Showing papers by "Oregon State University published in 1998"

Approximate statistical tests for comparing supervised classification learning algorithms

Abstract: This article reviews five approximate statistical tests for determining whether one learning algorithm outperforms another on a particular learning task. These test sare compared experimentally to determine their probability of incorrectly detecting a difference when no difference exists (type I error). Two widely used statistical tests are shown to have high probability of type I error in certain situations and should never be used: a test for the difference of two proportions and a paired-differences t test based on taking several random train-test splits. A third test, a paired-differences t test based on 10-fold cross-validation, exhibits somewhat elevated probability of type I error. A fourth test, McNemar's test, is shown to have low type I error. The fifth test is a new test, 5 × 2 cv, based on five iterations of twofold cross-validation. Experiments show that this test also has acceptable type I error. The article also measures the power (ability to detect algorithm differences when they do exist)...

Mitigation and Adaptation Strategies for Global Change

Abstract: ▶ Addresses a wide range of timely environment, economic and energy topics ▶ A forum to review, analyze and stimulate the development, testing and implementation of mitigation and adaptation strategies at regional, national and global scales ▶ Contributes to real-time policy analysis and development as national and international policies and agreements are discussed and promulgated ▶ 94% of authors who answered a survey reported that they would definitely publish or probably publish in the journal again

Power-aware routing in mobile ad hoc networks

Abstract: b this paper we present a case for using new power-aware metn.cs for determining routes in wireless ad hoc networks. We present five ~erent metriw based on battery power consumption at nodw. We show that using th=e metrics in a shortest-cost routing algorithm reduces the cost/packet of routing packets by 5-30% over shortwt-hop routing (this cost reduction is on top of a 40-70% reduction in energy consumption obtained by using PAMAS, our MAC layer prtocol). Furthermore, using these new metrics ensures that the mean time to node failure is increased si~cantly. An interesting property of using shortest-cost routing is that packet delays do not increase. Fintiy, we note that our new metrim can be used in most tradition routing protocols for ad hoc networks.

Geographical Variability of the First Baroclinic Rossby Radius of Deformation

Abstract: Global 1 83 18 climatologies of the first baroclinic gravity-wave phase speed c1 and the Rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles. These new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the Northern Hemisphere and the South Atlantic and with a 1 83 18 fine-resolution map of c1 for the tropical Pacific. It is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5%‐15% owing to seemingly minor computational errors. Geographical variations in the new high-resolution maps of c1 and l1 are discussed in terms of a WKB approximation that elucidates the effects of earth rotation, stratification, and water depth on these quantities. It is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the World Ocean. This is rationalized from consideration of the WKB approximation.

PAMAS—power aware multi-access protocol with signalling for ad hoc networks

Abstract: In this paper we develop a new multiaccess protocol for ad hoc radio networks. The protocol is based on the original MACA protocol with the adition of a separate signalling channel. The unique feature of our protocol is that it conserves battery power at nodes by intelligently powering off nodes that are not actively transmitting or receiving packets. The manner in which nodes power themselves off does not influence the delay or throughput characteristics of our protocol. We illustrate the power conserving behavior of PAMAS via extensive simulations performed over ad hoc networks containing 10-20 nodes. Our results indicate that power savings of between 10% and 70% are attainable in most systems. Finally, we discuss how the idea of power awareness can be built into other multiaccess protocols as well.

Entering the Century of the Environment: A New Social Contract for Science

Abstract: As the magnitude of human impacts on the ecological systems of the planet becomes apparent, there is increased realization of the intimate connections between these systems and human health, the economy, social justice, and national security. The concept of what constitutes “the environment” is changing rapidly. Urgent and unprecedented environmental and social changes challenge scientists to define a new social contract. This contract represents a commitment on the part of all scientists to devote their energies and talents to the most pressing problems of the day, in proportion to their importance, in exchange for public funding. The new and unmet needs of society include more comprehensive information, understanding, and technologies for society to move toward a more sustainable biosphere—one which is ecologically sound, economically feasible, and socially just. New fundamental research, faster and more effective transmission of new and existing knowledge to policy- and decision-makers, and better communication of this knowledge to the public will all be required to meet this challenge.

