Body size and measurement of species diversity in large grazing mammals

Species are by definition different from each other. This fact favours ranking rather than additive indices. However, ecologists have measured species diversity in terms of species richness, or by combining species richness with the relative abundance of species within an area. Both methods raise problems: species richness treats all species equally, while relative abundance is not a fixed property of species but varies widely temporally and spatially, and requires a massive sampling effort. The functional aspect of species diversity measurement may be strengthened by incorporating differences between species such as body size as a component of diversity. An index of diversity derived from a measure of variation in body size among species is proposed for large grazing mammals. The proposed diversity index related positively to species abundance, indicating that the use of body size as a surrogate for diversity is adequate. Because the proposed index is based on presence or absence data, the expensive and time consuming counting of individuals per species in each sampling unit is not necessary.     

Phylogenetic fields through time: temporal dynamics of geographical co-occurrence and phylogenetic structure within species ranges

Species co-occur with different sets of other species across their geographical distribution, which can be either closely or distantly related. Such co-occurrence patterns and their phylogenetic structure within individual species ranges represent what we call the species phylogenetic fields (PFs). These PFs allow investigation of the role of historical processes—speciation, extinction and dispersal—in shaping species co-occurrence patterns, in both extinct and extant species. Here, we investigate PFs of large mammalian species during the last 3 Myr, and how these correlate with trends in diversification rates. Using the fossil record, we evaluate species'' distributional and co-occurrence patterns along with their phylogenetic structure. We apply a novel Bayesian framework on fossil occurrences to estimate diversification rates through time. Our findings highlight the effect of evolutionary processes and past climatic changes on species'' distributions and co-occurrences. From the Late Pliocene to the Recent, mammal species seem to have responded in an individualistic manner to climate changes and diversification dynamics, co-occurring with different sets of species from different lineages across their geographical ranges. These findings stress the difficulty of forecasting potential effects of future climate changes on biodiversity.     

On size and area: Patterns of mammalian body size extremes across landmasses

We describe a biogeographic pattern in which mammalian body size extremes scale with landmass area. The relationship between the largest and the smallest mammal species found on different landbridge islands, mountaintops and continents shows that the size of the largest species increases, while that of the smallest species decreases, with increase in the area of the landmass. We offer two possible explanations: (1) that the pattern is the result of sampling artefacts, which we call the ‘statistical artefact hypothesis’, or (2) that the pattern is the result of processes related to the way body size affects the number of individuals that a particular species can pack in a given area, which we call the ‘area-scaling hypothesis’. Our results point out that the pattern is not a statistical artefact resulting from random sampling, but can be explained by considering the scaling of individual space requirements and its effect on population survival on landmasses of different area. This revised version was published online in July 2006 with corrections to the Cover Date.     

Potential decoupling of trends in distribution area and population size of species with climate change

Global climates are changing rapidly and biological responses are becoming increasingly apparent. Here, we use empirical abundance patterns across an altitudinal gradient and predicted altitudinal range shifts to estimate change in total population size relative to distribution area in response to climate warming. Adopting this approach we predict that, for nine out of 12 species of regionally endemic birds, total population size will decline more rapidly than distribution area with increasing temperature. Two species showed comparable loss and one species exhibited a slower decline in population size with change in distribution area. Population size change relative to distribution area was greatest for those species that occurred at highest density in the middle of the gradient. The disproportional loss in population size reported here suggests that extinction risk associated with climate change can be more severe than that expected from decline in distribution area alone. Therefore, if we are to make accurate predictions of the impacts of climate change on the conservation status of individual species, it is crucial that we consider the spatial patterns of abundance within the distribution and not just the overall range of the species.     

