浅析物种概念的演变历史

本文是一篇关于物种概念演变的简述。生物学家用不同的方法或标准划分物种, 就形成了不同的物种概念, 如生物学物种、形态学物种、生态学物种、进化物种、系统发生或支序物种, 或它们的组合, 等等。它们都揭示了物种属性的特定侧面, 都是不同物种客观存在的真实反映, 但都无法令所有人满意。对真核生物来说, 无论它们在形态上的差别有多大, 生殖隔离(不能产生可育的后代)应该是两个群体能否真正分化成不同物种的关键, 这种隔离机制可以是地理的、行为的或其他方式; 而生殖隔离总会伴随着一些形态或遗传上的变化, 虽然这些特征可能与生殖隔离本身并无多大关系, 但往往成为分类学家或分子进化生物学家区分种的依据,对已经灭绝的化石物种来说, 生殖隔离的物种划分方式就无能为力了。如何准确定义一个物种依然充满着矛盾, 因为基于生殖隔离的物种概念不实用, 而实用的物种概念(如形态学物种)又被认为是人为的。     

The number of species of rodent coccidia and of other protozoa

About 447 species of coccidia have been named from the 1687 living, known species of rodents; 207 host species, 92 host genera, and 15 host families are represented; this is about 12% of the known species of rodents. About 4600 species of apicomplexan protozoa have been named. Assuming that the same proportion of the total number of apicomplexan species has been named as of the coccidian species, there must actually be about 38,333 species of apicomplexan protozoa. There are 5.4 times as many protozoan genera as of apicomplexan genera. Assuming that the number of species in each genus is the same for all the protozoa as it is for the Apicomplexa, there may actually be 206,998 species of protozoa. This may be too conservative an estimate. Based on other criteria, an estimate of over 20 million species could be made.     

Introduction of a Brachylaima species (Digenea: Brachylaimidae) to Australia

A Brachylaima species recorded previously from the house mouse (Mus domesticus) in South Australia is shown to use the introduced European snails Cernuella virgata and Cochlicella barbara as first intermediate hosts, and the same two species and Theba pisana as second intermediate hosts. The life cycle is typical of Brachylaima species. The parasite is capable of infecting at least two species of native Australian rodent, Rattus fuscipes and Leporillus conditor. Because of the intermediate hosts used, it is hypothesized that this trematode species has been introduced from Europe. The parasite may be conspecific with one of a number of described European species but difficulties with the literature concerning these species have required that the present form be designated only as Brachylaima sp.     

Species and paleoanthropology

The biotic world is self-evidently “packaged” into units, of which the most basic is the species. It is necessary to develop an accurate understanding of what species are and how they are to be identified before we can proceed to more complex analyses of the evolutionary histories and relationships of extinct and extant taxa at all levels of the systematic hierarchy. In this article, we review the major species concepts current today among paleoanthropologists, and examine the limitations of their applicability to practical studies of extant and extinct faunas. The primary such limitation for paleoanthropologists is the fact that all major species definitions stress reproductive continuity (whether by exclusionary or inclusionary mechanisms), a quality that is inferential at best among forms known only as fossils (and, in many cases, in the extant fauna as well). The only reliable signal as to species status in the fossil record is morphology, yet speciation carries with it no specifiable quantity of morphological innovation. Some groups with autapomorphies are not species, and some species do not bear autapomorphies. How, then, are we to recognize species in the hominid and other fossil records? Noting that osteodental differences among congeneric primate species tend to be subtle, and that when consistent identifiable “morphs” can be found at least as many species are present, we recommend equating morphs based on several characters with species—realizing that only one or two distinctive characters may not make a morph. In this way, our views of the phylogenetic histories of higher taxa may be oversimplified, but their essential patterns will not be distorted.     

Cryopreservation of gametes and embryos of non-domestic species.

Many species of mammals are threatened or endangered. Methods of assisted reproduction that are being used with increasing frequency to produce offspring of domestic animals and humans are often viewed as offering innovative ways to reproduce non-domestic species as well. Uncounted millions of live young of domestic or laboratory species have been produced from gametes and embryos stored at -70 degrees C or below, sometimes for as long as 25 to 35 yrs. Such methods of cryopreservation are now being applied with increasing frequency and urgency to preserve gametes and embryos of non-domestic and threatened species to establish "genome resource banks" or "frozen zoos." But levels of success to produce live young from such cryopreserved gametes or embryos vary considerably from species to species, as well as from individual to individual. It is sometimes thought that differences among species in fundamental characteristics of their gametes may determine the efficacy of cryopreservation and the production of live young. However, it may not be that ineffective cryopreservation is responsible for low success rates. Rather, the limiting factor may be insufficient information and knowledge of the most basic reproductive biology of such non-domestic species. Even standard methods of cryopreservation may be completely adequate to act as a "temporary" expedient to preserve germplasm of non-domestic species to permit time to acquire a fuller understanding of the biology and behavior of non-domestic species.     