Profit, directional distance functions, and Nerlovian efficiency

Abstract: The directional technology distance function is introduced, given an interpretation as a min-max, and compared with other functional representations of the technology including the Shephard input and output distance functions and the McFadden gauge function. A dual correspondence is developed between the directional technology distance function and the profit function, and it is shown that all previous dual correspondences are special cases of this correspondence. We then show how Nerlovian (profit-based) efficiency measures can be computed using the directional technology distance function.

Integrated pest management: historical perspectives and contemporary developments.

Abstract: Twenty five years after its first enunciation, IPM is recognized as one of the most robust constructs to arise in the agricultural sciences during the second half of the twentieth century. The history of IPM, however, can be traced back to the late 1800s when ecology was identified as the foundation for scientific plant protection. That history, since the advent of modern organosynthetic pesticides, acquired elements of drama, intrigue, jealousy, and controversy that mark the path of many great scientific or technological achievements. Evolution of IPM followed multiple paths in several countries and reached beyond the confines of entomological sciences. Time and space constraints, however, bias this review toward entomology, among the plant protection sciences, and give it an obvious US slant, despite the global impact of IPM.

Computers and language learning: an overview

Abstract: Recent years have shown an explosion of interest in using computers for language teaching and learning. A decade ago, the use of computers in the language classroom was of concern only to a small number of specialists. However, with the advent of multimedia computing and the Internet, the role of computers in language instruction has now become an important issue confronting large numbers of language teachers throughout the world.

The nature of science and instructional practice: Making the unnatural natural

Abstract: The purpose of this study was to delineate the factors that mediate the translation of preservice teachers' conceptions of the nature of science (NOS) into instructional planning and classroom practice. Fourteen preservice secondary science teachers participated in the study. Prior to their student teaching, participants responded to an open-ended questionnaire designed to assess their conceptions of the NOS. Analysis of the questionnaires was postponed until after the completion of student teaching to avoid biasing the collection and/or analysis of other data sources. Throughout student teaching, participants' daily lesson plans, classroom videotapes, and portfolios, and supervisors' weekly clinical observation notes were collated. These data were searched for explicit references to the NOS. Following student teaching, participants were individually interviewed to validate their responses to the open-ended questionnaire and to identify the factors or constraints that mediate the translation of their conceptions of the NOS into their classroom teaching. Participants were found to possess adequate understandings of several important aspects of the NOS including the empirical and tentative nature of science, the distinction between observation and inference, and the role of subjectivity and creativity in science. Many claimed to have taught the NOS through science-based activities. However, data analyses revealed that explicit references to the NOS were rare in their planning and instruction. Participants articulated several factors for this lack of attention to the NOS. These included viewing the NOS as less significant than other instructional outcomes, preoccupation with classroom management and routine chores, discomfort with their own understandings of the NOS, the lack of resources and experience for teaching the NOS, cooperating teachers' imposed restraints, and the lack of planning time. In addition to these volunteered constraints, the data revealed others related to an intricate interaction between participants' perspectives on the NOS, pedagogy, and instructional outcomes. © 1998 John Wiley & Sons, Inc. Sci Ed82:417–436, 1998.

Dark septate endophytes: a review of facultative biotrophic root-colonizing fungi

Abstract: Dark septate root endophytes (DSE) are conidial or sterile fungi (Deuteromycotina, Fungi Imperfecti) likely to be ascomycetous and colonizing plant roots. They have been reported for nearly 600 plant species representing about 320 genera and 100 families. DSE fungi occur from the tropics to arctic and alpine habitats and comprise a heterogeneous group that functionally and ecologically overlaps with soil fungi, saprotrophic rhizoplane-inhabiting fungi, obligately and facultatively pathogenic fungi and mycorrhizal fungi. Numerous species of undescribed sterile and anamorphic taxa may also await discovery. Although DSE are abundant in washed root and soil samples from various habitats, and are easily isolated from surface-sterilized roots of ecto-, ectendo-, endo- and non-mycorrhizal host species, their ecological functions are little understood. Studies of DSE thus far have yielded inconsistent results and only poorly illustrate the role of DSE in their natural habitats. These inconsistencies are largely due to the uncertain taxonomic affinities of the strains of DSE used. In addition, because different strains of a single anamorph taxon seem to vary greatly in function, no clear generalizations on their ecological role have been drawn. This paper reviews the current literature on DSE and the ecology and discusses the need for and direction of future research.