中国斑腿蝗科特有种的分布及特有分布区划分

按照150km×150km对中国陆地部分进行栅格划分,收集整理了中国斑腿蝗科237个特有种在各栅格的分布信息,建立了物种(237)×栅格(168)数据矩阵,研究了中国斑腿蝗科特有种的分布规律并用PAE法进行特有分布区划分。结果表明:除天山山地分布的少数几个种外,中国斑腿蝗科特有种基本分布西南-东北走向。在该范围内南多北少。华南和西南是中国斑腿蝗科特有种最丰富的地区,在秦巴山区、藏东南和浙闽丘陵地带各有一个高密度的分布区。11个特有分布区中5个分布在东洋界部分,两个在中国东部古北和东洋界交界区,天山山地有一个分散的特有分布区,东北有2个特有分布区。特有分布区的分布和划分基本和中国动物地理区划及区系相一致,但台湾地区归入华中区;横断山和秦岭山地的栅格在支序图中多形成未决分类单元,特有分布区划分困难;华南和华中地区的特有分布区可以进一步划分成更小范围的特有分布区;从云南西北的腾冲、保山经过贵州南部到广西桂林的一个东西狭长的区域可以作为一个特有分布区     

The influence of scale and species pool on the relationship between vascular plant species richness and cover in an alpine area in Norway

Recent studies emphasise the potential importance of scale and species pool on the humped-back or unimodal relationship between species richness and productivity. We use a classic phytosociological data-set from Rondane, central south Norway, to evaluate the relative importance of these factors in an alpine area. The effect of species pool is assessed using plot scores from a Correspondence Analysis (CA) of the data. Generalised Additive Models (GAM) are used to relate vascular plant species richness to cover of vascular plants, CA plot scores, and plot area in different combinations. Species richness of vascular plants is unimodally related to total vascular plant cover. Plot scores of the first three CA axes (representing the effect of species pool) have a complex relationship with species richness, but explain a large fraction of the total deviance in richness. A humped relationship between richness and cover remains after accounting for CA plot scores in the model, i.e. the relationship is independent of species pool. The results suggest that the relationship between richness and cover changes from one vegetation type to another, as evaluated statistically through the importance of the interaction between cover and CA scores in explaining variation in richness. Plot area also influences the relationship. A unimodal relationship is only evident when small plot sizes are used, whereas a monotonically increasing relationship is found at large plot sizes. Plot area has the strongest effect on the unimodal relationship between richness and cover, whereas vegetation type has only a minor effect on this relationship. This revised version was published online in June 2006 with corrections to the Cover Date.     

The influence of a positive correlation between clutch size and offspring fitness on the optimal offspring size

Summary The effect is modeled of a positive relationship between clutch size and offspring fitness on the optimal investment in offspring. In species which meet the assumptions of the model, the model predicts a positive correlation between maternal resource level and offspring size. If larger mothers are able to allocate more resources to offspring, then the model would also predict a positive correlation between maternal size and offspring size when the assumptions of the model are met. Thus, this model may help explain both among and within individual variation in offspring size. When offspring are produced in groups and the number of offspring killed per clutch is limited by predator satiation, offspring in larger clutches may experience a higher probability of survival. Such a life style may be found in animals such as sea turtles. Offspring size is positively correlated with maternal size in some members of this group.     

The correlation between rDNA copy number and genome size in eukaryotes.

Both rDNA gene multiplicity and genome size vary widely among eukaryotes. For some time, there has been debate regarding any possible relationship between these two parameters. The present study uses data on genome size and rDNA copy number for 162 species of plants and animals to test the association between genome size and rDNA copy number, and provides the first convincing evidence of a strong positive relationship between the two within and among these two groups of organisms. No simple explanations exist for this relationship, but it is nevertheless of clear relevance from both practical and theoretical perspectives.     

A Survey of Tetrapod Tracksites Preserved in Pyroclastic Sediments,with Special Reference to Footprints of Hominids,Other Mammals and Birds

Pyroclastic sediments provide an unusual and favorable medium for the recording, burial, and preservation of tetrapod tracks and other traces. Twenty-two tracksites were reviewed for the purpose of determining how these deposits contribute to track formation, burial, and preservation. These include Jurassic sites in Argentina and Mexico, Cretaceous sites in Korea, Miocene sites in Mexico and the United States, Pliocene sites in Tanzania, Pleistocene sites in Mexico, Korea, and Italy, and Holocene sites in Mexico, Turkey, Italy, Japan, New Zealand, Nicaragua, and the United States. Twelve of the sites contain hominid tracks.

