Chapter 55: Ecosystems and Restoration Ecology

55.1: Physical laws govern energy flow and chemical cycling in ecosystemsCool Ecosystem

Ecosystem = sum of all organisms living in a given area and the abiotic factors with which they interact

o Can encompass a vast or small areao Biosphere = global ecosystem, composite of all local ecosystems

Dynamic processes of ecosystems:o Energy flow = usually as sunlight which is converted to chemical

energy by autotrophs passed to heterotrophs and dissipated as heato Chemical elements = commonly carbon and nitrogen, cycled among

abiotic and biotic components of an ecosystem Photosynthetic and chemosynthetic organisms assimilate

elements in organic form from air, soil, and water, and incorporate them into biomass consumed by animals

Returned in inorganic form to environment by metabolism of plants and animals by organisms like bacteria and fungi

Energy and matter and transformed in ecosystems through photosynthesis and feeding relationships

o Matter can be recycled, energy can’t ecosystem must be powered by continuous influx of energy from external sources (sun)

Resources critical to human survival are products of ecosystem processes Can study an ecosystem by altering environmental factors and see response

Conservation of Energy First law of thermodynamics: energy can’t be created or destroyed, only

transferred or transformedo Account for transfer of energy through an ecosystem from input as

solar radiation to release as heat from organisms Ecosystem ecology involves computing energy budgets and tracing energy

flow through ecosystems to understand factors that control energy transfero Helps determine how many organisms a habitat can support and how

much food humans can harvest Second law of thermodynamics: every exchange of energy increases entropy

of the universeo Energy conversions are inefficient, some energy is always lost as heat

Measure efficiency of ecological energy conversions Law of conservation of mass = matter cannot be created or destroyed

Allows determination of how much of a chemical element cycles within an ecosystem or is gained or lost by the ecosystem over time

Chemical elements are continually recycled within ecosystems Elements aren’t significantly gained or lost on a global scale but can be

gained or lost from a particular ecosystemo Most gains/losses are small compared to amounts recycled within

o Balance between input and output determines whether an ecosystem is a source or a sink for a given element

Energy, Mass, and Trophic Levels Primary producers = trophic level supports all others, consists of autotrophs

o Mostly photosynthetic organisms that use light energy to synthesize sugars and organic compounds used as fuel for cellular respiration and building material for growth

o Main autotrophs: plants, algae, photosynthetic prokaryotes Heterotrophs are in trophic levels above primary producers

o Depend on outputs of primary producers for energy Primary consumers = herbivores, eat plants and primary producers Secondary consumers = carnivores, eat herbivores Tertiary consumers = carnivores that eat other carnivores Detritivores/decomposers = heterotrophs that get their energy from detritus

o Detritus = nonliving organic material (dead organisms, feces, etc.)o Eaten by secondary and tertiary consumerso Important groups: prokaryotes and fungio Secrete enzymes that digest organic material and absorb breakdown

products linking consumers and primary producerso Recycle chemical elements back to primary producers

Convert organic matter from al trophic levels to inorganic compounds usable by primary producers, closing loop

Allows producers to recycle elements into organic compounds55.2: Energy and other limiting factors control primary production in ecosystemsEcosystem Energy Budgets

Primary production = amount of light energy converted to chemical energy in the form of organic compounds by autotrophs during a given time period

o Photosynthetic products = starting point for metabolism and energy flow studies

o In ecosystems where primary producers are chemoautotrophs initial energy input is chemical

Primary producers use light energy to synthesize energy rich organic molecules consumers acquire organic fuels secondhand in food webs

o Total amount of photosynthetic production sets spending limit for entire ecosystem’s energy budget

Global Energy Budgeto Earth atmosphere gets 1022 joules of solar radiation a dayo Intensity of solar energy striking earth varies with latitudeo Tropics get greatest inputo Incoming radiation is absorbed, scattered, or reflected

Amount of solar radiation that reaches surface limits photosynthetic output of ecosystems

o Only small part of sunlight that reaches surface is in photosynthesis because much strikes materials that don’t photosynthesize

Of radiation that hits only certain wavelengths are absorbed

Productiono Gross primary production (GPP) = total

primary production in an ecosystem, amount of energy from light/chemicals converted to chemical energy of organic molecules per unit time

o Net primary production (NPP) = gross primary production minus energy used by primary producers for “autotrophic respiration” (Ra)

