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Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

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Page 1: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Populations

Outline:

• Properties of populations

• Population growth

• Intraspecific population

• Metapopulation

Readings: Ch. 9, 10, 11, 12

Page 2: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Definition

• Population is a group of individuals of the same species that inhabit a given area

Page 3: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Unitary organisms

Page 4: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Modular organisms

Page 5: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

genet ramet

Page 6: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Distribution of a population

Page 7: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Distribution of a populationRed maple

Page 8: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Distribution of a populationMoss (Tetraphis pellucida)

Page 9: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Abundance

versus

Population density

Page 10: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Patterns of dispersion

Page 11: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Effect of scale on pattern of dispersion

Page 12: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Populations have age structure

Page 13: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Populations have age structure

Page 14: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Determining age

Page 15: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

wild turkey quail

grey squirel bat

Determining age

Page 16: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Dispersal

• Movement of individuals in space

• Moving out of subpopulation = emigration

• Moving into a subpopulation = immigration

• Moving and returning= migration

Page 17: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Yellow-poplar

Page 18: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Ring-necked duck

Gray whale

Page 19: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Gypsy-moth

Page 20: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

POPULATION GROWTH

Page 21: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Darwin’s 1st observation:

All species have such great potential fertility that their population size would increase exponentially if all individuals that are born reproduce successfully.

Page 22: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Example of exponential growth:the ring-necked pheasant, Phasianus colchicus

• Native to Eurasia• 1937: Eight birds introduced

to Protection Island (Washington state)

• 1942: Population had increased to 1,325 birds (a 166-fold increase!)

Page 23: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

N/t = (b - d) Nt

Page 24: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Population Growth Models

• Assume no immigration or emigration

• Let N = population size

• Let N/ t = change in population size/unit time= total # births - total # deaths

• Let mean birth rate per individual = b= # births / individual / unit time

• Let mean death rate per individual = d= probability of death for an individual / unit time

N/ t = bN - dN

• Let r = b-d

Page 25: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Population Growth Models

• r = instantaneous rate of increase a.k.a. per capita rate of increase

• Calculus notation is commonly used; N/t = dN/dt

• If r > 0, population will increase exponentially at rate, dN/dt, = rN

• For an exponentially growing population, the number of individuals at time t, Nt = N0e(rt) where No = initial population size and e = base of natural logarithms

Page 26: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Exponential growth model: Nt = N0 e(rt)

Page 27: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

St. Paul reindeer

Page 28: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Life tables

cohort - all individuals born within a periodcohort life table – survivorship of a cohort over time

Page 29: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

lx = represents the probability at birth of surviving to any given age

Life tables

Page 30: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

dx = represents the age-specific mortality

Life tables

Page 31: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

qx = represents the age-specific mortality rate

Life tables

Page 32: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Mortality curves

Page 33: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

sedum

Mortality curves

Page 34: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Survivorship curves - plot of lx vs. time

Page 35: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12
Page 36: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Red deer

Page 37: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Theoretical survivorship curves

Page 38: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

What happened to population in 1940s?

Page 39: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12
Page 40: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Human population growth

Page 41: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Darwin’s 2nd observation:

Populations tend to remain stable in size, except for seasonal fluctuations

Darwin’s 3rd observation:

Environmental resources are limited

Page 42: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

• In real world, populations don’t increase exponentially for very long

--> run out of resources

• An N increases, b decreases and/or d increases

Page 43: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Population limiting factors

Density-dependent: effect intensifies as N increases. E.g.:1. Intraspecific competition

– Between members of same species

2. Toxic waste accumulation – E.g. yeast cells: produce ethanol as by-

product of fermentation (see next slide)

3. Disease– Spreads more easily in crowded

environments

Page 44: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Effect of crowding on birth rate

Page 45: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Effect of crowding on survivorship

Page 46: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Intraspecific population regulation

Page 47: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Carrying capacity, K

= maximum number of individuals that a particular environment can support

• Take into account by the Logistic Growth Equation,

dN/dt = rN (1-N/K)

Page 48: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Logistic model

Page 49: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Logistic model

Page 50: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Exponential vs. logistic model

Gray squirrel

Page 51: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

How good is the logistic model?

