DOCSLIB.ORG

Energy Flow in Ecosystems Ecology Unit

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Energy Flow in Ecosystems Ecology Unit REMEMBER: YOU MUST Please finish notes HAND-WRITE YOUR on consumers NOTES!!! before taking Energy Flow Notes NOTES WILL BE DUE TOMORROW IN CLASS. Types of Consumers 1. Carnivores: kill and eat other animals. 2. Herbivores: obtain energy and nutrients by eating plant leaves, roots, seeds, or fruits. 3. Omnivores: diet includes both plant and animals. 4. Scavengers: consume the carcasses of dead animals. 5. Decomposers: “feed” by chemically breaking down organic matter. 6. Detritivores: feed on detritus particles. Beyond Consumer Categories Categorizing consumers does not express the real complexity in nature. Seeds and fruits are usually rich in energy and nutrients and easy to digest. Leaves are generally poor in nutrients are usually difficult to digest. Herbivores that eat leaves often differ greatly from animals that eat fruits and seeds. Energy Flow in Ecosystems Ecology Unit THINK ABOUT IT • What happens to energy stored in body tissues when one organism eats another? That energy moves from the “eaten” to the “eater.” • You have learned that the flow of energy through an ecosystem always begins with photosynthetic or chemosynthetic primary producers. • Where it goes from there depends literally on who eats whom! Food Chains and Food Webs Key Question: How does energy flow through ecosystems? In every ecosystem, primary producers and consumers are linked through feeding relationships. Energy flows through an ecosystem in a one-way stream, from primary producers to various consumers. ENERGY Food Chains Definition: a series of steps in which organisms transfer energy by eating and being eaten. Food chains may vary in length. Short: Grass is eaten by rabbit, which is then eaten by a fox. Long: Algae is eaten by herring; herring is eaten by cod; cod is eaten by a seal; and seals are eaten by orca whales. Primary Producers Terrestrial food chains: plants Aquatic food chains: phytoplankton and attached algae In most ecosystems, feeding relationships are much more Food Webs complicated than those described in a simple chain. One reason for this is that many animals eat more than one kind of food. Example: On Africa’s Serengeti Plain, lions may prey upon gazelles, buffalos, and zebras. Ecologists call this network of feeding interactions a food web. Food Chains Within Food Webs Each path you trace through a food web is a food chain. A food web is a network that contains all the food chains in an ecosystem. Food Webs Decomposers and Detritivores in Food Webs Decomposers and detritivores are as important in most food webs as other consumers are. Most producers die without being eaten. In the detritus pathway, decomposers convert that dead material into detritus, which is eaten by detritivores. The process of decomposition releases nutrients that can be used by primary producers. Therefore, decomposers recycle nutrients in food webs! Analyzing Energy Flow Through Trophic Levels Each step in a food chain or food web is called a trophic level. Primary producers make up the first trophic level. Various consumers make occupy the other levels. Ecological pyramids are models that show the relative amount of energy or matter contained within each trophic level in a given food chain or food web. Pyramids of energy. Pyramids of biomass. Pyramids of numbers. Analyzing Energy Flow Through Trophic Levels Pyramids of Energy Theoretically, there is no limit to the number of trophic levels in a food web or the number or organisms that live on each level. But… only a small portion of the energy that enters any trophic level is available to organisms at the next level. Energy availability limits the size of food webs. Organisms expend much of the energy they acquire on life processes, and most of the remaining energy is released into the environment as heat. On average, only 10% of the energy available within one trophic level is transferred to the next level. Analyzing Energy Flow Through Trophic Levels Pyramids of Biomass and Numbers The total amount of living tissue within a given trophic level is called its biomass. Unit: grams per unit area The amount of biomass a given trophic level can support is determined by the amount of energy available. A pyramid of biomass is a model that illustrates the relative amount of living organic matter available at each trophic level in an ecosystem. A pyramid of numbers is a model that shows the relative number of individual organisms at each trophic level in an ecosystem. In most ecosystems, the pyramid of numbers is similar in shape to the pyramid of biomass. The number of individuals on each level decrease from the level below. Analyzing Energy Flow Through Trophic Levels Pyramids of Biomass and Numbers: Special Case In some cases, consumers are much smaller in size and mass than the organisms they feed upon. Example: countless caterpillars can feed off a few oak trees. Oak trees have a large biomass. Oak tree only represents one organism. In such cases, the pyramid of numbers may be turned upside down, but the pyramid of biomass usually has the Pyramid of numbers is normal orientation. upside down..
