Ch 50

Ecology of Populations

Ecology: the study of interactions of

organisms with other organisms and

with the physical environment

Population: members of the same

species living in the same area

Community: all the different populations in

an area

Population or Community?

Ecosystem: the community plus the

nonliving factors

Biosphere: all the areas of the earth that

supports life

Ecologists ask questions about where species occur and why species occur where they do

Figure 40.12-3

Chemicalfactors

Why is speciesX absent froman area?

Does dispersallimit its

distribution?

Area inaccessibleor insufficient time

Predation, parasitism,competition, disease

Water, oxygen, salinity,pH, soil nutrients, etc.

Do biotic factors(other species)

limit itsdistribution?

Temperature, light,soil structure, fire,moisture, etc.

Do abiotic factorslimit its

distribution?

Physicalfactors

Yes

No

YesNo

Ch 52

Demography - the statistical study of a population; how they change over time (density, distribution, rate of growth)

Population density: number of individuals per unit area

Figure 40.14

Births andimmigrationadd individuals toa population.

Deaths andemigrationremove individualsfrom a population.

Births

Immigration

Deaths

Emigration

Factors that affect Density

Figure 40.15

(a) Clumped

(c) Random(b) Uniform

Why?

Population distribution:

pattern of dispersal of individuals: random, clumped, uniform

Life Table/Age Structure Diagrams

age-specific summary of the survival pattern of a population

It follows he fate of a cohort, a group of individuals of the same age, from birth to death

AGE STRUCTURE DIAGRAMS

Figure 46.16

Survivorship curve - probability of newborn individuals surviving to a particular age

Late Loss (Type I)Constant loss (Type II) - death is often unrelated to ageEarly loss (Type III)

Figure 46.4c

Figure 46.4d

You can create a

survivorship curve of a

human population by

studying cemetery data

(Demography Lab)

Compare the two curves below: Which country is probably the better place to live? Defend your answer.

Per Capita Rate of Increase

Change in population size can be defined by the equation

− −Change inpopulation

sizeBirths

Immigrantsentering

populationDeaths

Emigrantsleaving

Population

Population growth = rN

(r = growth rate, N = original population size)

The population growth rate can be expressed mathematically as

where N is the change in population size, t is the time interval, B is the number of births, and D is the number of deaths

Zero Population Growth

- same number enters as leaves the population

ΔNΔt

bN −mN

J-shaped curve showing exponential growth of a population

Requires unlimited resources

S-shaped curve shows how a population becomes limited by environmental factors

Logistic Growth

Carrying Capacity: the maximum size of a population that an area can support

dN = rN(K-N)dt K

dN = rNdt

Population Growth Models

Figure 40.18

6,000

Year

Ele

ph

ant

po

pu

lati

on

0

2,000

8,000

4,000

1900 1930 1940 1950 1960 19701910 1920

the elephant population in Kruger National Park, South Africa, grew exponentially after hunting was banned

Carrying capacity (K) is the maximum population size the environment can support

The Logistic Growth Model

per capita rate of increase declines as carrying capacity is reached

dNdt

rmaxN (K −N)

K

Figure 40.19

1,000

Number of generations

Po

pu

lati

on

siz

e (

N)

1.0N

100

0 155

2,000

1,500

500

1.0N

dt dN

Exponentialgrowth

Population growthbegins slowing here.

K 1,500

dt dN (1,500 N)

1,500

Logistic growth

Figure 40.20

1,000

Time (days)

Nu

mb

er

of

Pa

ram

ec

ium

/mL

100

0 155

(a) A Paramecium populationin the lab

800

200

400

600

Time (days)

1400

0 160

30

(b) A Daphnia (water flea) population in the lab

40 6020 100 12080

Nu

mb

er

of

Da

ph

nia

/50

mL

180

60

150

120

90

Regulation of Population Size

Density Independent Factors: weather and other natural disastersDensity Dependent Factors: food, space, water, parasitism, competition

Figure 46.10

Density Independent Factor (Flash Flood) – it will have the

same impact on a small pop as it does on a large pop.

60% loss for both

- growth limited by the environment

Figure 46.11

Density Dependent Factor – as number increases,

not all of them will have access to resources

-the denser the population, the faster the resources get used up

Figure 46.12

Life History Patterns

K-strategists - small numbers of offspring, usually parental care (Kangaroo)

R-strategists - large numbers of offspring, no care, low survivability (Roaches)

Figure 46.14a

Figure 46.14b

Figure 46.13

HUMAN POPULATION GROWTHCurrent World Population: 7 billion (and growing)

•The human population is now in an exponential part of a J-shaped growth curve.

•World population increases the equivalent of one medium-sized city (216,000) per day and 79 million per year.

•The doubling time is the length of time for a population size to double, now 53 years.

•Zero population growth is when the birthrate equals the death rate and the population size remains steady.

•The world population may level off at 8, 10.5 or 14.2 billion, depending on the decline in net reproductive rate.

http://www.census.gov/main/www/popclock.html

Biotic Potential: maximum rate at which a population could grow given optimal conditions (food, water, space)

Factors that influence biotic potential:

1. age of reproduction2. frequency of reproduction3. number of offspring produced4. reproductive life span5. average death rate under ideal conditions

Penguins only hatch ONE offspring during a season, never twins.  That offspring may not survive its first year.  Parents cannot start over if offspring dies. 

Don’t forget, a population can refer to plants,

fungi and bacteria…..

Algae bloom

How to calculate Population Size

Mark and recapturehttp://www.biologycorner.com/flash/mark_recap.swf

Random Sample