Competition between seed-eating rodents and ants in desert ecosystems

Three kinds of evidence indicate that desert rodents and ants compete for seeds: (i) extensive overlaps in diet, (ii) reciprocal increases when one taxon is experimentally excluded, and (iii) complementay patterns of diversity and biomass in georadients of productivity. The effect on seed resources and annual plan geoseems to be similar whether rodents, ants, or both are foraging.

A graphical judgmental aid which summarizes obtained and chance reliability data and helps assess the believability of experimental effects

Interval by interval reliability has been criticized for "inflating" observer agreement when target behavior rates are very low or very high. Scored interval reliability and its converse, unscored interval reliability, however, vary as target behavior rates vary when observer disagreement rates are constant. These problems, along with the existence of "chance" values of each reliability which also vary as a function of response rate, may cause researchers and consumers difficulty in interpreting observer agreement measures. Because each of these reliabilities essentially compares observer disagreements to a different base, it is suggested that the disagreement rate itself be the first measure of agreement examined, and its magnitude relative to occurrence and to nonoccurrence agreements then be considered. This is easily done via a graphic presentation of the disagreement range as a bandwidth around reported rates of target behavior. Such a graphic presentation summarizes all the information collected during reliability assessments and permits visual determination of each of the three reliabilities. In addition, graphing the "chance" disagreement range around the bandwidth permits easy determination of whether or not true observer agreement has likely been demonstrated. Finally, the limits of the disagreement bandwidth help assess the believability of claimed experimental effects: those leaving no overlap between disagreement ranges are probably believable, others are not.

Back to basics: Percentage agreement measures are adequate, but there are easier ways

Percentage agreement measures of interobserver agreement or "reliability" have traditionally been used to summarize observer agreement from studies using interval recording, time-sampling, and trial-scoring data collection procedures. Recent articles disagree on whether to continue using these percentage agreement measures, and on which ones to use, and what to do about chance agreements if their use is continued. Much of the disagreement derives from the need to be reasonably certain we do not accept as evidence of true interobserver agreement those agreement levels which are substantially probable as a result of chance observer agreement. The various percentage agreement measures are shown to be adequate to this task, but easier ways are discussed. Tables are given to permit checking to see if obtained disagreements are unlikely due to chance. Particularly important is the discovery of a simple rule that, when met, makes the tables unnecessary. If reliability checks using 50 or more observation occasions produce 10% or fewer disagreements, for behavior rates from 10% through 90%, the agreement achieved is quite improbably the result of chance agreement.

AN IMPROVED ANAEROBE JAR

There has been described a modification of the anaerobe jars of McIntosh and Fildes and of Smillie in which the oxygen is consumed by combustion with hydrogen under the catalytic action of platinized or palladinized asbestos. The special advantages of the apparatus described reside in its greater safety and in the fact that the catalyzer is heated electrically after the jar is closed and may be reheated at any time during incubation without opening the jar.

MODIFICATION OF AN IMPROVED ANAEROBE JAR

In the filtrates of typhus-infected tissues of guinea pigs can be occasionally found a substance which produces in these animals thermic reactions, lesions characteristic of experimental typhus, and, still less frequently, inimunity to later injections of active virus. The general indications are that this substance is not a living organism.

THE CULTURAL DIFFERENTIATION OF BETA HEMOLYTIC STREPTOCOCCI OF HUMAN AND BOVINE ORIGIN

None of the procedures described serves by itself to differentiate streptococci of human and bovine origin with certainty, though each of them serves as a strong presumptive test. Most strains fall easily into the human or bovine group by all the tests. Eliminating these from consideration we have left certain irregular strains listed in Table VII. See PDF for Structure Taking all characters into consideration we are inclined to regard Strains J-E7, Cheese 1, and Cheese 2 as undoubtedly of bovine origin. Strain J-MJ also is representative of a group of streptococci which Jones has found in milk and which is being further studied by him. There remains Strain J-C65 which for the present must be regarded as of doubtful origin.

