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Jeffrey C Nekola,
Craig D Allen, James H Brown,
Joseph R Burger,
Ana D Davidson,
Trevor S Fristoe,
Marcus J Hamilton,
Sean T Hammond,
Astrid Kodric-Brown,
Norman Mercado-Silva,
Jordan G Okie
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ABSTRACT: Two interacting forces influence all populations: the Malthusian dynamic of exponential growth until resource limits are reached, and the Darwinian dynamic of innovation and adaptation to circumvent these limits through biological and/or cultural evolution. The specific manifestations of these forces in modern human society provide an important context for determining how humans can establish a sustainable relationship with the finite Earth.
Trends in Ecology & Evolution 01/2013; · 15.75 Impact Factor
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Joseph R Burger,
Craig D Allen, James H Brown,
William R Burnside,
Ana D Davidson,
Trevor S Fristoe,
Marcus J Hamilton,
Norman Mercado-Silva,
Jeffrey C Nekola,
Jordan G Okie,
Wenyun Zuo
[show abstract]
[hide abstract]
ABSTRACT: The discipline of sustainability science has emerged in response to concerns of natural and social scientists, policymakers, and lay people about whether the Earth can continue to support human population growth and economic prosperity. Yet, sustainability science has developed largely independently from and with little reference to key ecological principles that govern life on Earth. A macroecological perspective highlights three principles that should be integral to sustainability science: 1) physical conservation laws govern the flows of energy and materials between human systems and the environment, 2) smaller systems are connected by these flows to larger systems in which they are embedded, and 3) global constraints ultimately limit flows at smaller scales. Over the past few decades, decreasing per capita rates of consumption of petroleum, phosphate, agricultural land, fresh water, fish, and wood indicate that the growing human population has surpassed the capacity of the Earth to supply enough of these essential resources to sustain even the current population and level of socioeconomic development.
PLoS Biology 06/2012; 10(6):e1001345. · 11.45 Impact Factor
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ABSTRACT: Theoretical and empirical studies of life history aim to account for resource allocation to the different components of fitness: survival, growth, and reproduction. The pioneering evolutionary ecologist David Lack [(1968) Ecological Adaptations for Breeding in Birds (Methuen and Co., London)] suggested that reproductive output in birds reflects adaptation to environmental factors such as availability of food and risk of predation, but subsequent studies have not always supported Lack's interpretation. Here using a dataset for 980 bird species (Dataset S1), a phylogeny, and an explicit measure of reproductive productivity, we test predictions for how mass-specific productivity varies with body size, phylogeny, and lifestyle traits. We find that productivity varies negatively with body size and energetic demands of parental care and positively with extrinsic mortality. Specifically: (i) altricial species are 50% less productive than precocial species; (ii) species with female-only care of offspring are about 20% less productive than species with other methods of parental care; (iii) nonmigrants are 14% less productive than migrants; (iv) frugivores and nectarivores are about 20% less productive than those eating other foods; and (v) pelagic foragers are 40% less productive than those feeding in other habitats. A strong signal of phylogeny suggests that syndromes of similar life-history traits tend to be conservative within clades but also to have evolved independently in different clades. Our results generally support both Lack's pioneering studies and subsequent research on avian life history.
Proceedings of the National Academy of Sciences 05/2012; 109(27):10937-41. · 9.68 Impact Factor
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ABSTRACT: The world's oceans are undergoing profound changes as a result of human activities. However, the consequences of escalating human impacts on marine mammal biodiversity remain poorly understood. The International Union for the Conservation of Nature (IUCN) identifies 25% of marine mammals as at risk of extinction, but the conservation status of nearly 40% of marine mammals remains unknown due to insufficient data. Predictive models of extinction risk are crucial to informing present and future conservation needs, yet such models have not been developed for marine mammals. In this paper, we: (i) used powerful machine-learning and spatial-modeling approaches to understand the intrinsic and extrinsic drivers of marine mammal extinction risk; (ii) used this information to predict risk across all marine mammals, including IUCN "Data Deficient" species; and (iii) conducted a spatially explicit assessment of these results to understand how risk is distributed across the world's oceans. Rate of offspring production was the most important predictor of risk. Additional predictors included taxonomic group, small geographic range area, and small social group size. Although the interaction of both intrinsic and extrinsic variables was important in predicting risk, overall, intrinsic traits were more important than extrinsic variables. In addition to the 32 species already on the IUCN Red List, our model identified 15 more species, suggesting that 37% of all marine mammals are at risk of extinction. Most at-risk species occur in coastal areas and in productive regions of the high seas. We identify 13 global hotspots of risk and show how they overlap with human impacts and Marine Protected Areas.