Load more

Recommended publications
  • Terrestrial Decomposition
    Terrestrial Decomposition • Objectives – Controls over decomposition • Litter breakdown • Soil organic matter formation and dynamics – Carbon balance of ecosystems • Soil carbon storage 1 Overview • In terrestrial ecosystems, soils (organic horizon + mineral soil) > C than in vegetation and atmosphere combined 2 Overview • Decomposition is: 1. Major pathway for C loss from ecosystems 2. Central to ecosystem C loss and storage 3 Overview 4 Incorporation 1 year later Overview • Predominant controls on litter decomposition are fairly well constrained 1. Temperature and moisture 2. Litter quality • N availability • Lignin concentration • Lignin:N • Mechanisms for soil organic matter stabilization: 1. Recalcitrance (refers to chemistry) 2. Physical protection • Within soil aggregates • Organo-mineral associations 3. Substrate supply regulation (energetic limitation) 5 Overview • Disturbance can override millenia in a matter of days or years: 1. Land use change 2. Invasive species 3. Climate change • Understanding the mechanistic drivers of decomposition, soil organic matter formation, and carbon stabilization help us make management decisions, take mitigation steps, and protect resources. 6 Overview Native Ōhiʻa - Koa forest Conversion to Reforestation in grass-dominated pasture (80 yr) Eucalyptus plantation (10 yr) Conventional sugar cane harvest. 20° C 18° C 16° C 14° C 7 Sustainable ratoon harvest. Decomposition • Decomposition is the biological, physical and chemical breakdown of organic material – Provides energy for microbial growth
    [Show full text]
  • A Study of Differences in Vertical Phosphorus Profiles Within the Sediments of Selected Florida Lakes As Related to Trophic Dynamics
    University of Central Florida STARS Retrospective Theses and Dissertations 1976 A Study of Differences in Vertical Phosphorus Profiles Within the Sediments of Selected Florida Lakes as Related to Trophic Dynamics Edgar Allen Stewart III University of Central Florida, [email protected] Part of the Engineering Commons Find similar works at: https://stars.library.ucf.edu/rtd University of Central Florida Libraries http://library.ucf.edu This Masters Thesis (Open Access) is brought to you for free and open access by STARS. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of STARS. For more information, please contact [email protected]. STARS Citation Stewart, Edgar Allen III, "A Study of Differences in Vertical Phosphorus Profiles Within the Sediments of Selected Florida Lakes as Related to Trophic Dynamics" (1976). Retrospective Theses and Dissertations. 258. https://stars.library.ucf.edu/rtd/258 • A STUDY OF DIFFEREilCES IN VERTICAL PHOSPHORUS PRO FILES WliHIN THE SEDIMENTS OF SELECTED FLORIUA LAKES AS [{ELATED TO °fROPfiiC DYNArHCS BY EDGAR ALLE N STEHART III B.S., University of Florida, 1971 THESIS SubmHted o'n partial fulfiliment of the requirements for the degree of Mdster of Science °in the Graduate Studies Program of the Co 11 eye of Engi neer i ng of Florida Technological University , Or l ando, Florida 1976 • A STUDY OF DIFFERENCES IN VERTICAL PHOSPHOROUS PROFILES WITHIN THE SEDIMENTS OF SELECTED FLORIDA LAKES AS RELATED TO TROPHIC DYNAMICS BY E. ALLEIJ STEWART I II \ ABSTRACT Seve"a 1 Flori da 1akes with different docu'llcnted traphi c sta te indi ces were se lected for sediment analysis .