A STUDY OF BACILLUS PYOGENES

Bacillus pyogenes is probably quite common in this country, as it is known to be in Europe. A careful study of twelve strains from cattle and one from a hog has disclosed the following characteristics which have not been reported or have been in dispute. Bacillus pyogenes is Gram-positive and pleomorphic, producing forms ranging from short chains of streptococcoid elements to branching filaments. It is hemolytic, producing the beta type of hemolysis in blood agar. It is not hemoglobinophilic, though its growth is greatly favored by some higher protein material such as egg albumin, serum, or blood. It ferments xylose in addition to the substances previously reported. The coagulation of milk by Bacillus pyogenes is primarily an enzyme coagulation and the subsequent digestion of the curd takes place in an acid medium. The intravenous injection of rabbits was invariably fatal. The lesions most commonly developed were those of the bones. Paralysis was frequently produced, and in each case was caused by lesions in the vertebrae exerting pressure against the ventral columns of the spinal cord. Muscle abscesses were also frequently produced. The authors regard the organism as belonging to the Corynebacteria rather than to the influenza group.

The reticulating phylogeny of island biogeography theory

Biogeographers study all patterns in the geographic variation of life, from the spatial variation in genetic and physiological characteristics of cells and individuals, to the diversity and dynamics of biological communities among continental biotas or across oceanic archipelagoes. The field of island biogeography, in particular, has provided some genuinely transformative insights for the biological sciences, especially ecology and evolutionary biology. Our purpose here is to review the historical development of island biogeography theory during the 20th century by identifying the common threads that run through four sets of contributions made during this period, including those by Eugene Gordon Munroe (1948, 1953), Edward O. Wilson (1959, 1961), Frank W. Preston (1962a,b), and the seminal collaborations between Wilson and Robert H. MacArthur (1963, 1967), which revolutionized the field and served as its paradigm for nearly four decades. This epistemological account not only reviews the intriguing history of island theory, but it also includes fundamental lessons for advancing science through transformative integrations. Indeed, as is likely the case with many disciplines, island theory advanced not as a simple accumulation of facts and an orderly succession of theories and paradigms, but rather in fits and starts through a reticulating phylogeny of ideas and alternating periods of specialization and reintegration. We conclude this review with a summary of the salient features of this scientific revolution in the contest of Kuhn's structure, which strongly influenced theoretical advances during this period, and we then describe some of the fundamental assumptions and tenets of an emerging reintegration of island biogeography theory.

Temperature dependence, spatial scale, and tree species diversity in eastern Asia and North America

The increase of biodiversity from poles to equator is one of the most pervasive features of nature. For 2 centuries since von Humboldt, Wallace, and Darwin, biogeographers and ecologists have investigated the environmental and historical factors that determine the latitudinal gradient of species diversity, but the underlying mechanisms remain poorly understood. The recently proposed metabolic theory of ecology (MTE) aims to explain ecological patterns and processes, including geographical patterns of species richness, in terms of the effects of temperature and body size on the metabolism of organisms. Here we use 2 comparable databases of tree distributions in eastern Asia and North America to investigate the roles of environmental temperature and spatial scale in shaping geographical patterns of species diversity. We find that number of species increases exponentially with environmental temperature as predicted by the MTE, and so does the rate of spatial turnover in species composition (slope of the species-area relationship). The magnitude of temperature dependence of species richness increases with spatial scale. Moreover, the relationship between species richness and temperature is much steeper in eastern Asia than in North America: in cold climates at high latitudes there are more tree species in North America, but the reverse is true in warmer climates at lower latitudes. These patterns provide evidence that the kinetics of ecological and evolutionary processes play a major role in the latitudinal pattern of biodiversity.

Population stability, cooperation, and the invasibility of the human species

The biogeographic expansion of modern humans out of Africa began approximately 50,000 years ago. This expansion resulted in the colonization of most of the land area and habitats throughout the globe and in the replacement of preexisting hominid species. However, such rapid population growth and geographic spread is somewhat unexpected for a large primate with a slow, density-dependent life history. Here, we suggest a mechanism for these outcomes by modifying a simple density-dependent population model to allow varying levels of intraspecific competition for finite resources. Reducing intraspecific competition increases carrying capacities, growth rates, and stability, including persistence times and speed of recovery from perturbations. Our model suggests that the energetic benefits of cooperation in modern humans may have outweighed the slow rate of human population growth, effectively ensuring that once modern humans colonized a region long-term population persistence was near inevitable. Our model also provides insight into the interplay of structural complexity and stability in social species.