• Describes growth of simple organisms well, e.g. Paramecium in a lab

• Water fleas (Daphnia spp.): population initially overshoots K until individuals use up stored lipids --> crash down to K

• Song sparrows: populations crash frequently due to harsh winter conditions– N never have time to reach K– Population growth not well described by the

logistic model

Page 52: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12
Page 53: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Life History Strategies

• When N is usually << K, natural selection favors adaptations that increase r

--> lots of offspring

= r selection– E.g. species that colonize short-lived environments

• When N is usually close to K, better to produce fewer, “better quality” (i.e. more competitive) offspring

= K selection• E.g species that live in stable, crowded environments

Page 54: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Density dependence

Page 55: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Density dependencewith Allee effect

Page 56: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

American ginseng

Density dependencewith Allee effect

Page 57: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Types of competition

• Competition: individuals use a common resource that is in short supply relative to the number seeking it

• Intraspecific vs. interspecific• Scramble vs. contest• Exploitation vs. interference

Page 58: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Density effect on growth

Page 59: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Density effect on growth

Page 60: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Density effect on growth

Page 61: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Horseweed

Density effect on growthSelf thinning

Page 62: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Density effect on reproduction

Page 63: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Territoriality

Page 64: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Grasshopper sparrowAmmodramus savannarum

Page 65: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Banding study in California: 24% of current territory holders had been floaters for 2-5 yrs. before acquiring a territory.

White-crowned sparrow, Zonotrichia leucophrys

Page 66: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12
Page 67: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Uniform distribution of plants occurs due to the development of resource depletion zones around each individual

Page 68: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Population limiting factors

Density-independent: effect does not depend on N. – E.g. weather / climate– Thrips insects:

• Feed on Australian crops (pest)• Population growth very rapid in early

summer• Drops in late summer due to heat,

dryness--> N never has time to get close to K

Page 69: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Density-independent factors

Page 70: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

DRYTurbid

WETClear

Density-independent factors

Page 71: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

e.g. Dungeness crabs

• Density-dependent factors: competition; cannibalism

• Density-independent factors: water temperature

Page 72: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Metapopulationsa population of populations

Chapter 12

Page 73: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Metapopulation: A group of moderately isolated populations linked by dispersal

Page 74: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Criteria for a metapopulation

1. Habitat occurs in discrete patches

2. Patches are not so isolated as to prevent dispersal

3. Individual populations have a chance of going extinct

4. The dynamics of populations in different patches are not synchronized

– i.e., they do not fluctuate or cycle in synchrony

Page 75: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Metapopulation dynamics:spatial scales

1. Local (within-patch)2. Metapopulation (regional)

Shifting mosaic of occupied and unoccupied patches

Page 76: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Checkerspot butterfly

Page 77: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Levin’s model of metapopulation dynamics

• E - subpopulation extinction rate = eP• e – probability of a patch going extinct/unit time• P – proportion of occupied patches

• C – colonization rate = mP (1-P)• m – dispersal rate• (1-P) – unoccupied habitats

Page 78: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

E = C equilibrium point,Where0 = [mP(1-P)] - eP

If C>E, P increases; If C<E, P decreasesPequilibrium= 1-e/m

Page 79: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Bush cricket

Page 80: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Larger patches have larger populations (and therefore lower risk of extinction)

Page 81: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Skipper butterfly

Page 82: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12
Page 83: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Effect of habitat heterogeneity

Page 84: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Mainland-island population structure: one large population (low extinction risk) provides colonists for many small populations (high risk)

Rescue effect: island recolonized from “mainland”• High quality / permanent population = source population• Temporary patches = sink populations

Checker-spot butterfly

Page 85: Populations Outline: Properties of populations Population growth Intraspecific population Metapopulation Readings: Ch. 9, 10, 11, 12

Skipper butterfly