    [Show full text]
  • Plant Species Effects on Nutrient Cycling: Revisiting Litter Feedbacks
    Review Plant species effects on nutrient cycling: revisiting litter feedbacks Sarah E. Hobbie Department of Ecology, Evolution and Behavior, University of Minnesota, St. Paul, MN 55108, USA In a review published over two decades ago I asserted reinforce those gradients and patterns of NPP, focusing that, along soil fertility gradients, plant traits change in on feedbacks operating through plant litter decomposition. ways that reinforce patterns of soil fertility and net Specifically, I evaluate two key assumptions underlying primary productivity (NPP). I reevaluate this assertion the plant litter feedback idea: (i) plant litter traits vary in light of recent research, focusing on feedbacks to NPP predictably along fertility gradients, and (ii) such variation operating through litter decomposition. I conclude that reinforces soil fertility gradients through effects on decom- mechanisms emerging since my previous review might position and litter N release. Given the number of synthetic weaken these positive feedbacks, such as negative cross-site analyses of plant traits and their consequences effects of nitrogen on decomposition, while others for nutrient cycling over the past two decades, the time is might strengthen them, such as slower decomposition ripe for revisiting my original assertions. Indeed, I show of roots compared to leaf litter. I further conclude that that my original assertion is more nuanced and complex predictive understanding of plant species effects on than originally claimed. In particular, I discuss the need to nutrient cycling will require developing new frameworks consider leaf litter decomposition more carefully and move that are broadened beyond litter decomposition to con- beyond consideration of leaf litter feedbacks to a more sider the full litter–soil organic matter (SOM) continuum.
    [Show full text]
  • Organic Matter Decomposition in Simulated Aquaculture Ponds Group Fish Culture and Fisheries Daily Supervisor(S) Dr
    O rganic matter decomposition in simulated aquaculture ponds Beatriz Torres Beristain Promotor: Prof. Dr. J.A .J. V erreth H oogleraar in de V isteelt en V isserij W ageningen U niversiteit C o-promotor: Dr. M .C .J. V erdegem U niversitair docent bij the Leerstoelgroep V isteelt en V isserij W ageningen U niversiteit Samenstelling promotiecommissie: Prof. Dr. Y . A vnimelech Technion, Israel Institute of Technology Prof. Dr. Ir. H .J. Gijzen U N ESC O -IH E, Delf, N etherlands Prof. Dr. Ir. M . W .A . V erstegen W ageningen U niversiteit Prof. Dr. Ir. A .A . K oelmans W ageningen U niversiteit Dit onderzoek is uitgevoerd binnen de onderzoekschool W IA S O rganic matter decomposition in simulated aquaculture ponds Beatriz Torres Beristain Proefschrift Ter verkrijging van de graad van doctor O p gezag van de rector magnificus van W ageningen U niversiteit, Prof. Dr. Ir. L. Speelman, In het openbaar te verdedigen O p dinsdag 15 A pril 2005 des namiddags te half tw ee in de A ula Torres Beristain, B. O rganic matter decomposition in simulated aquaculture ponds PhD thesis, Fish C ulture and Fisheries Group, W ageningen Institute of A nimal Sciences. W ageningen U niversity, P.O . Box 338, 6700 A H W ageningen, The N etherlands. - W ith R ef. œW ith summary in Spanish, Dutch and English ISBN : 90-8504-170-8 A Domingo, Y olanda y A lejandro Table of contents C hapter 1 General introduction. 1 C hapter 2 R eview microbial ecology and role in aquaculture ponds.
    [Show full text]
  • Fermentation and Anaerobic Decomposition in a Hot Spring
    Fermentation and anaerobic decomposition in a hot spring microbial mat by Karen Leigh Anderson A thesis submitted in partial fulfillment of requirements for the degree of Master of Science in Microbiology Montana State University © Copyright by Karen Leigh Anderson (1984) Abstract: Fermentation was investigated in a low sulfate hot spring microbial mat (Octopus Spring) according to current models on anaerobic decomposition. The mat was studied to determine what fermentation products accumulated, where in the mat they accumulated, and what factors affected their accumulation. Mat samples were incubated under dark anaerobic conditions to measure accumulation of fermentation products. Acetate and propionate (ca. 3:1) were the major products to accumulate in a 55&deg,C mat. Other products accumulated to a much lesser extent. Incubation of mat samples of varying thickness showed that fermentation occurred in the top 4mm of the mat. This has interesting implications for fermentative organisms in the mat due to the diurnal changes in mat oxygen concentrations. Fermentation measured in mat samples collected at various temperatures (50&deg,-70°C) showed acetate and propionate to be the major accumulation products. According to the interspecies hydrogen transfer model, the hydrogen concentration in a system affects the types of fermentation products produced. At a 65° C site, with natural high hydrogen levels, and at a 55°C site, with active methanogenesis, fermentation product accumulation was compared. There was a greater ratio of reduced fermentation products to acetate, with the exception of propionate, at 65°C. Ethanol accumulated at the 65°C site, as did lactate, though to a lesser extent.