Species Distributions, Land Values, and Efficient Conservation

Abstract: Efforts at species conservation in the United States have tended to be opportunistic and uncoordinated. Recently, however, ecologists and economists have begun to develop more systematic approaches. Here, the problem of efficiently allocating scarce conservation resources in the selection of sites for biological reserves is addressed. With the use of county-level data on land prices and the incidence of endangered species, it is shown that accounting for heterogeneity in land prices results in a substantial increase in efficiency in terms of either the cost of achieving a fixed coverage of species or the coverage attained from a fixed budget.

Marine reserves are necessary but not sufficient for marine conservation

Abstract: The intensity of human pressure on marine systems has led to a push for stronger marine conservation efforts. Recently, marine reserves have become one highly advocated form of marine conservation, and the number of newly designated reserves has increased dramatically. Reserves will be essential for conservation efforts because they can provide unique protection for critical areas, they can provide a spatial escape for intensely exploited species, and they can potentially act as buffers against some management miscalculations and unforeseen or unusual conditions. Reserve design and effectiveness can be dramatically improved by better use of existing scientific understanding. Reserves are insufficient protection alone, however, because they are not isolated from all critical impacts. Communities residing within marine reserves are strongly influenced by the highly variable conditions of the water masses that continuously flow through them. To a much greater degree than in terrestrial systems, the scales of fundamental processes, such as population replenishment, are often much larger than reserves can encompass. Further, they offer no protection from some important threats, such as contamination by chemicals. Therefore, without adequate protection of species and ecosystems outside reserves, effectiveness of reserves will be severely compromised. We outline conditions under which reserves are likely to be effective, provide some guidelines for increasing their conservation potential, and suggest some research priorities to fill critical information gaps. We strongly support vastly increasing the number and size of marine reserves; at the same time, strong conservation efforts outside reserves must complement this effort. To date, most reserve design and site selection have involved little scientific justification. They must begin to do so to increase the likelihood of attaining conservation objectives.

Net primary production of forests: a constant fraction of gross primary production?

Abstract: Considerable progress has been made in our ability to model and measure annual gross primary production (GPP) by terrestrial vegetation. But challenges remain in estimating maintenance respiration (R(m)) and net primary production (NPP). To search for possible common relationships, we assembled annual carbon budgets from six evergreen and one deciduous forest in Oregon, USA, three pine plantations in New South Wales, Australia, a deciduous forest in Massachusetts, USA, and a Nothofagus forest on the South Island of New Zealand. At all 12 sites, a standard procedure was followed to estimate annual NPP of foliage, branches, stems, and roots, the carbon expended in synthesis of these organs (R(g)), their R(m), and that of previously produced foliage and sapwood in boles, branches, and large roots. In the survey, total NPP ranged from 120 to 1660 g C m(-2) year(-1), whereas the calculated fraction allocated to roots varied from 0.22 to 0.63. Comparative analysis indicated that the total NPP/GPP ratio was conservative (0.47 +/- 0.04 SD). This finding supports the possibility of greatly simplifying forest growth models. The constancy of the NPP/GPP ratio also provides an incentive to renew efforts to understand the environmental factors affecting partitioning of NPP above and belowground.

Sources of Fine Organic Aerosol. 9. Pine, Oak, and Synthetic Log Combustion in Residential Fireplaces

Abstract: Combustion of wood in residential fireplaces contributes approximately 14% on an annual average of the total primary fine particle organic carbon (OC) emissions to the Los Angeles urban atmosphere and up to 30% of the fine particulate OC emissions on winter days. This paper presents comprehensive organic compound source profiles for smoke from burning pine, oak, and synthetic logs in residential fireplaces. Mass emission rates are determined for approximately 200 organic compounds including suites of the n-alkanes, n-alkenes, cyclohexylalkanes, n-alkanals, n-alkanoic acids, alkenoic acids, dicarboxylic acids, resin acids, hydroxylated/methyoxylated phenols, lignans, substituted benzenes/benzaldehydes, phytosterols, polycyclic aromatic hydrocarbons (PAHs), and oxy-PAHs. Wood smoke constituents reflect to a great extent the underlying composition of the wood burned: pine and oak logs produce smoke that is enriched in lignin decomposition products, pine smoke is enriched in resin acids and their thermal alteration products, while smoke from the synthetic log burned here bears the major signature of the petroleum products combined with traces of the sawdust components from which it is made. Resin acids are discussed as potential wood smoke tracers in the environment, and it is shown that the time series of resin acids concentrations in the Los Angeles atmosphere follows the extreme seasonal variation in wood use reported in previous emissions inventories for the Los Angeles urban area.

