approach. The pivotal concept has proved to be that of a biologically-relevant definition of similarity of two samples, and its utilization mainly in simple rank form, for example ‘sample A is more similar to sample B than it is to sample C’. Statistical assumptions about the data are thus minimized and the resulting non-parametric techniques will be of very general applicability. From such a starting point, a unified framework needs to encompass: (i) the display of community patterns through clustering and ordination of samples; (ii) identification of species principally responsible for determining sample groupings; (iii) statistical tests for differences in space and time (multivariate analogues of analysis of variance, based on rank similarities); and (iv) the linking of community differences to patterns in the physical and chemical environment (the latter also dictated by rank similarities between samples). Techniques are described that bring such a framework into place, and areas in which problems remain are identified. Accumulated practical experience with these methods is discussed, in particular applications to marine benthos, and it is concluded that they have much to offer practitioners of environmental impact studies on communities.

Non-parametric multivariate analyses of changes in community structure

Human alteration of Earth is substantial and growing. Between one-third and one-half of the land surface has been transformed by human action; the carbon dioxide concentration in the atmosphere has increased by nearly 30 percent since the beginning of the Industrial Revolution; more atmospheric nitrogen is fixed by humanity than by all natural terrestrial sources combined; more than half of all accessible surface fresh water is put to use by humanity; and about one-quarter of the bird species on Earth have been driven to extinction. By these and other standards, it is clear that we live on a human-dominated planet.

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Human Domination of Earth's Ecosystems

Pseudoreplication is defined. as the use of inferential statistics to test for treatment effects with data from experiments where either treatments are not replicated (though samples may be) or replicates are not statistically independent. In ANOVA terminology, it is the testing for treatment effects with an error term inappropriate to the hypothesis being considered. Scrutiny of 176 experi- mental studies published between 1960 and the present revealed that pseudoreplication occurred in 27% of them, or 48% of all such studies that applied inferential statistics. The incidence of pseudo- replication is especially high in studies of marine benthos and small mammals. The critical features of controlled experimentation are reviewed. Nondemonic intrusion is defined as the impingement of chance events on an experiment in progress. As a safeguard against both it and preexisting gradients, interspersion of treatments is argued to be an obligatory feature of good design. Especially in small experiments, adequate interspersion can sometimes be assured only by dispensing with strict random- ization procedures. Comprehension of this conflict between interspersion and randomization is aided by distinguishing pre-layout (or conventional) and layout-specifit alpha (probability of type I error). Suggestions are offered to statisticians and editors of ecological j oumals as to how ecologists' under- standing of experimental design and statistics might be improved.

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Pseudoreplication and the Design of Ecological Field Experiments

Sampling at two elevations from a tidal flat on the Shark Bay (Western Australia) shoreline at Monkey Mia revealed abundant suspension-feeding bivalves of numerous (> 17) species. Their total density increased by 3 x up the tidal elevation gradient from the subtidal margin of the flat to intertidal sites -97 cm higher. Factorial field experiments were used to test the effect of site (tidal elevation), local bivalve density, and their interaction on growth and survivorship of three species of suspension-feeding bivalves. Survivorship was high and did not vary significantly with site or local density. Individual growth was generally lower at higher density for both AnomaZocardia squamosus and Circe lenticularis, but growth of CaZZista impar never responded significantly to local density. Site effects on individual growth were far stronger than density effects and operated on all three species: growth at the intertidal site was substantially lower than at the subtidal site. The intensity of the site effect on individual growth about doubled from the first (February-June) to the second (June-December) experimental interval, probably because average daily exposure to air also doubled. Despite the success of tidal exposure in explaining seasonal variation in growth differences between sites, at a given season clams at the intertidal site grew substantially less than predicted from duration of aerial exposure and density. We hypothesize that density effects estimated locally within 1 -m2 areas fail to assess the full magnitude of food depletion that occurs over broader scales and that suspension feeders low on the flat deplete suspended foods in incoming tidal flows before they ever reach clams at higher elevations.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1987.32.1.0143

Resource depletion by active suspension feeders on tidal fiats: Influence of local density and tidal elevation1

