Chapter 20

Populations

3 Properties of Populations

Population Size

Population Density

Population Dispersion

Population Size

Population-groups of organisms that belong to the same species and live in a particular area at one time

Population size-number of individuals a population has

Sometimes there are too many to count so a sampling is used.

Scientists count a number of organisms in a certain area and multiply the area.

Population Density

Population density-measures how crowded a population is

The number is always expressed as the number of individuals per unit of area or volume

Some areas are densely populated and others are sparsely populated

Population DispersionDispersion is the spatial distribution of individuals within a population.There are three types of dispersion.Clumped dispersion occurs because resources and living space is clumped or because of behavior, herdingEven dispersion is the result of social behavior and organisms stay as far away from each other as possibleRandom dispersion results from wind distribution of seeds so plants usually have a random dispersal

Types of Dispersion

Population Dynamics

All populations are dynamic, meaning they change in size and composition over time.

Birth rate-number of births over time

Death rate (mortality rate)-number of deaths over time

Life expectancy- how long on average an individual is expected to live

Stopassignments: Lesson of the Kaibabhomework: Population Growth Graph

Age Structure

Age structure-distribution of individuals among different ages in a population

Different countries have different age structures.

We can use graphs to compare age structure.

Survivorship Curves

The mortality rate data of different species tend to conform to one of three curves on a graph.Type I organisms are more likely to die later in life. (humans and elephants) k-selectedType II organisms have a linear look because the probability of dying does not change. (birds)Type III organisms are more likely to die earlier in life. (oysters, salmon, insects) r-selected

Survivorship Curves

More Curves

Population Growth Rate

Growth rate- the amount by which a population’s size changes over time

Immigration-individuals moving into a population

Emigration-individuals moving out of a population

STOP

Assignments: Human Population Growth graph

Homework: w.s 20-1

Exponential Growth Model

Exponential Model- population increases rapidly after only a few generations; the larger the population gets, the faster it growsLimiting factor-a factor that restrains or stops the growth of a populationLimiting factors are available resources, space, waste accumulation, population density

Logistic Growth Model

Logistic model-builds on the exponential model but adds the limiting factors.

Carrying capacity (K)- the number of individuals the environment can support over a long period of time

Once carrying capacity is reached, the population remains constant

Population Regulation

Density-independent factors-weather, flood, fires; these reduce the population regardless of size

Density-dependent factors- food, nesting sites, illness; these occur as a result of population size

Perils of small populations- Inbreeding

The rapidly growing human population has caused extreme reductions in the populations of some other species and subspecies.Fewer than 200 Siberian tigers remain in the wild due to over hunting and habitat destructionThe California condor is down to 9 individuals.Fewer individuals means inbreeding or mating with relatives.This mean the babies will be more likely to have defects or diseases.