BIOL 4120: Principles of EcologyBIOL 4120: Principles of Ecology

Lecture 8: Life History Lecture 8: Life History PatternsPatterns

Dafeng HuiDafeng Hui

Office: Harned Hall 320Office: Harned Hall 320

Phone: 963-5777Phone: 963-5777

Email: dhui@tnstate.eduEmail: dhui@tnstate.edu

Life History Life History

Life history is species lifetime pattern of Life history is species lifetime pattern of growth, development and reproduction.growth, development and reproduction.

Measure of organismMeasure of organism’’s reproductive success s reproductive success is fitness: Those individuals who leave the is fitness: Those individuals who leave the largest number of mature offspring are the largest number of mature offspring are the most fit the environments.most fit the environments.

Trade-off between growth and reproduction: Trade-off between growth and reproduction: mode of reproduction, age at rep., mode of reproduction, age at rep., allocation to rep. number and size of eggs, allocation to rep. number and size of eggs, young or seeds, parental care.young or seeds, parental care.

Life History PatternsLife History Patterns

8.1 Reproduction may be sexual or asexual8.1 Reproduction may be sexual or asexual8.2 Sexual reproduction takes a variety of forms8.2 Sexual reproduction takes a variety of forms8.3 Mating systems8.3 Mating systems8.4 Mate selection8.4 Mate selection8.5 Females may acquire mates based on resources8.5 Females may acquire mates based on resources8.6 Organisms budget time and energy to reproduction8.6 Organisms budget time and energy to reproduction8.7 Species differ in the timing of reproduction8.7 Species differ in the timing of reproduction8.8 Parental investment8.8 Parental investment8.9 Fecundity depends on age and size8.9 Fecundity depends on age and size8.10 Food supply affects the production of young8.10 Food supply affects the production of young8.11 Reproductive effort may vary with latitude8.11 Reproductive effort may vary with latitude8.12 Habitat selection influences reproduction success8.12 Habitat selection influences reproduction success8.13 Environmental conditions influence the evolution of life 8.13 Environmental conditions influence the evolution of life

history characteristicshistory characteristics

8.1 Sexual or Asexual Reproduction8.1 Sexual or Asexual Reproduction

Asexual reproduction (produce offspring without involving Asexual reproduction (produce offspring without involving of egg and sperm)of egg and sperm)• New individuals are the same as the parentNew individuals are the same as the parent• Many plants (underground stem) such as strawberry;Many plants (underground stem) such as strawberry;• some animals (hydra, some aphids, parthenogenesis)some animals (hydra, some aphids, parthenogenesis)• If fitness is high, matches organism to environmentIf fitness is high, matches organism to environment• If fitness is low, possible extinction (less variation)If fitness is low, possible extinction (less variation)• Stress can result in use of sexual cycle to give new gene Stress can result in use of sexual cycle to give new gene

combinations (hydra, aphid)combinations (hydra, aphid) Sexual ReproductionSexual Reproduction

• More common form. More common form. • Can produce new gene combinations able to cope with a Can produce new gene combinations able to cope with a

changing environment.changing environment.• Greater energy commitmentGreater energy commitment

Specific organellesSpecific organelles Production of gametes, courtship activities, and mating are Production of gametes, courtship activities, and mating are

energetically expensive.energetically expensive. Feeding offspringFeeding offspring The expense of reproduction is not shared equally by both sexesThe expense of reproduction is not shared equally by both sexes

8.2 Types of sexual reproduction8.2 Types of sexual reproduction

DioeciousDioecious• Sexes are separate Sexes are separate

individualsindividuals• Greatest diversity of Greatest diversity of

offspringoffspring HermaphroditicHermaphroditic

• PerfectPerfect Male and females Male and females

organs in same organs in same flowerflower

Can result in Can result in significant significant inbreedinginbreeding

• MonoeciousMonoecious Separate male and Separate male and

female flowersfemale flowers Reduces but does Reduces but does

not eliminate not eliminate inbreedinginbreeding

Floral structure

Plants

AnimalsAnimals Most familiar form involves male and female Most familiar form involves male and female

individualsindividuals

HermaphroditicHermaphroditic• Simultaneous hermaphroditicSimultaneous hermaphroditic