Generalizations and kinds in natural science: the case of species

Species in biology are traditionally perceived as kinds of organisms about which explanatory and predictive generalizations can be made, and biologists commonly use species in this manner. This perception of species is, however, in stark contrast with the currently accepted view that species are not kinds or classes at all, but individuals. In this paper I investigate the conditions under which the two views of species might be held simultaneously. Specifically, I ask whether upon acceptance of an ontology of species as diachronic segments of the tree of life (this is one version of the species as individuals ontology) species can perform the epistemic role of kinds of organisms to which explanatory and predictive generalizations apply. I show that, for species-level segments of the tree of life, several requirements have to be met before the performance of this epistemic role is possible, and I argue that these requirements can be met by defining species according to the Composite Species Concept proposed by Kornet and McAllister in the 1990s.     

How weird can mimicry get?

Classical mimicry theory distinguishes clearly between the mutualistic resemblance between two or more defended species (muellerian mimicry), and the parasitic resemblance of a palatable species to a defended species (batesian mimicry). Modelling the behaviour of predators, without initially taking ecological complications into account, is a good strategy for exploring whether this division is valid. Two such behavioural models are described: conditioning theory, which simulates changes in motivational attack levels according to the norms of current learning theory; and saturation theory, which considers how a predator may become saturated with a particular toxic compound, and then cease feeding on the prey species that delivers it. This effect is to be clearly distinguished from simple satiation. Most formulations of the conditioning model allow the direction of reinforcement produced by a particular prey to change according the predator's current state of motivation: this leads to the existence of quasi-batesian mimicry, a parasitic mimicry between two species that could both be described as defended. At high densities, two prey species that share a chemical defense will be ‘muellerian mutualists’, mutually protecting each other against predators that have been saturated with the defensive compound. This mutualism may be accompanied by true muellerian mimicry of the colour patterns, or the patterns may be completely different. This can therefore be regarded as a form of mimicry in a non-visual communication channel. Even an apparently palatable prey species may be effectively unavailable to predators if its density is such as to deliver a particular nutrient in excess of the predator's need for a balanced diet. Such a nutrient in effect becomes a toxin, and such an abundant prey species would be partly defended and potentially able to act as the model in a mimicry system. Thus there might be protective mimicry between ‘palatable’ species, and a ‘palatable’ species might even function as the model for a ‘defended’ mimic. These unorthodox kinds of mimicry probably exist transiently during fluctuations of prey populations. It is less likely that these conditions persist for long enough to induce the evolution of mimicry, and the relationships perhaps usually occur when mimicry already exists for other reasons. Mimicry rings may be mutually stabilised by a combination of toxic mutualism and the exchange of species between the rings. Colour polymorphism in a defended species is strictly neutral whenever the population is dense enough to saturate the predator. This, as well as quasi-batesian mimicry, may help to explain the minority of warningly coloured species that are polymorphic. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Golden-spectacled Warbler: a complex of sibling species, including a previously undescribed species

The Golden-spectacled Warbler, usually treated as a single species, Seicercus burkii , is widely distributed in mountains of southern Asia. We argue that it should be treated as five different species, one of which is described here for the first time. Two species occur in sympatry in the Himalayas. The other three species are found in eastern Asia, where all three are sympatric in China, and two of these breed sympatrically also in Vietnam. In Burma and adjacent parts of India, one of the Himalayan species is sympatric with one of the east Asian species. We describe differences in morphology, vocalizations, altitudinal distribution and habitat between these five species, as well as results from playback tests, which show that all sympatric taxa differ and appear to be reproductively isolated from each other.     

Correlation between richness per unit area and the species pool cannot be used to demonstrate the species pool effect

Abstract. Significant correlation between the size of the species pool and richness per unit area is usually taken as a demonstration of the effect of the species pool on the species richness per unit area. This is not logically necessary. It has to be emphasized that such a correlation cannot be interpreted as a demonstration of the effect of species pool on the species richness per unit area. More generally, correlation cannot be used to demonstrate a one‐directional effect of one variable upon another, since several types of (functional) relationships could produce correlations between such variables; the same caution has to be taken when analysing the species pool vs. richness per unit area correlation. In this paper, a simple Monte Carlo simulation model is used to demonstrate that (1) statistical processes acting only at the local scale (such as competitive exclusion) can generate exactly the same correlation that has been used to infer the effect of the species pool on richness per unit area; (2) this correlation would be deemed significant even if the mathematical dependency between species pool and richness per unit area is taken into account; and (3) the strength of this relation depends on beta diversity within the contiguous area used to determine the species pool.     

