CHP. 52 - POPULATIONS

Population: group of individuals of a single species in an area.

Introduction

SIZE

DENSITYDISPERSION

Size = # of individuals in an areaDensity = # of individuals

area

SIZE Vs DENSITY

Size =4Density = 4/sq.inch

Measuring density:

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 52.1

Mark-recapture method.

Mark-recapture method.

Satellite Tracking

Mark-recapture method.: a way to estimate population size

10 crocodiles captured & marked 5 captured in next attempt; Out of 5, 2 marked or

recaptured# Captured = # Marked/ recaptured

Total (N) Total recaptured TOTAL (N) = (10 X 5) =

25 2

Patterns of dispersion

3) Dispersion = pattern of spacing

-Depends on resource/food distribution, mating opportunities, predator avoidance, strong attractions/repulsions

Clumped dispersion - individuals aggregate in patches - MOST COMMON (why?)

Fig. 52.2a

Protection, gathering food (swarms), ‘housing” may be limited (pill bugs), mating,

Uniform dispersion - individuals are evenly spaced - not as common

Fig. 52.2b

-very territorial species - ‘me casa ‘not your’ casa!’

Random dispersion - the position of each individual is independent of the others.

Fig. 52.2c

Very rare - like the dandelions in your yard - depends on where the seed landed

Recap: What factors can change pop. Size/density?1)Birth rate2)Death rate3)Immigration - into4)Emigration - out of5)Survivorship - how long you live6)Repoductive output - when you start makin’ babies ad how many?(last two together is 7) life history!)Evolution influences life history (K and r selection)

What affects population size?Demography -study of factors that affect the growth and decline ofpopulations

1) Birth Rate = # Births/ Time (1/8 sec)2) Death Rate = #Deaths/Time (1/13 sec)

Birth Rate = # Births/ Time (1/8 sec)Death Rate = #Deaths/Time (1/13 sec)

BIRTH AND DEATH RATES IN USA: FYI

Per Capita Birth Rate = # Births/Person ( 13.9 /1000 people) Per Capita Death Rate = # Deaths/Person (8.1 /1000 people)

5) Life Table: Age Specific Summary Of Survival Pattern In A Population

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin CummingsTable 52.1

This life table is important to ‘population size’ and ‘density’ because the longer a population lives, larger/denser it gets (humans)

5) Life Table - *Cohort (grp of individuals of the same age)

x-Age nx dx Ix ex

0 1000

200 1.00 2.7

1 800 100 0.80 2.25

2 700 200 0.70 1.50

3 500 300 0.50 0.90

4 200 200 0.20 0.50

5 0 0 0.00 --

TOTAL

1000

1000 2.7

x=Age Categorynx = # livingdx = # of Deaths

Ix=Survivorship – Proportion of offspring that survive to a particular age

ex = Life Expectancy

ex = Life Expectancy – How long a Person Can Expect To Live

How long can you expect to live past your retirement?

Your Current Age

Years

in

reti

rem

en

t

5) Life Table - *Cohort (grp of individuals of the same age)

x-Age nx dx Ix ex

0 1000

200 1.00 2.7

1 800 100 0.80 2.25

2 700 200 0.70 1.50

3 500 300 0.50 0.90

4 200 200 0.20 0.50

5 0 0 0.00 --

TOTAL

1000 2.7

x=Age Categorynx = # livingdx = # of Deaths

Ix=Survivorship – Proportion of offspring that survive to a particular age

ex = Life Expectancy

5)Survivorship Curve (these are drawn based on life tables)

Survivorship (%)

nx = # living

10

100

1000

10080604020

% of life

lived

nx

0% 1000

20% 800

30% 700

50% 500

80% 200

100% 0

•A Type I curve shows a low death rate early in life (humans) with most individuals living upto old age. (few babies compared to type 3)

•The Type II curve shows constant mortality (squirrels).

•Type III curve shows a high death rate early in life (oysters). Species lay a LOT of eggs in this type….why?

5) X axis shows how much life is left to live

6) Okay so apart from how long population lives, how many babies they make affects population size/densiy: Reproductive table: age-specific summary of the reproductive

output in a population.

x nx Ix mx

0 1000

1.00 0.0

1 800 0.80 0.5

2 700 0.70 0.8

3 500 0.50 0.9

4 200 0.20 0.0

5 0 0.00 0.0

mx = average # of offspring produced

6) Reproductive table – age specific summary of reproductive rates in a population

Ix mx

0.0

0.4

0.56

0.45

0.0

0.0

7) Life History: when you can start making babies, how many babies your population usually makes, when do you typically DIE (Survivorship)!All of these affect pop. Size/density!

•2 types: BIG BANG - invest in one massive reproductive effort - huge number of seeds/eggs once in many years (Semelparity); why?

Big Bang /Semelparity – once - reproduce

Iteroparity – several reproductions

7) Life History: when you can start making babies, how many babies your population usually makes, when do you typically DIE (Survivorship)!All of these affect pop. Size/density!

•2 types: Iteroparity- invest in several, regular reproductive efforts - few seeds/eggs once in a year or so - more dependable environment/resources

Big Bang /Semelparity – once - reproduce

Iteroparity – several reproductions

Can you have high reproduction and survivorship to increase pop. size?Red deer show a higher mortality rate in winters following reproductive episodes.What does this mean?There is usually a trade off

Fig. 52.5

Recap: What factors can change pop. Size/density?Birth rateDeath rateImmigration - move into an areaEmigration - move out of an areaSurvivorship - how long you liveRepoductive output - when you start makin’ babies ad how many?(last two together is life history!)Evolution influences life history (K and r selection)

Population Growth -what is it?