Tracksites occur most commonly in reworked tephra on the shorelines of rivers, lakes, and seas. They also occur on pyroclastic falls, flows, and surges, and on lahars. Most tracksites are in volcanic arcs, especially around the Pacific Rim. A few occur in continental rifts or near intraplate volcanoes. Most older tracksites (Jurassic, Cretaceous, and Miocene) occur in silicic tephras such as rhyolite and dacite. The younger tracksites are mostly associated with basaltic tephra, though other compositions are also represented.

Volcanic eruptions contribute to formation of substrates suitable for recording tracks by producing abundant fine-grained pyroclasts that interact physically and chemically with water to become cohesive. Hiatuses between eruptions provide time for tracks to accumulate, and in some cases, to lithify rapidly. Both physical processes (drying and compaction) and chemical processes (mineral precipitation) appear to be involved in early lithification. Eruptions also contribute to burial of tracks through rapid sedimentation and aggradation that typically follow a pyroclastic eruption. Multiple, closely spaced track horizons are common in pyroclastic sequences. Most tracksites are buried by either fallout tephra or reworked, waterlain deposits. Others are buried by lahars, pyroclastic flows and surges, or windblown ash. Upon exhumation pyroclastic deposits contribute to the formation of bedding planes through clay drapes, friable ash layers, and biotite-rich layers. Precipitation of authigenic minerals contributes to erosional resistance within beds. Bedding plane formation and erosional resistance facilitate discovery and study of tracks.     

Co-occurrence of tree species at fine spatial scale in a woodland cerrado,southeastern Brazil

Species co-occurrence at fine spatial scales is expected to be nonrandom in relation to species phylogenetic relatedness and functional similarity. On the one hand, closely related species that occur together and experience similar environmental conditions are likely to share phenotypic traits due to the process of environmental filtering. On the other hand, species that are too similar are unlikely to co-occur due to competitive exclusion. We surveyed a woodland cerrado, southeastern Brazil, to test whether co-occurrence in tree species shows functional or phylogenetic structuring at fine spatial scale. Searching for correlations between an index of species co-occurrence and both functional trait differences and phylogenetic distances, we provided evidence for a predominant role of environment filters in determining the co-occurrence of functionally similar tree species in cerrado. However, we did not find any effect of phylogenetic relatedness on tree species co-occurrence. We suggest that the phylogenetic relatedness of co-occurring cerrado tree species did not present a pattern, because the species functional traits were randomly distributed on the phylogeny. Thus, phylogenetic relatedness and functional similarity do not seem to limit the co-occurrence at fine spatial scale of cerrado tree species.     

Effects of metabolic level on the body size scaling of metabolic rate in birds and mammals

Metabolic rate is traditionally assumed to scale with body mass to the 3/4-power, but significant deviations from the '3/4-power law' have been observed for several different taxa of animals and plants, and for different physiological states. The recently proposed 'metabolic-level boundaries hypothesis' represents one of the attempts to explain this variation. It predicts that the power (log-log slope) of metabolic scaling relationships should vary between 2/3 and 1, in a systematic way with metabolic level. Here, this hypothesis is tested using data from birds and mammals. As predicted, in both of these independently evolved endothermic taxa, the scaling slope approaches 1 at the lowest and highest metabolic levels (as observed during torpor and strenuous exercise, respectively), whereas it is near 2/3 at intermediate resting and cold-induced metabolic levels. Remarkably, both taxa show similar, approximately U-shaped relationships between the scaling slope and the metabolic (activity) level. These predictable patterns strongly support the view that variation of the scaling slope is not merely noise obscuring the signal of a universal scaling law, but rather is the result of multiple physical constraints whose relative influence depends on the metabolic state of the organisms being analysed.     

