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Populations

Populations. Why they stop growing. Population density. The number of organisms in a given area Population growth is limited by several factors: One set of which depends on population density Another set does not depend on population density. Density Dependent Limiting Factors.

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Populations

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  1. Populations Why they stop growing

  2. Population density • The number of organisms in a given area • Population growth is limited by several factors: • One set of which depends on population density • Another set does not depend on population density

  3. Density Dependent Limiting Factors • Population limiting factors that operate more strongly on larger, denser populations than on small less crowed populations • These are: competition, predation, parasitism and crowding

  4. Competition • The more individuals the sooner they use up the available resources • The fewer the individuals the longer resources last • One of the most important factors in determining the carrying capacity of an environment • Can lower birth rates (fewer survivors); increase death rates

  5. Predation • Most species serve as food for other species • Predators and prey usually coexist for long periods of time • Prey evolved mechanisms (defenses) to avoid predators • Predators evolved mechanisms (counter-defenses) to better capture prey • Predator prey populations always change over time (see graph page 139)

  6. Parasitism • Organism that take nourishment from a host • Most effective when hosts are present in large numbers • Parasites are host specific • High density means access to more hosts • Successful parasites do not kill their hosts

  7. Crowding • Organisms have built in behavioral need for space (hunting, nesting) • Stress from crowding can interfere with hormone and immune systems • Changes in behavior can lead to less offspring being successful (no mating, eating offspring)

  8. Density Independent Limiting Factors • These factors limit populations regardless of how large or small the population is • Mostly abiotic (does not involve living things) • Weather is most important (hurricanes, cyclones, rain, drought) • Fires • Physical disruption of the environment (earthquakes, volcanoes, avalanche, rock slides, mudslides, floods) • Human activity (plowing, clear cutting, slash and burn, use of toxins on crops)

  9. Review • Population density • Density dependent limiting factors • Density independent limiting factors

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