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

Cannot exceed carrying capacity

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