Proceedings of the National Academy of Sciences 02/2012; 109(9):3395-400. · 9.68 Impact Factor
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ABSTRACT: Rensch's rule, which states that the magnitude of sexual size dimorphism tends to increase with increasing body size, has evolved independently in three lineages of large herbivorous mammals: bovids (antelopes), cervids (deer), and macropodids (kangaroos). This pattern can be explained by a model that combines allometry, life-history theory, and energetics. The key features are that female group size increases with increasing body size and that males have evolved under sexual selection to grow large enough to control these groups of females. The model predicts relationships among body size and female group size, male and female age at first breeding, death and growth rates, and energy allocation of males to produce body mass and weapons. Model predictions are well supported by data for these megaherbivores. The model suggests hypotheses for why some other sexually dimorphic taxa, such as primates and pinnipeds (seals and sea lions), do or do not conform to Rensh's rule.
The American Naturalist 02/2012; 179(2):169-77. · 4.72 Impact Factor
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Alistair R Evans,
David Jones,
Alison G Boyer, James H Brown,
Daniel P Costa,
S K Morgan Ernest,
Erich M G Fitzgerald,
Mikael Fortelius,
John L Gittleman,
Marcus J Hamilton,
Larisa E Harding,
Kari Lintulaakso,
S Kathleen Lyons,
Jordan G Okie,
Juha J Saarinen,
Richard M Sibly,
Felisa A Smith,
Patrick R Stephens,
Jessica M Theodor,
Mark D Uhen
[show abstract]
[hide abstract]
ABSTRACT: How fast can a mammal evolve from the size of a mouse to the size of an elephant? Achieving such a large transformation calls for major biological reorganization. Thus, the speed at which this occurs has important implications for extensive faunal changes, including adaptive radiations and recovery from mass extinctions. To quantify the pace of large-scale evolution we developed a metric, clade maximum rate, which represents the maximum evolutionary rate of a trait within a clade. We applied this metric to body mass evolution in mammals over the last 70 million years, during which multiple large evolutionary transitions occurred in oceans and on continents and islands. Our computations suggest that it took a minimum of 1.6, 5.1, and 10 million generations for terrestrial mammal mass to increase 100-, and 1,000-, and 5,000-fold, respectively. Values for whales were down to half the length (i.e., 1.1, 3, and 5 million generations), perhaps due to the reduced mechanical constraints of living in an aquatic environment. When differences in generation time are considered, we find an exponential increase in maximum mammal body mass during the 35 million years following the Cretaceous-Paleogene (K-Pg) extinction event. Our results also indicate a basic asymmetry in macroevolution: very large decreases (such as extreme insular dwarfism) can happen at more than 10 times the rate of increases. Our findings allow more rigorous comparisons of microevolutionary and macroevolutionary patterns and processes.
Proceedings of the National Academy of Sciences 01/2012; 109(11):4187-90. · 9.68 Impact Factor
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ABSTRACT: Aim We provide a new quantitative analysis of lizard reproductive ecology. Com-parative studies of lizard reproduction to date have usually considered life-history components separately. Instead, we examine the rate of production (productivity hereafter) calculated as the total mass of offspring produced in a year. We test whether productivity is influenced by proxies of adult mortality rates such as insularity and fossorial habits, by measures of temperature such as environmental and body temperatures, mode of reproduction and activity times, and by environ-mental productivity and diet. We further examine whether low productivity is linked to high extinction risk. Location World-wide. Methods We assembled a database containing 551 lizard species, their phyloge-netic relationships and multiple life history and ecological variables from the lit-erature. We use phylogenetically informed statistical models to estimate the factors related to lizard productivity. Results Some, but not all, predictions of metabolic and life-history theories are supported. When analysed separately, clutch size, relative clutch mass and brood frequency are poorly correlated with body mass, but their product – productivity – is well correlated with mass. The allometry of productivity scales similarly to metabolic rate, suggesting that a constant fraction of assimilated energy is allocated to production irrespective of body size. Island species were less productive than continental species. Mass-specific productivity was positively correlated with envi-ronmental temperature, but not with body temperature. Viviparous lizards were less productive than egg-laying species. Diet and primary productivity were not associated with productivity in any model. Other effects, including lower produc-tivity of fossorial, nocturnal and active foraging species were confounded with phylogeny. Productivity was not lower in species at risk of extinction. Main conclusions Our analyses show the value of focusing on the rate of annual biomass production (productivity), and generally supported associations between productivity and environmental temperature, factors that affect mortality and the number of broods a lizard can produce in a year, but not with measures of body temperature, environmental productivity or diet.
