Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.
PopulationRe gulationChapter 5
Preconditions… Populations change over time Populations cannot grow indefinitely Logistic curve Logistic equation repr...
Background Population regulation: fluctuations in  abundance with feedback mechanisms to  increase or decrease density to...
Patter ns ofPopulationFluctuationSmall-magnitude irregularfluctuations, Large-scale irregularfluctuations, Cycles, Irrupti...
Small-magnitude irregular fluctuations Small random  changes in density  of one order of  magnitude or less
Large-scale irregular fluctuations Large random  changes in  density of  several orders  of magnitude
Cycles  Regular interval changes in population   density
Irruptions  Occasional, unpredictable population   explosions
Equilibrium Theories Central difference among theories lies in the  relative importance of density-dependent  factors and...
Extrinsic Biotic School Accepts importance of density-dependent  factors Emphasizes external biotic factors   Food supp...
Food supply Evidence shows that food-supply is a strong  determinant of density. Birds frequently die of starvation. Ar...
Predation Difficult to establish (need to know density  differences of predators with varying prey  densities) Studies i...
Disease and parasitism Increased densities may increase the rate of  transmission Increased density frequently correlate...
The Intrinsic School Based on mechanisms intrinsic to the  population Aka the population is self-regulated Also relies ...
Stress, Territoriality Stress may regulate density by causing  physiological reactions to high densities Territoriality ...
Genetic Polymorphism Hypothesis, dispersal Genetic composition changes in response to  density Saturation dispersal, pre...
Nonequilibriumtheories ofpopulationre gulationAbiotic Extrinsic Regulation,Metapopulations, Chaos theory
Abiotic Extrinsic Regulation Density-independent, abiotic factors Weather, temperature, moisture, sun-  exposure, rainfa...
Metapopulations Population consisting of several patches of  populations linked by dispersal. Patches vary, may go extin...
Chaos Theory Unpredictable patterns of population growth Particularly interesting with r values above  2.69 Pattern dep...
Recapitulating Population Regulation There are equilibrium and non-equilibrium  populations Density-dependent and densit...
Invasions Four stages: Transport, Introduction,  Establishment, Spread Invasions follow the logistic curve, usually  wit...
 Zebra mussel figure
Anywhere, everywhere!
Extinction and Risk Analysis Extinction is a natural component of  populations (strongly aggravated by humans) Birth rat...
Demographic accidents Habitat loss creates population decrease With smaller populations, risk of extinction  increases, ...
Habitat fragmentation Habitat loss frequently leads to habitat  fragmentation This leads to a metapopulation structure ...
Genetic risks Smaller populations have increased  inbreeding and genetic drift Both lead to increased homozygosity  (bot...
Heath hen on Martha’s Vineyard Overhunting caused massive population  decline until 1907 Population increased moderately...
T he end.
Ch. 5   population regulation part
Ch. 5   population regulation part
Ch. 5   population regulation part
Ch. 5   population regulation part
Ch. 5   population regulation part
Upcoming SlideShare
Loading in …5
×

