Individuals And Life Histories Flashcards
What are unitary organisms?
Have determinate development - programmed from birth
Easy to recognise genetically separate individuals
Local damage has serious consequences
E.g. humans etc
What are modular organisms?
Have indeterminate development
Starts life as a single celled zygote but doesn’t follow a set developmental programme
Growth by repeated production of modules e.g. leaves
Individual genet not dead until all its modules are dead
What is a population?
A group of organisms of one species that interbreed and live in the same place at the same time
Compete for:
Food
Breeding sites
Breeding partners
What is population density?
The number of individuals in a given area
Why is the composition of a population important?
How many:
Of each age class
Males vs females
Juveniles vs adults
Sizes
These properties affect population growth and resilience
How is body size measured?
Using biomass as an aggregate measure of how much is there
What resources are species in competition for?
Food, breeding sites, breeding partners
What is life history?
The life history of a species is its typical schedule of survival and reproduction, along with the traits that impact these patterns
What are the key questions for life history?
When do you start to produce offspring?
How often do you reproduce?
How many offspring produced?
Many small or few large offspring?
What are the key traits of life history?
Rates: e.g. somatic growth and senescence
Timing: e.g. maturation and frequency of reproduction
Allocation: e.g. offspring size and number (invest in lots of small offspring or one or two large offspring)
What are ephemerals?
Plants and animals whose adult lifespan lasts only a few weeks or months e.g. desert annual plants, some amphibia
In what way are ephemerals adapted?
Adapted to living in highly variable and harsh environments
Remain dormant for most of life as seeds or eggs
Emerge and reproduce rapidly when conditions are good and complete life cycle in <8 weeks
What are annual life histories?
Have one generation per year i.e. growth to death in less than a year
Spend part of life in dormant stages with a fraction emerging each year
What is parity?
The number of times a female has reproduced
What is iteroparity?
Reproduction is spread out - produce offspring during repeated reproductive episodes
e.g. most mammals, perennial plants
What is semelparity?
Large number of offspring produced in a single reproductive event
The individual dies soon afterwards
e.g. annual plants
What is seasonal reproduction?
Strictly reproduces in a given season e.g. spring only
What is continuous reproduction?
There is reproduction at all times throughout the year
Tends to be observed on organisms that live in less seasonal environments
What are the three phases of life history?
Juvenile phase - organism is growing and developing but not reproducing
Reproductive phase
Post reproductive phase
What types of breeders are annuals?
Seasonal and semelparous
- Large growth phase
- One short reproductive phase
- No post reproductive phase
What types of breeders are birds?
Seasonal and iteroparous
- Short juvenile and post reproductive phase
- Long reproductive phase - multiple short events
What types of breeders are mammals?
Seasonal and iteroparous
- Medium length juvenile and post reproductive phases
- Multiple reproduction events - longer period of time for each event
What types of breeders are humans and primates?
Continuous and iteroparous
- Long juvenile phase and post reproductive phase
- More reproduction at an earlier age but can be at any time in the reproductive phase
What types of breeder are tropical insects?
Continuous and iteroparous
- More reproductive at older ages in the reproductive phase
- Short post reproductive phases
What types of breeder are fish?
Seasonal and semelparous
- Variable juvenile phase
- Short reproductive phase with one event
- No post reproductive phase
What should an optimal life history look like?
1) Should be shaped by natural selection to produce largest possible number of surviving offspring into future generations
2) Natural selection favours combinations of traits that maximise fitness
3) Maximise fitness by living a long time, reproducing early in life and produce a large number of offspring at frequent intervals
What is the principle of allocation?
Each organism has a limited amount of energy that it can allocate for maintenance, survival, growth and reproduction
- Energy allocated to one function is not available for another
What is a Darwinian Demon?
Organism that lives for hundreds of years, reproduces frequently and produces 1000s of offspring each time
Why can’t Darwinian Demons exist?
Life histories are constrained by external factors (resources, competitors, predators etc) and trade-offs among life history traits
- So natural selection is not able to fully shape life histories
What are intra-individual trade-offs?
Experienced by the individual and immediate offspring
e.g. reproduction vs survival
number of offspring vs size of offspring
number of offspring vs survival of offspring
What are Inter-generational trade-offs?
Parent-offspring conflicts
e.g. parental survival vs number of offspring
parental survival vs offspring condition
Would reproductive deer have higher or lower mortality?
Females have higher annual mortality
- Have spent energy
- Less left over for body maintenance etc