The relationship between genome size, development rate, and body size in copepods

Freshwater cyclopoid copepods exhibit at least a fivefold range in somatic genome size and a mechanism, chromatin diminution, which could account for much of this interspecific variation. These attributes suggest that copepods are well suited to studies of genome size evolution. We tested the nucleotypic hypothesis of genome size evolution, which poses that variation in genome size is adaptive due to the bulk effects of both coding and noncoding DNA on cell size and division rates, and their correlates. We found a significant inverse correlation between genome size and developmental (growth) rate in five freshwater cyclopoid species at three temperatures. That is, species with smaller genomes developed faster. Species with smaller genomes had significantly smaller bodies at 22 °C, but not at cooler and warmer temperatures. Species with smaller genomes developed faster at all three temperatures, but had smaller bodies only at 22 °C. We propose a model of life history evolution that adds genome size and cell cycle dynamics to the suite of characters on which selection may act to mold life histories and to influence the distribution of traits among different habitats.     

Rapid,simple and sensitive microassay for skeletal and cardiac muscle myoglobin and hemoglobin: use in various animals indicates functional role of myohemoproteins

A novel, simple, rapid, sensitive and reproducible microassay is described for determination of myoglobin and hemoglobin content of myocardial and skeletal muscle biopsy specimens from various mammals, birds and fish. As little as 50 mg of tissue is needed and myoglobin concentrations lower than 1 mg% can be detected. Myoglobin and hemoglobin are separated at alkaline pH by ammonium sulfate extraction followed by ultrafiltration. Heme content is determined by absorption of the Soret band when the hemoprotein extract is visibly colored or more sensitively by its peroxidase activity when the extract has low color. The heme reacts with tertiary-butyl hydroperoxide and orthotolidine to generate a blue color. Hemoglobin content is correlated with myoglobin content and is related to aerobic capacity and blood flow to the tissue. Myoglobin content varied over 5 orders of magnitude up to 7 per cent of the weight of tissue, whereas hemoglobin content varied over 2 orders of magnitude up to 6 per cent of tissue weight. Myoglobin content is increased in species with high basal metabolic rate, high physical activity, prolonged diving capacity, fatigue resistance, and red muscle, whereas it is decreased in white muscle, iron-deficient animals, animals with sedentary lifestyles, and in animals and tissues with small fiber diameters such as avian or fish hearts.     

Selection on body size and sexual size dimorphism differs between host species in a seed-feeding beetle

Sexual size dimorphism varies substantially among populations and species but we have little understanding of the sources of selection generating this variation. We used path analysis to study how oviposition host affects selection on body size in a seed-feeding beetle (Stator limbatus) in which males contribute large ejaculates (nuptial gifts) to females. Females use nutrients in these ejaculates for egg production. Male body size, which affects ejaculate size, affects female fecundity and is thus under fecundity selection similar in magnitude to the fecundity selection on female body size. We show that when eggs are laid on a host on which larval mortality is low (seeds of Acacia greggii) fecundity predicts fitness very well and fecundity selection is the major source of selection on both male and female adult size. In contrast, when eggs are laid on a host on which larval mortality is high (seeds of Parkinsonia florida) fecundity poorly predicts fitness such that fecundity selection is relaxed on both male and female size. However, because egg size affects larval mortality on this poor host (P. florida) there is selection on female size via the female size --> egg size --> fitness path; this selection via egg size offsets the reduction in fecundity selection on female, but not male, body size. Thus, differences in host suitability (due to differences in larval mortality) affect the relative importance of two sources of selection on adult body size; fecundity selection on both male and female body size is lower on the poor quality host (P. florida) relative to the high quality host (A. greggii) whereas selection on female body size via effects of egg size on offspring survival (body size --> egg size --> fitness) is greater on the poor quality host relative to the high quality host. Because selection via the egg size path affects only females the difference in larval survival between hosts shifts the relative magnitude of selection on female vs. male size. Researchers working on other study systems should be alerted to the possible importance of subtle, but consequential, indirect selection on their study organisms.