Edge effects and the extinction of populations inside protected areas

Theory predicts that small populations may be driven to extinction by random fluctuations in demography and loss of genetic diversity through drift. However, population size is a poor predictor of extinction in large carnivores inhabiting protected areas. Conflict with people on reserve borders is the major cause of mortality in such populations, so that border areas represent population sinks. The species most likely to disappear from small reserves are those that range widely-and are therefore most exposed to threats on reserve borders-irrespective of population size. Conservation efforts that combat only stochastic processes are therefore unlikely to avert extinction.     

One-third of reef-building corals face elevated extinction risk from climate change and local impacts

The conservation status of 845 zooxanthellate reef-building coral species was assessed by using International Union for Conservation of Nature Red List Criteria. Of the 704 species that could be assigned conservation status, 32.8% are in categories with elevated risk of extinction. Declines in abundance are associated with bleaching and diseases driven by elevated sea surface temperatures, with extinction risk further exacerbated by local-scale anthropogenic disturbances. The proportion of corals threatened with extinction has increased dramatically in recent decades and exceeds that of most terrestrial groups. The Caribbean has the largest proportion of corals in high extinction risk categories, whereas the Coral Triangle (western Pacific) has the highest proportion of species in all categories of elevated extinction risk. Our results emphasize the widespread plight of coral reefs and the urgent need to enact conservation measures.     

Extinction and ecosystem function in the marine benthos

Rapid changes in biodiversity are occurring globally, yet the ecological impacts of diversity loss are poorly understood. Here we use data from marine invertebrate communities to parameterize models that predict how extinctions will affect sediment bioturbation, a process vital to the persistence of aquatic communities. We show that species extinction is generally expected to reduce bioturbation, but the magnitude of reduction depends on how the functional traits of individual species covary with their risk of extinction. As a result, the particular cause of extinction and the order in which species are lost ultimately govern the ecosystem-level consequences of biodiversity loss.     

Selectivity of end-Cretaceous marine bivalve extinctions

Analyses of the end-Cretaceous or Cretaceous-Tertiary mass extinction show no selectivity of marine bivalve genera by life position (burrowing versus exposed), body size, bathymetric position on the continental shelf, or relative breadth of bathymetric range. Deposit-feeders as a group have significantly lower extinction intensities than suspension-feeders, but this pattern is due entirely to low extinction in two groups (Nuculoida and Lucinoidea), which suggests that survivorship was not simply linked to feeding mode. Geographically widespread genera have significantly lower extinction intensities than narrowly distributed genera. These results corroborate earlier work suggesting that some biotic factors that enhance survivorship during times of lesser extinction intensities are ineffectual during mass extinctions.     

延河流域植物功能性状变异来源分析

由于遗传背景对植物性状的影响,直接研究环境与植物性状的关系有一定的不确定性。因此,研究植物性状对环境变化的响应,必须明确遗传背景与环境对植物性状的相对影响,以排除遗传背景的作用。本研究以延河流域为研究区域,选取19个典型样点,调查了64种植物的6种功能性状,即比叶面积(SLA)、比根长(SRL)、叶片氮(LN)与磷含量(LP)、根的氮(RN)与磷含量(RP),并通过野外定位信息,从已有专题信息图中获取环境数据,采用方差分析和逐步回归的方法,分析了植物性状变异来源,研究了不同科属植物对环境变化的响应。结果表明：(1)不同气候条件下,植物的SLA、LN和RP性状存在显著差异,森林区植物SLA、RP较草原区植物偏低33.02%、19.94%,而LN则高于草原区植物19.33%;不同科属植物之间SLA、SRL、LN和RN存在显著差异,豆科植物具有较高的SLA、LN、RN,分别高出研究区平均值16.33%、65.23%、97.78%,而禾本科植物SRL具有最大值,高出平均值103.11%;(2)遗传背景差异是植物性状变异的首要决定因子,遗传背景对SRL、LN、RN变异的解释比例分别达到了27.86%、32.78%、42.70%,而LP、RP则受环境因子的影响更大,环境因子对LP、RP解释比例分别达到24%、15.58%;(3)豆科Leguminosae、禾本科Poaceae、菊科Asteraceae、蔷薇科Rosaceae植物性状的环境因子逐步线性回归模型,表明不同科属的植物对环境因子是否产生响应和响应的方式均不相同,豆科和禾本科植物对区域性气候条件较为敏感,而菊科和蔷薇科植物受地形因子和土壤含水量影响较大。     

