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James H Brown

Publications and source records attributed to James H Brown.

At least 19 recordsLinked to original sources
PubMed2006

Life-history evolution under a production constraint.

The recently formulated metabolic theory of ecology has profound implications for the evolution of life histories. Metabolic rate constrains the scaling of production with body mass, so that larger organisms have lower rates of production on a mass-specific basis than smaller ones. Here, we explore the implications of this constraint for life-history evolution. We show that for a range of very simple life histories, Darwinian fitness is equal to birth rate minus death rate. So, natural selection maximizes birth and production rates and minimizes death rates. This implies that decreased body size will generally be favored because it increases production, so long as mortality is unaffected. Alternatively, increased body size will be favored only if it decreases mortality or enhances reproductive success sufficiently to override the preexisting production constraint. Adaptations that may favor evolution of larger size include niche shifts that decrease mortality by escaping predation or that increase fecundity by exploiting new abundant food sources. These principles can be generalized to better understand the intimate relationship between the genetic currency of evolution and the metabolic currency of ecology.

Adaptation, Physiological↗
PubMed2006

Kinetic effects of temperature on rates of genetic divergence and speciation.

Latitudinal gradients of biodiversity and macroevolutionary dynamics are prominent yet poorly understood. We derive a model that quantifies the role of kinetic energy in generating biodiversity. The model predicts that rates of genetic divergence and speciation are both governed by metabolic rate and therefore show the same exponential temperature dependence (activation energy of approximately 0.65 eV; 1 eV = 1.602 x 10(-19) J). Predictions are supported by global datasets from planktonic foraminifera for rates of DNA evolution and speciation spanning 30 million years. As predicted by the model, rates of speciation increase toward the tropics even after controlling for the greater ocean coverage at tropical latitudes. Our model and results indicate that individual metabolic rate is a primary determinant of evolutionary rates: approximately 10(13) J of energy flux per gram of tissue generates one substitution per nucleotide in the nuclear genome, and approximately 10(23) J of energy flux per population generates a new species of foraminifera.

Animals↗
PubMed2006

The allometry of ornaments and weapons.

Exaggerated male traits that have evolved under sexual selection include ornaments to attract mates and weapons to deter rivals. Data from studies of many such traits in diverse kinds of organisms show that they almost universally exhibit positive allometries. Both ornaments and weapons increase disproportionately with overall body size, resulting in scaling exponents within species that are consistently >1.0 and usually in the range 1.5-2.5. We show how scaling exponents reflect the relative fitness advantages of ornaments vs. somatic growth by using a simple mathematical model of resource allocation during ontogeny. Because the scaling exponents are similar for the different taxonomic groups, it follows that the fitness advantages of investing in ornaments also are similar. The model also shows how selection for ornaments influences body size at first reproduction and explains why interspecific allometries have consistently lower exponents than intraspecific ones.

Animals↗
PubMed2006

Microbial biogeography: putting microorganisms on the map.

We review the biogeography of microorganisms in light of the biogeography of macroorganisms. A large body of research supports the idea that free-living microbial taxa exhibit biogeographic patterns. Current evidence confirms that, as proposed by the Baas-Becking hypothesis, 'the environment selects' and is, in part, responsible for spatial variation in microbial diversity. However, recent studies also dispute the idea that 'everything is everywhere'. We also consider how the processes that generate and maintain biogeographic patterns in macroorganisms could operate in the microbial world.

Archaea↗
PubMed2006

Temperature-dependence of biomass accumulation rates during secondary succession.

Rates of ecosystem recovery following disturbance affect many ecological processes, including carbon cycling in the biosphere. Here, we present a model that predicts the temperature dependence of the biomass accumulation rate following disturbances in forests. Model predictions are derived based on allometric and biochemical principles that govern plant energetics and are tested using a global database of 91 studies of secondary succession compiled from the literature. The rate of biomass accumulation during secondary succession increases with average growing season temperature as predicted based on the biochemical kinetics of photosynthesis in chloroplasts. In addition, the rate of biomass accumulation is greater in angiosperm-dominated communities than in gymnosperm-dominated ones and greater in plantations than in naturally regenerating stands. By linking the temperature-dependence of photosynthesis to the rate of whole-ecosystem biomass accumulation during secondary succession, our model and results provide one example of how emergent, ecosystem-level rate processes can be predicted based on the kinetics of individual metabolic rate.

Biomass↗
PubMed2005

The metabolic basis of whole-organism RNA and phosphorus content.

