CHAPTER 53 P O P U L A T I O N E C O L O G Y

CHAPTER 53 POPULATION ECOLOGY I. Dynamic processes influence population density, dispersion, and demographics  Population affected by:  Density  ...
Author: Branden Horn
1 downloads 0 Views 3MB Size
CHAPTER 53 POPULATION ECOLOGY

I. Dynamic processes influence population density, dispersion, and demographics  Population affected by:  Density 



# per unit area

Dispersion 

Pattern of spacing within population boundaries

A. Density and dispersion 1. DENSITY How to determine population size Count all

Sample a plot -> extrapolate Count # of blades of grass in a 200 square meter field? # individuals / sample area = density density X total area = total population

Count an indicator

Bobcat tracks

Eagle nest

Black bear scat

Mark-recapture Capture a random sample, tag, release Wait a few weeks Capture another random sample Estimate population size Hectors dolphin, New Zealand

x = number of marked dolphins in the second capture Fig 53.2 n = total number of dolphins in second capture s = number of marked dolphins N = total population size

N = sn/x

Births

Births and immigration add individuals to a population.

Immigration

Deaths

Deaths and emigration remove individuals from a population.

Emigration

2. DISPERSION Clumped dispersion Example: mushrooms group in areas that favor growth

Shitake

Pholiota

(a) Clumped

Uniform dispersion (rare)– can result from direct interactions between individuals such as territoriality

(b) Uniform

Example: creosote bush – competition for water creates uniform dispersion

Mohave desert

Random dispersion – unpredictable because each individual is independent from others

(c) Random

B. Demographics – study of population change over time

Factors that influence population density and dispersion 1. Life table

Follow a cohort = group of same age from birth to death

 Imagine a population of 1,000 individuals born at

the same time in the same place. As time progresses, some individuals die, so there are fewer and fewer individuals present each year. But when do most individuals die? Do most individuals live to old age or do many individuals die at young ages?

Belding’s ground squirrel life table

Compare male and female death rates

2. survivorship curve – plot data Number of survivors (log scale)

1,000

Relatively constant death rate but lower survival rate for males

100

Females 10

Males

1 0

2

4 6 Age (years)

8

10

 Survivorship curves

Type 1 curve - high survival rate of young, live out most of expected life span and die in old age.

Number of survivors (log scale)

1,000

I

100 II 10 III 1 0

50 Percentage of maximum life span

100

Survivorship curves (cont)  Type II curve- relatively constant death rate

throughout their life span.  Type III curve - many young, most of which die very early in their life.

3. Reproductive rates (females) Measure reproductive output of cohort

What does this data indicate?

II. The exponential model Exponential growth (geometric)

 

“unlimited resources” Why cant exponential growth continue forever?

The rate of increase is constant But, much higher number of individuals produced as population increases Example: Bacteria divide every 20’ when resources are unlimited

III. Logistic growth

 What is meant by “carrying capacity”?

 Maximum population size an environment can

support  Limiting factors include:  Water, energy, shelter, refuge, food, nesting sites……

 Note S-shaped curve

This approximates logistic growth

This population overshot the carrying capacity of the environment

IV. Life history traits are products of natural selection

A. Evolution and life history  Traits that effect reproduction and survival

 Variables  When reproduction begins (age)  Frequency of reproduction  Number of offspring

 1. semelparity  Produce once and die Pacific salmon hatches in a stream, migrates to the open ocean, requires 1 – 4 years to matures, returns to the stream to spawn, produces 1000s of eggs, dies.

Agave grows in desert for years, when there is wet year, it sends up a flowering stalk, produces seeds, dies

2. Iteroparity – repeated reproduction produce few, but large, offspring

Artic fox pups

 B. Evolutionary trade offs between reproduction

and survival  If you care for a large number of offspring, you

yourself may have compromised survival  Kestrel study

Transferred chicks around to make defined brood sizes Small 3 – 4 chicks Normal 5 – 6 chicks Large 7 – 8 chicks

Next  measure % of male and female parent birds that survive the winter Both parents care for young

Parents surviving the following winter (%)

RESULTS 100

Male Female

80 60 40 20 0

Reduced brood size

Normal brood size

Enlarged brood size

Selective pressures and natural selection if young have high mortality  produce large #s young Or

Make an extra parental investment

Brazil nut tree has a few large seeds with high nutrients

Sardines have many offspring

mouse pups

Squirrel monkey has 1 offspring

V. Many factors that regulate population growth are density dependent A. Mechanisms of density dependent regulation  1. competition for resources 

Example Soay sheep

 2. toxic wastes 

Example: yeast

 3. predation 

Example: trout

 4. intrinsic factors 

Example: mouse

 5. territoriality 

Example: cheetah

 6. disease 

Example: the flu

 Toxic wastes – yeast produce ethanol in

fermentation, and ethanol is toxic to yeast.

 Predation

Prey population size affects predator population Predators can switch prey when certain prey is plentiful

 Intrinsic factors

High population density  stress  hormonal changes  delay sexual maturation  decrease in birth rate

Territoriality

Increases resources for each animal  survival

(a) Cheetah marking its territory

Territoriality in nesting behavior

(b) Gannets

 Disease – increased transmission in dense

populations

B. Population Dynamics 

Study of interactions between biotic and abiotic factors that cause variation in population size

1. Stability and Fluctuation Most populations are relatively stable over time, but…. may fluctuate

 Soay sheep  Population fluctuates widely due to:  Harsh wet winters  food availability  High density  more parasites

2,100

Number of sheep

1,900

1,700 1,500

1,300 1,100

900 700

500 0 1955

1965

1975

1985 Year

1995

2005

 Predation may cause population density fluctuation

Changes in predation affect population size 2,500

50 Moose

40

2,000

30

1,500

20

1,000

10

500

0 1955

1965

1975

1985 Year

1995

0 2005

Number of moose

Number of wolves

Wolves

The human population is no longer growing exponentially but is still increasing rapidly  U.N. Says 7 Billion Now Share the World

6 5

4 3 2 The Plague

1 0 8000 B.C.E.

4000 3000 2000 1000 B.C.E. B.C.E. B.C.E. B.C.E.

0

1000 C.E.

2000 C.E.

Human population (billions)

7

To maintain zero growth either birth rate = death rate

This is demographic balance

 

Most of the population growth is in developing countries Access to health care, birth control, education for women in developing countries reduces family size

Rapid growth Afghanistan Male Female

10 8

6 4 2 0 2 4 6 Percent of population

Age 85+ 80–84 75–79 70–74 65–69 60–64 55–59 50–54 45–49 40–44 35–39 30–34 25–29 20–24 15–19 10–14 5–9 0–4 8 10 8

Slow growth United States Male Female

6 4 2 0 2 4 6 Percent of population

Age 85+ 80–84 75–79 70–74 65–69 60–64 55–59 50–54 45–49 40–44 35–39 30–34 25–29 20–24 15–19 10–14 5–9 0–4 8 8

No growth Italy Male Female

6 4 2 0 2 4 6 8 Percent of population

Age structure – the relative number of people of varying ages

 Infant mortality and life expectancy

80

50

Life expectancy (years)

Infant mortality (deaths per 1,000 births)

60

40 30

20

60

40

20

10 0

0 Indus- Less industrialized trialized countries countries

Indus- Less industrialized trialized countries countries

Global carrying capacity for humans  Estimate is 10 – 15 billion

 ecological footprint - the land and water area

needed to sustain humans  Countries vary greatly in footprint size

 What factors limit the carrying capacity?  Food  Water  Space  Non-renewable resources  Waste

Suggest Documents