Ecosystems and Biomes Study Guide

Ecosystem Basics

  • Individual: A single organism (e.g., elk).
  • Population: A group of individuals of the same species (e.g., a herd of elk).
  • Community: All living organisms in an area.
  • Ecosystem: All living and nonliving things in an area (e.g., plants, animals, rocks, soil, water, air).
  • Biome: A large area with similar climate conditions that determine the plant and animal species present (e.g., tropical rainforest).

Organism Interactions

  • Mutualism (+/+): A relationship benefiting both organisms (e.g., coral reef, lichen).
  • Competition (-/-): Organisms fighting over a resource like food or shelter, limiting population size.
  • Predation (+/-): One organism uses another for energy (e.g., hunters, parasites, herbivores).
  • Commensalism (+/0): A relationship benefiting one organism without impacting the other (e.g., birds nesting in trees).

Predation

  • True Predators: Carnivores that kill and eat prey for energy (e.g., leopard and giraffe).
  • Herbivores: Plant eaters that consume plants for energy (e.g., giraffe and tree).
  • Parasites: Use a host organism for energy, often without killing it, and frequently live inside the host (e.g., mosquitoes, tapeworms, sea lamprey).
  • Parasitoids: Lay eggs inside a host organism; the eggs hatch, and the larvae eat the host for energy (e.g., parasitic wasps, bot fly).

Symbiosis

  • Symbiosis involves organisms of different species living closely together. Mutualism, commensalism, and parasitism are all symbiotic relationships.
  • Coral and Algae: Corals provide reef structure and CO_2 for algae; algae provide sugars for the coral's energy.
  • Lichen: Composite organism of fungi living with algae; algae provide sugars (energy), and fungi provide nutrients.

Competition

  • Resource Partitioning: Different species using the same resource in different ways to reduce competition, which reduces population size.
  • Temporal Partitioning: Using resources at different times (e.g., wolves and coyotes hunting at different times).
  • Spatial Partitioning: Using different areas of a shared habitat (e.g., different length roots).
  • Morphological Partitioning: Using different resources based on evolved body features.

Terrestrial (Land) Biomes

  • Biomes are large areas sharing a combination of average yearly temperature and precipitation (climate).
  • The community of organisms (plants & animals) in a biome are uniquely adapted to live in that biome.
  • Examples: Camels & cacti in deserts; shrubs & wildflowers in grasslands.

Biome Characteristics

  • Biomes are defined by annual temperature and precipitation averages.
  • Latitude determines temperature and precipitation, influencing biome distribution.
  • Tundra & Boreal: Higher latitude (60°+).
  • Temperate: Mid-latitude (30°-60°).
  • Tropical: Closer to the equator.

Nutrient Availability

  • Tropical Rainforest: Nutrient-poor soil due to high competition.
  • Boreal Forest: Nutrient-poor soil due to low temperature and decomposition rate.
  • Temperate Forest: Nutrient-rich soil due to lots of dead organic matter and warm temperature/moisture for decomposition.
  • Frozen soils of tundra don’t allow nutrients in dead organic matter to be broken down by decomposers, leading to low soil nutrients, low water availability and few plants survive here.

Shifting Biomes

  • Biomes shift location on Earth as climate changes.
  • Example: Warming climate shifts boreal forests north as tundra permafrost melts.

Aquatic Biomes

  • Depth: Influences sunlight penetration for photosynthesis.
  • Temperature: Warmer water holds less dissolved O_2, supporting fewer organisms.
  • Salinity: Salt level determines species survival and water usability.
  • Flow: Influences plant and organism survival and O_2 dissolution.

Freshwater: Rivers & Lakes

  • Rivers: High O_2 due to flow, carrying nutrient-rich sediments.
  • Lakes: Standing bodies of fresh water.
    • Littoral: shallow water with emergent plants
    • Limnetic: where light can reach (photosynthesis), no rooted plants, only phytoplankton
    • Profundal: too deep for sunlight (no phots.)
    • Benthic: murky bottom where inverts (bugs) live, nutrient-rich sediments

Freshwater: Wetlands

  • Wetlands have soil submerged/saturated in water for at least part of the year, shallow enough for emergent plants.
  • Wetland plants are adapted to submerged roots (e.g., cattails, lily pads, reeds).
    • Stores excess water during storms, lessening floods
    • Recharges groundwater by absorbing rainfall into soil
    • Roots of wetland plants filter pollutants from water draining through
    • Highly plant growth due to lots of water & nutrients (dead organic matter) in sediments

Estuaries

  • Areas where rivers empty into the ocean, mixing fresh and salt water.
  • High productivity due to nutrients in sediments.
  • Salt Marsh: Temperate climate estuary habitat, a breeding ground for fish and shellfish.
  • Mangrove Swamps: Tropical climate estuary habitat with mangrove trees that stabilize shoreline and provide habitat.

Coral Reef

  • Warm, shallow waters beyond the shoreline; the most diverse marine biome.
  • Mutualistic relationship between coral (animals) and algae (plants).
  • Coral uses CO2 to create calcium carbonate exoskeleton and provides CO2 to algae; algae provide sugar to coral via photosynthesis.

