How many birds are there?

Attempts to assess the magnitude of global biodiversity have focused on estimating species richness. However, this is but one component of biodiversity, and others, such as numbers of individuals or biomass, are at least as poorly known and just as important to quantify. Here, we use a variety of methods to estimate the global number of individuals for a single taxon, birds. The different methods yield surprisingly consistent estimates of a global bird population of between 200 billion and 400 billion individuals (1 billion=109). We discuss some of the implications of this figure.     

How many species are there?

How many species are there is a question receiving more attention from biologists and reasons for this are suggested. Different methods of answering this question are examined and include: counting all species; extrapolations from known faunas and regions; extrapolations from samples; methods using ecological models; censusing taxonomists' views. Most of these methods indicate that global totals of 5 to 15 million species are reasonable. The implications of much higher estimates of 30 million species or more are examined, particularly the question of where these millions of species might be found.     

How many membrane proteins are there?

One of the basic issues that arises in functional genomics is the ability to predict the subcellular location of proteins that are deduced from gene and genome sequencing. In particular, one would like to be able to readily specify those proteins that are soluble and those that are inserted in a membrane. Traditional methods of distinguishing between these two locations have relied on extensive, time-consuming biochemical studies. The alternative approach has been to make inferences based on a visual search of the amino acid sequences of presumed gene products for stretches of hydrophobic amino acids. This numerical, sequence-based approach is usually seen as a first approximation pending more reliable biochemical data. The recent availability of large and complete sequence data sets for several organisms allows us to determine just how accurate such a numerical approach could be, and to attempt to minimize and quantify the error involved. We have optimized a statistical approach to protein location determination. Using our approach, we have determined that surprisingly few proteins are misallocated using the numerical method. We also examine the biological implications of the success of this technique.     

How many species of Cladocera are there?

An estimation of the number of taxa within families, genera and local faunas of Cladocera reveals that only c. 129 species (17% of all known species) may be considered as sufficiently well described (valid species), and c. 146 as rather well described (fair species) but needing further study using modern methods of investigation. The status of all other species is vague. The families Chydoridae, Daphniidae and Sididae and genera Diaphanosoma, Daphnia, (including Daphniopsis), Megafenestra, Scapholeberis, Eurycercus, Chydorus, Ephemeroporus and Pleuroxus have been comparatively studied best. The largest number of valid species is known from Europe, North America, Australia and South America, and the smallest number from Africa. Presence of large number of vague species of Cladocera negatively affects faunistic, zoogeographic, and ecological studies of continental waters.Dedicated to the memory of Professor D. J. Frey     

How many hydrogen-bonded α-turns are possible?

The formation of α-turns is a possibility to reverse the direction of peptide sequences via five amino acids. In this paper, a systematic conformational analysis was performed to find the possible isolated α-turns with a hydrogen bond between the first and fifth amino acid employing the methods of ab initio MO theory in vacuum (HF/6-31G*, B3LYP/6-311?+?G*) and in solution (CPCM/HF/6-31G*). Only few α-turn structures with glycine and alanine backbones fulfill the geometry criteria for the i←(i?+?4) hydrogen bond satisfactorily. The most stable representatives agree with structures found in the Protein Data Bank. There is a general tendency to form additional hydrogen bonds for smaller pseudocycles corresponding to β- and γ-turns with better hydrogen bond geometries. Sometimes, this competition weakens or even destroys the i←(i?+?4) hydrogen bond leading to very stable double β-turn structures. This is also the reason why an “ideal” α-turn with three central amino acids having the perfect backbone angle values of an α-helix could not be localized. There are numerous hints for stable α-turns with a distance between the \( {{\hbox{C}}_\alpha } \)-atoms of the first and fifth amino acid smaller than 6-7 Å, but without an i←(i?+?4) hydrogen bond.     

How many signal peptides are there in bacteria?

Over the last 5 years proteogenomics (using mass spectroscopy to identify proteins predicted from genomic sequences) has emerged as a promising approach to the high‐throughput identification of protein N‐termini, which remains a problem in genome annotation. Comparison of the experimentally determined N‐termini with those predicted by sequence analysis tools allows identification of the signal peptides and therefore conclusions on the cytoplasmic or extracytoplasmic (periplasmic or extracellular) localization of the respective proteins. We present here the results of a proteogenomic study of the signal peptides in Escherichia coli K‐12 and compare its results with the available experimental data and predictions by such software tools as SignalP and Phobius. A single proteogenomics experiment recovered more than a third of all signal peptides that had been experimentally determined during the past three decades and confirmed at least 31 additional signal peptides, mostly in the known exported proteins, which had been previously predicted but not validated. The filtering of putative signal peptides for the peptide length and the presence of an eight‐residue hydrophobic patch and a typical signal peptidase cleavage site proved sufficient to eliminate the false‐positive hits. Surprisingly, the results of this proteogenomics study, as well as a re‐analysis of the E. coli genome with the latest version of SignalP program, show that the fraction of proteins containing signal peptides is only about 10%, or half of previous estimates.     