Are species sets?

I construe the question ‘Are species sets?’ as a question about whether species can be conceived of as sets, as the term ‘set’ is understood by contemporary logicians. The question is distinct from the question ‘Are species classes?’: The conception of classes invoked by Hull and others differs from the logician's conception of a set. I argue that species can be conceived of as sets, insofar as one could identify a set with any given species and that identification would satisfy three desiderata: the set would be a set of organisms, the identification would be apposite, and the identification would permit the formulation of statements about species in set-theoretic terms. One cannot, however, identify a species with any given set. Understanding the claim that species are sets in this way enables one to understand better the dispute between some who accept the claim (e.g., Kitcher 1984, 1987) and some who apparently reject it (e.g., Mayr 1987).     

Osmoderma eremita as an indicator of species richness of beetles in tree hollows

The beetle Osmoderma eremita has received much attention in the last few years, as it is among those species with the highest priority in the European Union's Habitat Directive. In this paper the species is evaluated as a potential indicator and umbrella species for the endangered beetle fauna in tree hollows. To be useful as an indicator of a species-rich fauna it should be easy to inventory and be strongly correlated with the presence of other species. An umbrella species is a species which is so demanding that the protection of this species will automatically save many others. The species richness of saproxylic beetles and occupancy of O. eremita were surveyed in tree hollows in an area in southeastern Sweden by assessing the presence/absence of living and dead adults (including fragments) and larvae. The species richness was higher when O. eremita was present, both at tree and stand level. Several threatened species were associated with the presence of O. eremita, whereas others did not correlate with the occurrence of O. eremita. As O. eremita is easy to find and identify, it is useful as an indicator of stands with a rich beetle fauna in tree hollows. Osmoderma eremita can be used as an umbrella species, because if measures are taken to conserve O. eremita, many other species in the same habitat are also conserved. However, there are some beetles in tree hollows which seem to be more sensitive to habitat fragmentation than O. eremita, and may go extinct if only O. eremita is taken into consideration.     

Buffon, Darwin, and the Non-Individuality of Species – A Reply to Jean Gayon

Gayon's recent claim that Buffon developed a concept of species as physical individuals is critically examined and rejected. Also critically examined and rejected is Gayon's more central thesis that as a consequence of his analysis of Buffon's species concept, and also of Darwin's species concept, it is clear that modern evolutionary theory does not require species to be physical individuals. While I agree with Gayon's conclusion that modern evolutionary theory does not require species to be physical individuals, I disagree with his reasons and instead provide logical rather than historical reasons for the same conclusion.     

Phylogenetic skew: an index of community diversity

The distribution of divergence times between member species of a community reflects the pattern of species composition. In this study, we contrast the species composition of a community against the meta‐community, which we define as the species composition of a set of target communities. We regard the collection of species that comprise a community as a sample from the set of member species of the meta‐community, and interpret the pattern of the community species composition in terms of the type of species sampled from the meta‐community. A newly defined effective species sampling proportion explains the amount of the difference between the divergence time distributions of the community and that of the meta‐community, assuming random sampling. We propose a new index of phylogenetic skew (PS), as the ratio of the maximum‐likelihood estimate of the effective species sampling proportion to the observed sampling proportion. A PS value of 1 is interpreted as random sampling. If the value is >1, the sampling is suspected to be phylogenetically skewed. If it is <1, systematic thinning of species is likely. Unlike other indices, the PS does not depend on species richness as long as the community has more than a few members of a species. Because it is possible to compare partially observed communities, the index may be effectively used in exploratory analysis to detect candidate communities with unique species compositions from a large number of communities.     

The factors controlling species density in herbaceous plant communities: an assessment

