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Population ecology

Population ecology. Does population growth continue without limits?. Number of resources usually prevent populations from growing exponentially . Population growth. Carrying capacity (K) = maximum number of individual that an environment can support. When population reaches carrying capacity.

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Population ecology

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  1. Population ecology • Does population growth continue without limits? • Number of resources usually prevent populations from growing exponentially • Population growth • Carryingcapacity (K) = maximum number of individual that an environment can support • When population reaches carrying capacity • birth rate = death rate • population growth rate = 0 Where have all the sea otters gone?

  2. Adjustment for limited resources Population size Per capita growth rate Population growth rate Population ecology • Logistic growth model • Population growth rates decreases as population approaches its carrying capacity • Population growth Where have all the sea otters gone?

  3. Population ecology • Logistic growth model • Logistic growth produces S-shaped curve; population growth rate decreases as N approaches K • Population growth Population size (N) K Time (t) Where have all the sea otters gone?

  4. Population ecology • Examples of logistic growth • Population growth Where have all the sea otters gone?

  5. How does logistic growth model work? (1) Population size (N) Time (t) Population ecology • When N is very small (imagine N is 1 and K is 1000)... • Population growth is close to 1, so population grows exponentially Where have all the sea otters gone?

  6. Population size (N) Time (t) Population ecology • How does logistic growth model work? • When N approaches K (imagine N is 500, 600, ...900 and K is 1000)... • Population growth Gets closer and closer to 0, so population growth slowly approaches 0 Where have all the sea otters gone?

  7. Population size (N) Time (t) Population ecology • How does logistic growth model work? • When N equals K (imagine N is 1000 and K is 1000)... • Population growth is 0, so population growth is 0 Where have all the sea otters gone?

  8. Population ecology • Density-dependent population regulation • As populations near carrying capacity…population growth rate declines • Population growth • Per capita birth rates decrease (fewer resources available for production of offspring) • fewer resources available for production of offspring • Per capita death rates increase (fewer resources for survival, predators focus attention on common prey) • fewer resources for survival • predators focus attention on common prey Where have all the sea otters gone?

  9. Population ecology • Example of density-dependence • As population size increases, fecundity decreases • Population growth • As population size increases, mortality increases Where have all the sea otters gone?

  10. Population ecology • Density-dependent factors include: • disease • Population growth • predators • competition for resources • Not all density-dependent factors result in reduced population growth rates as population size increase • Alleeeffect = population growth rate reduced at low population density • Difficulty finding mates could reduce birth rates at low population size Where have all the sea otters gone?

  11. fires Population ecology • Sometimes population regulated by density-independent factors • Population growth • Birth rates decrease and death rates increase regardless of population size • Extremely cold winter • drought Where have all the sea otters gone?

  12. Population ecology • Example of density-independent regulation • Population growth Where have all the sea otters gone?

  13. Population ecology • Type of population regulation may influence life-history traits: • Species regulated by density-dependent factors are selected to be good competitors (populations are often close to carrying capacity) • Such species invest heavily in survival • But at a cost of reduced reproductive potential (i.e. a life history trade-off) • Called K-selected species • Examples: elephants, oak trees Where have all the sea otters gone?

  14. Population ecology • Type of population regulation may influence life-history traits: • Species regulated by density-independent factors are selected to be good reproducers (populations are often below carrying capacity) • Such species invest heavily in reproductive output • But at a cost of reduced survival (i.e. a life history trade-off) • Called r-selected species • Examples: cockroaches, birch trees Where have all the sea otters gone?

  15. Population ecology trait r-selected K-selected • age at 1st reproduction early late • r- and K-selected life history traits (ends of continuum) • lifespan short long • Survivorship low (type III) high (type I) • Fecundity high low • Parity semelparity iteroparity • Offspring size small large • Parental care* none lots * not a life-history trait Where have all the sea otters gone?

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