NPP = GPP - Ra

NPP is usually half GPP Represents storage of chemical energy available to consumers Expressed as energy per unit area per time (J/m2 yr) or as

biomass (g/ m2 yr) Amount of new biomass added in given period of time

o Standing crop = total biomass of photosynthetic autotrophso Satellites = tool for studying global patterns of primary production

Show that different ecosystems vary in NPP Tropical rainforests = most productive Oceans = unproductive

o Net ecosystem production (NEP) = measure of total biomass accumulation during given time

NEP = GPP – RT RT = total respiration of all organisms in system

Determines whether an ecosystem is gaining or losing carbon over time

Measure by measuring net flow of CO2 or O2 entering or leaving ecosystem

System giving off O2 is storing carbonPrimary Production in Aquatic Ecosystems

Depth of light penetration affects primary production through ocean Limiting nutrient = element that must be added for production to increase

o Nitrogen or phosphorus most often limits marine productiono Iron also limits some production, also a tool to remove CO2 from air

iron fertilization is controversial Nutrient availability determines marine primary production

Upwelling = deep nutrient rich waters circulate to ocean surface

o Have high primary productiono Stimulates growth of phytoplankton that form

base of food webso Host highly productive diverse ecosystems, prime

fishing locationso Most commonly occur in Atlantic Ocean, equator,

Peru, CA, west Africa Sewage and fertilizer runoff from farms/lawns add lots of

nutrients that cause cyanobacteria and algae to grow rapidly, reducing oxygen concentration

o Eutrophication = ecological impacts of this processPrimary Production in Terrestrial Ecosystems

Temperature and moisture = main factors controlling primary production

o Useful in predicting NPP Most productive ecosystems are warm

and wet (rainforests) while unproductive ecosystems are hot and dry or cold and dry

Actual evapotranspiration = total amount of water transpired by plants and evaporated from a landscape

o Increases with temperature and amount of solar energy available

Nutrient limitations and adaptations that reduce them: Evolution

o Mineral nutrients in soil limit primary production in terrestrial ecosystems

o Nitrogen limits plant growth mosto Phosphorus limitations are

common in older soils where phosphate molecules have been leached away by water

Low availability in desert soils/ecosystems with basic pHo Adaptations help plants increase uptake of limiting nutrients

Plants have root hairs and other features to increase root surface area contact with soil

Plants release enzymes etc. into soil to increase availability of limiting nutrients

Farmers maximize crop yields by using fertilizers Ex: symbiosis between plant roots and nitrogen fixing bacteria Ex: Mutualism between plant roots and fungi that supply

phosphorus

55.3: Energy transfer between trophic levels is typically on 10% efficientProduction Efficiency

Secondary production = amount of chemical energy in consumers’ food that is converted to their own biomass, growth

An animal stores some energy, the rest is passed in feces which is lost as heat after its consumed by detritivores

o Energy used for respiration is eventually also lost as heat

o Energy flows through, not cycle within, ecosystems Production efficiency = (net secondary

production/assimilation of primary production) * 100%o Net secondary production = energy stored in biomass represented by

growth and reproductiono Assimilation consists of total energy taken in not including losseso Production efficiency = percentage of energy stored in assimilated

food not used for respiration Birds and mammals have low production efficiencies because

they use so much energy maintaining constant high body temp Fish, insects, and microorganisms have high production

efficienciesTrophic Efficiency and Ecological Pyramids

Trophic efficiency = percentage of production transferred from one trophic level to the next

o Must be less than production efficiencies because take into account energy lost through respiration and contained in feces and energy in lower trophic level not consumed by next level

90% of the energy available at one trophic level is not transferred to next

o Loss multiplied over length of food chain (10% 1% etc.)

o Progressive loss of energy limits abundance of top level carnivores

Only .1% of chemical energy can flow to tertiary consumer

o Explains why food webs only have 4-5 trophic levels Pyramid of net production represents loss of energy with each transfer in a

food chain, where trophic levels are arranged in tierso Width of each tier is proportional to net production (in Joules)o Highest level represents top level predators, contains few individualso Small level of top predators is why they’re vulnerable to extinction

Biomass pyramid shows ecological consequence of low trophic efficiencies

o Each tier represents standing crop (total dry mass of all organisms) in one trophic level

o Narrow sharply from primary producers at the base to top level carnivores at the apex because energy transfers are inefficient

o Aquatic ecosystems can have inverted pyramids where primary consumers outweigh producers because phytoplankton have a short turnover time = small standing crop, consumed quickly