Heritability at the species level: analysis of geographic ranges of cretaceous mollusks

Geographic range has been regarded as a property of species rather than of individuals and thus as a potential factor in macroevolutionary processes. Species durations in Late Cretaceous mollusks exhibit statistically significant positive relationships with geographic range, and the attainment of a typical frequency distribution of geographic ranges in the cohort of species that originated just before the end-Cretaceous extinction indicates that species duration is the dependent variable. The strong relation between geographic ranges in pairs of closely related species indicates that the trait is, in effect, heritable at the species level. The significant heritabilities strengthen claims for processes of evolution by species-level selection, and for differential survivorship of organismic-level traits owing to extinction and origination processes operating at higher levels.     

Genetics of growth predict patterns of brain-size evolution

Experimental evidence is presented supporting a developmental model that explains the genetic basis for brain and body size associations. Evolutionary change in body size causes correlated change in brain size because some genes affect both traits. The commonly observed correlation between brain and body size results from genetic variation in growth determinants affecting both traits simultaneously during fetal and early postnatal growth. Later growth reduces brain-body correlation because of changes in the underlying causal components of growth in each trait. Brain-body size evolution shows a different pattern at higher taxonomic levels from that seen within and between closely related species because body-size evolution among higher taxa occurs primarily by change in early portions of growth, which share more genetic growth determinants with brain size.     

Species selection maintains self-incompatibility

Identifying traits that affect rates of speciation and extinction and, hence, explain differences in species diversity among clades is a major goal of evolutionary biology. Detecting such traits is especially difficult when they undergo frequent transitions between states. Self-incompatibility, the ability of hermaphrodites to enforce outcrossing, is frequently lost in flowering plants, enabling self-fertilization. We show, however, that in the nightshade plant family (Solanaceae), species with functional self-incompatibility diversify at a significantly higher rate than those without it. The apparent short-term advantages of potentially self-fertilizing individuals are therefore offset by strong species selection, which favors obligate outcrossing.     

Background and mass extinctions: the alternation of macroevolutionary regimes

Comparison of evolutionary patterns among Late Cretaceous marine bivalves and gastropods during times of normal, background levels of extinction and during the end-Cretaceous mass extinction indicates that mass extinctions are neither an intensification of background patterns nor an entirely random culling of the biota. During background times, traits such as planktotrophic larval development, broad geographic range of constituent species, and high species richness enhanced survivorship of species and genera. In contrast, during the, end-Cretaceous and other mass extinctions these factors were ineffectual, but broad geographic deployment of an entire lineage, regardless of the ranges of its constituent species, enhanced survivorship. Large-scale evolutionary patterns are evidently shaped by the alternation of these two macroevolutionary regimes, with rare but important mass extinctions driving shifts in the composition of the biota that have little relation to success during the background regime. Lineages or adaptations can be lost during mass extinctions for reasons unrelated to their survival values for organisms or species during background times, and long-term success would require the chance occurrence within a single lineage of sets of traits conducive to survivorship under both regimes.     

Species interactions in a parasite community drive infection risk in a wildlife population

Most hosts, including humans, are simultaneously or sequentially infected with several parasites. A key question is whether patterns of coinfection arise because infection by one parasite species affects susceptibility to others or because of inherent differences between hosts. We used time-series data from individual hosts in natural populations to analyze patterns of infection risk for a microparasite community, detecting large positive and negative effects of other infections. Patterns remain once variations in host susceptibility and exposure are accounted for. Indeed, effects are typically of greater magnitude, and explain more variation in infection risk, than the effects associated with host and environmental factors more commonly considered in disease studies. We highlight the danger of mistaken inference when considering parasite species in isolation rather than parasite communities.     

