Lecture 5. Community Ecology

8/13/2019 Lecture 5. Community Ecology

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Community Ecology


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CommunityAssemblage of species population that occurtogether in space and time.Component: Biotic and AbioticCommunity / Ecosystem EcologyConcerned with the passage of energy and nutrients throughcommunities and what effects energy and nutrients have onthose communities,Focuses on biodiversity and what influences the number ofspecies in an area


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Biotic Components1.Producers living organisms that are capable ofproducing their own foodPhotoautotrophic: self-feeding; convert light energy intochemical energy in the form of foodChemoautotrophic: chemosynthesizers; reduce inorganiccompounds to organic compounds.

2.Consumers living organisms that cannot synthesizetheir own foodHerbivores: regulate the population of the primary producers;helps in pollination as well as in fruit and seed dispersalPredators: act as natural enemies; maintain balance in anecosystem

- Secondary consumers: feed on herbivores

- Tertiary consumers: feed on other organisms; top predators


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Abiotic componentsSolar energy, air, water, substrateInorganic substances (e.g., sulfur, boron, tend tocycle through ecosystems)Organic compounds (such as proteins,carbohydrates, lipids, and other complexmolecules) form a link between biotic and abioticcomponents of the system.


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U48_02


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Food chain

The pathway along which food is transferredfrom one trophic level to another, started from asource (producer) to another (consumers)through a series of feeding relationships.The transfer of energy and materials / nutrientsthrough a series of organisms as each one is fedupon by the next.


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0634lThe arrow always points to the direction where the energy will flow.


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Food chain

(a) A simpleterrestrial foodchain.(b) A simple marinefood chain.


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Food chainThe number of levels in a food chain is limited (4/5)Loss of energy during energy transformationThe top predators can no longer support another level because theenergy that they have is just enough to maintain order within theirsystem.

The producer obtain energy directly from the sunlight toproduce energy-rich organic molecules (their own biomass)The consumers in a food chain can be classified as:

- Primary consumers (10) herbivores that consume energy-rich plants

- Secondary consumers (20) carnivores that obtain theirenergy from energy-rich organic molecules in herbivores

- Tertiary consumers (30) carnivores that obtain their energyfrom energy-rich organic molecules in carnivores


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54.1 Examples of terrestrial00024DA6 Dave's HD ABA78158:


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Food chainThere are 2 types of food chains, depending onwhether the producers, at the base of the chainare living plants or dead plant materials:

1.Grazing food chain2.Detritus / decomposer food chain


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Food chain1) Grazing food chain

-Begins with living plants as the producers and move on to primaryconsumers (herbivores), secondary consumers (carnivores) andfinally tertiary consumers.-Ex: living plant leaf . caterpillar . frog . snake

-Based on the size of the organism in each trophic level, it can bedivided into 2 types:

- predatory food chain

- parasitic food chain

-In parasitic food chain, the organisms at each level graduallybecome smaller and not bigger as in the predatory food chain.


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Predatory food chain(the size of organism become bigger as the trophic level increase)Grass .grasshopper .frog .snake .owlRice fields .rats .fleas . parasitic protozoa

Parasitic food chain(the size of organism become smaller as the trophic level increase)


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Food chain2)Detritus food chain-Begins with dead organic matter /dead plant materialas producer-Which are subsequently eaten by detritivores andtheir predators-Food chains in which most primary production isdecomposed or consumed as detritus are termeddetritus food chains.

Example:Dead plant leaf . earthworm . bird . eagle


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Food webThe combination of all thefeeding relationship that existin an ecosystem.Food chains that interconnectto form a large network.The greater the number ofpossible routes, the morestable the particularcommunity.

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Trophic StructureArrangement of organisms in the feeding systemwithin the community / ecosystem.Trophic level: feeding level with respect to the primarysource of energy; position that an organism occupiesin a food chain.Ex. Plants are producers, herbivores are secondaryconsumer & carnivores are tertiary consumerMany animals feed at several trophic level.


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Secondary consumerCarnivorePrimary consumerHerbivoreProducerTertiary consumerTop carnivoreTrophic level 4Trophic level 3Trophic level 2Trophic level 1


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Energy flow and Laws of Thermodynamics1st Law Energy can be changed from one form to anotherbut cannot be created nor destroyed.

2nd Law In all energy exchanges and conversions, if noenergy leaves or enters the system, the potential energyof the final state will always be less than the potentialenergy of the initial state

Energy flows one way and does not recycle


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Energy FlowEnergy transformation is always accompanied bydegradation of high form of energy to low form of energy.The release of low form of energy (heat) during energytransformation helps molecules in random motion. Innature, processes tend toward randomness or entropy.Therefore, living organisms require a steady input ofenergy to maintain highly organized cellular feature.