An overview of MODIS capabilities for ocean science observations

Abstract: The Moderate Resolution Imaging Spectroradiometer (MODIS) will add a significant new capability for investigating the 70% of the Earth's surface that is covered by oceans, in addition to contributing to the continuation of a decadal scale time series necessary for climate change assessment in the oceans. Sensor capabilities of particular importance for improving the accuracy of ocean products include high SNR and high stability for narrow or spectral bands, improved onboard radiometric calibration and stability monitoring, and improved science data product algorithms. Spectral bands for resolving solar-stimulated chlorophyll fluorescence and a split window in the 4-/spl mu/m region for SST will result in important new global ocean science products for biology and physics. MODIS will return full global data at 1-km resolution. The complete suite of Levels 2 and 3 ocean products is reviewed, and many areas where MODIS data are expected to make significant, new contributions to the enhanced understanding of the oceans' role in understanding climate change are discussed. In providing a highly complementary and consistent set of observations of terrestrial, atmospheric, and ocean observations, MODIS data will provide important new information on the interactions between Earth's major components.

Effects of global climate change on agriculture: an interpretative review

Abstract: Climate is the primary determinant of agricultural productivity. Concern over the poten- tial effects of long-term climatic change on agriculture has motivated a substantial body of research over the past decade. This body of research addresses possible physical effects of climatic change on agriculture, such as changes in crop and livestock yields, as well as the economic consequences of these potential yield changes. This paper reviews the extant literature on these physical and economic effects and interprets this research in terms of common themes or findings. Of particular interest are findings concerning the role of human adaptations in responding to climate change, possible regional impacts to agricultural systems and potential changes in patterns of food production and prices. Limi- tations and sensitivities of these findings are discussed and key areas of uncertainty are highlighted. Finally, some speculations regarding issues of potential importance in interpreting and using informa- tion on climate change and agriculture are presented.

Flux Sampling Errors for Aircraft and Towers

Abstract: Various errors and influences leading to differences between tower- and aircraft-measured fluxes are surveyed. This survey is motivated by reports in the literature that aircraft fluxes are sometimes smaller than tower-measured fluxes. Both tower and aircraft flux errors are larger with surface heterogeneity due to several independent effects. Surface heterogeneity may cause tower flux errors to increase with decreasing wind speed. Techniques to assess flux sampling error are reviewed. Such error estimates suffer various degrees of inapplicability in real geophysical time series due to nonstationarity of tower time series (or inhomogeneity of aircraft data). A new measure for nonstationarity is developed that eliminates assumptions on the form of the nonstationarity inherent in previous methods. When this nonstationarity measure becomes large, the surface energy imbalance increases sharply. Finally, strategies for obtaining adequate flux sampling using repeated aircraft passes and grid patterns are outlined.

Nature's Subsidies to Shrimp and Salmon Farming

Abstract: Although many fisheries stocks have declined precipitously throughout the world, fish farming--and especially shrimp and salmon farming--has boomed. The increasingly large scale of these enterprises is now having unforeseen ecological consequences on ocean resources through habitat destruction, effluent discharge, exotic species introductions, and heightened fish catch for feed use. Ending unsustainable production practices will require reorienting regulatory policies and fiscal incentives in shrimp- and salmon-producing counties, and enhancing restrictions on environmentally unsound practices.