扩散限制和环境筛选对子午岭森林群落构建的相对贡献

【目的】改善区域生态环境是促进农业生产、实现可持续发展的重要前提,而加强植被的恢复重建是改善生态环境的重要途径。本研究拟通过对黄土高原子午岭森林群落构建过程的研究,为该区的植被恢复重建提供理论依据。【方法】采用典范变异分解和Mantel检验两种互补的方法,通过分离环境因子/距离（度量环境筛选）和空间因子/距离（间接度量扩散限制）对群落物种组成/距离的相对贡献,确定环境筛选和扩散限制在该区植物群落构建中的相对重要性。【结果】不同群落类型间的物种组成差异显著,空间和环境因子共同解释了草本、灌木、乔木三层29%—65%的物种组成变异（P＜0.01）。而二者的贡献特点在不同层次有所差异,乔木层和灌木层主要以空间因子为主导;而在草本层中,空间和环境因子具有相似的贡献率。草本、灌木、乔木三层的物种非相似性距离与环境距离和地理距离都显著相关（P＜0.05）,草本层具有较大的环境距离相关系数,而灌木层和乔木层具有较大的地理距离相关系数。【结论】扩散限制和环境筛选相互作用,共同影响着黄土高原森林群落的构建过程。本研究的结果并没有否定环境筛选在黄土高原群落构建中的重要性,而是更加强调了扩散限制在该区的主导性。因此,在黄土高原森林群落的恢复重建中,应该同时考虑环境异质性和地理空间的差异性。     

Neotropical anachronisms: the fruits the gomphotheres ate

Frugivory by extinct horses, gomphotheres, ground sloths, and other Pleistocene megafauna offers a key to understanding certain plant reproductive traits in Central American lowland forests. When over 15 genera of Central American large herbivores became extinct roughly 10,000 years ago, seed dispersal and subsequent distributions of many plant species were altered. Introduction of horses and cattle may have in part restored the local ranges of such trees as jicaro (Crescentia alata) and guanacaste (Enterolobium cyclocarpum) that had large mammals as dispersal agents. Plant distributions in neotropical forest and grassland mixes that are moderately and patchily browsed by free-ranging livestock may be more like those before megafaunal extinction than were those present at the time of Spanish conquest.     

Cope's rule, hypercarnivory, and extinction in North American canids

Over the past 50 million years, successive clades of large carnivorous mammals diversified and then declined to extinction. In most instances, the cause of the decline remains a puzzle. Here we argue that energetic constraints and pervasive selection for larger size (Cope's rule) in carnivores lead to dietary specialization (hypercarnivory) and increased vulnerability to extinction. In two major clades of extinct North American canids, the evolution of large size was associated with a dietary shift to hypercarnivory and a decline in species durations. Thus, selection for attributes that promoted individual success resulted in progressive evolutionary failure of their clades.     

Trilobites and the origin of arthropods

While the question of whether the Arthropoda represent more than one phylum of animals is debatable, the jointed exoskeleton, a fundamental feature of arthropods, evolved independently in two groups that shared a worm-like common ancestor. The two major branches of Arthropoda, the primitively marine TCC and the primitively terrestrial (with one exception) Uniramia, independently arrived at arthropodization as the solution to the same problems of adaptation of the body mechanical system. New discoveries on trilobite anatomy show the unity of TCC as a group that shared a trilobite-like ancestor near the beginning of the Cambrian. With change in the constituency of Arthropoda through geologic time, the ways in which it would be categorized as a taxonomic group have also changed. The seeming isolation of the major modern arthropod groups is in large part an artifact of extinction of primitive intermediate forms such as trilobites which, in the Early Paleozoic, made the Arthropoda more diverse in basic modes of body organization than the group is at present. The appearance of fossilizable hard parts in arthropods resulted from shift in supporting function from the body cavity, primitively a hydrostatic skeleton, to the cuticle, which came to be strengthened in becoming an exoskeleton. Energetic efficiency, more than protection from predators or evolutionary size increase in itself, was probably the impetus behind the transition. On the scale provided by the general evolutionary trend toward progressive specialization of segments, TCC became arthropodized at earlier stages than did Uniramia. Among TCC, the shift may have been driven by the evolution of locomotory and feeding mechanisms that were exclusively geared to an aqueous medium.     

年龄、体重、体型及性别对健康犬骨量的影响

用钆－１５３双光子吸收法（ＤＰＡ）测定１２１只健康大、小型犬（其中大型犬７８只,小型犬４３只）的骨矿含量（ＢＭＣ）和骨密度（ＢＭＤ）。每只犬测量左右桡尺骨、肱骨、胫骨、股骨远端、腰椎（Ｌ－５或Ｌ－６,仅小型犬）、尾椎（Ｃ－７或Ｃ－８,仅大型犬）等１０个部位。结果表明,小型犬各部位骨量显著少于大型犬,两体型母犬骨量均比公犬低。经直线回归和多元回归分析,大、小型犬各部位骨量随年龄增长而下降,其中大型犬四肢骨量下降尤为明显。所有犬各部位骨量与体重呈显著正相关,小型犬每公斤体重的骨量增长率高于大型犬,两体型母犬骨量增长均低于公犬。结论：年龄、体重、体型和性别均是影响犬骨量的因素,其中体重和体型是主要因素,年龄对骨量亦产生一定作用。     

