lecture 1- ecosystems

8/8/2019 Lecture 1- Ecosystems

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Ecosystems

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Ecosystems are characterised by assemblages of organisms together with their

physical and chemical environment - the so-called abiotic frame.

Ecosystems are highly complex and distinct functional units such as a forest, a lake,an estuary which have relatively little exchange of energy or substances betweenthem compared with the innumerable transformations withineach of them.

Ecosystem ecology provides a framework for studying the transformation ofenergy and the cycling of elements within ecological systems.

Ecosystems

Organisms interact within food webs to accumulate, circulate, and transform organicand inorganic matter.

The abiotic frame of an ecosystem consists of all physical and chemical propertiessuch as morphometry, soil conditions, nutrient concentrations, light availability, flow,temperature, pH, which maintain food webs and nutrient cycling.

Ecosystems

Environmental Gradient

Abiotic frame

Organisms

Food web interactions

Changed abiotic frame

Environmental Gradient

Abiotic frame

Organisms

Food web interactions

Changed abiotic frame


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Ecosystems

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Ecosystems

Nutrient Cycling

Example of nutrient cycling in aquatic ecosystem:

Inorganic nutrients (CO2, phosphorus and nitrogen) in an ecosystem are utilised byautotrophs for photosynthesis. They are either imported or recycled from particulate anddissolved organic matter (detritus, excrements) by microbial and photochemical processes.


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Ecosystems

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Organic and inorganicmatter in an ecosystemhave distinct half-lifeconstants indicatingthe time that is neededto reduce theirconcentration by 50%.

Half-life constantsprovide information onrecycling (turn-over)times of differentmatter.

Nutrient Cycling

Seasonal dynamics ofnutrient cycles

Nutrient Cycling


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Ecosystems

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Food Webs

Organisms inecosystems arehierarchically structuredby biological interactionsbetweencarnivores (predators),herbivores (grazers),plants and decomposers

Food Webs

In an aquatic food web the toppredators (large piscivorous fish) arelimited by the availability of smallplanktivorous fish that is for its partlimited by the availability of carnivorous

and herbivorous zooplankton which isfor its part limited by the availability of

algae.

Algae are limited by sunlight andnutrients which are supplied externallyand recycled internally by benthivorousorganisms and bacteria.


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Ecosystems

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Trophic Cascades

Trophic cascadesdependonthenumberoftrophic levelsofthefoodwebanddeterminethestructure

andfunction

of

ecosystems.

Changes

in

the

abundance

at

one

trophic level

alter

the

abundance

of

othertrophic levelsacrossthefoodweb.

Oddnumberoftrophic levels:

Plantbiomassabundant

Evennumberoftrophic levels:

Plantbiomassreduced

Trophic Cascades

Through trophic cascades typically a carnivorous population A has an indirect positive

effect on a autotrophic population C by reducing the abundance of the herbivorous

population B.

A

B

C


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Ecosystems

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In food webs with 3 trophic levels, the carnivores are limited by herbivores, herbivores are limitedby predation, and autotrophs are limited by nutrients and light.

Trophic Cascades

Example of trophic cascades in the Simpson Dessert:

Heavy rainfall in summer 1991 triggered a temporary pulse of arid plants growth causing

an increased abundance of Long-haired Rats.

Rat-predators , in turn, increased after the arrival of rats. Both rats and their predatorsdisappeared by late 1992 after plants had died off.

Trophic Cascades


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Ecosystems

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Example of trophic cascades in Lake St George, Ontario:

A winterkill of fish in 1982 triggered a trophic cascade down the food web over the next 4years.

Trophic Cascades

Trophic CascadesExample of otter-urchin-kelp interactions in Alaska:

After increased predation of sea otters by killer whales in the mid 1990s the sea urchin

biomass increased significantly causing high grazing pressure on kelp


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Ecosystems

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Biomanipulation: Utilising trophic cascade effects for lake management

Trophic Cascades

The response of an ecosystem to disturbance (stress)can be characterised by following attributes:

- Resistance: Tendency not to change- Response: Magnitude of change- Resilience: Rate of return to original state- Recovery: Extent of return to original state- Change: Reaching a new stable state

Multiple Stable States of Ecosystems


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Ecosystems

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Ecosystems can have multiple stable states imposed by disturbances where the new abiotic

frame and assemblagesof

organisms are in a relative equilibrium.

Stability properties of ecosystems:

Stable equilibrium point

Unstable equilibrium point

Multiple equilibrium points bothstable and unstable

Nutrie

ntCon

centratio

ns

Temperate mesotrophic lake

Mediterranean eutrophic lake

Water Temperature

Stable state attime t

Transitionalstate at time t+i

LakeCategor

yI

LakeCategoryII

Stable state attime t+j

Time



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Ecosystems

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Temperate deciduous forest

Semi-arid shrub land

Air Temperature

Stable state attime t

Transitionalstate at time t+i

Forest

CategoryI

ForestCategoryII

Stable state attime t+j

SoilM

oisture

Time


Changingefficiency of

parasite attackupon the host

moving the systemfrom stable tounstable

equilibrium



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Ecosystems

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Multiple stable statesof lake ecosystems:

I

II

II

I


Multiple stable statesof shallow lake ecosystems:



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Ecosystems

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Ecological Processes

Ecological processes are determined by temporal and spatial interactions between

ecosystem components such as growth, predation, competition, mortality etc.Interaction diagrams and matrices can be used to represent ecological processes.