Both sets of organs at same timeBoth sets of organs at same time• EarthwormsEarthworms• Outbreeding, but maximizes Outbreeding, but maximizes

offspring (twice)offspring (twice)• Sequential hermaphroditicSequential hermaphroditic

First one sex then the other sexFirst one sex then the other sex• Mollusks, echinoderms Mollusks, echinoderms

Sometimes animals (fish)Sometimes animals (fish)• Allows all individual to Allows all individual to

participate in both sides of participate in both sides of sexual cyclesexual cycle

Largest female will become male when the male fish is missing

Plant can undergo sex change: jack-in-the-pulpit (Arisaema triphyllum)

Parrotfish

8.3 Mating Systems describe pairing of 8.3 Mating Systems describe pairing of males and femalesmales and females

Different mating strategies have different advantages Different mating strategies have different advantages and disadvantagesand disadvantages• Monogamy Monogamy (one to one, form of a lasting pair bond between one male (one to one, form of a lasting pair bond between one male

and one female)and one female) Most prevalent among birds, rare among mammalsMost prevalent among birds, rare among mammals Seasonal or permanentSeasonal or permanent

• Allows sharing of cost of raising offspringAllows sharing of cost of raising offspring• Increases survival chances of offspringIncreases survival chances of offspring• Cheating does occur and has specific advantages to fitnessCheating does occur and has specific advantages to fitness

• Polygamy Polygamy (one to two or more, a pair bond exists between individual (one to two or more, a pair bond exists between individual and each mate)and each mate)

More than one mate of one sex for a single individual of the other More than one mate of one sex for a single individual of the other sex (polygyny and polyandry)sex (polygyny and polyandry)

• Free individual to compete for resources and protect territoryFree individual to compete for resources and protect territory• Better food etc for matesBetter food etc for mates• Some protection of offspring from competitionSome protection of offspring from competition

• Promiscuity Promiscuity (one to one or many and no pair bound formed)(one to one or many and no pair bound formed) Greatest number of offspringGreatest number of offspring Large amount of competitionLarge amount of competition Female only responsible for offspring in terms of resourcesFemale only responsible for offspring in terms of resources

• Poorer survival chance for offspringPoorer survival chance for offspring

8.4 Sexual Selection8.4 Sexual Selection For Monogamy, Polygamy and For Monogamy, Polygamy and

PromiscuityPromiscuity• All involve the selection of a All involve the selection of a

mate and therefore sexual mate and therefore sexual selectionselection

• Selection for secondary sexual Selection for secondary sexual characteristicscharacteristics

Peacock versus PeahenPeacock versus Peahen• Large tail feathers, more Large tail feathers, more

matingmating• Smaller tail feathers, less Smaller tail feathers, less

matingmating DeerDeer

• Characters that aid Characters that aid competition such as competition such as hornshorns

HumansHumans• Faster sports car such as Faster sports car such as

a Ferraria Ferrari

Sexual selectionSexual selection

Intrasexual selectionIntrasexual selection• male-to-male competition for the opportunity male-to-male competition for the opportunity

to mateto mate• exaggerated secondary sexual characteristics exaggerated secondary sexual characteristics

such as large size, aggressiveness and organs such as large size, aggressiveness and organs of threat such as antler and hornsof threat such as antler and horns

Intersexual selectionIntersexual selection• Differential attractiveness of individuals of one Differential attractiveness of individuals of one

sex to anothersex to another• Characteristics in male such as bright or Characteristics in male such as bright or

elaborate plumage used in sexual display as elaborate plumage used in sexual display as well as these in intrasexual selection.well as these in intrasexual selection.

