Lec 7 Flashcards
Life history
Organism’s sequence of events relating to its birth, growth, development, reproduction, senescence (getting old), and death
INDIVIDUAL
Life History Strategy
Species’ overall pattern of life history events exhibited by all organisms within the species
POPULATION
Questions for life histories
How fast to grow and develop?
When to metamorphose?
How fast to grow?
How large to grow?
When to begin reproducing?
How many offspring and of what size?
How often to breed?
Whether to care for offspring?
How long to live?
Trade-offs of Life-Histories
Organisms allocate limited energy and resources to one structure or function at the expense of another
_____________ does the selecting in natural selection
ENVIRONMENT
What shapes and constrains life-history evolution?
Trade-offs
A life history maximizes an individual’s fitness and a lige history strategy adapts a species to its environment
These are NOT conscious decision-making events - they occur because they have been selected for
There is a ________ range of body sizes
LARGE
Mammals range from pygmy shrews (2g) to blue whales (80,000,000g)
Large animals tolerate _____________ best while small animals tolerate ________ best
COLD environments; WARM environments
SIZE trade-off
Large trees are less susceptible to ________ than small trees but are more susceptible to _______
FIRE; WIND
SIZE trade-off
Age at First Reproduction:
Allocating resources to reproduction takes resources away from:
Growth, maintenance, and defense
The cost of reproduction is therefore REDUCED survival, growth, and future reproduction
Age at 1st reproduction trade-off
Precocial
Species reproduce at a very EARLY age (i.e. mayflies)
INCREASE fitness quickly in population, but DECREASE survival and future reproduction
Age at 1st reproduction trade-off
Altricial
Species reproduce at a much LATER age (i.e. humans)
Fitness does NOT increase quickly, survival and future reproduction INCREASED
Age at 1st reproduction trade-off
Number of Reproductive Events: Semelparous
Reproduce ONE TIME ONLY (i.e. salmon, mayflies, annual plants, agave/century plants)
Trade-offs:
-Invest too many resources in reproduction to be able to survive afterwards
-Increase fitness by saving up resources over time and producing the highest quality offspring all at once
Number of Reproductive Events: Iteroparous
Reproduce several times (i.e. most trees, birds, mammals)
Trade-offs:
- Produce offspring without completely depleting resources
- INCREASE fitness by producing more frequently
Number and Size Offspring Trade-offs
An organism’s energy investment in its offspring can be measured by the size of the offspring
The larger an organism’s energy investment in each individual offspring, the fewer offspring it can produce
Parental Care: Trade-offs
Energy investment can also be measured by the amount of parental care provided
Organisms that provide parental care INCREASE the chances of their offspring surviving
However, they can produce far FEWER offspring
Metamorphosis
Complete rearrangement of an organism’s body plan during its lifetime
I.e.:
- Insects: eggs -> larvae -> pupae -> adults (butterflies and moths
- Amphibians: eggs -> tadpoles -> adults (frogs and salamanders
Metamorphosis: Advantages
Using different food sources and exploiting different habitats minimizes COMPETITION between the young and adults of a species
Larval forms are usually small and excellent as DISPERSING (via water or wind) to colonize new habitats
Metamorphosis: Disadvantages
Complex genetic task to reorganize body plan
Energetically VERY costly
Life cycles
Life histories of organisms often go beyond metamorphosis to include complex life cycles
Examples:
- Multiple hosts in the life cycle of a parasitic worm
- Both sexual and asexual reproduction in the life cycle of corals
Plant life cycle
Alternation of generations
- DIPLOID sporophyte produce HAPLOID spores by MEIOSIS, which grow into HAPLOID gametophytes by MITOSIS
- HAPLOID gametophytes produce HAPLOID gametes by MITOSIS, which undergo fertilization to form DIPLOID zygotes, which grow into DIPLOID sporophytes by MITOSIS
Same-> same: MITOSIS
Like-> Unlike: MEIOSIS
Resting stages
Resistant or inactive stages during periodic unfavorable conditions
Includes torpor, hibernation, diapause, and estivation in animals
- Dormancy in plants (seeds, winter or drought deciduous)
- -Annual plants
Trade-offs:
-Resting stages postpone immediate reproductive success and fitness for future (hopefully better) reproductive success and fitness
Longevity
Large range of lifespans in all groups of organisms
–Plants can live a few days (some annuals) to 5000+ years (bristlecone pines/Methusila)
TRADE-OFFS:
- Shorter lifespan = early mortality but SHORT generation times
- Natural selection acts FASTER to more quickly adapt short-lived species to environments
Putting it all together
Robert MacArthur and Edward O. Wilson developed a classification scheme for life histories in 1967
–r-selected strategies vs. k-selected strategies
