Answers to questions generated in population dynamics lecture.

Why might an understanding of population dynamics be relevant in an environmental geology course?

• The population determines the magnitude of resource use. Other factors area also important (per capita use behavior), but the population is a primary factor. For non-renewable resources the population history will determine depletion times. For potentially renewable resources it will figure into whether use exceeds the regeneration capacity.
• The population numbers determine the magnitude of pollutants produced. Again, other factors are involved but this is a primary one. For some types of pollutants there is a capacity of some natural systems to recycle them and render them harmless. Sewage is a simple but important example. Above certain levels harm is done.
• Population density determines fatalities and damage associated with natural events such as earthquakes, eruptions and flooding. Population increases can lead to more people living in unwise places such as floodplains.
• Population density and competition for resources can lead to undesirable human behavior. Many wars can be at least partly attributed to a conflict over resources.
• It can be argued that population growth is the fundamental underlying driving process behind most environmental concerns. At a certain level of population density environmental concerns will be minimized.

Exponential population growth versus consumption rate, which is the real culprit?

An argument that is sometimes cast about is that population growth shold not the real concern, but consumption rates are more important. Some countries with low population growth have very high per capita consumption rates (including the U.S.), and maybe the focus and when blame is being assigned, the blame should be laid here. A mathematical model of consumption rates for two different populations shows, however, that in the long term population growth can not be ignored and dominates as a factor. It reinforces the 'power' of exponential growth.

Consider a high birth rate versus low use group where every person produces 4 offspring and uses 1 unit of a resource in their lifetime, versus a group of low birth rate where every person procues 2 offspring but uses 10 units of that same resource. In other words the while the birth rate of one is twice as high as the other this group has a per capita resource use rate one tenth of the other. The below table produced shows that after 5 generations the high birth rate population quickly surpasses the low birth rate in cumulative resource use. Excel can be easily used to model other versions of this type of experiment.

 generations 1 2 3 4 5 6 7 population for high birth rate low use group 1 1 4 16 64 256 1024 4096 cumulative consumption for group 1 1 5 21 85 341 1365 5461 population for low birth rate high use group 2 1 2 4 8 16 32 64 cumulative consumption for group 2 10 30 70 150 310 630 1270

What should one conclude from this exercise? Per capita resource use is an important factor, but population growth can not be ignored.

What is the role between growth constant at any one time and environmental conditions?

The settlement of Greenland by the Vikings is a potentially good example. Greenland was settled in a time of relative warmth that permitted farming and maintenance of livestock. The settlements were quickly abandoned in the 1400s at the beginning of the Little Ice Age. Climate changes can be much more pronounced in polar regions. One explanation of the settlement collapse was simply that the Little Ice Age changed the local carrying capacity.