    [Show full text]
  • SCI Grade 7 Invasive Species
    Invasive Species: A Study of the Disruption of an Ecosystem’s Dynamics Life Science: Ecosystems, Interactions, Energy, and Dynamics, Grade 7 This unit engages students in an exploration of ecosystem dynamics as seen through the study of invasive species. The unit focuses on the effects of resource availability in an ecosystem and changes in biological or physical components of an ecosystem on organism populations. Students explore how invasive species are introduced and what impact they have on local food webs; and how ecosystems react to the introduction of invasive species. This unit is designed for students in grade 7, using research, models, data analysis, and writing about invasive species to understand changes in an ecosystem. This Model Curriculum Unit is designed to illustrate effective curriculum that lead to expectations outlined in the Draft Revised Science and Technology/Engineering Standards (www.doe.mass.edu/STEM/review.html) as well as the MA Curriculum Frameworks for English Language Arts/Literacy and Mathematics. This unit includes lesson plans, a Curriculum Embedded Performance Assessment, and related resources. In using this unit it is important to consider the variability of learners in your class and make adaptations as necessary. This work is licensed by the MA Department of Elementary & Secondary Education under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License (CC BY-NC-SA 3.0). Educators may use, adapt, and/or share. Not for commercial use. To view a copy of the license, visit http://creativecommons.org/licenses/by-nc-sa/3.0/ July 2015 Page 1 of 77 This document was prepared by the Massachusetts Department of Elementary and Secondary Education Mitchell D.
    [Show full text]
  • 102: Trophic Dynamics
    102: Trophic Dynamics CORY C CLEVELAND, ALAN R TOWNSEND AND DIANE M MCKNIGHT Institute of Arctic and Aipine Research, University of Coiorado, Bouider, CO, US The carbon (C) and water cycles are intimately linked in terrestrial ecosystems. Thus, an understanding of the processes regulating transfers of water in terrestrial ecosystems requires an understanding of the carbon cycle, and in particular, the factors constraining carbon movement in the soii-piant-atmo sphere continuum and through trophic levels in ecosystems. The linkages between the C and the water cycles are mediated primarily through biological processes, and are bidirectional in nature. For example, precipitation (and hence ecosystem water avaiiabiiity) strongly regulates plant growth and biogeochemicai cycling in soils. Subsequently, plant growth and soil biogeochemistry strongly influence evaporation and atmospheric water vapor (and hence precipitation). Plant growth and soil processes are also cyciicaiiy linked. Thus, plant and soil interactions can have important implications for water cycling. However, while major climatic variables (including precipitation) may drive biological patterns and processes at large scales, other ecological interactions also regulate both plant and soil processes. An appreciation of these ecological factors is important to understanding the relationship between C and water, and to predicting how global environmental change is likely to affect the interactions between the C and water cycles. INTRODUCTION ecosystems is fnndamental to onr nnderstanding of ecosys­ tem water balance, both at present and in the fntnre. From an ecological perspective, plant photosynthesis regn- lates the carbon balance and prodnctivity of the biosphere, PRIMARY PRODUCTION controls linxes of C between the biosphere and the atmo­ Gross Primary Production sphere, and is responsible for virtnally all of the biochemi­ In 1942, Lindeman ontlined the fnndamental ecological cal prodnction of organic matter.
