Catherine Badgley

Organic agriculture and the global food supply

The principal objections to the proposition that organic agriculture can contribute significantly to the global food supply are low yields and insufficient quantities of organically acceptable fertilizers. We evaluated the universality of both claims. For the first claim, we compared yields of organic versus conventional or low-intensive food production for a global dataset of 293 examples and estimated the average yield ratio (organic : non-organic) of different food categories for the developed and the developing world. For most food categories, the average yield ratio was slightly 1.0 for studies in the developing world. With the average yield ratios, we modeled the global food supply that could be grown organically on the current agricultural land base. Model estimates indicate that organic methods could produce enough food on a global per capita basis to sustain the current human population, and potentially an even larger population, without increasing the agricultural land base. We also evaluated the amount of nitrogen potentially available from fixation by leguminous cover crops used as fertilizer. Data from temperate and tropical agroecosystems suggest that leguminous cover crops could fix enough nitrogen to replace the amount of synthetic fertilizer currently in use. These results indicate that organic agriculture has the potential to contribute quite substantially to the global food supply, while reducing the detrimental environmental impacts of conventional agriculture. Evaluation and review of this paper have raised important issues about crop rotations under organic versus conventional agriculture and the reliability of grey-literature sources. An ongoing dialogue on these subjects can be found in the Forum editorial of this issue.

Faunal and environmental change in the late Miocene Siwaliks of northern Pakistan

Abstract The Siwalik formations of northern Pakistan consist of deposits of ancient rivers that existed throughout the early Miocene through the late Pliocene. The formations are highly fossiliferous with a diverse array of terrestrial and freshwater vertebrates, which in combination with exceptional lateral exposure and good chronostratigraphic control allows a more detailed and temporally resolved study of the sediments and faunas than is typical in terrestrial deposits. Consequently the Siwaliks provide an opportunity to document temporal differences in species richness, turnover, and ecological structure in a terrestrial setting, and to investigate how such differences are related to changes in the fluvial system, vegetation, and climate. Here we focus on the interval between 10.7 and 5.7 Ma, a time of significant local tectonic and global climatic change. It is also the interval with the best temporal calibration of Siwalik faunas and most comprehensive data on species occurrences. A methodological focus of this paper is on controlling sampling biases that confound biological and ecological signals. Such biases include uneven sampling through time, differential preservation of larger animals and more durable skeletal elements, errors in age-dating imposed by uncertainties in correlation and paleomagnetic timescale calibrations, and uneven taxonomic treatment across groups. We attempt to control for them primarily by using a relative-abundance model to estimate limits for the first and last appearances from the occurrence data. This model also incorporates uncertainties in age estimates. Because of sampling limitations inherent in the terrestrial fossil record, our 100-Kyr temporal resolution may approach the finest possible level of resolution for studies of vertebrate faunal changes over periods of millions of years. Approximately 40,000 specimens from surface and screenwash collections made at 555 localities form the basis of our study. Sixty percent of the localities have maximum and minimum age estimates differing by 100 Kyr or less, 82% by 200 Kyr or less. The fossils represent 115 mammalian species or lineages of ten orders: Insectivora, Scandentia, Primates, Tubulidentata, Proboscidea, Pholidota, Lagomorpha, Perissodactyla, Artiodactyla, and Rodentia. Important taxa omitted from this study include Carnivora, Elephantoidea, and Rhinocerotidae. Because different collecting methods were used for large and small species, they are treated separately in analyses. Small species include insectivores, tree shrews, rodents, lagomorphs, and small primates. They generally weigh less than 5 kg. The sediments of the study interval were deposited by coexisting fluvial systems, with the larger emergent Nagri system being displaced between 10.1 and 9.0 Ma by an interfan Dhok Pathan system. In comparison to Nagri floodplains, Dhok Pathan floodplains were less well drained, with smaller rivers having more seasonally variable flow and more frequent avulsions. Paleosol sequences indicate reorganization of topography and drainage accompanying a transition to a more seasonal climate. A few paleosols may have formed under waterlogged, grassy woodlands, but most formed under drier conditions and more closed vegetation. The oxygen isotopic record also indicates significant change in the patterns of precipitation beginning at 9.2 Ma, in what may have been a shift to a drier and more seasonal climate. The carbon isotope record demonstrates that after 8.1 Ma significant amounts of C4 grasses began to appear and that by 6.8 Ma floodplain habitats included extensive C4 grasslands. Plant communities with predominantly C3 plants were greatly diminished after 7.0 Ma, and those with predominantly C4 plants, which would have been open woodlands or grassy woodlands, appeared as early as 7.4 Ma. Inferred first and last appearances show a constant, low level of faunal turnover throughout the interval 10.7–5.7-Ma, with three short periods of elevated turnover at 10.3, 7.8, and 7.3–7.0 Ma. The three pulses account for nearly 44% of all turnover. Throughout the late Miocene, species richness declined steadily, and diversity and richness indices together with data on body size imply that community ecological structure changed abruptly just after 10 Ma, and then again at 7.8 Ma. Between 10 and 7.8 Ma the large-mammal assemblages were strongly dominated by equids, with more balanced faunas before and after. The pattern of appearance and disappearance is selective with respect to inferred habits of the animals. Species appearing after 9.0 Ma are grazers or typical of more open habitats, whereas many species that disappear can be linked to more closed vegetation. We presume exceptions to this pattern were animals of the mixed C3/C4 communities or the wetter parts of the floodplain that did not persist into the latest Miocene. The pace of extinction accelerates once there is C4 vegetation on the floodplain. The 10.3 Ma event primarily comprises disappearance of taxa that were both common and of long duration. The event does not correlate to any obvious local environmental or climatic event, and the pattern of species disappearance and appearance suggests that biotic interactions may have been more important than environmental change. The 7.8 Ma event is characterized solely by appearances, and that at 7.3 Ma by a combination of appearances and disappearances. These two latest Miocene events include more taxa that were shorter ranging and less common, a difference of mode that developed between approximately 9.0 and 8.5 Ma when many short-ranging and rare species began to make appearances. Both events also show a close temporal correlation to changes in floodplain deposition and vegetation. The 7.8 Ma event follows the widespread appearance of C4 vegetation and is coincident with the shift from equid-dominated to more evenly balanced large-mammal assemblages. The 7.3 to 7.0 Ma event starts with the first occurrence of C4-dominated floras and ends with the last occurrence of C3-dominated vegetation. Absence of a consistent relationship between depositional facies and the composition of faunal assemblages leads us to reject fluvial system dynamics as a major cause of faunal change. The close correlation of latest Miocene species turnover and ecological change to expansion of C4 plants on the floodplain, in association with oxygen isotopic and sedimentological evidence for increasingly drier and more seasonal climates, causes us to favor explanations based on climatic change for both latest Miocene pulses. The Siwalik record supports neither “coordinated stasis” nor “turnover pulse” evolutionary models. The brief, irregularly spaced pulses of high turnover are characteristic of both the stasis and pulse models, but the high level of background turnover that eliminates 65–70% of the initial species shows there is no stasis in the Siwalik record. In addition, the steadily declining species richness and abrupt, uncoordinated changes in diversity do not fit either model.