Mammal reproductive strategies driven by offspring mortality-size relationships

Trade-offs have long been a major theme in life-history theory, but they have been hard to document. We introduce a new method that reveals patterns of divergent trade-offs after adjusting for the pervasive variation in rate of resource allocation to offspring as a function of body size and lifestyle. Results suggest that preweaning vulnerability to predation has been the major factor determining how female placental mammals allocate production between a few large and many small offspring within a litter and between a few large litters and many small ones within a reproductive season. Artiodactyls, perissodactyls, cetaceans, and pinnipeds, which give birth in the open on land or in the sea, produce a few large offspring, at infrequent intervals, because this increases their chances of escaping predation. Insectivores, fissiped carnivores, lagomorphs, and rodents, whose offspring are protected in burrows or nests, produce large litters of small newborns. Primates, bats, sloths, and anteaters, which carry their young from birth until weaning, produce litters of one or a few offspring because of the need to transport and care for them.

Scaling relations for a functionally two-dimensional plant: Chamaesyce setiloba (Euphorbiaceae)

Many characteristics of plants and animals scale with body size as described by allometric equations of the form Y = βM(α), where Y is an attribute of the organism, β is a coefficient that varies with attribute, M is a measure of organism size, and α is another constant, the scaling exponent. In current models, the frequently observed quarter-power scaling exponents are hypothesized to be due to fractal-like structures. However, not all plants or animals conform to the assumptions of these models. Therefore, they might be expected to have different scaling relations. We studied one such plant, Chamaesyce setiloba, a prostrate annual herb that grows to functionally fill a two-dimensional space. Number of leaves scaled slightly less than isometrically with total aboveground plant mass (α ≈ 0.9) and substantially less than isometrically with dry total stem mass (α = 0.82), showing reduced allocation to leaf as opposed to stem tissue with increasing plant size. Additionally, scalings of the lengths and radii of parent and daughter branches differed from those predicted for three-dimensional trees and shrubs. Unlike plants with typical three-dimensional architectures, C. setiloba has distinctive scaling relations associated with its particular prostrate herbaceous growth form.

A general quantitative theory of forest structure and dynamics

We present the first part of a quantitative theory for the structure and dynamics of forests at demographic and resource steady state. The theory uses allometric scaling relations, based on metabolism and biomechanics, to quantify how trees use resources, fill space, and grow. These individual-level traits and properties scale up to predict emergent properties of forest stands, including size-frequency distributions, spacing relations, resource flux rates, and canopy configurations. Two insights emerge from this analysis: (i) The size structure and spatial arrangement of trees in the entire forest are emergent manifestations of the way that functionally invariant xylem elements are bundled together to conduct water and nutrients up from the trunks, through the branches, to the leaves of individual trees. (ii) Geometric and dynamic properties of trees in a forest and branches in trees scale identically, so that the entire forest can be described mathematically and behaves structurally and functionally like a scaled version of the branching networks in the largest tree. This quantitative framework uses a small number of parameters to predict numerous structural and dynamical properties of idealized forests.

Changes in a tropical forest support metabolic zero-sum dynamics

Major shifts in many ecosystem-level properties of tropical forests have been observed, but the processes driving these changes are poorly understood. The forest on Barro Colorado Island (BCI) exhibited a 20% decrease in the number of trees and a 10% increase in average diameter. Using a metabolism-based zero-sum framework, we show that increases in per capita resource use at BCI, caused by increased tree size and increased temperature, compensated for the observed declines in abundance. This trade-off between abundance and average resource use resulted in no net change in the rate resources are fluxed by the forest. Observed changes in the forest are not consistent with other hypotheses, including changes in overall resource availability and existing self-thinning models. The framework successfully predicts interrelated changes in size, abundance and temperature, indicating its utility for understanding changes in the structure and dynamics of ecosystems.

Zero sum, the niche, and metacommunities: long-term dynamics of community assembly

Recent models of community assembly, structure, and dynamics have incorporated, to varying degrees, three mechanistic processes: resource limitation and interspecific competition, niche requirements of species, and exchanges between a local community and a regional species pool. Synthesizing 30 years of data from an intensively studied desert rodent community, we show that all of these processes, separately and in combination, have influenced the structural organization of this community and affected its dynamical response to both natural environmental changes and experimental perturbations. In addition, our analyses suggest that zero-sum constraints, niche differences, and metacommunity processes are inextricably linked in the ways that they affect the structure and dynamics of this system. Explicit consideration of the interaction of these processes should yield a deeper understanding of the assembly and dynamics of other ecological communities. This synthesis highlights the role that long-term data, especially when coupled with experimental manipulations, can play in assessing the fundamental processes that govern the structure and function of ecological communities.

