1. Population and Community Ecology

2. Population Characteristics Density- # of individuals per unit of areaDensity- # of individuals per unit of area –Determined by… countscounts sample size estimatesample size estimate indirect indicatorsindirect indicators mark-recapturemark-recapture Dispersion- pattern of spacingDispersion- pattern of spacing –Types: Random- unpredictable, patternless spacing (c)Random- unpredictable, patternless spacing (c) Clumped- patchy aggregation (a)Clumped- patchy aggregation (a) Uniform- even spacing (b)Uniform- even spacing (b)

3. Immigration vs. Emigration ImmigrationImmigration –Movement into an area EmigrationEmigration –Movement out of an area

4. Demography: factors that affect growth & decline of populations Birthrate (natality, fecundity)- # of offspring producedBirthrate (natality, fecundity)- # of offspring produced Death rate (mortality)Death rate (mortality) Age structure- relative number of individuals of each ageAge structure- relative number of individuals of each age Survivorship curve- plot of numbers still alive at each ageSurvivorship curve- plot of numbers still alive at each age

5. Types of Survivorship Curves Type IType I –Relatively low death rates until later in life –Ex: humans Type IIType II –Constant death rate throughout lifespan –Ex: lizards Type IIIType III –More death of young individuals –Ex: Sea turtles

6. Population Growth Models Exponential model (blue)Exponential model (blue) –idealized population in an unlimited environment (J-curve) –r-selected species (r=per capita growth rate) Logistic model (red)Logistic model (red) – –carrying capacity (K): maximum population size that a particular environment can support (S-curve) – –K-selected species

7. Life History “Strategies” r-selected (opportunistic)r-selected (opportunistic) –Short maturation & lifespan –Many (small) offspring; usually 1 (early) reproduction; no parental care –High death rate K-selected (equilibrial) –Long maturation & lifespan –Few (large) offspring; usually several (late) reproductions; extensive parental care –Low death rate

8. Population Limiting Factors Density-dependent factorsDensity-dependent factors –competition –predation –stress/crowding –waste accumulation Density-independent factorsDensity-independent factors –weather/climate –periodic disturbances

9. Community Ecology CommunityCommunity –an assemblage of populations living close enough together for potential interaction

10. Community Structure Richness (number of species) & abundanceRichness (number of species) & abundance Species diversitySpecies diversity Hypotheses:Hypotheses: –Individualistic- chance assemblage with similar abiotic requirements –Interactive- assemblage locked into association by mandatory biotic interactions

11. Interactions Interspecific- interactions between populations of different species within a community:Interspecific- interactions between populations of different species within a community: –Predation Includes herbivory and parasitismIncludes herbivory and parasitism –Competition –Commensalism –Mutualism

12. Predation Defense Cryptic (camouflage) colorationCryptic (camouflage) coloration Aposematic (warning) colorationAposematic (warning) coloration Mimicry- superficial resemblance to another speciesMimicry- superficial resemblance to another species –Batesian- palatable/ harmless species mimics an unpalatable/ harmful model –Mullerian- 2 or more unpalatable, aposematically colored species resemble each other

13. Competition: a closer look Interference- actual fighting over resourcesInterference- actual fighting over resources Exploitative- consumption or use of similar resourcesExploitative- consumption or use of similar resources Competitive Exclusion Principle- 2 species with similar needs for the same limiting resources cannot coexist in the same placeCompetitive Exclusion Principle- 2 species with similar needs for the same limiting resources cannot coexist in the same place –Gause experiment

14. The Niche Ecological niche- the sum total of an organism’s use of biotic and abiotic resources in its environment; its “ecological role”Ecological niche- the sum total of an organism’s use of biotic and abiotic resources in its environment; its “ecological role” –Fundamental- the set of resources a population is theoretically capable of using under ideal conditions –Realized- the resources a population actually uses 2 species cannot coexist in a community if their niches are identical2 species cannot coexist in a community if their niches are identical

15. Competition Evidence Resource partitioning-Resource partitioning- –sympatric species consume slightly different foods or use other resources in slightly different ways Character displacement-Character displacement- –Allopatric species are similar –Sympatric species show morphological differences

16. Species Richness and Diversity RichnessRichness –Total number of different species Relative AbundanceRelative Abundance –Proportion each species represents of the total individuals

17. Trophic Structure Transfer of food energy through a communityTransfer of food energy through a community –About 10% of the energy can be transferred from one level to the next Food Chain- linear feeding relationshipFood Chain- linear feeding relationship Food Web- shows all the possible feeding relationshipsFood Web- shows all the possible feeding relationships

18. Arctic Food Web

19. Special Species Dominant SpeciesDominant Species –Most abundant Keystone SpeciesKeystone Species –Strong control on community structure –Not necessarily most abundant Foundation SpeciesFoundation Species –Cause physiological changes to community

20. Succession Ecological succession- transition in species composition over ecological timeEcological succession- transition in species composition over ecological time PrimaryPrimary –begun in lifeless area; no soil, perhaps volcanic activity or retreating glacier SecondarySecondary –an existing community has been cleared by some disturbance that leaves the soil intact