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Energy flow in an ecosystemProducers (plants andphotosynthesis organisms)Heat energy (in theform of respiration,transpiration andexcretion)Consumers (animals, etc)

Chemical energyHeat energy (in theform of respirationand excretion)

Sunlight


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55_04EnergyNutrientFlow-UKeyChemical cyclingEnergy flowSunHeatPrimary producers

PrimaryconsumersSecondary andtertiary consumers

DetritusMicroorganismsand otherdetritivoresEnergy flow and nutrient cycling are inseparable.


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A trophic level is composed of all theorganisms that feed at a particular link in afood chain.Feeding relationship are graphically represented byplotting the energy content, number of organisms, orbiomass (the total weight of organic matter) at each trophiclevel.


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Ecological PyramidA graphical statement that is used to summarize andquantify the structure and functions of a communitywithin a specific ecosystem.Each trophic level of a food chain forms a tier on thepyramid; that is each successive trophic level is stackedon top of the level that represents its food source.Feeding relationship are graphically represented byplotting the energy content, number of organisms, orbiomass (the total weight of organic matter) at eachtrophic level


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Ecological PyramidPrimary Producers

HerbivoresPrimary carnivoresTop carnivoresIn general, only about 10% of the energy of one trophic level is availableto the next trophic level.


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Ecological Pyramid1.Pyramids of numbers based on counting thenumbers of individual organisms at each trophic level.2.Pyramids of biomass which note the weight (usuallytotal dry weight) of organisms at each trophic level.3.Pyramids of energy which monitor the energycontent of the organisms at each trophic level and therate of energy flow.


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Pyramid of NumbersIn a numbers pyramid based on trophic levels, theorganisms of a given area are first counted and thengrouped into their trophic levels.When this is done, a progressive decrease in thenumber of organisms at each successive level is oftenfound.In an ecosystem, the population size of small animals islarge and the population size of large animals isprogressively smaller.The energy that is available to higher trophic levels ismuch less that in lower trophic levelsThe size of predators is basically larger than the preys


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Pyramids of numbers show how the levels in thepyramids biomass are proportional to the numberof individuals present in each trophic level.


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30 C:\Documents and Settings\Admin\Desktop\gambar\pyramid no.JPG


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C:\Documents and Settings\Admin\Desktop\gambar\upright-pyramid-of-numbers-grassland-pond.JPGPyramids of number can be either upright or inverted (orpart of it inverted) depending on whether the size ofindividual organism is either small (as in phytoplankton) orlarge (as in a tree).If the size of organisms is progressively larger, the pyramidis upright


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The number pyramid can be (partly) inverted if thebase is smaller than one or more levels above it. Thisoccurs if the size of producer is large but smaller innumberExample : A single large producer such as tree

CaterpillarsLarge treebirds ParasitesAphids

Rose bush


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Pyramid of BiomassSince all organisms are made of roughly the sameorganic molecules in similar proportions, a measure oftheir total dry weight is a rough measure of the energythey contain.A count of the population, multiplied by the weight of thepopulation gives the biomass (or standing crop = totaldry mass of all organisms) of a population.


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Most biomass pyramids narrow sharply (sharplydecreases) from primary producers to top-level carnivoresbecause energy transfers are inefficient.


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The pyramid of biomass may be inverted, if the average sizeof organisms at lower trophic levels is much smaller than theaverage size of organisms at higher trophic levels- Example: if the size of a producer is very small and the size of theconsumer is very large, the total weight of consumers may be larger atany one time. The metabolism and reproductive system of smallproducer will produce an output that is larger than their biomass


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The biomass of the producer are small, have short life cycle & highrate of reproduction.- Ex. Zooplankton consume the phytoplankton so quickly that theproducers never develop a large population size.- But, the phytoplankton continue to replace their biomass at arapid rate (because they reproduces at rapid rate), so they cansupport a biomass of zooplankton bigger than their own biomass

Zooplankton (10g)Phytoplankton

Fish (3g)


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Based on the conditions of an ecosystem, three general variations ofthe biomass pyramid can be developed:1)In terrestrial ecosystem such as grasslands, tropical rainforests the producers are larger and live longer, so the biomass pyramid islikely to be fairly stable and have a large base.2)In sea and ocean ecosystems, the producers are small and do notlive long and therefore the condition of the producers may varysignificantly and an inverted pyramid may be produced.3)In lake and pond (aquatic) ecosystems, the producers are mainlyvery small rooted plants, tiny algae and other phytoplankters andthe consumers may be Daphnia sp. and fish. Thus, the biomasspyramid is likely to be partially inverted and has a small base.


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Pyramid of BiomassAdvantages:

More accurate than pyramid of number because using dryweight indicator at each trophic levels.

Disadvantages:

Difficult to determine the biomass because it must be kill anddry of organism to obtain their dry mass.Biomass may change with time.Comparison with wet weight is also inaccurate because thewater content of organism may change.Sometimes two organism may have same mass but differentamounts of energy.


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Pyramid of EnergyThe most fundamental and ideal way ofrepresenting relationships between organisms indifferent trophic levels.

It shows the rate of energy flow or production ateach trophic levels.This has a number of advantages such as it isnever inverted.


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