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. 1 Clumped dispersion - individuals in groups. 2 Uniform dispersion – individuals evenly spaced out. 3 Random 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. 1 Big-bang reproduction (produce large number of offspring sometimes followed by the organism’s death) Known as semelparity.

The agave plant

2 Repeated 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. 1 K-selection - live and reproduce around K. 2 r-selection - high rates of reproduction, but live in environments where populations are well below K.

2 factors determine the growth of a population. 1 Density-dependent factors increase their effect as density increases (negative feedback) 2 Density-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 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.

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