Transport processes can be driven by hydrological and meteorologicalconditions :

RainfallSurfaceWate

rRunoff

TerrestrialNutr

ientExport

Terrestrial Nutrient ExportAquaticNutrie

ntImport

Surface Water Runoff


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Ecosystems

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Growth processes can be driven by meteorological and climateconditions :

Solar Radiation

Plan

tGrowth

Nutrient ConcentrationTemperature

PlantGrowth

PlantGrowth


Growth processes can be driven by inter-specific nutrientcompetition:

Silica, Phosphorus, Nitrogen

DiatomG

rowth

AnabaenaPhosphorus

AnabaenaGrowth

Diatoms


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Ecosystems

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Growth processes can be driven by food-web interactions such as

grazing and predation:

Algae Biomass

Zooplan

ktonGrowth

Zooplankton Biomass

SmallFishGrowth

Small Fish Biomass

LargeF

ishGrowth

Ecosystems are highly complex, non-linear

and stochastic

- Complexity of ecosystems is determined by the formation ofhierarchical food webs and cycling of nutrients

- Nonlinearity of ecosystems is determined by distinct feedbackrelationshipsbetween their organisms and the abiotic frame

- Stochasticity of ecosystems is determined by the random nature ofclimatic, meteorological, hydrological, epidemical, chemical drivingvariables such as occurrence of droughts, floods, thunderstorms,tornados, fire, diseases, pollution.


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Ecosystems

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Temporal Scales and Patterns

Different temporal scales producedifferent temporal patterns.

CyclicDynamics

Diurnalpatterns:

Photosynthesisgreaterinmorningthanafternoon;plantsarehungry forcarboninthemorning

Diurnalzooplanktonmigrationwithgreateralgalgrazingintheeveningthaninthemorning

Seasonalpatterns:

Plantsgrowinresponsetophotoperiodrapidlyinspringbutsenesceinautumn

Productionexceedsherbivory insummer

Herbivory exceedsproductioninwinter

SeasonalchangesinecosystemCbalance

Seasonalsuccessionbetweendiatoms,greenalgae,dinoflagellates andbluegreenalgae

Interannual patterns: ElNinoeventsoccurevery3to7yearsbylargescaleairseainteractionsthat

coupleatmosphericpressurechangeswithchangesintheoceantemperatureover

theequatorialPacificOcean



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Ecosystems

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Instantaneousevents:

Raineffectsonsoilmoisture

Overcasteffectsonphotosynthesis

Predatoreffectsonpreyactivity

Speciesmigration

Longtermevents:

Regimeshiftsinfoodwebsandecosystemevolution

Salinisation ofsoilsandfreshwaterinaridclimates

Eutrophication ofaquaticecosystems


Similarities and Differences between

Aquatic and Terrestrial Ecosystems

Criteria Aquatic Terrestrial

Habitat Water, Sediments Soil

Limiting Factors for Biota Light, Nutrients Water, Nutrients

Variations of

Temperature

Low High

Variations of O2 and CO2 High Low

Variations in Productivityand Diversity byChanging Climate

Low High

Sources of Phosphorusand Nitrogen

Water (Dissolved),

Sediments (Particulate)

Soil (Dissolved andParticulate)

Typical Ecosystems Oceans, Estuaries,Lakes, Wetlands,Ponds,

Rivers, Streams, Springs

Tundra, Forests,Rainforests, Mangrove

Forests, Grasslands,Tropical Savannah


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Ecosystems

Basic Properties of Water and Air that Influence Ecosystem Processes

Property Water Air Ratio water:airOxygen concentration (ml L-1) 7.0 209.0 1:30Density (kg L-1) 1.000 0.0013 800:1Viscosity (cP) 1.0 0.02 50:1Heat capacity (cal L-1 (C)-1) 1000.0 0.31 3000:1Diffusion coefficient (mm s-1)Oxygen 0.00025 1.98 1:8000Carbon dioxide 0.00018 1.55 1:9000

Terrestrial and aquatic ecosystems have

fundamentally different physical environment

Similarities and Differences betweenAquatic and Terrestrial Ecosystems

Similarities and Differences between

Production and Natural EcosystemsProd Ecosystem Natural Ecosystem

Species Diversity and Life Forms:

Spatial Pattern:

Temporal Pattern:

Pathways of Nutrient Cycles:

Spatio-Temporal Scales of Processes:

lecture 1- ecosystems

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