UNIT-X ECOLOGYUNIT-X ECOLOGY

Chp.13-Organisms & Chp.13-Organisms & PopulationsPopulations

Organism & Its EnvironmentOrganism & Its Environment

Change in seasons, annual variation in Change in seasons, annual variation in precipitation precipitation ( rain + snow) results in ( rain + snow) results in formation of major formation of major biomesbiomes..

Major biomes of India –(a) Tropical rain Major biomes of India –(a) Tropical rain forest (b) Deciduous forest (c) Desert (d) forest (b) Deciduous forest (c) Desert (d) Sea coast.Sea coast.

Regional and local variations in biomes Regional and local variations in biomes lead to the formation of different habitats.lead to the formation of different habitats.

Major Abiotic factorsMajor Abiotic factorsTEMPERATURETEMPERATURE – –

- Sub zero levels in Sub zero levels in polar areaspolar areas and and highhigh altitudes altitudes to > 50to > 500 0 C in C in tropical desertstropical deserts..

- In thermal springs and deep sea In thermal springs and deep sea hydrothermal vents > 100hydrothermal vents > 10000 C. C.

- Temperature effects the kinetics of Temperature effects the kinetics of enzymes. enzymes.

- Eurythermal Eurythermal – organisms that can tolerate a – organisms that can tolerate a wide range of temperature.wide range of temperature.

- StenothermalStenothermal –organisms restricted to a –organisms restricted to a narrow range of temperature.narrow range of temperature.

WATERWATER- The productivity & distribution of plants is The productivity & distribution of plants is

heavily dependent on water.heavily dependent on water.- EuryhalineEuryhaline - organisms are tolerant of a - organisms are tolerant of a

wide range of wide range of salinitiessalinities..- StenohalineStenohaline – organisms are restricted to – organisms are restricted to

a narrow range of salinities.a narrow range of salinities.

LIGHTLIGHT- Photosynthesis.Photosynthesis.- FloweringFlowering- Animals use diurnal & seasonal variations Animals use diurnal & seasonal variations

in light intensity and duration as cues for in light intensity and duration as cues for timing of timing of foragingforaging, , reproductivereproductive and and migratory activitiesmigratory activities..

SOILSOIL- Nature and properties of soil depends on Nature and properties of soil depends on (i) Climate (ii) Weathering process (i) Climate (ii) Weathering process (iii) Transported or sedimentary (iii) Transported or sedimentary (iv) How soil development occurred(iv) How soil development occurred- Percolation & water holding capacity is determined by Percolation & water holding capacity is determined by

soil composition, grain size and aggregation.soil composition, grain size and aggregation.- Above factors along with pH, mineral composition and Above factors along with pH, mineral composition and

topography determine the topography determine the vegetationvegetation and type of and type of animals animals that can be supported.that can be supported.

- In aquatic environment In aquatic environment sediment characterestics sediment characterestics determine the type of benthic animals.determine the type of benthic animals.

Responses to Abiotic factorsResponses to Abiotic factors

Internal level

External level

Conformers

Regulaters

Partial regulaters

HomeostasisHomeostasis – Organisms try to maintain the constancy – Organisms try to maintain the constancy of its internal environment.of its internal environment.

RegulateRegulate Organisms are able to maintain constant body Organisms are able to maintain constant body

temperature , osmotic concentration.temperature , osmotic concentration. ConformConform Organisms cannot maintain a constant internal Organisms cannot maintain a constant internal

environment.environment. Body temperature and osmotic concentrationBody temperature and osmotic concentration changes with that of the ambient environment. changes with that of the ambient environment.

MigrateMigrate Organisms move temporarily from the stressful habitat to Organisms move temporarily from the stressful habitat to

a more hospitable area and return when stressful period a more hospitable area and return when stressful period is over.is over.

SuspendSuspend- Bacteria , Fungi form thick walled spores to survive Bacteria , Fungi form thick walled spores to survive

unfavourable conditions.unfavourable conditions.- HibernationHibernation – Winter sleep - eg. – Winter sleep - eg. BearBear- AestivationAestivation - Summer sleep – eg. - Summer sleep – eg. FishFish- Diapause Diapause – Suspended development stage in – Suspended development stage in

zooplanktonszooplanktons

ADAPTATIONSADAPTATIONS

Adaptation is an attribute of the organism that enables Adaptation is an attribute of the organism that enables the organism to survive & reproduce in its habitat.the organism to survive & reproduce in its habitat.

