Bio 104 5/31/96

Populations: Chapter 20
1. measured by size (n)
   • total number of individuals within the population
2. density: the total number of individuals per area/or volume occupied
3. dispersion: the way that the individuals are organized in an area
   1. clumped (ex. cities)
   2. uniform
   3. random SEE FIGURE 20.3 Random (a), Clumped (b), and Uniform (c) dispersion. Figure 20.3
4. Age structure
   • a triangle represents rapidly growing populations
     • the largest chunk of the population are still in their reproductive years
   • a rectangle represents stable population growth
   • a upside-down triangle represents a decline in population
5. survivorship curves
   1. Type I-most individuals survive to middle age and after that mortality is high SEE FIGURE 20.10 Survivorship curves. Figure 20.10
      • raised by diet, health care, not smoking, and using condoms so not to get anything that could kill all of your T-cells
   2. Type II-random
      • death rate high at any age; constant at all ages
   3. Type III-most die young
6. growth rate
   • bacteria, for example grow exponentially, the theme of this story is that a lot of bacteria can grow in a very short amount of time
   • doubling time is the amount of time it takes to double the population size reproductive rate=(births-deaths)/population size
   • carrying capacity (k) is how much an ecosystem can support SEE FIGURE 20.6 The sigmoid growth curve. Figure 20.6

1. Reproductive Rate (r) strategists (think roaches): rapid growth, small off-spring, no parental care, and mature rapidly
   example -insects, -bacteria
2. Carrying capacity (k) strategists: slow growing, few off-spring, parental care, large in size, and take a long time to mature Many k strategists now extinct.

   -Mike said kangaroos, but I think humans.

Human population growth
• time it takes for population to double is doubling time:
• 6000 BC 5 million humans
• 1650 AD 500 million doubling time 1000 years
• 1850 AD 1 billion doubling time 200 years
• 1930 AD 2 billion doubling time 80 years
• 1975 AD 4 billion doubling time 45 years
• 2000 AD 6 billion - do the math!

  SEE FIGURE 20.12

By 2090 there will be 14 billion people on this earth! What is the carrying capacity?

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