Counting individuals in mammalian fossil assemblages from fluvial environments

Many paleoecological analyses utilize estimates of the relative abundances of taxa in fossil or subfossil assemblages. Such estimates depend upon determination of the number of individuals present or some other measure of the amount of material collected for each taxon. I assess the validity of methods currently used to estimate numbers of individuals per taxon in mammalian assemblages. For any method of counting selected, the underlying assumptions about the probability of association among skeletal elements should correspond to processes of accumulation for the assemblage, as inferred from its taphonomic characteristics. No method is appropriate for all mammalian assemblages. Equating the number of individuals with the number of specimens per taxon is the appropriate method when formerly articulated material has been widely dispersed and has accumulated as isolated specimens. Determining the minimum number of individuals represented by multiple skeletal elements is appropriate when material originally accumulated in articulation. For mammalian assemblages from Middle Siwalik (late Miocene) sediments of Pakistan, different methods of counting are appropriate for assemblages from different sedimentary environments. For assemblages produced by current transport, I counted each specimen as a single individual. For assemblages produced by the activities of predators and scavengers, I determined the minimum number of individuals. Two taphonomic processes that influence the degree of association among skeletal remains are mortality and transport. Taphonomic histories that combine different causes of mortality and different conditions of transport produce fossil assemblages with expected taphonomic characteristics. These include the amount of articulated material, the spatial distribution of specimens, the presence of hydraulic sorting, the frequency of juvenile remains, and patterns of bone damage. Taphonomic characteristics of fossil assemblages do not permit all combinations of mortality and transport to be distinguished. Processes of transport generally obscure taphonomic characteristics imposed by different agents of mortality. INTRODUCTION