    [Show full text]
  • Long-Term Nutrient Enrichment Decouples Predator and Prey Production
    Long-term nutrient enrichment decouples predator and prey production John M. Davisa,1,2, Amy D. Rosemonda, Susan L. Eggertb, Wyatt F. Crossa,3, and J. Bruce Wallacec aOdum School of Ecology, University of Georgia, Athens, GA 30602; bUS Department of Agriculture Forest Service, Northern Research Station, Grand Rapids, MN 55744; and cDepartment of Entomology, University of Georgia, Athens, GA 30602 Edited by William Bowden, University of Vermont, and accepted by the Editorial Board November 23, 2009 (received for review July 28, 2009) Increased nutrient mobilization by human activities represents one amplify variability in predator–prey cycles and even extirpate of the greatest threats to global ecosystems, but its effects on predator populations (i.e., “the paradox of enrichment”) (9). ecosystem productivity can differ depending on food web structure. More recent models predict that nutrient enrichment can fur- When this structure facilitates efficient energy transfers to higher ther alter predator–prey interactions by increasing the dominance trophic levels, evidence from previous large-scale enrichments of predator-resistant primary consumers, diverting energy flow to suggests that nutrients can stimulate the production of multiple predator-resistant pathways that are relatively inaccessible to top trophic levels. Here we report results from a 5-year continuous predators (10, 11). Small-scale mesocosm experiments have nutrient enrichment of a forested stream that increased primary shown that such a reduction in trophic efficiency can ultimately consumer production, but not predator production. Because of decrease predator production, even with sustained increases in strong positive correlations between predator and prey production primary consumer productivity (i.e., resulting in a trophic decou- (evidence of highly efficient trophic transfers) under reference pling) (12, 13).
    [Show full text]
  • Decomposition Responses to Climate Depend on Microbial Community Composition
    Decomposition responses to climate depend on microbial community composition Sydney I. Glassmana,b,1, Claudia Weihea, Junhui Lic, Michaeline B. N. Albrighta,d, Caitlin I. Loobya,e, Adam C. Martinya,c, Kathleen K. Tresedera, Steven D. Allisona, and Jennifer B. H. Martinya aDepartment of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697; bDepartment of Microbiology and Plant Pathology, University of California, Riverside, CA 92521; cDepartment of Earth System Science, University of California, Irvine, CA 92697; dBioscience Division, Los Alamos National Laboratory, Los Alamos, NM 87545; and eDepartment of Biological Sciences, University of Denver, CO 80210 Edited by Mary K. Firestone, University of California, Berkeley, CA, and approved October 10, 2018 (received for review June 29, 2018) Bacteria and fungi drive decomposition, a fundamental process in soil moisture and extracellular enzyme production across a natural the carbon cycle, yet the importance of microbial community climate gradient (16). composition for decomposition remains elusive. Here, we used an Given that the factors regulating decomposition are often 18-month reciprocal transplant experiment along a climate gradient context dependent and can vary in their influence across a range in Southern California to disentangle the effects of the microbial of spatial and temporal scales (17, 18), we hypothesized that community versus the environment on decomposition. Specifically, decomposition responses to changing climatic conditions would we tested whether the decomposition response to climate change depend on microbial community composition. To test this hy- depends on the microbial community. We inoculated microbial pothesis, we conducted the largest microbial community trans- decomposers from each site onto a common, irradiated leaf litter plant experiment to date.
    [Show full text]
  • Organic Matter Decomposition and Ecosystem Metabolism As Tools to Assess the Functional Integrity of Streams and Rivers–A Systematic Review
    water Review Organic Matter Decomposition and Ecosystem Metabolism as Tools to Assess the Functional Integrity of Streams and Rivers–A Systematic Review Verónica Ferreira 1,* , Arturo Elosegi 2 , Scott D. Tiegs 3 , Daniel von Schiller 4 and Roger Young 5 1 Marine and Environmental Sciences Centre–MARE, Department of Life Sciences, University of Coimbra, 3000–456 Coimbra, Portugal 2 Faculty of Science and Technology, University of the Basque Country (UPV/EHU), P.O. Box 644, 48080 Bilbao, Spain; [email protected] 3 Department of Biological Sciences, Oakland University, Rochester, MI 48309, USA; [email protected] 4 Department of Evolutionary Biology, Ecology and Environmental Sciences, Institut de Recerca de l’Aigua (IdRA), University of Barcelona, Diagonal 643, 08028 Barcelona, Spain; [email protected] 5 Cawthron Institute, Private Bag 2, Nelson 7042, New Zealand; [email protected] * Correspondence: [email protected] Received: 4 November 2020; Accepted: 8 December 2020; Published: 15 December 2020 Abstract: Streams and rivers provide important services to humans, and therefore, their ecological integrity should be a societal goal. Although ecological integrity encompasses structural and functional integrity, stream bioassessment rarely considers ecosystem functioning. Organic matter decomposition and ecosystem metabolism are prime candidate indicators of stream functional integrity, and here we review each of these functions, the methods used for their determination, and their strengths and limitations for bioassessment. We also provide a systematic review of studies that have addressed organic matter decomposition (88 studies) and ecosystem metabolism (50 studies) for stream bioassessment since the year 2000. Most studies were conducted in temperate regions. Bioassessment based on organic matter decomposition mostly used leaf litter in coarse-mesh bags, but fine-mesh bags were also common, and cotton strips and wood were frequent in New Zealand.