Turnover time = Standing crop (g/m2) / Production (g/m2 day) Pyramid of production is still bottom-heavy

Energy flow through ecosystems show that humans could be much more efficient as primary consumers eating plants

o Carrying capacity relies on diet55.4: Biological and geochemical processes cycle nutrients and water in ecosystemsBiogeochemical Cycles = nutrient cycles, have both biotic and abiotic components

Chemical elements are only available in limited amounts life depends on recycling essential chemical elements

o Chemicals replaced as nutrients are assimilated and waste releasedo When an organism dies atoms are returned in simpler compounds to

atmosphere, water, or soil by decomposers Global cycles = gas forms of carbon, oxygen, sulfur, and nitrogen occur in the

atmosphere Local cycles = heavier elements like phosphorus, potassium, and calcium are

too heavy to occur as gas so transported in dust more locally (global in aquatic ecosystems, carried by currents)

Some cycling involves main reservoirs of elements and processes that transfer elements between reservoirs

Each reservoir is defined by whether it contains organic or inorganic materials and whether the materials are directly available for use

o Nutrients are available when consumers feed and when detritivores consume nonliving organic matter

o Inorganic materials dissolved in water or in soil or air are available for use- organisms assimilate materials from and return to chemicals through cellular respiration, excretion, and decomposition

o Nutrients in rocks that can’t be directly tapped into may slowly become available through weathering and erosion

o Living organic material that moved to fossilized organic reservoir long ago cannot be assimilated directly, accessed when fossil fuels are burned releasing exhaust into atmosphere

Important Cycles The Water Cycle

o Importance: Water is essential Availability influences rates of

ecosystem processes and primary production and decomposition

o Forms available: Mostly liquid, some use vapor Ice can limit availability

o Reservoirs: Oceans contain 97% of water in biosphere Glaciers, lakes, rivers, and groundwater have the rest

o Processes: Evaporation of liquid water by solar energy Condensation of water vapor into clouds Precipitation Transpiration by terrestrial plants puts water in atmosphere Surface and groundwater flow returns water to oceans

The Carbon Cycleo Importance: carbon forms framework of

essential organic moleculeso Forms available: Photosynthetic organisms

use CO2 for photosynthesis, convert carbon to organic forms used by consumers

o Reservoirs: Fossil fuels, soils, sediments of aquatic

ecosystems, oceans, plant and animal biomass, atmosphere (CO2)

Largest is sedimentary rocks but slow turnover

o Key processes: Photosynthesis by

plants/phytoplankton removes atmospheric CO2 in amounts equal to CO2 added by respiration

Burning of fossil fuels and wood adds CO2 to atmosphere Volcanoes add CO2 over geologic time

The Nitrogen Cycleo Importance: nitrogen is part of amino acids, proteins, and nucleic

acids, limiting plant nutriento Forms available:

Animals can only use organic forms

Plants can use two inorganic forms: ammonium (NH4+) and nitrate (NO3-) and some other forms like amino acids

Bactria can use all plant forms and nitrite (NO2-)o Reservoirs:

Main reservoir is atmosphere which is 80% free gas (N2) Others are soils and sediments of lakes, rivers, oceans, surface

and groundwater, and biomass of living organismso Processes:

Enter through nitrogen fixation = conversion of N2 to forms that can be used to synthesize organic nitrogen compounds

Bacteria and lightning fix nitrogen naturally Some bacteria convert nitrogen to different forms Some do dentrification = reduction of nitrate to

nitrogen gases Nitrogen inputs from human activities outpace natural inputs

through fertilizers and legume crops that fix nitrogen through bacteria on their roots

Also release reactive nitrogen gases to atmosphere

The Phosphorus Cycleo Importance:

Organisms require in nucleic acids, phospholipids, ATP and other energy-storing molecules

Mineral constituent of bones and teetho Forms available: inorganic form = phosphate (PO4 -3), plants absorb

and use in synthesis of organic compoundso Reservoirs:

Largest accumulations in sedimentary rocks Also lots in phosphorus in soil, oceans, and organisms

Soil binds phosphate recycling is localized

o Key processes: Weathering of rocks

gradually adds phosphate to soil which may go into groundwater and surface water, reaching the sea

Phosphate taken up by producers and incorporated into biological molecules may be eaten by consumers

Phosphate is returned to soil/water by decomposition of biomass or excretion by consumers