Three aspects of the study of effects of pollution in marine systems are discussed. First is the evaluation of relative sensitivities and reliabilities of different methods of detecting pollution, includ~ng a brief contrast of processes operating in mesocosms and in the field. Second is the problem of interpretation of pollution, i e determining the importance of the observed effects of pollution to the biological system. Species selected for detecting pollution may not provide useful information about the econoinic effects on explo~ted parts of natural systems, nor about trophic structure of a community, nor about future sizes of populations of important species. The choice of appropriate species a s indicators or detectors of pollution also requires determination of how representative they are of other species likely to be affected by pollution. Finally, there is the problem of prediction of future consequences of pollution. Some methods used to detect pollutants might be useful a s early warnings of future deleterious effects, although the usefulness of these measures may be lessened by the decoupling of reproductive rates of many marine invertebrates from the eventual recruitment to adult populations. Other measures such as patterns in whole assemblages of species can usually only detect pollutants after sufficient time has elapsed for populations to have changed. Nevertheless, these offer more direct measurements of the importance of pollution to the continued functional well-being of the system. A mixture of different types of measures allows the best synthesis of predictive power while providing the most useful information for interpretation of the consequences of pollution to a marine system. INTRODUCTION: THE RATIONALE FOR STUDIES OF POLLUTION IN THE SEA The need to identify sensitive, robust and repeatable methods for detecting marine pollutants is widespread. Their practical use in field situations is usually stimulated by evidence that some putative pollutant has entered, or is entering, a biological system. The evidence is usually chemical, but it might be casual observation or public opinion. The first step in a study of pollution is therefore to test, formally, the null hypothesis that there is no pattern of difference among samples (using any appropriately chosen biological variable) that is correlated with the known amounts of putative pollutants. This requires den~onstration of 2 different things. First, there must be differences among samples and, second, the patterns of difference must be correlated with concentrations of pollutants (and not some other environmental variables). The methods investigated in the GEEP Workshop were all designed to test this null hypothesis, with varying degrees of sophistication, precision, power and cost. Formally, the correlation established in rejecting this null hypothesis should be demonstrably causal. Where possible, this will best be achieved by some comparison of experimentally polluted sites with control, unpolluted samples. Ideally, this would be done in a properly controlled and replicated field experiment to remove interference from naturally confounding variables (or in suitable laboratory conditions such as the Solbergstrand mesocosms; see Bakke et al. 1988, Warwick et al. 1988, and other papers in this MEPS SPECIAL). Alternatively, prior knowledge of well-established causal links between pollutants and their known effects would suffice to demonstrate that pollutants caused the observed dfferences. For most of this workshop, the causal relationship was considered as though it had been demonstrated. One synthetic aim of the GEEP Workshop was to evaluate various techniques to determine which are the O Inter-Research/Printed in F. R. Germany 228 GEEP WORKSHOP. CONCLUSIONS most reliable, sensitive and cost-effective. This paper is primarily concerned with the subsequent procedures those used after the initial null hypotheses have been rejected, and there is no doubt that polluti.on is causing some measured biological response. Four different, but related, ecological research programmes become appropriate, although not all are directly relevant to the aims of the workshop, and not all will be discussed here. A suggested framework for investigations of existing pollution is illustrated in Fig. 1. One important area of research (EXPLANATION) is to determine why a particular method for detecting pollution works. What processes at the level of a community, population, individual organism, organ system, tissue, etc., actually cause the measured response? What is the action of polluting chemicals that leads to a detectable change in the biology of affected organisms? This area of research will not be directly discussed here. It is, however, important because, without P e r G = problem l Pollutal?rs enter the system -1 I 1 Step I: Is rhere a response to pollutron by the system? I Null Hypothesis 1: There is no temporal change lnor SpatIal pattern of var~ationl In any chosen biological var iab le that might he attributable to the pollutants 1 Test: By any of the methods used In the :EFP Workshop I Retaln null Tnere Is no problem 1 Step 2 : 1% t;;dr~~y;~;ea~;~;a;~;i;;;~?rhe p01 luranc

/pdf/towards-an-ecological-framework-for-investigating-pollution-1ouykfmvun.pdf

Towards an ecological framework for investigating pollution

Rapid population growth and coastal development are primary drivers of marine habitat degradation. Although shoreline hardening or armoring (the addition of concrete structures such as seawalls, jetties, and groins), a byproduct of development, can accelerate erosion and loss of beaches and tidal wetlands, it is a common practice globally. Here, we provide the first estimate of shoreline hardening along US Pacific, Atlantic, and Gulf of Mexico coasts and predict where future armoring may result in tidal wetland loss if coastal management practices remain unchanged. Our analysis indicates that 22 842 km of continental US shoreline – approximately 14% of the total US coastline – has been armored. We also consider how socioeconomic and physical factors relate to the pervasiveness of shoreline armoring and show that housing density, gross domestic product, storms, and wave height are positively correlated with hardening. Over 50% of South Atlantic and Gulf of Mexico coasts are fringed with tidal wetlands that...

Engineering away our natural defenses: an analysis of shoreline hardening in the US

Preliminary review of adaptation options for climate-sensitive ecosystems and resources. A report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research

In 57 l-m2 samples within a meadow of Halodule wrightii in Bogue Sound, North Carolina, USA, densities of the clams Mercenaria mercenaria and Chione cancellata were positively associated with seagrass cover. Where seagrass was experimentally removed, marked individuals of both clam species exhibited high rates of mortality in fine sand sediments during two successive experiments spanning 13 months. In the unaltered (control) seagrass meadow, M. mercenaria density remained constant over 13 months and C. cancellata density declined at a slower rate than in the unvegetated plots. Seagrass provides these clams with a refuge from whelk (Busycon carica, B. contrarium, and B. canaliculatum) predation, the major cause of mortality and population decline in experimentally unvegetated plots. In 2 factorial field experiments in unvegetated substratum in which densities of M. mercenaria and C. cancellata were varied independently, first over 5 levels (0 X, 1/2X, 1 X, 2 X, 4 X) and subsequently over 4 levels (0 X, 1/4 X, 1 X, 4 X), there was no repeatable intra- or interspecific effect of density on percent survival, or on the rate of any mortality type. Whelk predation fell preferentially on larger size classes of both species, whereas factors which contribute to clam disappearance usually acted more intensely on smaller sizes. Experimental exclusion of large predators by caging demonstrated that even in unvegetated substratum survivorship of both clam species was high in the absence of whelks and other predators. Individuals of C. cancellata live closer to the sediment surface than those of M. mercenaria, which may explain why seagrass does not serve as effectively to protect them from whelk predation. The mechanism of whelk inhibition may depend upon sediment binding by the H. wrightii root mat, which produces a demonstrable decrease in the physical penetrability of surface sediments.

Charles H. Peterson

Papers

Resource depletion by active suspension feeders on tidal fiats: Influence of local density and tidal elevation1

Towards an ecological framework for investigating pollution

Engineering away our natural defenses: an analysis of shoreline hardening in the US

Preliminary review of adaptation options for climate-sensitive ecosystems and resources. A report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research

Clam predation by whelks (Busycon spp.): Experimental tests of the importance of prey size, prey density, and seagrass cover