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.
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
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
Chapter 52: Population Ecology
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
Chapter 52: Population Ecology
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
Chapter 52: Population Ecology
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?
Chapter 52: Population Ecology
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
Chapter 52: Population Ecology
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.