Chapter 7: Life History

Front 1

Life history characteristics

Back 1

1.) Age & size at sexual maturity

2.) Amount & timing of reproduction

3.) Survival & mortality rates

Front 2

Natural selection

Back 2

favors individuals whose life history traits result in better chance of survival and reproducing

Front 3

Phenotypic plasticity

Back 3

describes how one genotype may produce different phenotypes (morphs) under different environmental conditions

changes in life history traits can result in changes in adult morphology (Ponderosa pines in different climates = different shapes)

Front 4

Polyphensim

Back 4

describes condition where a single genotype produces several distinct morphs

(Spadefoot toad tadpoles have small omnivore morphs and larger carnivore morphs)

Front 5

Modes of reproduction

Back 5

1.) Asexual reproduction (cell division): prokaryotes and protists

*some multicellular organisms reproduce

sexually and asexually - corals*

2.) Sexual reproduction: fusion of male and female gametes

Front 6

Pros & cons of sexual reproduction

Back 6

PROS: recombination promotes genetic variation & better ability to respond to environmental change

CONS: individuals transmits half of its genome to next generation; population growth rate is slower

Front 7

Complex life cycles

Back 7

have at least 2 stages, with different body forms capable of living in different habitats

metamorphosis is an abrupt transition in form occurring between larval and juvenile stage

insects, marine invertebrates, amphibians, fishes, plants, algae, and protists

Front 8

Simple life cycles

Back 8

do not have abrupt transitions

vertebrates

Front 9

Semelparous

Back 9

species reproduce only once

agave, giant Pacific octopus, annual plants

Front 10

Iteroparous

Back 10

reproduce multiple times

pines/spruces, large mammals

Front 11

r-selection

Back 11

r = rate of increase of population

high population growth rate; advantage in uncrowded conditions

short life spans, rapid development, early maturation, low parental investment, high reproduction rates

insects, small vertebrates, weedy plants

Front 12

K-selection

Back 12

K = carrying capacity for population

slower growth rates; advantage in crowded conditions

long-lived, develop slowly, late maturation, invest in each offspring, low reproduction rates

large mammals, reptiles (tortoises and crocs), long-lived plants (oak and maple trees)

Front 13

Grime’s classification

Back 13

focuses on plant life histories

based on habitat stress (abiotic factors limiting growth) and disturbances (processes destroying biomass)

Front 14

Low stress / Low disturbance

Back 14

competitive plants

superior ability to acquire light, minerals, water, and space

have selective advantage

Front 15

High stress / Low disturbance

Back 15

stress-tolerant plants with phenotypic plasticity

slow rates of water and nutrient use

defenses to herbivores

Front 16

Low stress / High disturbance

Back 16

ruderal plants

short life span

rapid growth rates

heavy investment in seed production

opportunistic

Front 17

High stress / High disturbance

Back 17

not suitable for plant growth

Front 18

Charnov approach

Back 18

examine and compare life history traits by removing influence of size and time

divide species’ average age of maturity by average life span = dimensionless ratio (c)

dimensionless ratio allow comparisons of different life histories

c differs between ectothermic and endothermic animals (takes fish and lizards longer to mature than mammals and birds)

Front 19

Trade-offs

Back 19

organisms allocate limited energy/resources to one function versus another

Front 20

Trade-offs of different life histories

Back 20

size vs. # - larger investment in each offspring means fewer offspring produced

in species w/o parental care, resources are invested in propagules (eggs/seeds)

size of propagules is trade-off with # produced

Front 21

Trade-offs between current / future reproduction efforts

Back 21

some iteroparous organisms - earlier it reproduces, the more times it can reproduce in lifetime; trade-off of # of offspring increases with size & age of organism

advantages in delaying reproduction and investing more energy in growth and survival

(a fish with 5-yr lifespan can increase total reproductive output by delaying maturation by 1 yr.)

BUT if adult survival rate is low, future reproduction may never occur; early reproduction would be favored

Front 22

Senescence

Back 22

decline in physiological function with age

onset can set upper age limit for reproduction

semelparous species undergo rapid senescence and death following reproduction

Front 23

Different selection pressures at different life cycle stages

Back 23

as selection pressures change, different morphologies and behaviors can be adapted at different life stage cycle stages

small early life stages often vulnerable, small size weakness offset because early stages can do things/have abilities that adult stage does not

*parental investment: provisioning

eggs/embryos with yolk and protective

covering for eggs and parental care —> lessens

early pressures

*dispersal: small offspring well-suited for

dispersal —> reducing competition and

allowing increased colonization of new areas or

escaping from diseased/high predation areas

(plants, fungi, marine invertebrates)

*dormancy: state of suspended growth and

development so organism can survive

unfavorable conditions (small seeds, spores)

Front 24

Justification for complex life cycles

Back 24

Functional specialization of stages is a common feature

Insects: larval stage stays in small area and larvae are specialized for feeding and growth; adults specialized for dispersal and reproduction

Marine invertebrates: larvae specialized for feeding and dispersal in ocean currents and have structures to deter predators