Understanding the storage, flux, and turnover of nutrients in organisms is important for quantifying contributions of biota to biogeochemical cycles. Here we present a model that predicts the storage of phosphorus-rich RNA and whole-body phosphorus content in eukaryotes based on the mass- and temperature-dependence of ATP production in mitochondria. Data from a broad assortment of eukaryotes support the model's two main predictions. First, whole-body RNA concentration is proportional to mitochondrial density and consequently scales with body mass to the -1/4 power. Second, whole-body phosphorus content declines with increasing body mass in eukaryotic unicells but approaches a relatively constant value in large multicellular animals because the fraction of phosphorus in RNA decreases relative to the fraction in other pools. Extension of the model shows that differences in the flux of RNA-associated phosphorus are due to the size dependencies of metabolic rate and RNA concentration. Thus, the model explicitly links two biological currencies at the individual level: energy in the form of ATP and materials in the form of phosphorus, both of which are critical to the functioning of ecosystems. The model provides a framework for linking attributes of individuals to the storage and flux of phosphorus in ecosystems.

Animals↗
PubMed2005

The origin of allometric scaling laws in biology from genomes to ecosystems: towards a quantitative unifying theory of biological structure and organization.

Life is the most complex physical phenomenon in the Universe, manifesting an extraordinary diversity of form and function over an enormous scale from the largest animals and plants to the smallest microbes and subcellular units. Despite this many of its most fundamental and complex phenomena scale with size in a surprisingly simple fashion. For example, metabolic rate scales as the 3/4-power of mass over 27 orders of magnitude, from molecular and intracellular levels up to the largest organisms. Similarly, time-scales (such as lifespans and growth rates) and sizes (such as bacterial genome lengths, tree heights and mitochondrial densities) scale with exponents that are typically simple powers of 1/4. The universality and simplicity of these relationships suggest that fundamental universal principles underly much of the coarse-grained generic structure and organisation of living systems. We have proposed a set of principles based on the observation that almost all life is sustained by hierarchical branching networks, which we assume have invariant terminal units, are space-filling and are optimised by the process of natural selection. We show how these general constraints explain quarter power scaling and lead to a quantitative, predictive theory that captures many of the essential features of diverse biological systems. Examples considered include animal circulatory systems, plant vascular systems, growth, mitochondrial densities, and the concept of a universal molecular clock. Temperature considerations, dimensionality and the role of invariants are discussed. Criticisms and controversies associated with this approach are also addressed.

Body Size↗
PubMed2004

The rate of DNA evolution: effects of body size and temperature on the molecular clock.

Observations that rates of molecular evolution vary widely within and among lineages have cast doubts on the existence of a single "molecular clock." Differences in the timing of evolutionary events estimated from genetic and fossil evidence have raised further questions about the accuracy of molecular clocks. Here, we present a model of nucleotide substitution that combines theory on metabolic rate with the now-classic neutral theory of molecular evolution. The model quantitatively predicts rate heterogeneity and may reconcile differences in molecular- and fossil-estimated dates of evolutionary events. Model predictions are supported by extensive data from mitochondrial and nuclear genomes. By accounting for the effects of body size and temperature on metabolic rate, this model explains heterogeneity in rates of nucleotide substitution in different genes, taxa, and thermal environments. This model also suggests that there is indeed a single molecular clock, as originally proposed by Zuckerkandl and Pauling [Zuckerkandl, E. & Pauling, L. (1965) in Evolving Genes and Proteins, eds. Bryson, V. & Vogel, H. J. (Academic, New York), pp. 97-166], but that it "ticks" at a constant substitution rate per unit of mass-specific metabolic energy rather than per unit of time. This model therefore links energy flux and genetic change. More generally, the model suggests that body size and temperature combine to control the overall rate of evolution through their effects on metabolism.

Animals↗
PubMed2004

The scaling of animal space use.

Space used by animals increases with increasing body size. Energy requirements alone can explain how population density decreases, but not the steep rate at which home range area increases. We present a general mechanistic model that predicts the frequency of interaction, spatial overlap, and loss of resources to neighbors. Extensive empirical evidence supports the model, demonstrating that spatial constraints on defense cause exclusivity of home range use to decrease with increasing body size. In large mammals, over 90% of available resources may be lost to neighbors. Our model offers a general framework to understand animal space use and sociality.

Animals↗
PubMed2004

Similarity of mammalian body size across the taxonomic hierarchy and across space and time.