Authigenic carbonates from the Cascadia subduction zone and their relation to gas hydrate stability

Abstract: Authigenic carbonates are intercalated with massive gas hydrates in sediments of the Cascadia margin. The deposits were recovered from the uppermost 50 cm of sediments on the southern summit of the Hydrate Ridge during the RV Sonne cruise SO110. Two carbonate lithologies that differ in chemistry, mineralogy, and fabric make up these deposits. Microcrystalline high-magnesium calcite (14 to 19 mol% MgCO3) and aragonite are present in both semiconsolidated sediments and carbonate-cemented clasts. Aragonite occurs also as a pure phase without sediment impurities. It is formed by precipitation in cavities as botryoidal and isopachous aggregates within pure white, massive gas hydrate. Variations in oxygen isotope values of the carbonates reflect the mineralogical composition and define two end members: a Mg-calcite with δ18O =4.86‰ PDB and an aragonite with δ18O =3.68‰ PDB. On the basis of the ambient bottom-water temperature and accepted equations for oxygen isotope fractionation, we show that the aragonite phase formed in equilibrium with its pore-water environment, and that the Mg-calcite appears to have precipitated from pore fluids enriched in 18O. Oxygen isotope enrichment probably originates from hydrate water released during gas-hydrate destabilization.

Chain reactions linking acorns to gypsy moth outbreaks and Lyme disease risk.

Abstract: In eastern U.S. oak forests, defoliation by gypsy moths and the risk of Lyme disease are determined by interactions among acorns, white-footed mice, moths, deer, and ticks. Experimental removal of mice, which eat moth pupae, demonstrated that moth outbreaks are caused by reductions in mouse density that occur when there are no acorns. Experimental acorn addition increased mouse density. Acorn addition also increased densities of black-legged ticks, evidently by attracting deer, which are key tick hosts. Mice are primarily responsible for infecting ticks with the Lyme disease agent. The results have important implications for predicting and managing forest health and human health.

Kinetic Bias in Estimates of Coastal Picoplankton Community Structure Obtained by Measurements of Small-Subunit rRNA Gene PCR Amplicon Length Heterogeneity

Abstract: Marine bacterioplankton diversity was examined by quantifying natural length variation in the 5′ domain of small-subunit (SSU) rRNA genes (rDNA) amplified by PCR from a DNA sample from the Oregon coast. This new technique, length heterogeneity analysis by PCR (LH-PCR), determines the relative proportions of amplicons originating from different organisms by measuring the fluorescence emission of a labeled primer used in the amplification reaction. Relationships between the sizes of amplicons and gene phylogeny were predicted by an analysis of 366 SSU rDNA sequences from cultivated marine bacteria and from bacterial genes cloned directly from environmental samples. LH-PCR was used to compare the distribution of bacterioplankton SSU rDNAs from a coastal water sample with that of an SSU rDNA clone library prepared from the same sample and also to examine the distribution of genes in the PCR products from which the clone library was prepared. The analysis revealed that the relative frequencies of genes amplified from natural communities are highly reproducible for replicate sets of PCRs but that a bias possibly caused by the reannealing kinetics of product molecules can skew gene frequencies when PCR product concentrations exceed threshold values.

Cytokine-induced survival of activated T cells in vitro and in vivo

Abstract: Many antigen-specific T cells die after exposure to antigen in animals. These cells also die if they are isolated from animals shortly after activation and cultured. Various cytokines were tested for their ability to interfere with this in vitro death. Surprisingly, tumor necrosis factor α and other inflammatory cytokines did not prevent the in vitro death of activated T cells, even though these cytokines do prevent activated T cell death in animals. Therefore, the inflammatory cytokines probably act on T cells in vivo via an intermediary factor. Four cytokines, interleukin (IL)-2, IL-4, IL-7, and IL-15, did prevent activated T cell death in vitro, with IL-4 and IL-15 more effective than IL-2 or IL-7. These cytokines share a component of their receptors, the common γ chain, γc. Therefore, their collective ability to protect activated T cells from death may be mediated by signals involving γc. To assess their activity in vivo, two of the cytokines, IL-2 and IL-4, were expressed in animals at local sites of superantigen responses. Both cytokines increased the numbers of T cells found at the local sites 14 days later. Interleukin 4 was more effective than IL-2, even though IL-2 stimulates T cell proliferation better than IL-4. This result suggested that IL-4 and related cytokines can promote T cell survival in vivo as well as in vitro. The ability of these cytokines to prevent the death of activated T cells may be important at certain stages of immune responses in animals.

