BIOL 4120: Principles of EcologyBIOL 4120: Principles of Ecology

Lecture 7: Life Histories and Lecture 7: Life Histories and Evolutionary FitnessEvolutionary Fitness

Dafeng HuiDafeng Hui

Office: Harned Hall 320Office: Harned Hall 320

Phone: 963-5777Phone: 963-5777

Email: Email: dhui@tnstate.edu

Http://faculty.tnstate.edu/dhui/biol4120Http://faculty.tnstate.edu/dhui/biol4120

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.

Reproduction efforts vary with Reproduction efforts vary with latitudelatitude

Why same species of birds, for Why same species of birds, for example, songbirds in tropics, lay example, songbirds in tropics, lay fewer eggs at a time than their fewer eggs at a time than their counterparts that breed at high counterparts that breed at high latitudes?latitudes?

Reproduction effort may vary with Reproduction effort may vary with latitudelatitude

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 springspringDuck and blackbird

David Lack, Oxford University1947

Birds would increase fitness by increasing clutch size, unless reduced survival of offspring in large broods offset this advantage

Hypotheses:1.Chicks in larger broods would be survive poorly2.At temperate and arctic latitudes, birds have longer days to gather food during summer when they reproduce young.

Experiments that adding eggs decrease survival of offspring

Hogstedit, Science 1980: European magpie: Average clutch is 7 (maximum the pair can handle), add more or reduce could reduce the fitness.

Life History and Evolutionary FitnessLife History and Evolutionary Fitness7.1 Trade-offs in the allocation of resources provide a 7.1 Trade-offs in the allocation of resources provide a

basis for understanding life historiesbasis for understanding life histories7.2 Life histories vary along a slow-fast continuum7.2 Life histories vary along a slow-fast continuum7.3 Life histories balance trade-offs between current and 7.3 Life histories balance trade-offs between current and

future reproductionfuture reproduction7.4 Semelparous organisms breed once and then die7.4 Semelparous organisms breed once and then die7.5 Senescence is a decline in physiological function with 7.5 Senescence is a decline in physiological function with

increasing ageincreasing age7.6 Life histories respond to variations in the environment7.6 Life histories respond to variations in the environment7.7 Individual life histories are sensitive to environmental 7.7 Individual life histories are sensitive to environmental

influencesinfluences7.8 Animals forage in a manner that maximizes their 7.8 Animals forage in a manner that maximizes their

fitnessfitness

7.1 Trade-offs in the allocation of 7.1 Trade-offs in the allocation of resources provide a basis for resources provide a basis for understanding life historiesunderstanding life histories

There are many trade-offs involved in There are many trade-offs involved in reproduction effort decisionreproduction effort decision

Allocation of resources: Given time and Allocation of resources: Given time and resources are limited, how can the resources are limited, how can the organisms best use them to achieve its organisms best use them to achieve its maximum possible fitness?maximum possible fitness?

Important stage of life history:Important stage of life history:Maturity, Age of first reproduction; Parity, number of Maturity, Age of first reproduction; Parity, number of episodes of reproduction; Fecundity, number of offspring episodes of reproduction; Fecundity, number of offspring produced per reproductive episode; Longevity, age to live.produced per reproductive episode; Longevity, age to live.

7.2 Life histories vary along a slow-fast continuum

Life history traits of different species vary consistently with respect to environments; variation in one life history traits is often correlated to others. Variations can be arranged along a single continuum of values.

Environmental conditions influence the Environmental conditions influence the evolution of life history traitsevolution of life history traits

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 organisms K-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.

7.3 Life histories balance trade-offs 7.3 Life histories balance trade-offs between current and future reproductionbetween current and future reproduction

Age at first reproductionAge at first reproduction Trade-off between fecundity and Trade-off between fecundity and

survivalsurvival Trade-off between growth and Trade-off between growth and

fecundityfecundity

Important stage of life history:Important stage of life history:Maturity, Age of first reproduction; Parity, number of Maturity, Age of first reproduction; Parity, number of episodes of reproduction; Fecundity, number of offspring episodes of reproduction; Fecundity, number of offspring produced per reproductive episode; Longevity, age to live.produced per reproductive episode; Longevity, age to live.

Age at first reproduction

Long-lived organisms typically begin to reproduce at an older age than short-lived ones.Albatrosses (sea bird): high annual survival rate (94%), start at 10 yrs.Small songbirds: 50% survival rate, start at 1 yr.Natural selection favors the age of maturity that results in the greatest number of offspring over the lifetime of the individual.