Scaling theory for information networks

Networks distribute energy, materials and information to the components of a variety of natural and human-engineered systems, including organisms, brains, the Internet and microprocessors. Distribution networks enable the integrated and coordinated functioning of these systems, and they also constrain their design. The similar hierarchical branching networks observed in organisms and microprocessors are striking, given that the structure of organisms has evolved via natural selection, while microprocessors are designed by engineers. Metabolic scaling theory (MST) shows that the rate at which networks deliver energy to an organism is proportional to its mass raised to the 3/4 power. We show that computational systems are also characterized by nonlinear network scaling and use MST principles to characterize how information networks scale, focusing on how MST predicts properties of clock distribution networks in microprocessors. The MST equations are modified to account for variation in the size and density of transistors and terminal wires in microprocessors. Based on the scaling of the clock distribution network, we predict a set of trade-offs and performance properties that scale with chip size and the number of transistors. However, there are systematic deviations between power requirements on microprocessors and predictions derived directly from MST. These deviations are addressed by augmenting the model to account for decentralized flow in some microprocessor networks (e.g. in logic networks). More generally, we hypothesize a set of constraints between the size, power and performance of networked information systems including transistors on chips, hosts on the Internet and neurons in the brain.

Two-phase increase in the maximum size of life over 3.5 billion years reflects biological innovation and environmental opportunity

The maximum size of organisms has increased enormously since the initial appearance of life >3.5 billion years ago (Gya), but the pattern and timing of this size increase is poorly known. Consequently, controls underlying the size spectrum of the global biota have been difficult to evaluate. Our period-level compilation of the largest known fossil organisms demonstrates that maximum size increased by 16 orders of magnitude since life first appeared in the fossil record. The great majority of the increase is accounted for by 2 discrete steps of approximately equal magnitude: the first in the middle of the Paleoproterozoic Era (approximately 1.9 Gya) and the second during the late Neoproterozoic and early Paleozoic eras (0.6-0.45 Gya). Each size step required a major innovation in organismal complexity--first the eukaryotic cell and later eukaryotic multicellularity. These size steps coincide with, or slightly postdate, increases in the concentration of atmospheric oxygen, suggesting latent evolutionary potential was realized soon after environmental limitations were removed.

Energy uptake and allocation during ontogeny

All organisms face the problem of how to fuel ontogenetic growth. We present a model, empirically grounded in data from birds and mammals, that correctly predicts how growing animals allocate food energy between synthesis of new biomass and maintenance of existing biomass. Previous energy budget models have typically had their bases in rates of either food consumption or metabolic energy expenditure. Our model provides a framework that reconciles these two approaches and highlights the fundamental principles that determine rates of food assimilation and rates of energy allocation to maintenance, biosynthesis, activity, and storage. The model predicts that growth and assimilation rates for all animals should cluster closely around two universal curves. Data for mammals and birds of diverse body sizes and taxa support these predictions.

Chihuahuan Desert kangaroo rats: nonlinear effects of population dynamics, competition, and rainfall

Using long-term data on two kangaroo rats in the Chihuahuan Desert of North America, we fitted logistic models including the exogenous effects of seasonal rainfall patterns. Our aim was to test the effects of intraspecific interactions and seasonal rainfall in explaining and predicting the numerical fluctuations of these two kangaroo rats. We found that logistic models fit both data sets quite well; Dipodomys merriami showed lower maximum per capita growth rates than Dipodomys ordii, and in both cases logistic models were nonlinear. Summer rainfall appears to be the most important exogenous effect for both rodent populations; models including this variable were able to predict independent data better than models including winter rainfall. D. merriami was also negatively affected by another kangaroo rat (Dipodomys spectabilis), consistent with previous experimental evidence. We hypothesized that summer rainfall influences the carrying capacity of the environment by affecting seed availability and the intensity of intraspecific competition.