黄喉拟水龟母体大小对繁殖性能的影响

对黄喉拟水龟Mauremys mutica同一种群中3种规格（小型个体783.0 g±55.2 g、中型个体991.3 g±62.3 g和大型个体1248.5 g±122.9 g）母体的繁殖性能进行了研究。结果表明：在繁殖季节,不同规格母体的月产卵量差异较明显,其中小型母体在产卵期首月和末月产卵量所占比例相对较高;3种规格母体的平均产卵量、受精率和孵化率与母体的大小呈正相关,平均窝数与母体大小则呈负相关;窝卵数、卵重、卵宽也与母体规格呈正相关,其中窝卵数的差异极显著（P〈0.001）。在代表卵形状的卵长径与短径比值中,小规格母体产的卵略长,但差异不显著;大规格母体产的稚龟则显著大于小规格母体产的稚龟（P〈0.05）。本研究结果表明,以大规格母体作为繁殖亲本,可以获得更多的后代。     

初生仔马鹿体尺和体重的聚类与主成分分析

对55只初生仔马鹿的14个体尺性状指标进行聚类与主成分分析,结果表明,聚类与主成分分析的结果是一致的,都可以把14个性状指标根据相似性关系分为胸部因子、尻部因子、头部因子和尾部因子共4类,并根据累积贡献率和特征向量在信息含量表达式中的大小,选出体重、胸围、体斜长、体高、尻宽、头宽、尾长为代表性的性状指标.     

Morphological disparity of ammonoids and the mark of Permian mass extinctions

The taxonomic diversity of ammonoids, in terms of the number of taxa preserved, provides an incomplete picture of the extinction pattern during the Permian because of a strongly biased fossil record. The analysis of morphological disparity (the variety of shell shapes) is a powerful complementary tool for testing hypotheses about the selectivity of extinction and permits the recognition of three distinct patterns. First, a trend of decreasing disparity, ranging for about 30 million years, led to a minimum disparity immediately before the Permian-Triassic boundary. Second, the strongly selective Capitanian crisis fits a model of background extinction driven by standard environmental changes. Third, the end-Permian mass extinction operated as a random, nonselective sorting of morphologies, which is consistent with a catastrophic cause.     

横断山区湿地优势植物水葱种子繁殖性状对环境变化的响应

选择对环境变化较为敏感的横断山区纳帕海湿地、拉市海湿地以及滇池流域为采样地点,研究这些区域的湖滨带优势植物水葱(Schoenoplectus tabernaemontani)种子繁殖性状,包括穗长、小穗数、每穗种子产量、种长、种宽以及种长/种宽等指标对环境变化的响应及适应策略。结果显示:除种宽外,上述水葱种子繁殖性状在不同采样地点间均存在显著差异。逐步回归模型分析表明,年均气温和最暖月均气温的变化是影响水葱种子繁殖性状的主要原因,其中穗长主要受年均气温和最暖月均气温的共同影响,小穗数和种长主要受年均气温的影响,每穗种子产量和种长/种宽主要受最暖月均气温的影响,而种宽与本研究所有环境因子间的相关性均不显著。温度是影响横断山区湿地植物种子繁殖过程的重要环境因子,而降水和饱和大气压差对这一过程的影响相对较小。     

The aftermath of megafaunal extinction: ecosystem transformation in Pleistocene Australia

Giant vertebrates dominated many Pleistocene ecosystems. Many were herbivores, and their sudden extinction in prehistory could have had large ecological impacts. We used a high-resolution 130,000-year environmental record to help resolve the cause and reconstruct the ecological consequences of extinction of Australia's megafauna. Our results suggest that human arrival rather than climate caused megafaunal extinction, which then triggered replacement of mixed rainforest by sclerophyll vegetation through a combination of direct effects on vegetation of relaxed herbivore pressure and increased fire in the landscape. This ecosystem shift was as large as any effect of climate change over the last glacial cycle, and indicates the magnitude of changes that may have followed megafaunal extinction elsewhere in the world.