RecapRecapAcclimation and Developmental responseAcclimation and Developmental response

Life historyLife historyLife histories vary along a slow-fast continuumLife histories vary along a slow-fast continuum

Grime’s plants: Competitors, Ruderal, and Grime’s plants: Competitors, Ruderal, and Stress ToleratorsStress Tolerators

r- and k-selected strategists r- and k-selected strategists Life histories balance trade-offs between current and Life histories balance trade-offs between current and

future reproductionfuture reproduction Age at first productionAge at first production

Age at first reproduction

Long-lived organisms typically begin to reproduce at an older age than short-lived ones.Albatrosses (sea bird): high annual survival rate (94%), start at 10 yrs.Small songbirds: 50% survival rate, start at 1 yr.Natural selection favors the age of maturity that results in the greatest number of offspring over the lifetime of the individual.

Trade-off

Experimental study to demonstrate that chicks with more competing siblings grow more slowly and fewer survive to reach adulthood.

European kestrels Dijkstra et al. 1990.

Trade-off between fecundity and survival

Trade-off between fecundity and survival

F = S + S0 B S=SNSR

F = SNSR + S0 BSR = F/SN – (S0/SN) B

F: adult’s fitnessS: survival probability; SR: adult survival related to reproduction; SN: not directly related to reproduction; S0: survival to one year of age offspringB: # of offspring produced

Relationship of adult’s fitness and fecundity

Survival rate and fecundity

Different adult fitness

High F, high survival of reproductive risk

Large slope: high S0 and low Sn (high offspring survive and low adult survive)

The trade-off between growth and fecundity

Indeterminate growth: fish, reptiles, amphibiansDifferent investments on growth and reproduction

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.

Mortality rate influences life historyExperiment of David Reznick et al. , UC Riverside, on guppy Poecilia reticulataStreams in Trinidad: waterfalls created two environments: below waterfalls, predators fish species (pike cichild and killifish); above waterfalls, relatively predator-free.

Predators transplant experiment confirmed that after a few generations of adding predators, they showed same life histories.

7.4 Semelparous organisms breed once 7.4 Semelparous organisms breed once and then dieand then die

SemelparitySemelparity• One reproductive effort with all resources, then die One reproductive effort with all resources, then die • 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.

Agaves and Lobelia telekii are semelparous plants

Other semelparous examplesOther semelparous examplesSockeye salmon swim as far as 6,000 km from Sockeye salmon swim as far as 6,000 km from

Pacific Ocean feeding grounds to spawning Pacific Ocean feeding grounds to spawning streams, lay thousands of eggs, then die from streams, lay thousands of eggs, then die from

the exertion.the exertion.

periodical cicadas

Parental investment depends on the 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

7.5 Senescence is a decline in 7.5 Senescence is a decline in physiological function with physiological function with increasing ageincreasing age

Senescence: A gradual increase in Senescence: A gradual increase in mortality and a decline in fecundity as mortality and a decline in fecundity as physiological function deteriorates over physiological function deteriorates over time.time.

It’s a fact of life. Caused by natural wear It’s a fact of life. Caused by natural wear and tear. Environments also influence, and tear. Environments also influence, but mostly, it is under genetic control.but mostly, it is under genetic control.

The strength of selection varies with extrinsic mortality rates

The strength of selection for changes in mortality and fecundity at a particular age is related to the proportion of individuals in the population alive at that age, which depends largely on rates of mortality caused by extrinsic factors earlier in life.

7.6 Life histories respond to variations in 7.6 Life histories respond to variations in the environmentthe environment

Storage of food and buildup of Storage of food and buildup of reservesreserves

DormancyDormancy Stimuli for changeStimuli for change

Storage for food and buildup of reserves

Plants and animals can store food and build reserves during the good environments. For example, Desert Cacti to store water; plants store nutrients; Arctic animals accumulate fat during mild weather in winter; winter active mammals (squirrels) and birds (acorn woodpeckers) cache food supplies.

Chaparral plants store food reserves in fire-resistant root crowns.

DormancyDormancy

Dormancy: physiologically inactive state.Dormancy: physiologically inactive state.• Tropical and subtropical trees shed Tropical and subtropical trees shed

leaves during droughtleaves during drought• Temperate and Arctic trees shed leaves Temperate and Arctic trees shed leaves

in fallin fall HibernateHibernate

• Mammals: squirrels, bears? Mammals: squirrels, bears? Diapause: some insects entering resting Diapause: some insects entering resting

statestate

RecapRecap Life histories balance trade-offs between current and future Life histories balance trade-offs between current and future

reproductionreproduction Age at first productionAge at first production Survival and fecunditySurvival and fecundity Growth and fecundityGrowth and fecundityParity and parental investmentParity and parental investmentSenescenceSenescenceLife histories respond to variations in the environmentLife histories respond to variations in the environment Storage of resourcesStorage of resources DormancyDormancy Stimuli for changeStimuli for change

Stimuli for changeStimuli for changeMany events in life history of an organism are Many events in life history of an organism are

timed to match predictable change in timed to match predictable change in environments.environments.

