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Population and Community Ecology

Population and Community Ecology. Population Characteristics. Density - # of individuals per unit of area Determined by… counts sample size estimate indirect indicators mark-recapture Dispersion - pattern of spacing Types:

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Population and Community Ecology

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  1. Population and Community Ecology

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

  3. Immigration vs. Emigration • Immigration • Movement into an area • Emigration • Movement out of an area

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

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

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

  7. 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 Life History “Strategies”

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

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

  10. Community Structure • Richness (number of species) & abundance • Species diversity • 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: • Predation • Includes herbivory and parasitism • Competition • Commensalism • Mutualism

  12. Predation Defense • Cryptic (camouflage) coloration • Aposematic (warning) coloration • Mimicry- 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 resources • Exploitative- consumption or use of similar resources • Competitive 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” • 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 identical

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

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

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

  18. Arctic Food Web

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

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

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