Small amounts move through atmosphere is dust/sea spray Ecologists worked out details of chemical cycling using isotopes

o Follow movement of naturally occurring nonradioactive isotopes through biotic and abiotic components of ecosystem

o Add tiny amounts of radioactive isotopes of specific elements and tracing progress

o Use radioactive carbon released into the atmosphere during bomb testing to trace where and how carbon flows into ecosystems

Decomposition and Nutrient Cycling Rates Decomposition is controlled by the same factors that limit primary

production in aquatic and terrestrial ecosystemso Include temp, moisture, and nutrient availability

Decomposers grow faster and decompose material more quickly in warmer ecosystems due to higher temps and more precipitation

o Decomposition faster in tropical rainforests (months to a few years) few organic matter accumulates as leaf litter on the forest floor

Most nutrients in ecosystem in trunks of trees, less in soilo Decomposition slower in temperate forests (4-6 years)

Most nutrients in soil Decomposition on land is slower when conditions are too dry or wet to

supply decomposers with enough oxygeno Cold and wet ecosystems store lots of organic matter because

decomposers grew poorly production exceeds decomposition Decomposition in anaerobic muds take 50+ years in aquatic ecosystems

o Ecosystems are productive only when there is an interchange between bottom layers of water and surface water

Nutrient Cycling in Hubbard Brook Experimental Forest: Case Study Ecologists Bormann and Likens studied cycling at Hubbard Brook

Experimental Forest in NH, deciduous forest that grows in valleys drained by a single creek, with impenetrable bedrock under soil

Determined mineral budget for six valleys by measuring input and outflow of key nutrients

Collected rainfall at several sites to measure water and dissolved minerals added to ecosystem

Constructed dam to measure loss of water and minerals Found that 60% of water added to ecosystem as rainfall and snow exits

through stream, rest is lost to evapotranspiration Internal cycling conserved most mineral nutrients in system Deforestation of watershed dramatically increased flow of water + minerals

o Water runoff increased because no plants to absorb water from soilo Calcium, potassium, and nitrate concentrations increased

Showed that amount of nutrients leaving an intact forest ecosystem helps maintain productivity of systems and avoid problems caused by runoff

55.5: Restoration ecologists help return degraded ecosystems to a more natural stateOverview

Ecosystems can recover naturally from disturbances through ecological succession stages but can take centuries

o Can be damaged through farming, irrigation, chemical/oil spills etc. Restoration ecologists seek to initiate/speed up ecosystem recovery Balance views that environmental damage is partially reversible with

ecosystems not bing infinitely resilient When disturbance is so severe that restoration is impractical try to reclaim

as much as possible First physical reconstruction, then biological restoration

Bioremediation = using organisms (prokaryotes, fungi, plants usually) to detoxify polluted ecosystems

Some plants adapted to soils with heavy metals can accumulate toxic metals in tissues

Use some prokaryotes to metabolize elements converting soluble forms of elements to insoluble elements less likely to leach into streams

Biological augmentation = using organisms to add essential materials to a degraded ecosystem

Need to determine which factors have been lost and limit recovery Encouraging growth of plants that thrive in nutrient poor soils speeds up

succession and ecosystem recovery Restoring physical structure doesn’t ensure that animal species will

recolonize a site and persist there necessary for plant survival so ecologists help them

Ex: nitrogen fixing plants raise soil nitrogen concentrationRestoration Projects Worldwide

Adaptive management = experimenting with several promising types of management to learn what works best

Long term goal = return an ecosystem to predisturbance state as much as possible

Kissimmee River, FL: converted from river to canal threatening fish and birdso Restoration reestablished river channel

Truckee River, NV: damming and diversions reduced flow declines in riverside forests

o Worked to ensure sufficient water released for trees Tropical dry forest, Costa Rica: agriculture eliminated forest

o Used domestic livestock to disperse seeds of native trees Rhine River, Europe: dredging and channeling for navigation straightened it

o Reconnecting river to side channels to increase diversity of habitats, improve water quality and provide flood protection

Succulent Karoo, South Africa: overgrazing damaged desert regiono Restoring by revegetating land and employing sustainable resource

management Coastal Japan: reduced seaweed and seagrass beds impacted fish

o Beds being restored through transplanting natural beds and artificial substrates

Maungatautari, New Zealand: introduced species pose threat to native plants and animals

o Restoration project trying to exclude exotic mammals from reserve