Proximate factors: day length etc, no direct Proximate factors: day length etc, no direct effect on fitness;effect on fitness;

Ultimate factors: such as food suppliesUltimate factors: such as food supplies Photoperiod: length of daytimePhotoperiod: length of daytime

• Different populations of a single species may differ greatly in Different populations of a single species may differ greatly in their responses to photoperiod.their responses to photoperiod.

• Side oats gama grass: southern, flower in winter (>13 hours); Side oats gama grass: southern, flower in winter (>13 hours); northern, flower in summer (>16 hrs)northern, flower in summer (>16 hrs)

• Water fleas: Michgan, enter diapause in mid-Sept (<=12 hrs); Water fleas: Michgan, enter diapause in mid-Sept (<=12 hrs); Alaska, diapause in mid-August (<=20 hrs)Alaska, diapause in mid-August (<=20 hrs)

7.7 Individual life histories are sensitive to 7.7 Individual life histories are sensitive to environmental influencesenvironmental influences

Relationship between age and size at metamorphosis between frogs raised with high and low food suplies.

Travis 1984.

Marbled salamanders and spotted salamanders

Gape-limited predation

The probability of survive from fire increases with increasing stem diameter.

When fires are frequent, there is a strong selection of the rapid growth of stem at the expense of developing root systems.

7.8 Animals forage in a manner that 7.8 Animals forage in a manner that maximizes their fitnessmaximizes their fitness

Foraging involves many different decisions to make, such as where to forage, how long to feed in a certain patch of habitat, which type of food to eat etc.

Food supplies vary spatially, temporally, and with respect to the quality of food items;Foraging is dangerous as it expose the individual to predation.

Optimal foraging: try to explain these behavioral responses in terms of the likely costs and benefits of each possible alternative behavior.

Central place foragingCentral place foraging

When birds feed offspring in a nest, the chicks are When birds feed offspring in a nest, the chicks are tied to a single location, while the parents are tied to a single location, while the parents are free to search for food at some distance from the free to search for food at some distance from the nest. This situation is referred to as Central Place nest. This situation is referred to as Central Place Foraging.Foraging.

Trade-offs:Trade-offs:• Increase foraging distance, increase food availability, Increase foraging distance, increase food availability,

also increase the time, energy and risk costs of foragingalso increase the time, energy and risk costs of foraging• Is there some best distance from the nest at which a Is there some best distance from the nest at which a

parent bird should forage, and how much food should parent bird should forage, and how much food should the parent bring to its brood with each trip? How much the parent bring to its brood with each trip? How much time should the parent gathering food before it returns time should the parent gathering food before it returns to its nest?to its nest?

European starlings:European starlings:

• Forage on lawns or pasture for leatherjackets: capture Forage on lawns or pasture for leatherjackets: capture time increases with number of prey already caught, time increases with number of prey already caught, maximum 8 can carriesmaximum 8 can carries

• Foraging trip including both the time spent at the Foraging trip including both the time spent at the foraging area and traveling time between foraging area foraging area and traveling time between foraging area and nestand nest

• Rate at which a parent can delivers food to its offspring Rate at which a parent can delivers food to its offspring is the number of prey caught divided by the time of is the number of prey caught divided by the time of foraging tripsforaging trips

• How to maximum the rate?How to maximum the rate?

an individual can spend an intermediate amount of time an individual can spend an intermediate amount of time at the foraging area during each trip and bring back at the foraging area during each trip and bring back something less than the maximum possible food load.something less than the maximum possible food load.

Optimal foraging model can be used to predict behavior

Using a controlled experiment, Alex Kacelnik of Oxford University, tested how food load change with travel times

Changed food availability and distance

Risk-sensitive foraging

Foraging is potential dangerous: risk factor

James Gilliam and Douglas Fraser’s fish experiment

The EndThe End

Global warming and flowering time

Henry David Thoreau (1817-1862)

Started flowering observation study in Concord, Massachusetts

1852-1858: 500 plant species, weekly

Alfred Hosmer: 1878, 1888-1902, 700 plant species

Pennie Logemann: 1863-1993, 250 species

Richard Primack and Arbaham Miller-Rushing (Boston University) 2003-2006, 43 common species

Penology network: http://www.usanpn.org/

Mean annual T increased by 2.4 oC from 1852 to 2006

Flowering time of some species did not change, on average, flowering time today is 7 days earlier than 150 years ago

Blueberry is 3-4 weeks earlier

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

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

The EndThe End

No only clutch size, the incubation time also varies

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)