How many processes are responsible for phenotypic evolution?

SUMMARY In addressing phenotypic evolution, this article reconsiders natural selection, random drift, developmental constraints, and internal selection in the new extended context of evolutionary developmental biology. The change of perspective from the "evolution of phenotypes" toward an "evolution of ontogenies" (evo-devo perspective) affects the reciprocal relationships among these different processes. Random drift and natural selection are sibling processes: two forms of post-productional sorting among alternative developmental trajectories, the former random, the latter nonrandom. Developmental constraint is a compound concept; it contains even some forms of natural ("external" and "internal") selection. A narrower definition ("reproductive constraints") is proposed. Internal selection is not a selection caused by an internal agent. It is a form of environment-independent selection depending on the level of the organism's internal developmental or functional coordination. Selection and constraints are the main deterministic processes in phenotypic evolution but they are not opposing forces. Indeed, they are continuously interacting processes of evolutionary change, but with different roles that should not be confused.     

How many flowering plants are pollinated by animals?

It is clear that the majority of flowering plants are pollinated by insects and other animals, with a minority utilising abiotic pollen vectors, mainly wind. However there is no accurate published calculation of the proportion of the ca 352 000 species of angiosperms that interact with pollinators. Widely cited figures range from 67% to 96% but these have not been based on firm data. We estimated the number and proportion of flowering plants that are pollinated by animals using published and unpublished community‐level surveys of plant pollination systems that recorded whether each species present was pollinated by animals or wind. The proportion of animal‐pollinated species rises from a mean of 78% in temperate‐zone communities to 94% in tropical communities. By correcting for the latitudinal diversity trend in flowering plants, we estimate the global number and proportion of animal pollinated angiosperms as 308 006, which is 87.5% of the estimated species‐level diversity of flowering plants. Given current concerns about the decline in pollinators and the possible resulting impacts on both natural communities and agricultural crops, such estimates are vital to both ecologists and policy makers. Further research is required to assess in detail the absolute dependency of these plants on their pollinators, and how this varies with latitude and community type, but there is no doubt that plant–pollinator interactions play a significant role in maintaining the functional integrity of most terrestrial ecosystems.     

How many soldiers are optimal for an aphid colony?

A number of aphid species produce sterile soldiers that defend their colony-mates against predators. How many soldiers should a colony produce? Assuming logistic growth of the aphid colony, we can theoretically deduce that soldiers will be produced until the marginal defensive efficacy of a soldier diminishes to rm/K, a ratio of two exogenous variables of the logistic equation, which are the maximum intrinsic rate of increase and carrying capacity. This conclusion holds true irrespective of the number of founders. As the number of founders increases, the entire colony size becomes larger, thus decreasing the percentage of soldiers. In case of multiple founders, each clone will produce the same number of reproductives that remain on the hostplant.     

How many fold types of protein are there in nature?

Many protein structures have now been determined and reveal that protein molecules can adopt the same fold despite having very different sequences. It has been suggested that, owing to different stereochemical constraints, the number of ways that a sequence can fold may be limited. Therefore, it is reasonable to ask how many fold types exist in nature. Several groups have tackled this problem with very different results. In the present study, a novel statistical sampling approach is used to reestimate this number. The results suggest that the number of protein folds in nature is probably several hundreds. © 1996 Wiley-Liss, Inc.     

How many markers or how many alleles per system are appropriate in zygosity testing?

Due to the development in DNA-PCR-technique more and more systems with a high number of alleles have been established in twin diagnosis. Because of their high effectiveness in resolving of genetic questions it is not amazing that some authors have postulated the thesis that typing of 5 to 10 DNA-PCR systems can prove monozygosity. For this paper the use of different systems (conventional and PCR systems) has been tested for twin diagnosis and the observed effects are discussed.     

How many lethal alleles?

Knowledge of the frequency of lethal mutant alleles in a population is important for our understanding of population genetics and evolution, and yet there have been few attempts to measure their number in wild populations. A new study has revealed unexpectedly low numbers of segregating lethal alleles in two species of fish. More experiments are needed, however, to know whether this result is general.