4. Population Ecology (Population Dynamics, Human Population Growth)

the study of population dynamics

focuses on the complex interactions between biotic and abiotic factors that cause variation in population sizeq

• examples of a boom-and-bust cycle

• hare populations

3 hypotheses proposed to explain the hare’s 10 year interval

• Hypothesis I: hare pop cycle follows a cycle of winter food supply

  • if correct, cycles should stop if the food supply is increased

  • study provided additional food and the pop increased in size

  • no hares appeared to have died of starvation

• Hypothesis II: hare pop cycle is driven by pressure from other predators

  • study conducted, 90% of the hares were killed by predators

  • data support this hypothesis

• Hypothesis III: hare pop cycle is linked to sunspot cycles

  • sunspot activity affects light quality, which in turn effects the quality of the hares food

  • there is good correlation between sunspot activity and hare pop size

• both predation and sunspot activity regulate hare numbers and that food availability plays less important roles

metapopulations

groups of populations linked by immigration and emigration

metapopulation in theory

patch- matrix view

metapopulations in reality

patch-mosaic view

can a population grow indefinitely

no

one important demographic factor in present and future growth trends is a countries age structure

which is the relative number of individuals at each age

infant mortality and life expenctancy at birth vary greatly among developed and developing countries but do not capture the wide range of the human condition

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global carrying capacity

how many humans can the biosphere support?

10-15 billion

• limited by food, space, nonrenewable resources, buildup of wastes