Although it is commonly assumed that closely related animals are similar in body size, the degree of similarity has not been examined across the taxonomic hierarchy. Moreover, little is known about the variation or consistency of body size patterns across geographic space or evolutionary time. Here, we draw from a data set of terrestrial, nonvolant mammals to quantify and compare patterns across the body size spectrum, the taxonomic hierarchy, continental space, and evolutionary time. We employ a variety of statistical techniques including "sib-sib" regression, phylogenetic autocorrelation, and nested ANOVA. We find an extremely high resemblance (heritability) of size among congeneric species for mammals over approximately 18 g; the result is consistent across the size spectrum. However, there is no significant relationship among the body sizes of congeneric species for mammals under approximately 18 g. We suspect that life-history and ecological parameters are so tightly constrained by allometry at diminutive size that animals can only adapt to novel ecological conditions by modifying body size. The overall distributions of size for each continental fauna and for the most diverse orders are quantitatively similar for North America, South America, and Africa, despite virtually no overlap in species composition. Differences in ordinal composition appear to account for quantitative differences between continents. For most mammalian orders, body size is highly conserved, although there is extensive overlap at all levels of the taxonomic hierarchy. The body size distribution for terrestrial mammals apparently was established early in the Tertiary, and it has remained remarkably constant over the past 50 Ma and across the major continents. Lineages have diversified in size to exploit environmental opportunities but only within limits set by allometric, ecological, and evolutionary constraints.

Animals↗
PubMed2004

The contribution of small individuals to density-body size relationships: examination of energetic equivalence in reef fishes.

A key relationship in ecology is that between density and body size, with the emphasis placed on energetic rules constraining the abundance of larger organisms below that of smaller organisms. Most studies have focused upon the density-body size relationship at the species level. However, energy is gathered at an individual level. We therefore examined this relationship in a coral reef fish assemblage, focusing on individuals. Using a comprehensive data set, with over 14,000 observations we found that the relationship between local density and adult body size differs from the linear relationship predicted by the 'energetic equivalence rule'. However, excluding the smallest size classes, the relationship between body size and individual abundance for intermediate to larger fish did not depart from the predicted -0.75. Unlike plants and intermediate to large reef fishes, the smallest fishes appear to have constraints that may reflect different patterns of resource acquisition.

Animals↗
PubMed2004

Effects of body size and temperature on population growth.

For at least 200 years, since the time of Malthus, population growth has been recognized as providing a critical link between the performance of individual organisms and the ecology and evolution of species. We present a theory that shows how the intrinsic rate of exponential population growth, rmax, and the carrying capacity, K, depend on individual metabolic rate and resource supply rate. To do this, we construct equations for the metabolic rates of entire populations by summing over individuals, and then we combine these population-level equations with Malthusian growth. Thus, the theory makes explicit the relationship between rates of resource supply in the environment and rates of production of new biomass and individuals. These individual-level and population-level processes are inextricably linked because metabolism sets both the demand for environmental resources and the resource allocation to survival, growth, and reproduction. We use the theory to make explicit how and why rmax exhibits its characteristic dependence on body size and temperature. Data for aerobic eukaryotes, including algae, protists, insects, zooplankton, fishes, and mammals, support these predicted scalings for rmax. The metabolic flux of energy and materials also dictates that the carrying capacity or equilibrium density of populations should decrease with increasing body size and increasing temperature. Finally, we argue that body mass and body temperature, through their effects on metabolic rate, can explain most of the variation in fecundity and mortality rates. Data for marine fishes in the field support these predictions for instantaneous rates of mortality. This theory links the rates of metabolism and resource use of individuals to life-history attributes and population dynamics for a broad assortment of organisms, from unicellular organisms to mammals.

Animals↗
PubMed2002

Global biodiversity, biochemical kinetics, and the energetic-equivalence rule.

The latitudinal gradient of increasing biodiversity from poles to equator is one of the most prominent but least understood features of life on Earth. Here we show that species diversity can be predicted from the biochemical kinetics of metabolism. We first demonstrate that the average energy flux of populations is temperature invariant. We then derive a model that quantitatively predicts how species diversity increases with environmental temperature. Predictions are supported by data for terrestrial, freshwater, and marine taxa along latitudinal and elevational gradients. These results establish a thermodynamic basis for the regulation of species diversity and the organization of ecological communities.

Animals↗
PubMed2002

The fractal nature of nature: power laws, ecological complexity and biodiversity.

Underlying the diversity of life and the complexity of ecology is order that reflects the operation of fundamental physical and biological processes. Power laws describe empirical scaling relationships that are emergent quantitative features of biodiversity. These features are patterns of structure or dynamics that are self-similar or fractal-like over many orders of magnitude. Power laws allow extrapolation and prediction over a wide range of scales. Some appear to be universal, occurring in virtually all taxa of organisms and types of environments. They offer clues to underlying mechanisms that powerfully constrain biodiversity. We describe recent progress and future prospects for understanding the mechanisms that generate these power laws, and for explaining the diversity of species and complexity of ecosystems in terms of fundamental principles of physical and biological science.

Ecosystem↗