Ch. 5 population regulation part

  • Login to see the comments

Ch. 5 population regulation part

  1. 1. PopulationRe gulationChapter 5
  2. 2. Preconditions… Populations change over time Populations cannot grow indefinitely Logistic curve Logistic equation represents equilibrium view of population regulation (if perturbed, population returns to equilibrium value, K) Other views see population fluctuations as random over time, without returning to equilibrium (due to disturbance)
  3. 3. Background Population regulation: fluctuations in abundance with feedback mechanisms to increase or decrease density toward K Population control: ecological mechanisms which control upper limit of density Density is a result of combination of factors In general: ΔN = (b + i) – (d + e), where N is population size, b is births, d is deaths, i is immigrants, e is emigrants
  4. 4. Patter ns ofPopulationFluctuationSmall-magnitude irregularfluctuations, Large-scale irregularfluctuations, Cycles, Irruptions
  5. 5. Small-magnitude irregular fluctuations Small random changes in density of one order of magnitude or less
  6. 6. Large-scale irregular fluctuations Large random changes in density of several orders of magnitude
  7. 7. Cycles  Regular interval changes in population density
  8. 8. Irruptions  Occasional, unpredictable population explosions
  9. 9. Equilibrium Theories Central difference among theories lies in the relative importance of density-dependent factors and density-independent factors. Density-dependent factors have an increasing effect with increasing density Density-independent factors have an effect that does not vary with density
  10. 10. Extrinsic Biotic School Accepts importance of density-dependent factors Emphasizes external biotic factors Food supply Predation Disease
  11. 11. Food supply Evidence shows that food-supply is a strong determinant of density. Birds frequently die of starvation. Areas with high food supplies tend to have high bird densities. (correlation Vs. causation) Artificially supplemented food studies Naturally supplemented food studies
  12. 12. Predation Difficult to establish (need to know density differences of predators with varying prey densities) Studies indicate that predator species depress prey populations Removal experiments yield ambiguous results “Top-down” or “bottom-up” controversy
  13. 13. Disease and parasitism Increased densities may increase the rate of transmission Increased density frequently correlates with increased disease rate However, correlation may not indicate causation (food supply, red grouse)
  14. 14. The Intrinsic School Based on mechanisms intrinsic to the population Aka the population is self-regulated Also relies on density-dependence Stress, territoriality, genetic polymorphism hypothesis, dispersal
  15. 15. Stress, Territoriality Stress may regulate density by causing physiological reactions to high densities Territoriality may regulate density by excluding some individuals from reproducing
  16. 16. Genetic Polymorphism Hypothesis, dispersal Genetic composition changes in response to density Saturation dispersal, presaturation dispersal (reduces inbreeding)
  17. 17. Nonequilibriumtheories ofpopulationre gulationAbiotic Extrinsic Regulation,Metapopulations, Chaos theory
  18. 18. Abiotic Extrinsic Regulation Density-independent, abiotic factors Weather, temperature, moisture, sun- exposure, rainfall, etc… These factors are sufficient to explain density variations. Populations do not encounter ideal conditions long enough for density- dependent factors to be of importance.
  19. 19. Metapopulations Population consisting of several patches of populations linked by dispersal. Patches vary, may go extinct; not in equilibrium, but overall population survives due to dispersal among patches Metapopulations are particularly important in fragmented habitats
  20. 20. Chaos Theory Unpredictable patterns of population growth Particularly interesting with r values above 2.69 Pattern depends on initial conditions Not stochastic Property of the growth itself (growth equation)
  21. 21. Recapitulating Population Regulation There are equilibrium and non-equilibrium populations Density-dependent and density-independent factors affect populations (biotic and abiotic factors) It is undeniable that there is no single explanation: rather, a combination of theories applies. To what extent in each case is the relative contribution becomes the question.
  22. 22. Invasions Four stages: Transport, Introduction, Establishment, Spread Invasions follow the logistic curve, usually with longer lag phase, followed by exponential growth Invasions reach high densities (e.g. zebra mussels, Opuntia cactus and cactoblastis moth) Escape from density-dependent factors? Probably not. Other possibilities.
  23. 23.  Zebra mussel figure
  24. 24. Anywhere, everywhere!
  25. 25. Extinction and Risk Analysis Extinction is a natural component of populations (strongly aggravated by humans) Birth rate decreases, mortality increases Very low populations suffer the Allee effect Anthropogenic habitat loss creates three risk factors: demographic accidents, habitat fragmentation, genetic risk
  26. 26. Demographic accidents Habitat loss creates population decrease With smaller populations, risk of extinction increases, due to demographic accidents Chance events have a greater impact on small populations Severe winter, epidemic, predators, etc…
  27. 27. Habitat fragmentation Habitat loss frequently leads to habitat fragmentation This leads to a metapopulation structure Single patches may not be large enough to support a breeding population Dispersal may not be possible to support supplying of extinct patches Patches may go extinct simultaneously
  28. 28. Genetic risks Smaller populations have increased inbreeding and genetic drift Both lead to increased homozygosity (bottlenecking effect leads to loss of alleles) Increased homozygosity decreases fitness, and thus places population at risk
  29. 29. Heath hen on Martha’s Vineyard Overhunting caused massive population decline until 1907 Population increased moderately thereafter (genetic risks?) In 1916, fire, storm, cold winter, invasion reduced population to 50 pairs (demographic accidents-more genetic risk) Subsequent years showed sex-ratio skewed toward males (demographic accident) Extinct by 1932 (any habitat fragmentation?)
  30. 30. T he end.

×