Intertidal Zones

  • Narrow coastline band between high and low tide.
  • Organisms adapted to crashing waves and direct sunlight/heat.
    *Different organisms are adapted to live in different Zones. Example: Spiral wrack (type of seaweed) curls up & secretes mucus to retain water during low tide

Open Ocean

  • Low productivity per area, with algae and phytoplankton.
  • Photic zone: area where sunlight can reach (photosynthesis).
  • Aphotic zone (abyssal): area too deep for sunlight
  • Algae & phytoplankton of ocean produce a lot of earth’s O2 & absorb a lot of atmospheric CO2.

Carbon Cycle Overview

  • Movement of carbon-containing molecules (CO2, glucose, CH4) between sources and sinks.
  • Some steps are very quick (FF combustion); some are very slow (sedimentation & burial)
  • Leads to imbalance in which reservoirs or sinks are storing carbon.
  • Atmosphere is a key C reservoir; increasing levels in the atmosphere lead to global warming.
  • Carbon Sink: A reservoir storing more carbon than it releases (e.g., ocean, plants, soil).
  • Carbon Source: Processes adding carbon to the atmosphere (e.g., fossil fuel combustion, animal agriculture, deforestation).

Photosynthesis & Cellular Respiration

  • Photosynthesis removes CO_2 from the atmosphere and converts it to glucose.
  • Cellular respiration is done by plants and animals to release stored energy, using O2 to break down glucose and release CO2 into atmosphere.
  • Both processes are very quick, cycle C between biosphere & atmosphere in balanced amount (no net C increase in atm.)
  • Photosynthesis is CO2 sink, cellular respiration is CO2 source (adds CO_2 to atm.).

Ocean & Atmosphere

  • Direct exchange: CO_2 moves directly between the atmosphere and the ocean.
  • Increasing atmospheric CO2 increases ocean CO2, leading to ocean acidification.
  • Algae & phytoplankton take CO_2 out of the ocean & atm. through photosynthesis.
  • Sedimentation: Marine organisms' bodies sink, breaking down into sediments containing C.
  • Burial: Pressure compresses sediments into sedimentary stone over time, creating a long-term C reservoir.

Burial, Extraction, & Combustion

  • Burial is a slow, geological process storing C in underground sinks like sedimentary rock or fossil fuels.
  • Fossil Fuels (FF): coal, oil, and Nat. gas are formed from fossilized remains of org. Matter. Ex: dead ferns (coal) or marine algae & plankton (oil)
  • Burial (formation of FFs) takes far longer than extraction & combustion, which means they increase concentration of CO_2 in atmosphere.

Nitrogen Cycle Overview

  • Nitrogen = critical plant & animal nutrient
    *Atmosphere = main N reservoir
    *All living things need N for DNA & amino acids to make proteins
  • Nitrogen in the atmosphere exists mostly as N_2 gas, which is not usable by plants or animals.

Nitrogen Fixation

  • Process of turning N2 gas into useable NH3 (ammonia) or NO_3-(nitrate).
  • Bacterial Fixation: Bacteria convert N2 into ammonia (NH3), in symbiotic relationship with plant root nodules
  • Synthetic Fixation: Humans combust FFs to convert N2 gas into nitrate (NO3-

Other Nitrogen Cycle Steps

  • Nitrification: Conversion of NH4 into nitrite (NO2 -) and then nitrate (NO_3) by soil bacteria.
  • Ammonification: Soil bacteria, microbes & decomposers converting waste & dead biomass back into NH_3 and returning it to soil
  • Assimilation: Plants and animals taking N in and incorporating it into their bodies.
  • Denitrification: Conversion of soil N (NO3) into nitrous oxide (N2O) gas which returns to atmosphere.

Human Impacts on Nitrogen Cycle

  • Leaching & Eutrophication: Fertilizers lead to nitrates leaching into water.
    *Nitrates runoff into local waters, causing algae blooms that block sun & kill other aq. plants
  • Ammonia Volatilization: Excess fertilizer results in NH_3 gas entering the atmosphere.
  • Climate: Nitrous oxide is a greenhouse gas produced by denitrification of nitrate in agricultural soils.
  • NH_3 gas in atm = acid precipitation (rain) and respiratory irritation in humans & animals.

Phosphorus Cycle Basics

  • Movement of P atoms & molecules between sources & sinks/reservoirs
    *Rocks & sediments containing P minerals = major reservoirs
    *Takes a long time for P minerals to be weathered out of rocks & carried into soil/bodies of water
  • No gas phase occurs in P Cycle (doesn’t enter atmosphere).
  • P is a limiting nutrient, limiting plant growth in ecosystems often limited by P availability in soil/water
    *P is needed by all organisms for DNA, ATP (energy), bone & tooth enamel in some animals

Phosphorus Sources

  • Weathering of rocks is a major natural source, releasing phosphate (PO_4^{-3}).
  • Synthetic sources = mining phosphate minerals and adding to products like synthetic fertilizers & detergents/cleaners
  • Phosphates from detergents & cleaners enter bodies of water via wastewater from homes
    *Weathering is so slow that P is often a limiting nutrient in aquatic & terrestrial ecosystems

Assimilation & Excretion/Decomp.