Global Ecology and Biogeography 01/2012; 21:592-602.. · 5.14 Impact Factor
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Joseph R Burger,
Craig D Allen, James H Brown,
William R Burnside,
Ana D Davidson,
Trevor S Fristoe,
Marcus J Hamilton,
Norman Mercado-Silva,
Jeffrey C Nekola,
Jordan G Okie,
Wenyun Zuo
[show abstract]
[hide abstract]
ABSTRACT: The discipline of sustainability
science has emerged in
response to concerns of natural
and social scientists, policymakers,
and lay people about whether the
Earth can continue to support
human population growth and economic
prosperity. Yet, sustainability
science has developed largely independently
from and with little
reference to key ecological principles
that govern life on Earth. A
macroecological perspective highlights
three principles that should
be integral to sustainability science:
1) physical conservation laws govern
the flows of energy and materials
between human systems and
the environment, 2) smaller systems
are connected by these flows to
larger systems in which they are
embedded, and 3) global constraints
ultimately limit flows at
smaller scales. Over the past few
decades, decreasing per capita rates
of consumption of petroleum, phosphate,
agricultural land, fresh water,
fish, and wood indicate that the
growing human population has
surpassed the capacity of the Earth
to supply enough of these essential
resources to sustain even the current
population and level of socioeconomic
development.
PLoS Biology 01/2012; 10(6):e1001345. · 11.45 Impact Factor
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[hide abstract]
ABSTRACT: The temperature size rule (TSR) is the tendency for ectotherms to develop faster but mature at smaller body sizes at higher temperatures. It can be explained by a simple model in which the rate of growth or biomass accumulation and the rate of development have different temperature dependence. The model accounts for both TSR and the less frequently observed reverse-TSR, predicts the fraction of energy allocated to maintenance and synthesis over the course of development, and also predicts that less total energy is expended when developing at warmer temperatures for TSR and vice versa for reverse-TSR. It has important implications for effects of climate change on ectothermic animals.
Proceedings of the Royal Society B: Biological Sciences 11/2011; 279(1734):1840-6. · 5.41 Impact Factor
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ABSTRACT: Humans have a dual nature. We are subject to the same natural laws and forces as other species yet dominate global ecology and exhibit enormous variation in energy use, cultural diversity, and apparent social organization. We suggest scientists tackle these challenges with a macroecological approach-using comparative statistical techniques to identify deep patterns of variation in large datasets and to test for causal mechanisms. We show the power of a metabolic perspective for interpreting these patterns and suggesting possible underlying mechanisms, one that focuses on the exchange of energy and materials within and among human societies and with the biophysical environment. Examples on human foraging ecology, life history, space use, population structure, disease ecology, cultural and linguistic diversity patterns, and industrial and urban systems showcase the power and promise of this approach.
Biological Reviews 07/2011; 87(1):194-208. · 9.07 Impact Factor
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ABSTRACT: Over many millions of years of independent evolution, placental, marsupial and monotreme mammals have diverged conspicuously in physiology, life history and reproductive ecology. The differences in life histories are particularly striking. Compared with placentals, marsupials exhibit shorter pregnancy, smaller size of offspring at birth and longer period of lactation in the pouch. Monotremes also exhibit short pregnancy, but incubate embryos in eggs, followed by a long period of post-hatching lactation. Using a large sample of mammalian species, we show that, remarkably, despite their very different life histories, the scaling of production rates is statistically indistinguishable across mammalian lineages. Apparently all mammals are subject to the same fundamental metabolic constraints on productivity, because they share similar body designs, vascular systems and costs of producing new tissue.
