Demecology – the Ecology of Populations

Topics: Demography, Population, Population growth Pages: 7 (1584 words) Published: July 4, 2013
Topic 3: Demecology – the ecology of populations

The main idea: Note how mathematical models are used to examine variation in growth of a population.

Lecture outline:
1. Statistic and dynamic characteristics of population.
2. Growth curves patterns: J-shaped curve and S-shaped curve 3. Population regulation: Density-dependent and density-independent factors. 4. Human population patterns:
- Population numbers.
- Demographic transition and structure
- Population urbanization

1. Statistic and dynamic characteristics of population
Population – is a group of individuals of the same species that live in the same area. Population is an elementary and evolutionary unit of biosphere. Statistic characteristics:
• Population Number - number of individuals in a given population. • Population Density – the number of individuals in a population in given area. Population density = 100 fish / 1.000m3 of water = 1fish/ 10 m3 of water or 10 plants/ 1m2 Dynamic characteristics:

• Population growth – an increase in a population at a given time. • Population growth rate – the change in the number of individuals in a population over time

2. Growth Curves Patterns:
Growth Curves – a graph showing the number of individuals in a population over time. • The J-shaped curve – a growth curve that shows population growth which occurs indefinitely at a constant reproductive rate.

The J-shaped curve presents two phases of population growth: Lag-phase: little or no increase occurs in a population.
Exponential phase: an increase occurs in a population so rapidly that the number of individuals doubles in a specific time interval and keeps doubling in increasingly shorter periods of time. The J-shaped curve is also called as Exponential curve.

Biotic potential – the maximum rate at which a population could increase under ideal conditions – an environment with unlimited resources. The biotic potential is rarely achieved by population in natural environment. • The S-shaped curve – a growth curve that shows the period of relative stability in a population that occurs because of environmental resistance (after its lag and exponential phases). Carrying capacity – the largest population that a particular environment can support sustainably (long-term), assuming there are no changes in that environment. Environmental resistance – unfavorable environmental conditions that prevent organisms from reproducing indefinitely at their biotic potential. Factors that tend to reduce population growth rates: limits of food, light, space, oxygen etc. Notice that the J-shaped curve is the lower part of the S-shaped curve!

|[pic] |[pic] | | | | |J-shaped curve (Exponential curve) |S-shaped curve (Sigmoidal or Logistic curve) shows that | |Note that a population grows slowly during the early lag |population growth levels off after the exponential phase. The | |phase and then very rapidly during the exponential phase. |top of this curve indicates the carrying capacity of an | | |ecosystem. |

Survivorship rate – a number of individuals survived over specific period of time. Types of bell curves of survivorship rate: strait diagonal, convex, concave. Population dynamics – periodical or not periodical changes in number, sex and age of a population affected by abiotic and biotic factors (stable, changeable, explosive).

3. Population Regulation:
• Density-dependent factors – are factors that affect populations (reproduction and mortality rates) in different ways depending on population density (availability of food, space,...
Continue Reading

Please join StudyMode to read the full document

You May Also Find These Documents Helpful

  • population ecology Research Paper
  • Population Ecology Essay
  • Essay about Population Ecology
  • Population Ecology Theory Essay
  • Chapter 19 Population Ecology Essay
  • Population Ecology Essay
  • Population Ecology Essay
  • Ecology Assignment Essay

Become a StudyMode Member

Sign Up - It's Free