Population Growth Rate ‘r’ = Per Capita Birth Rate –

Per Capita Death Rate

Zero population growth rate (r= 0):

Birth rate = Death rate

1) Type: Exponential Population Growth

Example of exponential growth

1) Exponential Population Growth

1) Exponential Population Growth

Change in number over time

rNdtdN =

Population growth rate

Number of individuals

The number of individuals in each generation is a multiple of the previous generation

Ideal conditions, LOTS of resources

1) Exponential Population Growth

1) Exponential Population Growth

J Shaped Curve

Density Independent

Two stages in Exponential Pop. Growth: First it starts out slow (why?); then it escalates rapidly (why?)Answer: -not enough mating parters in first case, then as pop. Grows to a critical mass, there are plaenty of “happy” people!

Population Growth can be negative!

r > 0(+)

r = 0

r < 0(-)

Example for a population of algae

6 offspring in a lifetime - elephants , within 750 years - 19million!

Bacteria - doubling every 20 min. 1 foot of bacteria around the globe in 36 hrs!

2) Logistic Population Growth

•Carrying capacity (K) – maximum stable population size a particular environment can support.

2)Logistic Population Growth

⎟⎠

⎞⎜⎝

⎛ −=K

NrN

dt

dN1

S Shaped Curve

Density Dependent

•4 phases: a) slow start (same reason from before); b) rapid exponential growth (lots of resources still around…); c)slowing down (why?); d) population stabilizes - that means NO growth

Density Dependent Checks - these are limitations/checks imposed on growing populations to

keep their growth down

1)Intraspecific Competition: within one species

Food is limited

Density Dependent Checks

2)Interspecific Competition: competition between species.

Food and space are limited. If they are by themslves, they show higher pop. growth

Density Dependent Checks

3) Decrease in Reproductive Output: less babies!

Density Dependent Checks

4) Accumulation of wastes: living in your own poop is not healthy!

Density Dependent Checks

5)Predation: Boom Bust 10 year cycle –snowshow hare and lynx show a cycling rise and fll in population that are correlated (why?)

Density Dependent Checks

6) Disease:has to serious enough to wipe out populations or sections of it: plague/black death

Boccaccio said that the victims of plague, "ate lunch with their friend and dinner with their ancestors in paradise."

2) Logistic Population Growth

•Carrying capacity (K) – maximum stable population size a particular environment can support.

Density-dependent factorsincrease their affect on apopulation as populationdensity increases.

This is a type of negativefeedback.

Density-independent factorsare unrelated to populationdensity, and there is nofeedback from the populationBoth keep populations at equilibrium

Fig. 52.13

Density Independent Population Checks: can act anytime!

Natural Disasters

•drought •freezes •hurricane •floods •forest fires

K and r selection - based on logistic growth evolution favors different traits dependng on how close a popultion is to

carrying capacity K selection:

Near carrying capacity; few-but-large-young

r selection:Low population

density; small-and-unprotected young

K Selection for K strategies: (elephants, tortoise, endangered species)

1.They mature slowly2.They have long life spans. 3.They begin breeding later in life. 4.They usually have long generation times. 5.Most produce small numbers of offspring. 6.They take good care of their young (parental investment)7. They are usually found in stable habitats8. Very good at exploiting their minimal habitat

(close to carrying capacity; r = 0).

R Selection for R strategies: (mice (pests), oysters; r is ‘rapid’)1.They mature rapidly.

2.They have short life spans. 3.They begin breeding early in life. 4.They usually have short generation times 5.They produce large numbers of offspring. 6.They take little care of their offspring, and infant mortality is huge.7.They have efficient means of dispersal to new habitats.8. They are usually found in disturbed and/or transitory habitats

(far away from carrying capacity; r > 0).

DEMOGRAPHIC TRANSITION has 5 stages

Human Population

•Zero population growth = high birth rates – high death rates.

•Zero population growth = low birth rates – low death rates.

•The movement from the first toward the second state is called the demographic transition. Age structure changes simultaneously

Age Structure Defined

Share of people younger than 30 in a population compared to share of people age 60+Each country is one of 4 major types of age structures:

1. Very Young (>67% under 30) 2. Youthful (60-67% under 30)3. Transitional (45-60% under 30)4. Mature (<45% under 30)

Very Young Age Structures

62 countries:most of sub-Saharan Africa, Syria, Iraq, Afghanistan,3 countries in Central America, Haiti, Laos

High mortality and fertility rates (stage 2)

Youthful Age Structures 27 countries:

Bangladesh, Bolivia, Jordan, Morocco, Nepal, Peru, Philippines, Saudi Arabia

Fertility rates declining, but still above replacement level (stage 2)

Transitional Age Structures

40 countries: Brazil, China, India, Israel, Indonesia, Lebanon, Malaysia, Mexico, Sri Lanka, Thailand, Vietnam

Middle of demographic transition (stage 3)

Mature Age Structures

47 countries:Nearly all of Europe, Canada, Cuba, Russia,South Korea, Australia, U.S.

Low mortality and fertility rates (stages 4/5)

Age Structure and Conflict

80% of all new conflicts occurred in countries in which at least 60% of the population was under age 30.

Age Structure and Governance

Nearly 90% of countries with very young structures had autocratic or weakly democratic governments.

More than 80% of countries with mature age structures were fully democratic.

Mexico 1975 - 2005

Transitional59% under 30

Very Young73% under 30

World Age Structures 2005

Human Population – Age Structure

•Age structure is the relative number of individuals of each age - changes with each stage of demographic transition.

•can reveal a population’s growth trends, future social conditions.