Proceedings of the Royal Society B: Biological Sciences 02/2011; 278(1705):560-6. · 5.41 Impact Factor
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James H Brown,
William R Burnside,
Ana D Davidson,
John P Delong,
William C Dunn,
Marcus J Hamilton,
Norman Mercado-Silva,
Jeffrey C Nekola,
Jordan G Okie,
William H Woodruff,
Wenyun Zuo
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ABSTRACT: The human population and economy have grown exponentially and now have impacts on climate, ecosystem processes, and biodiversity far exceeding those of any other species. Like all organisms, humans are subject to natural laws and are limited by energy and other resources. In this article, we use a macroecological approach to integrate perspectives of physics, ecology, and economics with an analysis of extensive global data to show how energy imposes fundamental constraints on economic growth and development. We demonstrate a positive scaling relationship between per capita energy use and per capita gross domestic product (GDP) both across nations and within nations over time. Other indicators of socioeconomic status and ecological impact are correlated with energy use and GDP. We estimate global energy consumption for alternative future scenarios of population growth and standards of living. Large amounts of energy will be required to fuel economic growth, increase standards of living, and lift developing nations out of poverty. metabolic ecology (McMahon and Bonner 1983, Schneider and Kay 1995, Brown et al. 2004) and empirical approaches from macroecology (Brown 1995) to document energetic constraints on human ecology that have important implica-tions for modern humans. The central role of energy Economic growth and development require that energy and other resources be extracted from the environment to manufacture goods, provide services, and create capital. The central role of energy is substantiated by both theory and data. Key theoretical underpinnings come from the laws of thermodynamics: first, that energy can be neither created nor destroyed, and second, that some capacity to perform useful work is lost as heat when energy is converted from one form to another. Complex, highly organized systems, including human economies, are maintained in states far from thermodynamic equilibrium by the continual intake and transformation of energy. Empirically, the central role of energy in modern human economies is demonstrated by the positive relationship between energy use and economic growth (Shafiee and Topal 2008, Smil 2008, Payne 2010). Here, we take a macroecologi-cal perspective and quantify statistical relationships between energy use and economic activity for 220 nations over 24 years, using data from the International Energy Agency (IEA; www.iea.org/stats/index.asp) and World Resources Institute (WRI; http://earthtrends.wri.org/index.php). Per capita energy consumption for each country is calculated as the sum of human biological metabolism plus the energy obtained from T he human species has an interesting duality. On the one
BioScience 01/2011; 61(19). · 4.62 Impact Factor
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Jonathan L Payne,
Craig R McClain,
Alison G Boyer, James H Brown,
Seth Finnegan,
Michał Kowalewski,
Richard A Krause,
S Kathleen Lyons,
Daniel W McShea,
Philip M Novack-Gottshall,
Felisa A Smith,
Paula Spaeth,
Jennifer A Stempien,
Steve C Wang
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ABSTRACT: The high concentration of molecular oxygen in Earth's atmosphere is arguably the most conspicuous and geologically important signature of life. Earth's early atmosphere lacked oxygen; accumulation began after the evolution of oxygenic photosynthesis in cyanobacteria around 3.0-2.5 billion years ago (Gya). Concentrations of oxygen have since varied, first reaching near-modern values ~600 million years ago (Mya). These fluctuations have been hypothesized to constrain many biological patterns, among them the evolution of body size. Here, we review the state of knowledge relating oxygen availability to body size. Laboratory studies increasingly illuminate the mechanisms by which organisms can adapt physiologically to the variation in oxygen availability, but the extent to which these findings can be extrapolated to evolutionary timescales remains poorly understood. Experiments confirm that animal size is limited by experimental hypoxia, but show that plant vegetative growth is enhanced due to reduced photorespiration at lower O(2):CO(2). Field studies of size distributions across extant higher taxa and individual species in the modern provide qualitative support for a correlation between animal and protist size and oxygen availability, but few allow prediction of maximum or mean size from oxygen concentrations in unstudied regions. There is qualitative support for a link between oxygen availability and body size from the fossil record of protists and animals, but there have been few quantitative analyses confirming or refuting this impression. As oxygen transport limits the thickness or volume-to-surface area ratio-rather than mass or volume-predictions of maximum possible size cannot be constructed simply from metabolic rate and oxygen availability. Thus, it remains difficult to confirm that the largest representatives of fossil or living taxa are limited by oxygen transport rather than other factors. Despite the challenges of integrating findings from experiments on model organisms, comparative observations across living species, and fossil specimens spanning millions to billions of years, numerous tractable avenues of research could greatly improve quantitative constraints on the role of oxygen in the macroevolutionary history of organismal size.