- Desert plants have –Desert plants have – (i) thick cuticle on leaf surfaces.(i) thick cuticle on leaf surfaces. (ii) stomata arranged in deep pits.(ii) stomata arranged in deep pits. (iii) In (iii) In Opuntia Opuntia leaves are reduced to leaves are reduced to spines and photosynthesis is taken over spines and photosynthesis is taken over by flattened stems.by flattened stems.- Mammals from colder climates have shorter ears and - Mammals from colder climates have shorter ears and

limbs to minimise heat loss. ( limbs to minimise heat loss. ( Allen’s RuleAllen’s Rule ) )

Population attributesPopulation attributes

Post reproductive

Reproductive

Pre reproductive

EXPANDING

Post reproductive

Reproductive

Pre reproductive

STABLE

Post reproductive

Reproductive

Pre reproductive

DECLINING

Population GrowthPopulation Growth

Natality Natality –– no. of births during a given period in no. of births during a given period in the population.the population.Mortality Mortality –– no. of deaths in the population no. of deaths in the population during a given period.during a given period.Immigration Immigration –– no. of individuals of the same no. of individuals of the same species that have come into the habitat.species that have come into the habitat.EmigrationEmigration – – no. of individuals who left the no. of individuals who left the habitat.habitat.

NATALITY

(B)

POPULATIONDENSITY

(N)

MORTALITY

(D)

EMIGRATION

(E)

IMMIGRATION( I)

+

+

-

-

If N is the If N is the population densitypopulation density at time at time t t then its density at time t+1 is then its density at time t+1 is

NNt+1t+1= N= Ntt + [(B + I ) – (D + E ) ] + [(B + I ) – (D + E ) ]

- Population density will increase if Population density will increase if no.no. of birthsof births plus plus the no. of immigrantsthe no. of immigrants

- (B+I) is more than (B+I) is more than the no. of deathsthe no. of deaths plus plus the no. of emigrantsthe no. of emigrants (D+E). (D+E).

GROWTH MODELSGROWTH MODELS

(i) (i) Exponential growthExponential growth- When resources in the habitat are unlimited, population grows When resources in the habitat are unlimited, population grows

in an exponential or geometric fashion.in an exponential or geometric fashion.- If in a population of size If in a population of size N N per capita birth rate is per capita birth rate is b b and death and death

rate israte is d d then increase or decrease in then increase or decrease in N N during a unit time during a unit time period-period-

dN/dt = (b – d ) NdN/dt = (b – d ) N If b – d = If b – d = r r (intrinsic rate of natural increase)(intrinsic rate of natural increase)

dN/dt = rNdN/dt = rNIt gives a J – shaped growth curveIt gives a J – shaped growth curve

Integral form of the exponentialIntegral form of the exponential growth equationgrowth equation N t = N= N00 e e r tr t

N N tt = Population density after = Population density after time t time t NN0 = Population density at time = Population density at time 00 r = intrinsic rate of natural increaser = intrinsic rate of natural increase e = the base of natural logarithms (2.71828)e = the base of natural logarithms (2.71828)

(ii) (ii) Logistic growthLogistic growth A population growing in a habitat with limited A population growing in a habitat with limited

resources show –resources show – -a lag phase.-a lag phase. -phases of acceleration & -phases of acceleration & deceleration.deceleration. -an asymptote, when population -an asymptote, when population density reaches the carrying capacity.density reaches the carrying capacity. - It results in a - It results in a sigmoid curvesigmoid curve.. - This type of growth is called - This type of growth is called Verhulst – PearlVerhulst – Pearl

Logistic Growth.Logistic Growth.

Population

Density

( N )

Time (t)

K

dN/dt = rN

dN/dt = rN ( K – N )

K

Population InteractionsPopulation Interactions

(i) (i) PREDATIONPREDATION - act as conduits for energy transfer across trophic levels.- act as conduits for energy transfer across trophic levels. - keep prey populations under control.- keep prey populations under control. Prey species could achieve very high population Prey species could achieve very high population

densities and cause ecosystem instabilitydensities and cause ecosystem instability When exotic species are introduced in a geographical When exotic species are introduced in a geographical

area, they spread very fast as invaded land does not area, they spread very fast as invaded land does not have natural predators.have natural predators.

Eg. Prickly pear cactus introduced in Australia in 1920 & Eg. Prickly pear cactus introduced in Australia in 1920 & spread in millions of hectares. It was brought under spread in millions of hectares. It was brought under control by introducing a cactus feeding moth.control by introducing a cactus feeding moth.

Predators help in maintaining species Predators help in maintaining species diversity in a community by reducing diversity in a community by reducing intensity of competition amongintensity of competition among competingcompeting prey speciesprey species

Pisaster ( Star fish ) in rocky intertidal American Pisaster ( Star fish ) in rocky intertidal American pacific coast when removed from an enclosed pacific coast when removed from an enclosed area leads to extinction of more than 10 area leads to extinction of more than 10 species of invertebrates.species of invertebrates.

