r and K selection.pdf

R and k selection

1. Rounak Choudhary
M.Sc.(GoldMedalist),UGC-NET&ICAR-ASRBNETEnvironmentalScience,DCBOrnithology,PGDIndustrialSafety,HealthandEnvironment
r -and K -selection

2. •Onewayofclassifyingenvironments(orspecies
habitats)relatestotheirvariabilityintime.Wecan
envisiontwocontrastingtypesofhabitats:(1)those
thatarevariableintimeorshort-lived,and(2)those
thatarerelativelystable(long-livedandconstant),with
fewrandomenvironmentalfluctuations.
•TheecologistsRobertMacArthurofPrinceton
University,E.O.WilsonofHarvardUniversity,andlater
E.PiankaoftheUniversityofTexasusedthis
dichotomytodeveloptheconceptofr-andK-
selection.

3. •Thetheoryofr-andK-selectionpredictsthat
speciesadaptedtothesetwodifferent
environmentswilldifferinlifehistorytraits
suchassize,productiveness,ageatfirst
reproduction,numberofreproductiveevents
duringalifetime,andtotallifespan.

4. •Speciespopularlyknownasr-strategistsare
typicallyshort-lived.
•Theyhavehighreproductiverates,rapid
development,smallbodysize,largenumberof
offspring(withlowsurvival),andminimal
parentalcare.
•Theymakeuseoftemporaryhabitats.Many
inhabitunstableorunpredictableenvironments
thatcancausecatastrophicmortality
independentofpopulationdensity.
•Environmentalresourcesarerarelylimiting.They
exploitnoncompetitivesituations.Somer-
strategists,suchasweedyspecies,havemeansof
widedispersal,aregoodcolonizers,andrespond
rapidlytodisturbance.

5. •K-strategistsarecompetitivespecieswithstable
populationsoflong-livedindividuals.
•Theyhaveaslowergrowthrate.
•K-strategistscancopewithphysicalandbioticpressures.
•Theypossessbothdelayedandrepeatedreproductionand
havealargerbodysizeandslowerdevelopment.
•Theyproducefewseeds,eggs,oryoung.Amonganimals,
parentscarefortheyoung;amongplants,seedspossess
storedfoodthatgivestheseedlingsastrongstart.
•Mortalityrelatesmoretodensitythantounpredictable
environmentalconditions.Theyarespecialists,efficient
usersofaparticularenvironment,buttheirpopulationsare
atornearcarryingcapacity(maximumsustainable
populationsize)andareresourcelimited.
•Thesequalities,combinedwiththeirlackofmeansforwide
dispersal,makeK-strategistspoorcolonizersofnewand
emptyhabitats.

6. •ThetermsrandKusedtocharacterizethese
twocontrastingstrategiesrelatetothe
parametersofthelogisticmodelofpopulation
growth.
•risthepercapitarateofgrowth,andKisthe
carryingcapacity(maximumsustainable
populationsize).

11. MCQs

14. Which is not the characteristic of ‘r’
selected species?
1.Reproduce quickly
2.Parental care
3.A low survival rate of progenies
4.Produce a large number of progenies