Photosynthesis Research 01/2011; 107(1):37-57. · 3.24 Impact Factor
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Felisa A Smith,
Alison G Boyer, James H Brown,
Daniel P Costa,
Tamar Dayan,
S K Morgan Ernest,
Alistair R Evans,
Mikael Fortelius,
John L Gittleman,
Marcus J Hamilton,
Larisa E Harding,
Kari Lintulaakso,
S Kathleen Lyons,
Christy McCain,
Jordan G Okie,
Juha J Saarinen,
Richard M Sibly,
Patrick R Stephens,
Jessica Theodor,
Mark D Uhen
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ABSTRACT: The extinction of dinosaurs at the Cretaceous/Paleogene (K/Pg) boundary was the seminal event that opened the door for the subsequent diversification of terrestrial mammals. Our compilation of maximum body size at the ordinal level by sub-epoch shows a near-exponential increase after the K/Pg. On each continent, the maximum size of mammals leveled off after 40 million years ago and thereafter remained approximately constant. There was remarkable congruence in the rate, trajectory, and upper limit across continents, orders, and trophic guilds, despite differences in geological and climatic history, turnover of lineages, and ecological variation. Our analysis suggests that although the primary driver for the evolution of giant mammals was diversification to fill ecological niches, environmental temperature and land area may have ultimately constrained the maximum size achieved.
Science 11/2010; 330(6008):1216-9. · 31.20 Impact Factor
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Ana D Davidson,
Eduardo Ponce,
David C Lightfoot,
Ed L Fredrickson, James H Brown,
Juan Cruzado,
Sandra L Brantley,
Rodrigo Sierra-Corona,
Rurik List,
David Toledo,
Gerardo Ceballos
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ABSTRACT: Megaherbivores and small burrowing mammals commonly coexist and play important functional roles in grassland ecosystems worldwide. The interactive effects of these two functional groups of herbivores in shaping the structure and function of grassland ecosystems are poorly understood. In North America's central grasslands, domestic cattle (Bos taurus) have supplanted bison (Bison bison), and now coexist with prairie dogs (Cynomys spp.), a keystone burrowing rodent. Understanding the ecological relationships between cattle and prairie dogs and their independent and interactive effects is essential to understanding the ecology and important conservation issues affecting North American grassland ecosystems. To address these needs, we established a long-term manipulative experiment that separates the independent and interactive effects of prairie dogs and cattle using a 2 x 2 factorial design. Our study is located in the Janos-Casas Grandes region of northwestern Chihuahua, Mexico, which supports one of the largest remaining complexes of black-tailed prairie dogs (C. ludovicianus). Two years of posttreatment data show nearly twofold increases in prairie dog abundance on plots grazed by cattle compared to plots without cattle. This positive effect of cattle on prairie dogs resulted in synergistic impacts when they occurred together. Vegetation height was significantly lower on the plots where both species co-occurred compared to where either or both species was absent. The treatments also significantly affected abundance and composition of other grassland animal species, including grasshoppers and banner-tailed kangaroo rats (Dipodomys spectabilis). Our results demonstrate that two different functional groups of herbivorous mammals, burrowing mammals and domestic cattle, have distinctive and synergistic impacts in shaping the structure and function of grassland ecosystems.
Ecology 11/2010; 91(11):3189-200. · 4.85 Impact Factor
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ABSTRACT: Recent studies suggest that species with similar functional traits will have similar effects on ecosystems, but evidence for redundancy of species impacts is limited. Here we use a long-term experiment to gain insight into functional relationships within a desert rodent community. Experimental removal of kangaroo rats, Dipodomys spp., coupled with the recent, serendipitous colonization of a single species of large pocket mouse Chaetodipus baileyi yielded treatments that differed in the diversity of large granivorous rodents present. We evaluated functional overlap of C. baileyi and the other resident large granivores (i.e. the kangaroo rats) by comparing total energy use of granivorous rodents and total abundance and species richness of small granivores across treatments before and after the arrival of C. baileyi. We found that C. baileyi almost completely compensated for the changes in these key ecosystem-level properties caused by kangaroo rat removal, but it differentially impacted the population dynamics of individual small granivorous rodent species. Thus, its effects were largely complementary, rather than redundant, to those of the missing kangaroo rats. Although short-term or single-measure analyses may suggest redundancy, our results support the longstanding dictum that niches of coexisting species are often similar but rarely, if ever, identical.
