Populationschangeover time • Lots of factorsaffectpopulations • Theorganismsthemselves • Thehabitat • Howthey reproduce • Predator – preyinteractions (and lots more!!)
Limiting Factor • Thisisany factor orconditionthatlimitsthegrowth of a population in anecosystem. • Eg: A largepopulation of predatorswilllimitthepopulation of preybut a smallpopulation of preywilllimitthepopulation of predators. • Toomuchortoolittle of bioticorabioticfactorsmakesanecosystemunstablechange. • Food, water, light, nutrients, algaeusing up oxygen etc.
CarryingCapacity • Living thingshavecertainminimumrequirementsforfood, water and living space. • When a population can no longergrowit has reacheditscarryingcapacity. Thisisthemaximumnumber of individualsthatanecosystem can support. • Itisdifferentforeachpopulation. • Bothbiotic and abioticfactors can belimiting: interactionsbetweenpopulations (competition, predation, parasitism); temperature; availability of water; minerals; exposuretowind etc.
Ecosystemschangeover time • Succession • The gradual change in anecosystem in whichonebiologicalcommunityisreplacedbyanother.
PrimarySuccession • Whenplantsmoveintoanarea and bringit back tolife. A new biologicalcommunityisformed. • After a lava flowAfter a glaciar retreats.
Pioneerspecies • Thefirst living thingstomoveinto a barren environment. Oftenmoss, lichen etc. Theygrow, startto break down rock etc and prepare theenvironmentforforests.
SecondarySuccession • Takes place after a majordisturbance. • Soilisstillthere. Itis more surfacedamage. • Couldbe a fire, flood, humanactivity.
Keystonespecies • A speciesthat has a disproportionately large effect on its environment relative to its abundance. • They play a critical role in the structure of an ecological community. • Help to determine the types and numbers of various other species in the community. • An ecosystem may experience a dramatic shift if a keystone species is removed, even though that species was a small part of the ecosystem by measures of biomass or productivity.
Example • Some sea stars may prey on sea urchins, mussels and other shellfish that have no other natural predators. • If the sea star is removed from the ecosystem, the mussel population explodes uncontrollably, driving out most other species, while the urchin population annihilates coral reefs.
Anotherexample Sea otters protect kelp forests from damage by sea urchins. Kelp "roots", called holdfasts, are anchors, and not the vast nutrient gathering networks of land plants. Sea urchins only need to eat the roots of the kelp, a tiny fraction of the plant's biomass, to remove it from the ecosystem.
Whatdidyouunderstand? • 1. Describe threefactorsthatcouldlimitthesize of a population in a habitat. • 2. Listtwo natural disturbances and twohuman-madedisturbancesthat can lead tosuccession. • 3. What role do pioneerspeciesplay in succession? • 4. Imagine you are thewildlife manager for a forest reserve thatsupportsbothmoose and wolves. Whattypes of informationshouldyoucollectto determine thecarryingcapacityforeachspecies? • 5. What are keystonespecies?
Now YOU are goingtoworkwithpredator and prey ‘species’ • Objective:toenhanceyourunderstanding of populationdynamicsyou are goingto open a new habitat and thensimulatecompetitionbetweenfoxes and micethat are goingto use thehabitat.
Participants Control Beads (Otheranimalsfound in thehabitat)
Group roles • 5 / group • 1 person records data and addsbeads • 4 people are predators
Basic rules 1) Eachgenerationwillbeginwith at least10 mice and 1 fox. 2) Themicewilldoubletheirsurvivingnumbereachgeneration. 3) Thehabitat can support no more than100 mice(itscarryingcapacity) 4) Eachpredator in eachgeneration MUST capture at least5 micetosurvive and produce offspring. 5) Yellow control beadsshouldalwaysbereturnedafterEACH predatorhas had a turn. 6) PredatorsMAY NOT LOOK whilepickingoutthebeads.
TheGraph Remember: X = prey O = predator Jointhelines