EcologyEcology

Lecture 12Lecture 12

Landscape EcologyLandscape EcologyEcological system aare made up Ecological system aare made up of mosaics of patches containing of mosaics of patches containing different ecologiesdifferent ecologiesLandscape ecology studies how Landscape ecology studies how these patches form and continue these patches form and continue to existto existA patch is a relatively A patch is a relatively homogenous area that differs homogenous area that differs from its surrounding areafrom its surrounding areaPatches vary in sizePatches vary in sizeMany patches make up the Many patches make up the matrixmatrixPatches form both naturally and Patches form both naturally and due to human interventiondue to human interventionHuman intervention is usually Human intervention is usually dominant in many areadominant in many areaOther forces are geology, fire, Other forces are geology, fire, grazinggrazingSize of patches can vary from Size of patches can vary from meters to kilometersmeters to kilometersWhen patches meet, they When patches meet, they interactinteractThese are called transition zonesThese are called transition zones

Most obvious feature of a transition zoneMost obvious feature of a transition zone– Edge of each patchEdge of each patch– Change in physical conditionsChange in physical conditions

When long term physical features fit edgeWhen long term physical features fit edge– Inherent edgeInherent edge

StableStable

Edges due to natural disturbance, e.g. fire, or human Edges due to natural disturbance, e.g. fire, or human interventionintervention– Induced edgeInduced edge

Less stable and may require continuous maintenanceLess stable and may require continuous maintenance

Place where one edge meets another edgePlace where one edge meets another edge– BorderBorder

Two edges and a borderTwo edges and a border– BoundaryBoundary– Can be sharpCan be sharp– Can be gradual, namely an ecotoneCan be gradual, namely an ecotone

Boundaries can be very different to either patchBoundaries can be very different to either patch– Edge effectEdge effect

Certain species of animals and plants prefer boundaries Certain species of animals and plants prefer boundaries and ecotones. Some species only inhabit edgesand ecotones. Some species only inhabit edges– Edge speciesEdge species– PlantsPlants

Shade intolerantShade intolerantBetter tolerant of dry conditionsBetter tolerant of dry conditions

– AnimalsAnimalsRequire two plant communities to survive and reproduceRequire two plant communities to survive and reproduce

Mosaic of patches, edges and Mosaic of patches, edges and boundaries is not stableboundaries is not stableHuman continuous fragment patchesHuman continuous fragment patchesIf size of patch becomes to smallIf size of patch becomes to small– Local extinction occursLocal extinction occurs

What size of patch maintains What size of patch maintains greatest diversity of speciesgreatest diversity of speciesAt what size due area-sensitive At what size due area-sensitive species disappearspecies disappearLarge patchesLarge patches– Greater population densityGreater population density– Greater species richnessGreater species richness– Support more individuals in their Support more individuals in their

optimal environmentoptimal environment– Large carnivores require a large Large carnivores require a large

home range and are therefore limited home range and are therefore limited by small patchesby small patches

– Only when a patch is large enough Only when a patch is large enough will the edges be far enough away for will the edges be far enough away for the development of proper interior the development of proper interior conditionsconditions

Interior speciesInterior species– Need stable environmentNeed stable environment– Area sensitiveArea sensitive

Some species are area insensitiveSome species are area insensitive

Note relationship betweenNote relationship between– Patch size and interior areaPatch size and interior area– Patch shape and interior areaPatch shape and interior area

Note different responses of birds to areaNote different responses of birds to area

Island biogeography works Island biogeography works for patchesfor patchesLarge island have more Large island have more species than small islandsspecies than small islandsEquilibrium is reached Equilibrium is reached when immigation equals when immigation equals extinction rateextinction rateHowever, species still However, species still changechange– Turnover rateTurnover rate

Larger island have a lower Larger island have a lower extinction rateextinction rate– More variety of habitatsMore variety of habitats

Any patch separated from Any patch separated from other similar patches by other similar patches by inhospitable terrain can be inhospitable terrain can be treated as an islandtreated as an islandNote effects of size and Note effects of size and distance to nearest similar distance to nearest similar environmentenvironmentNote also that there are Note also that there are fewer barrier to movement fewer barrier to movement in a fragmented landscape in a fragmented landscape than for a oceanic islandthan for a oceanic island– Corridors exist on landCorridors exist on land– Join patchesJoin patches– Hedgerows, ditches, Hedgerows, ditches,

bridgesbridges

Patches form Patches form metapopulationsmetapopulationsMetapopulations decrease Metapopulations decrease vunerability to local vunerability to local extinctionextinction– See movement by See movement by

corridors and immigrationcorridors and immigrationPatchesPatches– InbreedingInbreeding

