chapter 52: population ecology

Chapter 52: Population Ecology

1. What is a population?- Individuals of a single species that occupy the same general area

2. What is the difference between density & dispersion?- Density – number of individuals per unit area or volume- Dispersion – pattern of spacing within the boundaries of population

Figure 52.2 Population dynamics

Births and immigration add individuals to a population.

Births Immigration

PopuIationsize

Emigration

DeathsDeaths and emigration remove individuals from a population.

Factors that influence density…..

Increase

Decrease

Fig. 52.3 Patterns of dispersion within a population’s geographic range

(b) Uniform. Birds nesting on small islands, suchas these king penguins on South Georgia Islandin the South Atlantic Ocean, often exhibit uniformspacing, maintained by aggressive interactionsbetween neighbors.

(a) Clumped. For many animals, such as thesewolves, living in groups increases theeffectiveness of hunting, spreads the workof protecting and caring for young, and helpsexclude other individuals from their territory.

(c) Random. Dandelions grow from windblown seeds that land at random and later germinate.


1. What is a population?- Individuals of a single species that occupy the same general area

2. What is the difference between density & dispersion?- Density – number of individuals per unit area or volume- Dispersion – pattern of spacing within the boundaries of population

3. What factors influence population size?- Birth rate – fecundity - Death rate- Generation time- Sex ratio

4. What do the survivorship curves mean?

Figure 52.5 Idealized survivorship curves: Types I, II, and III

I

II

III

50 10001

10

100

1,000

Percentage of maximum life span

Num

ber o

f sur

vivo

rs (l

og s

cale

)

Type I – most born survive & live to their maximum life span – us – k-selectedType II – constant death rate – each day has an equal opportunity for life or deathType III – high early death rate but survivors live to maximum life span – r-selected


1. What is a population?2. What is the difference between density & dispersion?3. What factors influence population size?4. What do the survivorship curves mean?5. What are the 2 main populations growth curves?

- Exponential – “J”-curve

Figure 52.9 Population growth predicted by the exponential model

0 5 10 150

500

1,000

1,500

2,000

Number of generations

Pop

ulat

ion

size

(N

)

dNdt

1.0N

dNdt

0.5N

dN = Δ population sizedt = Δ timermax = Births – deaths (intrinsic rate of increase)N = population size

Species whose population size is primarily determined by birth rate = r-selected species

Self-Quiz• A uniform dispersion pattern for a

population may indicate that– A. the population is spreading out and

increasing its range.– B. resources are heterogeneously distributed.– C. individuals of the population are competing

for some resource, such as water and minerals for plants or nesting sites for animals.

– D. there is an absence of strong attractions or repulsions among individuals.

Self-Quiz• I would expect the potential for social

interactions among individuals to be maximized when individuals– A. are randomly distributed in their

environment.– B. are uniformly distributed in their

environment.– C. have a clumped distribution in their

environment.– D. are non-randomly distributed in their

environment.

Self-Quiz• Humans are an example of an organism

with a type I survivorship curve. This means– A. mortality rates are highest for younger

individuals.– B. mortality rates are highest for older

individuals.– C. mortality rates are constant over the life

span of individuals.– D. the population growth rate is high.

Ticket Out the Door


1. What is a population?2. What is the difference between density & dispersion?3. What factors influence population size?4. What do the survivorship curves mean?5. What are the 2 main populations growth curves?

- Exponential - Logistic

Figure 52.12 Population growth predicted by the logistic model

dNdt

1.0N Exponential growth

Logistic growth

dNdt

1.0N1,500 N

1,500

K 1,500

0 5 10 150

500

1,000

1,500

2,000

Number of generations

Pop

ulat

ion

size

(N

)

K = carrying capacity

Species whose population size is primarily determined by carrying capacity= k-selected species


1. What is a population?2. What is the difference between density & dispersion?3. What factors influence population size?4. What do the survivorship curves mean?5. What are the 2 main populations growth curves?6. What is the difference between r-selected & k-selected species?

r-selected (generalists) k-selected (equilibrial)Maturation time: short longLifespan: short longDeath rate high lowOffspring/episode: many fewSize of offspring/eggs: small largeParental care: none extensiveTiming of 1st reproduction: early late in lifeReproductions/lifetime: usually 1 severalExamples: insects, fish, frogs mammals, birds

7. What factors limit a population?


1. What is a population?2. What is the difference between density & dispersion?3. What factors influence population size?4. What do the survivorship curves mean?5. What are the 2 main populations growth curves?6. What is the difference between r-selected & k-selected species?7. What factors limit a population?

- Density – dependent factors – intensify as population size increases- Resource limitation- Health- Predation- Waste accumulation

- Density – independent factors – effect population regardless of density- Weather- Climate - Environmental disasters

Figure 52.21 Population cycles in the snowshoe hare and lynx

Year1850 1875 1900 1925

0

40

80

120

160

0

3

6

9

Lynx

pop

ulat

ion

size

(th

ousa

nds)

Har

e po

pula

tion

size

(th

ousa

nds)

Lynx

Snowshoe hare


1. What is a population?2. What is the difference between density & dispersion?3. What factors influence population size?4. What do the survivorship curves mean?5. What are the 2 main populations growth curves?6. What is the difference between r-selected & k-selected species?7. What factors limit a population?8. How has the human population changed & how is it shown?

Figure 52.22 Human population growth (data as of 2003)

8000 B.C.

4000 B.C.

3000 B.C.

2000 B.C.

1000 B.C.

1000 A.D.

0

The Plague

Hum

an p

opul

atio

n (b

illio

ns)

2000 A.D.

0

1

2

3

4

5

6

Figure 52.25 Age-structure pyramids for the human population of three countries (data as of 2003)

Rapid growth Afghanistan

Slow growth United States

Decrease Italy

Male Female Male Female Male FemaleAge Age

8 6 4 2 0 2 4 6 8 8 6 4 2 0 2 4 6 8 8 6 4 2 0 2 4 6 8Percent of population Percent of population Percent of population

80–8485

75–7970–7465–6960–6455–5950–5445–4940–4435–3930–34

20–2425–29

10–145–90–4

15–19

80–8485

75–7970–7465–6960–6455–5950–5445–4940–4435–3930–34

20–2425–29

10–145–90–4

15–19

Babies

Groupmaking babies

GroupNOT making babies

Wide base = rapid growth Same width = slow growth Narrow base = decreasing

Self-Quiz

• A population’s carrying capacity is– A. the number of individuals in that

population.– B. a constant that can be estimated for all

populations.– C. inversely related to r.– D. The population size that can be supported

by available resources for that species within the habitat.

chapter 52: population ecology

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