    [Show full text]
  • Inherent Factors Affecting Soil Organic Matter
    Soil organic matter (SOM) is the organic component of soil, consisting of three primary parts including small (fresh) plant residues and small living soil organisms, decomposing (active) organic matter, and stable organic matter (humus). Soil organic matter serves as a reservoir of nutrients for crops, provides soil aggregation, increases nutrient exchange, retains moisture, reduces compaction, reduces surface crusting, and increases water infiltration into soil. Components vary in proportion and have many intermediate stages (Figure 1). Plant residues on the soil surface such as leaves, manure, or crop residue are not considered SOM and are usually removed from soil samples by sieving through a 2 mm wire mesh before analysis. Soil organic matter content can be estimated in the field and tested in a lab to provide estimates for Nitrogen, Phosphorus and Sulfur mineralized available for crop production and adjust fertilizer recommendations. Soil organic matter impacts the rate of surface applied herbicides along with soil pH necessary to effectively control weeds. Soil organic matter impacts the potential for herbicide carryover for future crops, and amount of lime necessary to raise pH. Figure 1. Major soil organic matter components (Source: The Soil Food Web, USDA-NRCS). Inherent Factors Affecting Soil Organic Matter Inherent factors affecting soil organic matter such warm and humid and slower in cool, dry climates. as climate and soil texture cannot be changed. Organic matter also decomposes faster when soil is Climatic conditions, such as rainfall, temperature, well aerated (higher oxygen levels) and much moisture, and soil aeration (oxygen levels) affect slower on saturated wet soils (refer to soil the rate of organic matter decomposition.
    [Show full text]
  • Soil Food Web: Implications to Soil Health
    Soil Food Web: Implications to Soil Health Dr. Sajeemas “Mint” Pasakdee, Soil Scientist/Agronomist Advisor, Student Operated Organic Farm CIT-Jordan College of Agri. Sci. & Tech., Fresno State 1 Outline • Soil organisms and their interactions • What do soil organisms do? • Where do soil organisms live? • Food web structure • When are soil organisms active? • How is the food web measured? • Living soils—Bacteria; Fungi; Earthworms • Soil Environment 2 Organisms & Their Interaction 3 4 What do soil organisms do? Soil organisms support plant health as • decompose organic matter, • cycle nutrients, • enhance soil structure, • control the populations of soil organisms including crop pests. 5 Organic Matter • Food sources for soil organisms • Agricultural top soil ~1-6% (In CA, ~1-3% SOM) 6 Where do soil organisms live? • Around roots(rhizosphere) • Plant litter (C sources) • Humus (stabilized organic matter) • Surface of soil aggregates 7 Typical Food Web Structure • bacterial-dominated food webs o Grassland & Agri Soils o Ratio of fungi to bacteria, ~1:1 for productive agri. soils • fungal-dominated food webs o Ratio of fungal to bacterial, ~5:1 to 10:1 in a deciduous forest and 100:1 to 1000:1 in a coniferous forest 8 9 When are soil organisms active? 10 How is the food web measured? • Counting. Organism groups (bacteria, protozoa, arthropods, etc.); or subgroups (bacterial-feeding, fungal-feeding, and predatory nematodes), are counted and through calculations, can be converted to biomass. • Measuring activity levels. The amount of by-products, i.e., respiration (CO2); nitrification and decomposition rates • Measuring cellular constituents. Biomass carbon, nitrogen, or phosphorus; Enzymes; Phospholipids and other lipids; DNA and RNA 11 12 Soil Bacteria • One-celled organisms – generally 4/100,000 of an inch wide (1 µm) • A teaspoon of productive soil generally contains between 100 million and 1 billion bacteria (~two cows per acre).
    [Show full text]