This paper evaluates both the ideas and empirical evidence pertaining to the control of species density in herbaceous plant communities. While most theoretical discussions of species density have emphasized the importance of habitat productivity and disturbance regimes, many other factors (e.g. species pools, plant litter accumulation, plant morphology) have been proposed to be important. A review of literature presenting observations on the density of species in small plots (in the vicinity of a few square meters or less), as well as experimental studies, suggests several generalizations: (1) Available data are consistent with an underlying unimodal relationship between species density and total community biomass. While variance in species density is often poorly explained by predictor variables, there is strong evidence that high levels of community biomass are antagonistic to high species density. (2) Community biomass is just one of several factors affecting variations in species density. Multivariate analyses typically explain more than twice as much variance in species density as can be explained by community biomass alone. (3) Disturbance has important and sometimes complex effects on species density. In general, the evidence is consistent with the intermediate disturbance hypothesis but exceptions exist and effects can be complex. (4) Gradients in the species pool can have important influences on patterns of species density. Evidence is mounting that a considerable amount of the observed variability in species density within a landscape or region may result from environmental effects on the species pool. (5) Several additional factors deserve greater consideration, including time lags, species composition, plant morphology, plant density and soil microbial effects.Based on the available evidence, a conceptual model of the primary factors controlling species density is presented here. This model suggests that species density is controlled by the effects of disturbance, total community biomass, colonization, the species pool and spatial heterogeneity. The structure of the model leads to two main expectations: (1) while community biomass is important, multivariate approaches will be required to understand patterns of variation in species density, and (2) species density will be more highly correlated with light penetration to the soil surface, than with above-ground biomass, and even less well correlated with plant growth rates (productivity) or habitat fertility. At present, data are insufficient to evaluate the relative importance of the processes controlling species density. Much more work is needed if we are to adequately predict the effects of environmental changes on plant communities and species diversity.     

Species-specific markers for early detection of marine invertebrate invaders through eDNA methods: Gaps and priorities in GenBank as database example

Non-indigenous species (NIS) invasions are global phenomena that are the main drivers for ecosystem change and can often drastically affect the structure and function of novel ecosystems. Early detection is of prime importance for preventing the establishment and potential dispersal of NIS, making eradication and control more efficient and less costly since the species is present at very low densities. However, species at low density generally require intensive sampling efforts to be detected.An important shortcut to reduce sampling effort is to analyze environmental DNA (eDNA). Eukaryotic organisms leave traces of their presence in the environment where they live. In environments that are difficult to access, such as aquatic environments, DNA present in the water can be extracted and amplified using PCR target markers to identify the species that inhabit therein. Using species-specific markers, the presence of target species’ DNA from water samples can be detected using PCR and simple electrophoresis in agarose gel. This is an efficient and convenient approach when the target species is known that puts the focus on detection. However, a critical challenge of this methodology is the design of appropriate species-specific markers. They must be specific to one target species, without any cross-amplification even in close species. For this purpose, a DNA database with as many different species, genetic markers and haplotypes as possible is essential for genetic marker design. The principal aim of this work is to analyze the state-of-the-art of the databases, in this case GenBank, which is the most complete database in number of markers and species, in order to assess its utility in the design of species-specific primers for invasive species early detection.     

Phlebotomine vectors of the leishmaniases: a review

ABSTRACT. An account is given of work published during the past 10 years incriminating species of phlebotomine sandflies as vectors of Leishmania species which infect man.
An assessment is made of the degrees of certainty of the vectorial roles of eighty-one species and subspecies of sandflies (thirty-seven Old World and forty-four New World) in the transmission of twenty-nine leishmanial parasites of mammals. At least one species of sandfly is considered to be a proven vector of each of ten parasites.
Of the eighty-one sandfly taxa, evidence is judged to be sufficient to incriminate nineteen as proven vectors (eleven Phlebotomus species and eight Lutzomyia species or subspecies) and evidence for a further fourteen (nine Phlebotomus species and five Lutzomyia species or subspecies) is considered to be strong.
The suggested criteria for incrimination of a vector are anthropophily and common infection with the same leishmanial parasite as that found in man in the same place. More weight should be given to natural infections persisting after the digestion of a bloodmeal than those in the presence of blood. Supporting evidence is a concordance in the distribution of the fly and the disease in man, proof that the fly feeds regularly on the reservoir host, a flourishing development of the parasite in infected flies and the experimental transmission of the parasite by the bite of the fly.     

The roles of ecological and behavioral observation in species recognition among primates

Closely related living mammal species present numerous difficulties of recognition and delineation, not least because populations as well as individual organisms fulfill both genetic and economic functions. However, since species are often distributed geographically across multiple ecosystems or environments, it is evident that species as wholes, except where coterminous with the local populations of which they are composed, cannot be said to play unitary ecological roles. Aspects of the economic activity of organisms thus may not be admitted as elements in species recognition. Those who study the behavior of mammals in their natural habitats must therefore focus upon behaviors which preserve the genetic integrity of species if they wish to contribute to the systematic question of species identification. «Isolation» concepts of species are not served by data of this kind, since they emphasize interspecies discontinuities; the «recognition» concept of species, however, specifically focuses upon behaviors of this kind as they contribute to the «Specific-Mate Recognition System». Among primates such behaviors are likely to involve signalling of various kinds; where this is visual it is reasonable to expect to find morphological or chromatic correlates; where such cues are auditory or, to a lesser extent, olfactory, it is less probable that such correlates will be found to exist.