1: Individuals & life histories Flashcards
Describe unitary organisms
- Easy to recognise genetically separate individuals
- Determinate development (programmed from birth)
- Strong programming = local damage has serious consequences
- E.g a sheep has 4 legs, count no. of legs in a flock and divide by 4 = no. of sheep
Describe the development of a modular organism
A genetic individual (the genet), starts life as a single celled zygote but doesn’t follow a set developmental programme = Indeterminate development
Describe the growth of modular organisms
- Growth occurs by repeated production of modules e.g leaves, polyps
- Not predictable
- Individual genet is not dead until all its modules are dead - local damage in unimportant
How is it hard to count & describe the state of modular organisms?
- Cannot estimate the number of trees in a forest by counting no. of leaves
- Body size hard to define & measure
Mass?
Trunk diameter?
Height?
What is a population?
→ group of organisms of the same species that interbreed and live in the same place at the same time
What do populations compete for?
Food
Breeding sites
Breeding partners
What are some ways to look at population composition?
How many of each age class?
How many males vs females?
How many juveniles vs adults?
Sizes (modular)
= all affect things like pop. growth and resilience
What does life history theory predict?
‘predicts how natural selection should shape the way organisms parcel their resources into making babies’ - Reznick, D. N (2010)
What are the key traits of life history theory?
- Rates e.g somatic growth and senescence
- Timing e.g maturation and frequency of reproduction
- Allocation e.g offspring size and number
Define iteroparity
Reproduces multiple times
- Reproduction spread out over multiple reproductive episodes
- e.g most mammals, the majority of perennial plants, many insects
Describe semelparity
- Big bang reproduction
- Large no. of offspring produced in a single event
- After which the individual soon dies
- .g many annual plants, some perennial plants, many insects and a few vertebrates
Describe seasonal breeding
Organisms reproduce only in certain seasons e.g spring
- Iteroparous e.g many vertebrates e.g a blue tit
- Semelaprous e.g some fish and plants
Describe continuous reproduction
Organisms that reproduce continuously throughout the year
- Iteroparous (long lived) e.g humans
Describe annual life history, ‘annuals’
- Adaptation to living in seasonal environs - to avoid harsh winter conditions
- Characterised by having 1 generation per year
- Annuals spend part of their life as dormant seeds
- In many species seeds can be viable for 10 or 100s of years!
- From seed to death is therefore not always a year (meaning that generation time is not actually 1 year)
Describe semelparous annuals + example
→ common with crop weeds
Emerge in winter/spring
Then period of growth and seed in summer, then reproduce and die
Describe seasonally iteroparous annuals + example
→ ‘ruderal’ species e.g rosebay willowherb, nettle
- Germinate early spring. Late winter
- Reproduce continually throughout year
- Die off
What force is life history shaped by?
Natural selection → to produce the largest no. of surviving offspring into future gens
If an organism could maximize their fitness by living for a long time and produce a huge no. of organisms, why don’ they?
Why aren’t there ‘Darwinian Demons’? (Law 1979)
- Life history constrained by external factors e.g predation & trade offs
- Natural selection doesn’t have a ‘free hand’ to shape life histories
What is Levins 1968 Principle of allocation?
Each organism has a limited amount of energy that it can allocate for maintenance, survival, growth and reproduction
= energy allocation to one function is not available for another
List some intra-individual trade offs
- Reproduction vs survival
- Reproduction vs growth
- Reproduction vs condition
- Current reproduction vs future reproduction
- No. of offspring vs size of offspring
- No. of offspring vs survival offspring
Describe some inter-generational trade-offs (parent-offspring conflicts)
- Parental survival vs number of offspring
- Parental survival vs offspring