Prey species have evolved variousPrey species have evolved various defensesdefensesCamouflage- some insects & frogs.Camouflage- some insects & frogs.Monarch butterfly is highly distasteful to Monarch butterfly is highly distasteful to predators ( bird ) due to a chemical acquired by predators ( bird ) due to a chemical acquired by it at caterpillar stage by feeding on a poisonous it at caterpillar stage by feeding on a poisonous weed.weed.Calotropis produces highly poisonous cardiac Calotropis produces highly poisonous cardiac glycosides. glycosides.

( ii ) ( ii ) COMPETITION COMPETITION occurs when closely related species compete for the same resource that is occurs when closely related species compete for the same resource that is

limiting limiting but it is not true all the timesbut it is not true all the times In South American shallow lakes In South American shallow lakes Flamingoes & fishes Flamingoes & fishes compete for compete for

zooplanktons.zooplanktons. Interfering & inhibitory presence of a species reduces feeding efficiency of Interfering & inhibitory presence of a species reduces feeding efficiency of

other species even if resources are abundant. (other species even if resources are abundant. (Interference CompetitionInterference Competition ).).

DefinitionDefinition Competition is a process in which fitness of one species (increase inCompetition is a process in which fitness of one species (increase in r r – –

intrinsic rate of natural increase ) is lowered in presence of another intrinsic rate of natural increase ) is lowered in presence of another species.species.

Eg.- Eg.- Abingdon tortoiseAbingdon tortoise in Galapagos island became extinct within a in Galapagos island became extinct within a decade after decade after goatsgoats were introduced on island due to greater browsing were introduced on island due to greater browsing efficiency of goats.efficiency of goats.

Competitive releaseCompetitive release- A species whose distribution is restricted to a small geographical A species whose distribution is restricted to a small geographical

area due to a competitively superior species area due to a competitively superior species expands its range expands its range of distributionof distribution dramatically dramatically when competing species is when competing species is experimentally removed.experimentally removed.

Eg. Eg. Connels elegant field experimentsConnels elegant field experiments On rocky coasts of Scotland,competitivelyOn rocky coasts of Scotland,competitively superior superior barnacle barnacle – – Balanus Balanus dominate and exclude smaller dominate and exclude smaller

barnacle –barnacle – Chathmalus Chathmalus.. Gause’s competitive exclusion principleGause’s competitive exclusion principle Two closely related species competing for the same resource Two closely related species competing for the same resource

cannot co-exist indefinitely and inferior one will be eliminated. ( If cannot co-exist indefinitely and inferior one will be eliminated. ( If resources are limiting ).resources are limiting ).

(iii) (iii) PARASITISMPARASITISM- host- specific.host- specific.- Special adaptationsSpecial adaptations – loss of unnecessary sense – loss of unnecessary sense

organs , presence of adhesive organs or suckers , loss organs , presence of adhesive organs or suckers , loss of digestive system , high reproducing capacity.of digestive system , high reproducing capacity.

- Complex life cycles Complex life cycles – – - Liver fluke has two intermediate hosts – a snail and a - Liver fluke has two intermediate hosts – a snail and a

fish.fish. - Malarial parasite needs mosquitoes as vector.- Malarial parasite needs mosquitoes as vector. - Ectoparasites and endoparasites.- Ectoparasites and endoparasites.- - Brood parasitism Brood parasitism - birds- birds

(iv) (iv) COMMENSALISMCOMMENSALISM One species benefits and other neither One species benefits and other neither

harmed nor benefited.harmed nor benefited. Eg.- Eg.- An orchidAn orchid ( ( epiphyte epiphyte ) on a mango ) on a mango

branch.branch. - - A Cattle egretA Cattle egret . . - - Sea anemone & clown fishSea anemone & clown fish – fish gets – fish gets

protection from predators.protection from predators.

(v) (v) MUTUALISMMUTUALISMBenefit to both the interacting species.Benefit to both the interacting species.--Lichens Lichens – fungus + algae.– fungus + algae.--Mycorrhizae Mycorrhizae – fungi + roots of higher plants.– fungi + roots of higher plants.A given A given Fig speciesFig species is pollinated only by it’s partner is pollinated only by it’s partner WaspWasp species.species.

Female wasp uses the fruit as anFemale wasp uses the fruit as an oviposition site & feed its larvae on oviposition site & feed its larvae on developing seeds.developing seeds.Mediterranean orchid Mediterranean orchid Ophrys Ophrys employs employs sexual deceitsexual deceit. One petal . One petal of its flower bears resemblance to the female of bee in size , of its flower bears resemblance to the female of bee in size , colour, markings. The male bee pseudocopulates with the flower colour, markings. The male bee pseudocopulates with the flower and dusted with pollen grains.and dusted with pollen grains.