Physical Activity and Minority Women: A Qualitative Study

Abstract: Few physical activity research studies have been conducted with minority women. The purpose of this study was to explore patterns of physical activity among minority women. Focus groups were conducted with volunteers older than age 40. Each group was led by a trained moderator familiar with the ethnic community targeted. The sessions were audiotaped and professionally transcribed. Constructs were researched and codes were developed. Data were analyzed using NUD*IST qualitative analysis program. While participants did not identify themselves as "exercisers," they indicated they got enough physical activity from caregiving, housekeeping, and workday activities. The most common environmental barriers to becoming more physically active included safety, availability, and cost. Personal barriers included lack of time, health concerns, and lack of motivation. Results indicate the importance of terminology and assessment when conducting physical activity research in these populations. Also, results suggest many barriers are changeable with policies and interventions.

The sensitivity of snowmelt processes to climate conditions and forest cover during rain‐on‐snow: a case study of the 1996 Pacific Northwest flood

Abstract: A warm, very wet Pacific storm caused significant flooding in the Pacific Northwest during February 1996. Rapid melting of the mountain snow cover contributed to this flooding. An energy balance snowmelt model is used to simulate snowmelt processes during this event in the Central Cascade Mountains of Oregon. Data from paired open and forested experimental sites at locations at and just below the Pacific Crest were used to drive the model. The event was preceded by cold, stormy conditions that developed a significant snow cover down to elevations as low as 500 m in the Oregon Cascades. At the start of the storm, the depth of the snow cover at the high site (1142 m) was 1.97 m with a snow water equivalent (SWE) of 425 mm, while at the mid-site (968 m) the snow cover was 1.14 m with a SWE of 264 mm. During the 5‐6 day period of the storm the open high site received 349 mm of rain, lost 291 mm of SWE and generated 640 mm of runoA, leaving only 0.22 m of snow on the ground. The mid-site received 410 mm of rain, lost 264 mm of SWE to melt and generated 674 mm of runoA, completely depleting the snow cover. Simulations at adjacent forested sites showed significantly less snowmelt during the event. The snow cover under the mature forest at the high site lost only 44 mm of SWE during the event, generating 396 mm of runoA and leaving 0.69 m of snow. The model accurately simulated both snow cover depth and SWE during the development of the snow cover prior to the storm, and the depletion of the snow cover during the event. This analysis shows that because of the high temperature, humidity and relatively high winds in the open sites during the storm, 60‐90% of the energy for snowmelt came from sensible and latent heat exchanges. Because the antecedent conditions extended the snow cover to very low elevations in the basin, snowmelt generated by condensation during the event made a significant contribution to the flood. Lower wind speeds beneath the forest canopy during the storm reduced the magnitude of the turbulent exchanges at the snow surface, so the contribution of snowmelt to the runoA from forested areas was significantly less. This experiment shows the sensitivity of snowmelt processes to both climate and land cover, and illustrates how the forest canopy is coupled to the hydrological cycle in mountainous areas. #1998 John Wiley & Sons, Ltd.

The role of stress in the mortality of midwestern oaks as indicated by growth prior to death

Abstract: Tree mortality is a critical attribute of forest ecosystems. But the factors responsible for tree mortality are poorly understood, particularly for trees in relatively healthy forests. I evaluated a conceptual model of the tree-mortality process that attributes tree death to a sequence of environmental stresses: long-term stresses that predispose trees to injury by short-term, inciting stresses. Tree-ring growth data from 63 dead overstory oaks (Quercus spp. L.) from seven Midwestern (USA) oak–hickory forests were employed as long-term records of tree vigor. Tree-ring growth data from surviving oaks from the same sites were utilized for comparison and as an indicator of year-to-year variations in environmental stress at each site. Utilizing time-series regression analysis, evidence of the action of inciting stresses was sought in the form of sudden and permanent declines, or interventions, in individual tree growth rates coincident with environmental stresses. Utilizing hierarchical regression analysis, e...

Alteration of Oceanic Volcanic Glass: Textural Evidence of Microbial Activity

Abstract: The subsurface biosphere may constitute as much as 50 percent of Earth9s biomass. Direct and indirect evidence suggests that an extensive biosphere exists in the rocks below the sea floor. This survey of basalts of the Atlantic, Pacific, and Indian Oceans supports the hypothesis that bacteria have colonized much of the upper oceanic crust, which has a volume estimated at 1018 cubic meters. Although this is the largest habitat on Earth, its low abundance of bacteria constitutes much less than 1 percent of Earth9s biomass.