  • Plants absorb P through roots, assimilating it into tissues; animals assimilate P by eating plants or animals.
  • Animal waste, plant matter, & other biomass is broken down by bacteria/soil decomposers that return phosphate to soil.
  • P sediments can be compressed into sed. rock over long time periods by pressure of overlying water

Eutrophication (too much N & P)

  • Extra N and P lead to eutrophication (excess nutrients), fueling excessive algae growth.
    *Can occur from fertilizer runoff, human/animal waste contamination
    *Algae bloom covers surface of water, blocking sunlight & killing plants below surface
    *Lower O_2 levels (dissolved oxygen) in water kills aquatic animals, especially fish

Hydrologic (Water) Cycle Overview

  • Movement of H_2O (in different states) between sources & sinks
  • Energy from the sun drives the H_2O cycle.
  • Ocean = largest water reservoir. Ice caps & groundwater are smaller reservoirs, but contain fresh, useable water for humans

Evaporation & Evapotranspiration

  • 2 main sources of water cycle it from liquid on earth back into the atmosphere.
    *Transpiration: process plants use to draw groundwater from roots up to their leaves
    *Evapotranspiration: amount of H_2O that enters atm. from transpiration & evap. combined
  • Both processes are driven by energy from the sun.

Runoff & Infiltration

  • Precipitation (rain) either flows over the earth’s surface into a body of water (runoff) or trickles through soil down into groundwater aquifers (infiltration)
  • Precipitation recharges groundwater through infiltration, but only if ground is permeable (able to let water pass through)
  • Runoff recharges surface waters, but can also carry pollutants into water sources

Primary Productivity

  • Primary Productivity: rate that solar energy is converted into org. compounds via photosynthesis over a unit of time. Units: kcal/m2/yr.
    *Aka: rate of photosynthesis of all producers in an area over a given period of time
    *High PP = high plant growth = lots of food & shelter for animals. Ecosystems with high PP are usually more biodiverse (more div. of species) than ecosystems with low PP

Calculating PP

  • Gross Primary Productivity (GPP): The total amount of sun energy (light) that plants capture and convert to energy (glucose) through photosynthesis
  • Net Primary Productivity (NPP): The amount of energy (biomass) leftover for consumers after plants have used some for respiration

NPP = GPP - RL

  • Respiration loss (RL): plants use up some of the energy they generate via photosynthesis by doing cell. respiration

Ecological Efficiency

  • The portion of incoming solar energy captured by plants & converted into biomass (NPP or food available for consumers)
  • Generally, only 1% of all incoming sunlight is captured & converted into GPP via photosynthesis
  • Of that 1%, only about 40% (or 0.4% of total incoming solar energy) is converted into biomass/plant growth (NPP)

Trends in Productivity

  • The more productive a biome is, the wider the diversity of animal life it can support (high. biodiv.)
  • Water availability, higher temperature, and nutrient availability are all factors that lead to high NPP
    *Shortage of any of these three factors will lead to decreased NPP
    Ex: Desert (low H2O & nutrients) Tundra (low temp & liquid H2O) Open ocean (low nutrients)

Conservation of Matter & Energy

  • Matter & energy are never created or destroyed; they only change forms
    Biogeochem. cycles demonstrate conservation of matter (C/N/H_2O/P)
    Food webs demonstrate conservation of energy
  • 1st law of thermodynamics: energy is never created or destroyed

2nd Law of Thermodynamics

  • Each time energy is transferred, some of it is lost as heat
  • 10% Rule: in trophic pyramids, only about 10% of the energy from one level makes it to the next level; the other 90% is used by the organism & lost as heat
    *Because *available* energy decreases with each step up the food chain, a trophic pyramid (trohp = nourishment or growth) is used to model how energy moves through an ecosystem

Trophic Levels & 10% Biomass

  • Producers (plants) convert sun’s light energy into chemical energy (glucose)
  • Primary Consumers eat plants (herbivores)
  • Secondary Consumers eat primary consumers (carnivores & omnivores)
  • Tertiary Consumers eat secondary consumers (top predators)
  • Since energy is needed for growth & only 10% of energy transfers from one level to the next, only 10% of the biomass can be grown/supported

Calculating Biomass & Energy

  • To calculate biomass or energy available at the next level up, move the decimal place one spot to the left (or divide by 10)

Food Web Basics

  • Shows how matter & energy flow through an ecosystem, from organism to organism
  • Arrows in food webs indicate direction of energy flow (point to the org. taking in the energy)

Food Web vs. Chain

  • Food chains just show one, linear path of energy & matter
  • Food webs have at least 2 different, interconnected food chains
    *Webs show that organisms can exist at different trophic levels grass → hare → owl (sec. cons.) grass → grasshopper → robin → owl (tert. cons.)

Interactions & Trophic Cascade

  • Food webs show how increases or decreases in pop. size of a given species impact the rest of the food web
    *Trophic cascade: removal or addition of a top predator has a ripple effect down through lower troph. Levels Ex: decline in wolf pop. = increase in deer pop. which leads to overgrazing & decline in trees