What is the mate really looking for What is the mate really looking for in sexual selectionin sexual selection

In most cases the sexually selected In most cases the sexually selected characteristic is an indirect measure of characteristic is an indirect measure of resources or fitnessresources or fitness• Bigger males have captured more resources Bigger males have captured more resources

(large territories, abundance of food etc) (large territories, abundance of food etc) Sports carSports car

• Is this just a displayIs this just a display Big red car that makes a lot of noiseBig red car that makes a lot of noise

• Or does it measure resourcesOr does it measure resources Ferraris are expensiveFerraris are expensive

8.5 Organisms budget time and 8.5 Organisms budget time and energy to reproductionenergy to reproduction

Reproductive effort: Time and Reproductive effort: Time and energy allocated to energy allocated to reproductionreproduction

Trade-off between growth, Trade-off between growth, maintenance and maintenance and reproduction.reproduction.• There is a negative There is a negative

relationship between relationship between annual plant growths and annual plant growths and the allocation to the allocation to reproduction.reproduction.

Percentage of annual Percentage of annual production to reproduction:production to reproduction:

Perennials: 15-20% Perennials: 15-20% Wild annuals: 15-30%Wild annuals: 15-30%Crops: 25-30%Crops: 25-30%Corn and barley: 35-40%Corn and barley: 35-40%Lizard: 7-9%Lizard: 7-9%Salamander: 48%Salamander: 48%

Species’ trait

Production of offspring

Costs of care and nourishment

Bird species (dots) illustrate the tradeoff between “fast” organisms Bird species (dots) illustrate the tradeoff between “fast” organisms (high fecundity, high mortality) versus “slow” ones (long life, low (high fecundity, high mortality) versus “slow” ones (long life, low

annual fecundity)annual fecundity)

Species differ in timing of Species differ in timing of reproductionreproduction

SemelparitySemelparity• One reproductive effort with all resources, then death One reproductive effort with all resources, then death • Most insects and other invertebrates, some fish (salmon) Most insects and other invertebrates, some fish (salmon)

and many plants (bamboo, ragweed) and many plants (bamboo, ragweed) • Some are small, short lived, grown in disturbed habitats; Some are small, short lived, grown in disturbed habitats; • Environmental effect can be disastrousEnvironmental effect can be disastrous

IteroparityIteroparity• Produce fewer young at one time and repeat Produce fewer young at one time and repeat

reproduction throughout their lifetimereproduction throughout their lifetime• Multiple cycles of reproduction means the organism Multiple cycles of reproduction means the organism

must balance growth, maintenance, escaping predators, must balance growth, maintenance, escaping predators, defending territory, etc against reproductiondefending territory, etc against reproduction

• Most vertebrates, perennial herbaceous plants, shrubs, Most vertebrates, perennial herbaceous plants, shrubs, and trees. and trees.

Timing production: When Timing production: When –– early or late early or late How many offspring: cost of the fecundity and its own How many offspring: cost of the fecundity and its own

survival.survival.

Sockeye salmon, for example, swim as far as Sockeye salmon, for example, swim as far as 6,000 km from Pacific Ocean feeding grounds 6,000 km from Pacific Ocean feeding grounds to spawning streams, lay thousands of eggs, to spawning streams, lay thousands of eggs,

then die from the exertion.then die from the exertion.

8.6 Parental investment depends on the 8.6 Parental investment depends on the number and size of offspringnumber and size of offspring

Given certain resource allocated to rep., one can produce many Given certain resource allocated to rep., one can produce many small young or few large ones. The number of offspring affects small young or few large ones. The number of offspring affects parental investment.parental investment.

