Week’s Lab IV: Student-Driven Project 1Complete Homework 6 at home: Correlation/RegressionBring 3 abstracts to trade with group + TAComplete SDP1 Proposal Worksheet - Indiv. Use pg. 109-114

Next lectureChapter 11:Sex and Evolution

EXAM 1 next Tuesday 12:30 here Lectures/Chapters thru Thursday

Practice exam with answers: On course website on Exam date

Format: Choice of ?s to answer Longer: 4 of 5 (interpret figures) Shorter: 4 of 6

Questions?

6

***Sample exam question.A species of scale insects extracts fluids from branches of pine trees. They have very limited movement. In an experiment, these insects were transplanted 1) between branches of the same pine tree, and 2) from one pine tree to another pine tree of the same size.

1. State the hypothesis/prediction that was being

tested as an “If…then…”

2. Summarize the results in one concise sentence.

3. Do the results support the hypothesis?

4. Predict whether gene flow or natural selection would be a more powerful force affecting the genetic structure of this insect. Explain your choice.

5. Predict whether the genetic makeup of populations of the insect on adjacent trees would be homogeneous or differentiated. Explain your choice.

Today:Ch 10: Life Histories and Evolution

Objectives• Define life history• How to study life history?• Correlated life history traits in contrasting

environments• Resource allocation and tradeoffs• Age of maturity• Fecundity• Parity (no. times reproduce/lifetime)• Aging and lifespan

*** Sample exam questionLife history traits often represent ‘tradeoffs’.

Graph the expected relationship for each pair of traits. Label axes. Then explain the nature of each tradeoff.

A. Seed size vs. seed number

1. Graph 2. Explanation

B. Number of offspring per breeding attempt vs. adult survival between successive breedings

1. Graph 2. Explanation

A search for a set of rules when particular traits affecting reproduction and survival may be favored by natural selection.

Lack: life history in an evolutionary context.

• As life history traits contribute to reproductive success, they influence evolutionary fitness.

• Life histories vary consistently with environmental factors; hence may be molded by natural selection.

How study life history evolution?Wide variation among organisms in life history traits: use of comparative methods

temperate tropical

Clutch size of birds increases with latitude.

Latitude

Clutch size

***Possible hypothesis?

***Experimental test of hypothesis:Number of eggs per clutch is limited byfood supply. Normal clutch size = 7.Do the data support the hypothesis?

What type of selectiondoes this demonstrate?a. Directionalb. Stabilizingc. Disruptive

Is genetic variation beingmaintained or reduced?

Life histories vary along a slow-fast continuum. Traits are correlated in contrasting environments.• Slow (K-species) = in persistent habitats population near carrying capacity• slow development• delayed maturity• large adult size• low reproductive rate• high parental investment/offspring• low mortality• long life• in persistent habitats• low dispersal• Fast (r-species) = in disturbed habitats

population can grow rapidly • opposite traits

Life history results from rules and choices influencing survival and reproduction.

Juvenile survival

Repeated reproduction

Life history: schedule of organism’s life, including:

• age at first reproduction (maturity) • number and size of offspring (fecundity)• number of reproductive events (parity)• aging (life span)

• The values of these traits are solutions to the problem of allocating limited time and resources among various structures, physiological functions, and behaviors.

Resource Allocation

• Organisms face a problem of allocation of scarce resources. (or can organisms increase overall performance without trading off one function against another?)

Alternative pathways for resource allocation

growth reproduction maintenance

Energy + matter

reproduction

increased survival

increasedcompetitive ability

immediateprofit

delayed profit

increasednumbers

Investing in reproduction lowers survival.

• Tradeoffs: Allocation of time, energy, or materials devoted to one structure or function cannot be allotted to another.

• Costs: Allocation to current reproduction affects survival, growth, and future reproduction.

***Tradeoffs

1. Graph

2. Explain

Looking for correlation or cause/effect?

Can axes be switched?

Prob ofsurvivalfor 15 yr

No. fruits per year No. flowersin 1st season

Plant sizein 2nd season

Variation in one life history trait is often correlated with variation in other traits.

*** Explain this tradeoff: reproduction vs. mortality

***Does this experiment support the ‘tradeoff hypothesis’ of parental care vs. adult survival? Explain.

Prop surviving

Brood size

• Life histories balance trade-offs between current reproduction and future reproduction.

• Great variation among organisms in resolving the fundamental tradeoff between fecundity and adult growth and survival.

• Principle: limited time and resources are allocated among competing functions so as to maximize lifetime reproductive success.