Oikos 10/2010; 119(11):1719 - 1726. · 3.06 Impact Factor
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ABSTRACT: It has been known for decades that the metabolic rate of animals scales with body mass with an exponent that is almost always <1, >2/3, and often very close to 3/4. The 3/4 exponent emerges naturally from two models of resource distribution networks, radial explosion and hierarchically branched, which incorporate a minimum of specific details. Both models show that the exponent is 2/3 if velocity of flow remains constant, but can attain a maximum value of 3/4 if velocity scales with its maximum exponent, 1/12. Quarter-power scaling can arise even when there is no underlying fractality. The canonical "fourth dimension" in biological scaling relations can result from matching the velocity of flow through the network to the linear dimension of the terminal "service volume" where resources are consumed. These models have broad applicability for the optimal design of biological and engineered systems where energy, materials, or information are distributed from a single source.
Proceedings of the National Academy of Sciences 09/2010; 107(36):15816-20. · 9.68 Impact Factor
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ABSTRACT: The diversification of life involved enormous increases in size and complexity. The evolutionary transitions from prokaryotes to unicellular eukaryotes to metazoans were accompanied by major innovations in metabolic design. Here we show that the scalings of metabolic rate, population growth rate, and production efficiency with body size have changed across the evolutionary transitions. Metabolic rate scales with body mass superlinearly in prokaryotes, linearly in protists, and sublinearly in metazoans, so Kleiber's 3/4 power scaling law does not apply universally across organisms. The scaling of maximum population growth rate shifts from positive in prokaryotes to negative in protists and metazoans, and the efficiency of production declines across these groups. Major changes in metabolic processes during the early evolution of life overcame existing constraints, exploited new opportunities, and imposed new constraints.
Proceedings of the National Academy of Sciences 07/2010; 107(29):12941-5. · 9.68 Impact Factor
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ABSTRACT: Arid systems are characterized by spatiotemporal variability in resources and, as such, make ideal systems for examining the role of resource limitation in the long-term dynamics of populations. Using 28 years of data, we examine the long-term relationships of 3 guilds of desert rodent consumers with precipitation and primary productivity in a changing environment. Lags in rodent response to precipitation increased with increasing trophic level over the entire time series, consistent with resource limitation. However, we found that consumer– resource dynamics are complex and variable through time. Precipitation exhibited increasing influence on both primary producers and consumers in this system over time. Experimental evidence suggests that reorganization of community composition, coincident with environmental change, likely explains some of the increasing influence of precipitation. Additional, indirect evidence suggests some role for increasing shrub density and changing precipitation regimes. Results from our long-term study demonstrate that the global phenomena of changing precipitation regimes, increasing frequency of extreme climatic events, and shrub encroachment are likely to have strong, interactive impacts in reorganizing ecological communities, with significant consequences for ecosystem dynamics.
Journal of Mammalogy 03/2010; 91:787-797. · 1.61 Impact Factor
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ABSTRACT: Aim Ecogeographical ‘rules’, large-scale patterns in ecological variables across geographical space, can provide important insights into the mechanisms of evolution and ecological assembly. However, interactions between rules could obscure both the observation of large-scale patterns and their interpretation. Here, we examine a system of three variables interrelated by ecogeographical rules – the latitudinal increase in body size within closely related homeotherms (Bergmann’s rule), the negative allometry of clutch size (Calder’s rule) and the latitudinal increase in clutch size (Lack’s rule) – in a global dataset of birds.Location Global.Methods We used linear regressions and meta-analysis techniques to quantify the three rules across clades and through the taxonomic hierarchy. Path analysis was used to quantify interactions between rules at multiple taxonomic levels, as a function of both phylogenetic inheritance of traits and indirect feedbacks between the three rules. Independent contrasts analyses were performed on four clades with available phylogenies, and the taxonomic partitioning of variation in each trait was quantified.Results Standardizing across all clades, Lack’s and Bergmann’s rules were supported at all taxonomic levels, with Calder’s rule being supported at the order level. Lack’s rule was consistently stronger and more often detected than the other two rules. Path analysis showed that the indirect effects often outweighed the direct effects of Calder’s rule at the genus level and Bergmann’s rule at the order level. Strong interactions between Calder’s and Bergmann’s rules led to a trade-off between the rules depending on taxonomic resolution.Main conclusions We found strong interactions between Bergmann’s, Lack’s and Calder’s rules in birds, and these interactions varied in strength and direction over the taxonomic hierarchy and among avian clades. Ecogeographical rules may be masked by feedbacks from other, correlated variables, even when the underlying selective mechanism is operating. The apparently conflicting pairwise relationships among clutch size, body size and latitude illustrate the difficulty of interpreting individual pairwise correlations without recognition of interdependence with other variables.
Journal of Biogeography 12/2009; 37(1):47 - 56. · 4.54 Impact Factor