Produce large number of offspring, less or no parental care Produce large number of offspring, less or no parental care (fish-eggs, plants-seeds) (fish-eggs, plants-seeds)

Produce helpless offspring (produce young, spend less Produce helpless offspring (produce young, spend less energy in incubation, but require considerable parental care)energy in incubation, but require considerable parental care)• AltricialAltricial• MiceMice

Longer period sucklingLonger period suckling• RobinRobin

Other bird feedsOther bird feeds Produce more mature offspring (longer gestation, born in Produce more mature offspring (longer gestation, born in

advantaged stage of development)advantaged stage of development)• PrecocialPrecocial• Chicken, cow, deer, turkeyChicken, cow, deer, turkey

Humans ?Humans ? Family care (Grandmothers, Grandfathers, Aunts, Uncles, Brothers and Sisters)Family care (Grandmothers, Grandfathers, Aunts, Uncles, Brothers and Sisters)

African elephants produce one offspring at a time, African elephants produce one offspring at a time, once every few years over a long lifetime, and once every few years over a long lifetime, and protect each offspring intensively (much like protect each offspring intensively (much like

humans) humans)

Few NumberFew Number• More resources per individualMore resources per individual• More chance of accidental lossMore chance of accidental loss

By contrast, many plants and some insects, reproduce By contrast, many plants and some insects, reproduce once (annually), producing vast numbers of once (annually), producing vast numbers of

seeds/eggs that are poorly protected, if at all seeds/eggs that are poorly protected, if at all

Desert annuals

Large NumberLarge Number

Less resources Less resources per individualper individual

More chances of More chances of successsuccess

Extreme Extreme with with released released eggs of eggs of some fish some fish such as cod such as cod (millions of (millions of eggs) etceggs) etc

8.7 Fecundity depends on age and 8.7 Fecundity depends on age and sizesize

For many species, number of offspring produced For many species, number of offspring produced varies with the age and size of parent.varies with the age and size of parent.

But some species do not have a characteristic adult size But some species do not have a characteristic adult size and can continue to grow through their adults lives and can continue to grow through their adults lives ((indeterminate growthindeterminate growth))• Many plants and ectothermic (cold-blooded) animals Many plants and ectothermic (cold-blooded) animals

(fish, reptiles, amphibians, and invertebrates)(fish, reptiles, amphibians, and invertebrates)

PlantsPlants Perennial: delay flowering until they have Perennial: delay flowering until they have

attained a sufficiently large sizeattained a sufficiently large size Biennial: delay flowering beyond 2-yr life Biennial: delay flowering beyond 2-yr life

span under poor environmentsspan under poor environments Annual: small plants produce less seedsAnnual: small plants produce less seeds

Animals:Animals:

Ectothermic (cold-blooded) animalsEctothermic (cold-blooded) animals

Production of offspring in fish increases with size, which increases Production of offspring in fish increases with size, which increases with agewith age

Gizzard shad: 2-yr, 59,000 eggsGizzard shad: 2-yr, 59,000 eggs

3-yr, 379,000 eggs3-yr, 379,000 eggs

Endothermic (warm-blooded):Endothermic (warm-blooded):

similar patterns exist for some animalssimilar patterns exist for some animals

European red squirrel: body weight and reproduction success; <300 European red squirrel: body weight and reproduction success; <300 g, do not reproduce.g, do not reproduce.

8.8 Reproduction effort may vary 8.8 Reproduction effort may vary with latitudewith latitude

Birds in temperate Birds in temperate regions have a larger regions have a larger clutch size than clutch size than tropical birdstropical birds• Food supply, with longer Food supply, with longer

day length in springtime day length in springtime to forage for food to to forage for food to support larger broodssupport larger broods

• large climate variation, large climate variation, decreases popul. below decreases popul. below carrying capacity, need carrying capacity, need more youngmore young

• Greater mortality in Greater mortality in winter results in more winter results in more food for survivors next food for survivors next springspring

Habitat SelectionHabitat Selection

Process in which organisms actively choose a specific location is called Process in which organisms actively choose a specific location is called habitat selection.habitat selection.