Ecological changes in Miocene mammalian record show impact of prolonged climatic forcing

Geohistorical records reveal the long-term impacts of climate change on ecosystem structure. A 5-myr record of mammalian faunas from floodplain ecosystems of South Asia shows substantial change in species richness and ecological structure in relation to vegetation change as documented by stable isotopes of C and O from paleosols. Between 8.5 and 6.0 Ma, C4 savannah replaced C3 forest and woodland. Isotopic historical trends for 27 mammalian herbivore species, in combination with ecomorphological data from teeth, show three patterns of response. Most forest frugivores and browsers maintained their dietary habits and disappeared. Other herbivores altered their dietary habits to include increasing amounts of C4 plants and persisted for >1 myr during the vegetation transition. The few lineages that persisted through the vegetation transition show isotopic enrichment of δ13C values over time. These results are evidence for long-term climatic forcing of vegetation structure and mammalian ecological diversity at the subcontinental scale.

Taphonomy of mammalian fossil remains from Siwalik rocks of Pakistan

Siwalik rocks of Pakistan are a virtually continuous, continental sedimentary sequence, extend- ing in age from 18 to 1 ma B.P. This paper describes taphonomic features of late Miocene mammalian assemblages from a highly fossiliferous interval about 400 m thick, based on field documentation of sedimentary environments at 42 fossil localities and systematic fossil collection of 21 localities. Within a broadly fluvial system, I recognize four sedimentary environments of bone accumulation, distinguished by lithology, unit-thickness, unit-geometry, contacts, sedimentary structures, and relationship to adjacent units. Each environment corresponds to an association of lithofacies. Facies Association I is interpreted as the persistent, major channel bodies of a meandering fluvial system; Facies Association II as coarse-grained flood deposits, such as crevasse splays, deposited beyond the main channels; Facies Association III as channel margins, including levees and swales; and Facies Association IV as predominantly subaerial floodplains. Taphonomic features of bone assemblages from each facies association include skeletal-element com- position, surface distribution of specimens, degree of articulation, hydraulic equivalence between organic and inorganic sedimentary particles, frequency of juvenile remains, size distribution of fauna, and an estimate of duration of accumulation of individual fossil localities. The distribution of these features among the four facies associations suggests that bone assemblages in Facies Associations I and II accu- mulated by the action of currents in river channels or floods, whereas bone assemblages in Facies Associ- ations III and IV accumulated through concentration by biological agents and/or attrition at a repeatedly used site of predation. Inclusion in fluvial accumulations depends on initial availability of skeletal remains and hydraulic characteristics of individual skeletal elements, but not taxonomic identity per se. For biological accumu- lations, however, taxonomic composition reflects the preferences of the individual agents of accumulation. The probability of preservation of taxa in fluvial accumulations is probably mainly a function of body size, as reflected in the sizes of isolated skeletal elements. Thus, in this Siwalik system, bone assemblages that experienced fluvial transport are better representations of original community composition than bone

Can organic agriculture feed the world

Renewable Agriculture and Food Systems is a multidisciplinary journal which focuses on the science that underpins economically environmentally and socially sustainable approaches to agriculture and food production. The journal publishes original research and review articles on the economic, ecological and environmental impacts of agriculture; the effective use of renewable resources and biodiversity in agro-ecosystems; and the technological and sociological implications of sustainable food systems. It also contains an open discussion Forum, which presents lively discussions on new and provocative topics. However, the opinions of the Forum and responses are solely those of the authors and do not necessarily reflect the opinions of Renewable Agriculture and Food Systems or Cambridge University Press.

Diversity dynamics of Miocene mammals in relation to the history of tectonism and climate

Continental biodiversity gradients result not only from ecological processes, but also from evolutionary and geohistorical processes involving biotic turnover in landscape and climatic history over millions of years. Here, we investigate the evolutionary and historical contributions to the gradient of increasing species richness with topographic complexity. We analysed a dataset of 418 fossil rodent species from western North America spanning 25 to 5 Ma. We compared diversification histories between tectonically active (Intermontane West) and quiescent (Great Plains) regions. Although diversification histories differed between the two regions, species richness, origination rate and extinction rate per million years were not systematically different over the 20 Myr interval. In the tectonically active region, the greatest increase in originations coincided with a Middle Miocene episode of intensified tectonic activity and global warming. During subsequent global cooling, species richness declined in the montane region and increased on the Great Plains. These results suggest that interactions between tectonic activity and climate change stimulate diversification in mammals. The elevational diversity gradient characteristic of modern mammalian faunas was not a persistent feature over geologic time. Rather, the Miocene rodent record suggests that the elevational diversity gradient is a transient feature arising during particular episodes of Earths history.

