2: Age-structured Populations
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Determining the age-structure of a population helps governments plan economic development. Age-structure theory can also help evolutionary biologists better understand a species’s life-history. An age-structured population occurs because offspring are born to mothers at different ages. If average per capita birth and death rates at different ages are constant, then a stable age-structure arises. However, a rapid change in birth or death rates can cause the age-structure to shift distributions. In this section, we develop the theory of age-structured populations using both discrete- and continuous-time models. We also present two interesting applications: (1) modeling age-structure changes in China and other countries as these populations age, and; (2) modeling the life cycle of a hermaphroditic worm. We begin this section, however, with one of the oldest problems in mathematical biology: Fibonacci’s rabbits. This will lead us to a brief digression about the golden mean, rational approximations and flower development, before returning to our main topic.
- 2.2: The Golden Ratio Φ
- The number Φ is known as the golden ratio. Two positive numbers x and y , with x>y , are said to be in the golden ratio if the ratio between the sum of those numbers and the larger one is the same as the ratio between the larger one and the smaller.