Fall 2010 IB Workshop Seriessponsored by IB academic advisors

Winning Resumes for IB Students

Wednesday, Sept. 224:00-5:00pm 161 Noyes Lab

Career Center staff will discuss the basics of writing a resume including format and objectives. Cover letters and special

situations are also addressed.

ASSIGNMENT FOR THURSDAY

1) Complete Problem Set 3: 223-226 in

lab manual

2) Go to:

Course website for Sept. 24

Read article BEFORE class

‘Human Population Explosion’

3) No LO or PPT for Thursday; only ICA.

This lecture Ch 10 + 12:Population Dynamics and StructureRead LO Major Concepts

Objectives• Temporal dynamics: fluctuations through time• Density-dependent vs. independent regulation• Types and causes of fluctuations• Models with time delays

• Population abundance• How to estimate?• Age and sex structure

• Spatial structures• Distribution (range)• Density• Dispersion

What determines the abundance and distribution of populations?

Read LO I + II

What controls population size?

time

time

time

N

density-dependent

change in environment

density-independent

K

Chance??

Logistic equation assumes:• Instantaneous (d-d) feedback of K onto N• If time lags in response --> fluctuation of N

around K• Longer lags---> more fluctuation; may crash.

N

K

time

How well do populations fit the logistic growth model?

Density-dependent factors drive populations toward equilibrium (stable population size),

• BUT

• they also fluctuate around equilibrium due to:

1) changes in environmental conditions

2) chance

3) intrinsic dynamics of population

responses

• Fluctuation is the rule for natural populations.• Less fluctuation for large animals with • long life span because of: • greater homeostasis• many overlapping generations--> high intrinsic stability

• Fluctuations greater if small/short lifespan– little homeostasis– populations turn over rapidly--> – low intrinsic stability

Population cycles synchronized among species in a region. Periodic cycles with peaks separated by same number of years.

Other species may vary in their response to changes in the environment --> asynchronized cycles.

Environmental fluctuations (extrinsic factors) (and organism responses) tend to be irregular, not periodic.

But many populations change with periodic, non-random frequency. *** Is an extrinsic or intrinsic factor likely to be responsible? Explain.

Some populations exhibit regularfluctuations (cycles) in size.

What density-dependent factor causes grouse populations to cycle? Consider abiotic and biotic interactions…

What factor causes grouse populations to cycle? ICA 1• Hypothesis: Density-dependent infections by a

parasitic roundworm cause the cycles.• Prediction: Populations treated with anti-

roundworm drugs will not crash following treatments, but control populations will.

• Graph the prediction. Label axes.

Control:no drugs

Control:

No drugsQuickTime™ and a

TIFF (LZW) decompressorare needed to see this picture.

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Experimental #

Control #

Drug Drug

What is conclusion?Is hypothesis proven?

Time

Results

An intrinsic mechanism for population cycles?

• ‘Momentum’ by high birth rate at low density --> overshoot K.

• Low survival at high density--> overcompensate and decrease below K.

• Population cycles result from time delays in the birth and death rates of populations in response to their own densities.

Discrete-time models with density-dependence:• Built-in time delay ---> can’t continually adjust• Patterns of oscillations depend on value of R• (per capita growth rate)

>>2 chaos

Population dynamics reflect a complex interaction of biotic and abiotic influences, and are rarely stable.

Population: all individuals of a species in an areaSubpopulations: in different habitat patches*** What are structures (traits) of populations?• Size (abundance)• Age structure• Sex ratio

• Distribution (range) • Density (#/unit area)• Dispersion (spacing)

• Genetic structure

Population size may be estimated by several methods, e.g. mark-recapture

Aerial censuses

Censusing a population

• Number of individuals

• Sex ratio

• Age structure

• complex if:

• can’t age

• size does not = age (plants)

• Long-term vs. short-term

Size classes of individuals of same age.

***What’s the ‘take-home message’ = main conclusion?

Temporal variation in recruitment of new individuals affects age structure --->

long-term implications on population growth.

Species distributions (ranges): are they really continuous? Read LO II

What must happen for species to extend range at periphery?

What prevents it from doing so?

***What factors limit the (geographic) distribution (+ range) of organisms?

• Phenology• Dispersal• Behavior (habitat selection)• Biotic factors (other species)• Abiotic factors (chemical / physical)• Human introductions• Chance• History

Geographic distributions are discontinuous. Within itsrange, only suitable habitatsare occupied. What factor determines this distribution?

•Transplant 2 species to range of elevations --> measure fitness components.

What is the main result :for lowland species on L?for highland species on R?

What is the main conclusion?

LOW HIGH

ICA 2

Geographic range includes all areas occupiedduring entire life history; must include migration.

Geographic ranges with migration - know nopolitical boundaries…adds complexity to protection.

Are ranges stable through time?

Introducedstarlings

Population density declines as body size increases.

ICA 3 Summarize the major result in Fig. 1.

Fig. 1

Summarize major result in Fig. 2

Range

Summarize major result in Fig. 3

Within its range, population density (#/area) varies with differences in habitat quality.

ICA 4 What accounts for this owl’s distribution?

Owl location‘Old growth’ forest

Density and reproduction success are dependent on amount of suitable habitat for prey.

Older forest (%)

Numberper km2

Contrasting patterns of dispersion

Dispersion = spacing of individuals with respect to others in a population

• Which is most common in plants? animals?

(Even)

***What factors influence dispersion of individuals within populations?

• habitat heterogeneity

• dispersal limitation• reproductive mode• social interactions

Dispersal mode of plants affects their spatialdispersion.

ICA 5 What type of dispersion is shown here? Hypothesize what causes the pattern.

A B