Sampling and faunal turnover in early Eocene mammals

Badgley, C. and Gingerich, P. D., 1988. Sampling and faunal turnover in Early Eocene mammals. Palaeogeogr., Palaeoclimatol., Palaeoecol., 63: 141-157. Faunal turnovers in the fossil record are episodes of synchronous appearance and disappearance of species from a community, often resulting in net change in species richness. We studied the biostratigraphic record of faunal turnover involving early Wasatchian (early Eocene) mammals from the Clarks Fork Basin, Wyoming, U.S.A. Two faunal turnovers occur in this record -- one at the base of the Wasatchian, comprised mainly of appearances of taxonomically and ecologically distinctive species, and a later one, Biohorizon A of Schankler (1980), comprised mainly of disappearances, especially of carnivorous species. This study focuses on Biohorizon A. In the record of the Clarks Fork Basin, Biohorizon A may be an artifact of sampling. Sample size and species richness are highly correlated (r = 0.95) throughout this record. Moreover, sample size and species richness fluctuate markedly between successive stratigraphic intervals; peaks of appearances coincide with large sample sizes and peaks of disappearances with low sample sizes. The peaks and valleys in fossil productivity over time mask the real timing of appearances and disappearances of species. Changes in fossil productivity in the stratigraphic section may result from changes in exposure area, taphonomic factors, or ecological factors. Evaluation of the effects of sampling is a necessary prerequisite for investigating the chronological and ecological significance of faunal turnovers.

Comparative paleoecology of Paleogene and Neogene mammalian faunas: body-size structure

Abstract Species size is correlated with many aspects of life history, ecology, and behavior, which means that size changes within species, lineages, and faunas represent an important component of evolutionary paleoecology. Comparison of Paleogene mammalian faunas from the Bighorn, Clarks Fork, and Crazy Mountains basins of Wyoming and Montana with Neogene mammalian faunas from the Siwalik Group of northern Pakistan reveals similarities and differences in patterns of size change through intervals of 10 m.y. Two approaches to size change are presented. The first is to evaluate changes in the size distribution of faunas over three time intervals in each sequence. Rank-ordered size distributions, or cenograms, are used to depict faunal size structure for non-carnivorous species. The slopes and gaps in different regions of the size spectrum reflect conditions of vegetation and climate, by analogy with modern mammalian faunas (Legendre, 1986, 1989). For the Paleogene and Neogene faunas, subtle changes over time in size structure reflect changes in local vegetation and climate. The Paleogene cenograms suggest a habitat shift from mesic to humid forest, and the Neogene cenograms suggest a shift from open woodland to savannah scrub. These interpretations are supported by concurrent changes in trophic structure, faunal turnover, and in floral and geologic indicators. The second approach focuses on size change within species and lineages in several families of predominantly herbivorous species. For 60 Paleogene species and 39 Neogene species, change in average species size over successive biostratigraphic intervals is assessed by a criterion of doubling or halving of body mass relative to the preceding interval. New occurrences are compared to established species of the same genus and of the same family. In both records, size increases occur slightly more often than size decreases. The size distribution of groups changes more often through appearances of species of more than double or less than half the size of established species of the same group or by disappearances, rather than through rapid change of size within species. The pattern of change in median size and size range of contemporaneous species varies among families in both records. Three causes of evolutionary size change—climatic change, competition, and predation—are evaluated. In both records, climatic change and interspecific competition are considered the principle mechanisms for the observed changes.

Flat latitudinal gradient in Paleocene mammal richness suggests decoupling of climate and biodiversity

Mammal faunas from western North America exhibit no significant change in species richness with latitude during the Torrejonian (ca. 63–60 Ma) and Tiffanian (ca. 60–58 Ma) North American Land Mammal Ages, in contrast to a strong richness gradient in modern mammalian faunas of the same region today. The latitudinal gradient in oxygen isotope composition of mammalian bioapatite from the Paleocene faunas is similar to that of modern meteoric and surface waters, suggesting that the temperature gradient in the Paleocene was similar to the modern one. The flat richness gradient in the middle Paleocene indicates either different responses to climatic gradients of faunas dominated by extinct clades of placental mammals or distinct ecological processes during the Paleocene diversification of mammals following the end-Cretaceous mass extinction.