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

Humans are altering the composition of biological communities through a variety of activities that increase rates of species invasions and species extinctions, at all scales, from local to global. These changes in components of the Earth's biodiversity cause concern for ethical and aesthetic reasons, but they also have a strong potential to alter ecosystem properties and the goods and services they provide to humanity. Ecological experiments, observations, and theoretical developments show that ecosystem properties depend greatly on biodiversity in terms of the functional characteristics of organisms present in the ecosystem and the distribution and abundance of those organisms over space and time. Species effects act in concert with the effects of climate, resource availability, and disturbance regimes in influencing ecosystem properties. Human activities can modify all of the above factors; here we focus on modification of these biotic controls. The scientific community has come to a broad consensus on many aspects of the re- lationship between biodiversity and ecosystem functioning, including many points relevant to management of ecosystems. Further progress will require integration of knowledge about biotic and abiotic controls on ecosystem properties, how ecological communities are struc- tured, and the forces driving species extinctions and invasions. To strengthen links to policy and management, we also need to integrate our ecological knowledge with understanding of the social and economic constraints of potential management practices. Understanding this complexity, while taking strong steps to minimize current losses of species, is necessary for responsible management of Earth's ecosystems and the diverse biota they contain.

/pdf/effects-of-biodiversity-on-ecosystem-functioning-a-consensus-13j8vabcus.pdf

Effects of biodiversity on ecosystem functioning: a consensus of current knowledge

The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. 
The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. 
The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. 
The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

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Modern Applied Statistics With S

Summary


1. In species-habitat models, curves describing the changes in correlation strength between habitat cover and species occurrence over a continuum of spatial scales tend to be hump-shaped, and the correlation maximum is generally assumed to indicate the ecologically most meaningful scale of habitat influence on the species. This approach does not take account of the fact that distant habitat is overrated by increasing area with larger buffer sizes whilst habitat influence decays with distance. We devised four levels of distance weighting, down-weighting more distant habitat with increasing realism.



2. We analysed correlation strength across scale (200 m − 50 km) in simulations assuming a Gaussian distance kernel of habitat influence and in empirical data for Eurasian lynx (Lynx lynx) covering Central Europe. Regressions were run with the four levels of distance weighting.



3. Both in the simulated data and the empirical data distance weighting transformed humped correlation curves into saturation curves with high correlations at large scales, thereby eliminating a well-defined correlation maximum.



4. We argue that saturation curves naturally reflect the integration of habitat influence over increasing buffer areas. We conclude that without distance weighting, the correlation strength between habitat cover and species occurrence is prone to misinterpretation. We present two approaches to implementing distance weighting in species-habitat regressions.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/j.2041-210X.2011.00130.x

Distance weighting avoids erroneous scale effects in species‐habitat models

How do soil fauna and soil microbiota respond to beech forest growth

Unlike rare or specialised species, widespread abundant species have often been neglected when studying effects of habitat fragmentation. However, recently, it was shown that in the widespread abundant bush cricket Pholidoptera griseoaptera gene flow becomes restricted when the share of suitable habitat dropped below a threshold of 20% at the landscape scale. Here, using the same highly fragmented landscape, we studied the impact of habitat configuration and matrix quality on genetic variation and population differentiation of P. griseoaptera at a small spatial scale. We investigated four clusters of three populations that were either disconnected or connected and had either low quality (arable land) or high quality (grassland) matrix. The number of alleles was significantly lower in disconnected than in connected clusters, irrespective of matrix quality. Genetic differentiation was equally high in the two disconnected clusters and in the connected cluster with low quality matrix (G
 ST ≥ 0.030; D ≥ 0.082), whereas it was significantly reduced when connected habitats were embedded in a high quality grassland matrix (G
 ST = 0.004; D = 0.011). Analyses of least-cost paths showed that grassy landscape elements in fact represent high quality matrix, but that linear grassy margins are costly for dispersal. The effect of habitat configuration on genetic diversity may be explained by lower effective population sizes in disconnected habitats. The fact that only the connected populations in high quality matrix were not differentiated indicates that landscape management should simultaneously consider habitat configuration and matrix quality to effectively promote small and dispersal-limited species, also at small spatial scales.

Matrix quality and habitat configuration interactively determine functional connectivity in a widespread bush cricket at a small spatial scale

Studies on earthworms in rice-based ecosystems tend to focus on some pest species, while the potential of these important soil engineers for beneficially affecting carbon storage and cycling is widely ignored. We carried out a microcosm experiment to quantify the impact of the tropical earthworm Pheretima sp. on the C turnover in paddy soils under different conditions of water saturation and N fertilization. The soil was sampled at the lowland farm of the International Rice Research Institute (Philippines). In the absence of earthworms, soil respiration showed a distinct hump-shaped maximum at intermediate levels of water saturation (4-fold higher than in hand-dry soil) and increased 1.5-fold with increasing amounts of N fertilization. Amounts of CH 4 emitted, in contrast, were small at low to moderate soil humidity and became very high under conditions of water saturation (80-fold higher than hand-dry soil). No response to nitrogen addition was observed. Earthworms suppressed both the respiration maximum at intermediate saturation levels (by a factor of 1.4) and the stimulating impact of N fertilization (1.7-fold at maximum fertilizer level). On the other hand, earthworms strongly increased CH 4 release under conditions of high water saturation (3-fold). No consistent response of the soil microflora (bacterial abundance, soil enzymes) to earthworm activity could be established. Our findings suggest that the stabilization of soil organic C via earthworm bioturbation is confined to the range of soil humidity that allows high activity of Pheretima sp. Under conditions of intensive agriculture, the stabilizing effect of the worms may even be augmented by the fact that they offset the positive effect of N fertilization on microbial respiration. Earthworms may thus play a vital role in reducing the CO 2 flush from paddy soils after the conversion to non-flooded crops such as aerobic rice or maize. Acceleration of methane emission in very humid soils nevertheless points to a certain risk that is associated with increasing earthworm abundance in production systems that are still exposed to temporary flooding during the wet season.

Earthworm bioturbation stabilizes carbon in non-flooded paddy soil at the risk of increasing methane emissions under wet soil conditions

Spatial distributions of trophic interactions define the spatial heterogeneity of food webs and differences between local and macroecological food webs. The concept of co-occurrence has to be given up when larger spatial scales are considered that integrate different local community food webs into a metacommunity food web. This chapter provides two examples. First, some large-bodied predators are too low in numerical abundance to invade all local community food webs simultaneously. Second, not all potential resource species in a metacommunity can persist under strong top-down pressure by their consumer species and thus avoid coexistence in the same local communities. Food webs consist of organisms that vary in their taxonomic identity, body size, trophic interactions, and trophic position and thus might have very different spatial scales of interactions. Recognition of the importance of spatial scale in food web studies has several implications for food web theory. In particular, the potential food webs that are frequently described by ecologists will often differ from how food webs are realized in actual space and time. Clearly, choosing the right spatio-temporal scale for a food web study depends on the species studied and the study objective. Integrating spatial processes such as extinction and colonization by dispersal in food web models is an important step towards understanding population dynamics in complex communities, and understanding the consequences of habitat loss for the community structure and food web dynamics.

Volkmar Wolters

Papers

Distance weighting avoids erroneous scale effects in species‐habitat models

How do soil fauna and soil microbiota respond to beech forest growth

Matrix quality and habitat configuration interactively determine functional connectivity in a widespread bush cricket at a small spatial scale

Earthworm bioturbation stabilizes carbon in non-flooded paddy soil at the risk of increasing methane emissions under wet soil conditions

Spatial Aspects of Food Webs