Increase in homozygosity Increase in homozygosity due to mating with close due to mating with close relativesrelatives

– Genetic driftGenetic driftChange in gene Change in gene frequency due to frequency due to sampling effect of small sampling effect of small population causing allele population causing allele lossloss

– Minimum viable populationMinimum viable populationEffective size >100Effective size >100Actual size >1000Actual size >1000Metapopulation >?Metapopulation >?

Sources patchesSources patches– Reproductive rate exceeds Reproductive rate exceeds

mortalitymortalitySink patchesSink patches– Reproductive rate less Reproductive rate less

than mortalitythan mortality

Disturbances affect Disturbances affect communitiescommunities– Fire, flood, drought, etcFire, flood, drought, etc

Single eventSingle event– RareRare

Regular eventRegular event– Linked disturbance regimeLinked disturbance regime

IntensityIntensity– Proportion of total Proportion of total

biomass killedbiomass killed

ScaleScale– Spatial extentSpatial extent

FrequencyFrequency– Events per unit timeEvents per unit time

Small scaleSmall scale– Loss of a single treeLoss of a single tree

Creates gapCreates gapNew conditions for New conditions for colonizationcolonizationReorganization of Reorganization of populations close to sitepopulations close to site

Large scaleLarge scale– Intensity and scale are Intensity and scale are

largelargeLocal extinctionLocal extinctionChange to sites physical Change to sites physical environmentenvironment

Examples of disturbance effectsExamples of disturbance effects– FireFire

Some seeds need fire to germinateSome seeds need fire to germinateSurface fireSurface fire

– Burns litter onlyBurns litter only– No harm to roots, stalks, tubers, etcNo harm to roots, stalks, tubers, etc

Crown fireCrown fire– Burns tops of plants, kills patches down to ground Burns tops of plants, kills patches down to ground

allowing migrationallowing migration

Ground fireGround fire– Cosumes all organic matter down to bare rock or Cosumes all organic matter down to bare rock or

mineralsminerals– Irreversibly changes landscapeIrreversibly changes landscape

– HerbivoresHerbivoresSeed distributionSeed distributionElephant in game parksElephant in game parks

– ManManForestsForestsMadagascar and tropical rain forest coverMadagascar and tropical rain forest cover

EcosystemEcosystem– Closed systemClosed system

No inputsNo inputs– Open systemOpen system

At least one inputAt least one input– Three componentsThree components

Non-livingNon-livingAutotrophsAutotrophsHeterotrophsHeterotrophs

InputInput– Fixation and transfer of energy from SunFixation and transfer of energy from Sun– Increase in net primary production by Increase in net primary production by

autotrophsautotrophs– Goes into different sectors of biomassGoes into different sectors of biomass– Affected byAffected by

RainfallRainfallTemperatureTemperatureLength of photosynthetic periodLength of photosynthetic periodEvapotranspirationEvapotranspiration

Primary Primary productivity productivity varies with varies with ecosystemecosystem

Primary production varies with nutrient Primary production varies with nutrient availabilityavailability

Primary production varies with timePrimary production varies with time

Primary productivity limits Primary productivity limits secondary productivitysecondary productivity

Secondary producers are not Secondary producers are not neceassarily highly efficientneceassarily highly efficient

Normally ecosystems have two major food Normally ecosystems have two major food chainschainsTerrestial grazing chain not very importantTerrestial grazing chain not very important– Only 2.6% of primary productionOnly 2.6% of primary production

Insects very importantInsects very importantDetrital chain is very importantDetrital chain is very important– 35% of primary production35% of primary production

Food chains are interconnectedFood chains are interconnectedEnergy flows through trophic levelsEnergy flows through trophic levelsEnergy decreases with each tropgic levelEnergy decreases with each tropgic level

Assimilation efficiencies vary widely Assimilation efficiencies vary widely among endotherms and ectothermsamong endotherms and ectotherms

Pattern of flow variesPattern of flow varies

Result is an ecological Result is an ecological pyramidpyramid

Describes loss at each Describes loss at each levellevel