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Population Ecology

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Population Ecology

Chapter 52

- Population - group of individuals living in same area at same time.
- Population density - # of individuals per unit area.
- Population dispersion - arrangement of population in area.

- Dispersion patterns happen 3 ways.
- 1Clumped dispersion - individuals in groups.
- 2Uniform dispersion – individuals evenly spaced out.
- 3Random dispersion - individuals live regardless of where other individuals live.

CLUMPED

UNIFORM

RANDOM

- Demography - study of statistics of a population.
- Life tables - show summary of specific ages of population and survival rates.

- Survivorship curve - can see how many individuals are alive at specific ages.

- Reproductive tables - reproductive rates at various ages.
- Focus only on females and not males in these tables.

- Life history - traits that affect organism’s schedule of reproduction and survival.
- 1Big-bang reproduction (produce large number of offspring sometimes followed by the organism’s death)
- Known as semelparity.

The agave plant

- 2Repeated reproductive episode - organism produces smaller numbers of offspring.
- This is also known as iteroparity.

- Change in population - # of births minus # of deaths during that same time.
- Equation : N/t = r; r= difference between birth and death rates, N= change in population size, and t= change in time.

- Limitations on population growth due to resources.
- K = carrying capacity.
- Carrying capacity – max # of individuals an area can handle based on resources.

- Logistic population growth model - incorporates affect of population density on rate of increase.
- Carrying capacity cannot be exceeded - graph is S-shaped.

Carrying capacity

equals change in

population size

Carrying

capacity

Cannot exceed

carrying capacity

- Life histories - predict how population will reproduce.
- 1K-selection - live and reproduce around K.
- 2r-selection - high rates of reproduction, but live in environments where populations are well below K.

- 2 factors determine the growth of a population.
- 1Density-dependent factors increase their effect as density increases (negative feedback)
- 2Density-independent factors - not affected by density increase.

- Negative feedback - caused by several different factors.
- One - resources (force populations to stop reproducing if conditions are crowded)

As # of planted seeds increase,

# reproducing decreases

- Competition for resources can force decreased reproduction rates.
- Need to defend space can reduce population size.
- Predation can decrease the size.

- Human population has been steadily growing since 1650.
- Zero transition growth # of births = # of deaths.
- Only way to steady out population growth.

- One of the difficulties with population growth is looking at the distribution of ages.
- The problem is that the carrying capacity of Earth has not been determined.

- http://www.youtube.com/watch?v=GECJcW2Ifm4