Filling the available niches (enough food, water etc) and keeping out Filling the available niches (enough food, water etc) and keeping out competitors (find neighbors), may settle in less ideal habitats competitors (find neighbors), may settle in less ideal habitats

Exception humansException humans• All habitatsAll habitats• Left Africa and adapted the environment rather than adapted to the Left Africa and adapted the environment rather than adapted to the

environmentenvironment

Neotropical warblers

8.9 Environmental conditions influence the 8.9 Environmental conditions influence the evolution of life history characteristicsevolution of life history characteristics

Idea was conceived by Robert Idea was conceived by Robert MacArthur and Edward O. Wilson: MacArthur and Edward O. Wilson: ““r- r- vs. K-selected strategistsvs. K-selected strategists””

Derivation of the terminology comes Derivation of the terminology comes from population models (see future from population models (see future lecture): lecture): • ““rr”” is population growth rate; r- is population growth rate; r-

selected species have traits that selected species have traits that increase rincrease r

• ““KK”” is population carrying is population carrying capacity; K-selected species have capacity; K-selected species have traits that increase carrying traits that increase carrying capacity and competitive ability capacity and competitive ability when populations fill when populations fill environmentenvironment

Spotted and redback salamanders

Examples of r- and K-selected organismsExamples of r- and K-selected organisms

r-selected organismsr-selected organisms——short-lived, e.g., short-lived, e.g., dandelion, with rapid population growth dandelion, with rapid population growth rate, small body size, early maturity, larger rate, small body size, early maturity, larger number of offspring, minimal parental care number of offspring, minimal parental care (animals). Inhabit unstable conditions, (animals). Inhabit unstable conditions, disturbed areas.disturbed areas.

K-selected organismsK-selected organisms ––competitive species, competitive species, long-lived, e.g., oak tree with long life, long-lived, e.g., oak tree with long life, production of few, large seeds that can production of few, large seeds that can grow readily in shaded environments, but grow readily in shaded environments, but lack of mean of wide dispersal, poor lack of mean of wide dispersal, poor colonizers of new or empty habitats. colonizers of new or empty habitats.

Summary of life-history traits in r-selected Summary of life-history traits in r-selected versus K-selected strategistsversus K-selected strategists

““strategystrategy”” r-strategist r-strategist K-strategistK-strategist 1. Environment1. Environment variablevariable constant, constant,

predictablepredictable 2. Mortality2. Mortality density independent.density independent. dens.-dep.dens.-dep. 3. Population size3. Population size variable, below Kvariable, below K constant, at Kconstant, at K 4. Competition?4. Competition? variable, laxvariable, lax keenkeen 5. Favored traits5. Favored traits rapid developmentrapid development (opposites)(opposites) early reproductionearly reproduction small body sizesmall body size semelparitysemelparity short generation timeshort generation time good dispersal, colonizing abilitygood dispersal, colonizing ability high allocation to reproduction (smallhigh allocation to reproduction (small offspring/seed sizes; many offspring)offspring/seed sizes; many offspring)

The EndThe End

Reproduction effort Reproduction effort may vary with latitudemay vary with latitude

Illinois Panama

Set nest boxes at two places

Monitor and collect newly laid eggs over one breeding

season

Eggs are marked by date and weighted

Hatched in incubators at 37.8~38oC, RH 85-90%

Another interesting thing is that it takes the same amount of time to hatch in nature and incubators (for current setting)

Conclusions:Conclusions: Ecologists have made great progress explaining Ecologists have made great progress explaining

many (but by no means all) life history traits, using many (but by no means all) life history traits, using arguments based on individual level natural arguments based on individual level natural selectionselection

Life-history traits are often correlated in their Life-history traits are often correlated in their distribution because of the effect of habitats on distribution because of the effect of habitats on multiple traitsmultiple traits

Tradeoffs among different traits are also very Tradeoffs among different traits are also very common, indicating the inability to evolve one common, indicating the inability to evolve one phenotype that is perfect in all situations: phenotype that is perfect in all situations: Organisms have been selected to allocate resources Organisms have been selected to allocate resources differentially in different environmentsdifferentially in different environments

RuderalSmall and rapid lifecycle to invade

new sites. Large dispersal areaCompetitive

Stable environment, slower lifecycleWith more resources to growthStress-tolerant

Limited resources. Ability to adapt