Population growth & life histories Flashcards
Which 4 processes affect population size?
Births
Immigration
Deaths
Emigration
What is the calculation for change in population size?
Change in pop size = (births + immigration) - (deaths + emigration)
What are intrinsic factors?
Factors that affect a population size from within a population
e.g. age of 1st reproduction
What are extrinsic factors?
Factors that affect a population size from outside the population
e.g. predation, weather
How can intrinsic factors be divided up?
Density-dependent factors
= population rate decreases as population size & crowding increase
e.g. effects of food supply & breeding sites
Density-independent factors
= influence populations independently of population size
e.g. effects of weather & catastrophes - volcanoes
What happens to the populations of most plants & animals over time?
What is the most likely reasoning behind fluctuations in a population size?
Fluctuate
Extrinsic factors
What does r represent?
Intrinsic growth rate = b-d
(per capita)
where:
b = per capita birth rate
d = per capita death rate
What is the equation for the tangent on a population growth curve?
dN/dt = rN
r at that instant
What is the equation for the change in population size over a time?
/\N / /\t = rN
Describe pop growth when growth rate is constant.
What prevents populations growing indefinitely?
Exponential
Limited resources
When does growth decrease?
Define K
As the no. of indivs approaches the carrying capacity of the environment (K)
Limit at which populations stop growing
The rate at which growth slows depends on what?
How close the pop size is to K
When N=K, no growth
What is an example of a factor besides K that can affect real pop growth?
(Not shown by the logistic model)
Lag-time in response to change in conditions
r is the same for which types of growth?
logistic & exponential
Exponential growth describes pop growth when?
There’s no shortage of supplies
The logistic model describes what?
Approx growth of most natural pops
What are life history traits?
The pattern of survival & reproduction events typical for a member of that species.
Represent optimisation of trade-offs between growth, survival & reproduction
Give examples of life history traits.
>Age & size at reproduction >No. of reproductive seasons - semelparous = once - iteroparous = many >Life span - annual vs perennial >No. & size of offspring
Describe the perfect life history
Why doesn’t this exist?
What is thus generated?
Sexually mature at birth
Continuously produces high-quality offspring in large no.s
Lives forever
Amount of resources available = finite
Trade-offs
What happens to your reproductive output as you max lifespan increases?
Decreases
Define life span
Define senescence
The avg length of life
(determined by senescence if in protected enviro)
Gradual deterioration of functional characteristics
aka ageing
Even if orgs had the ability to live forever, why wouldn’t they?
Random chance
Predators
Parasites
The probability of reproducing reduces with…?
Age
Why don’t orgs reproduce v young?
Due to small size + no. of low quality offspring that would be produced
–> low chance of survival
Describe the example that shows reproduction is costly
Red deer
Mothers caring for infants have higher chance of dying than those not nursing
What are the 2 commonly studied trade-offs shaped by natural selection?
Life span vs reproductive output
offspring size vs no. of offspring
What was David Lack’s (1947) hypothesis?
Natural selection will favour the clutch size that produces the most surviving offspring
If it’s better to maximise the no. of offspring, why do such extremes exist where an org will produce 1 large offspring?
Diff envrios may favour diff strategies
What features do ‘r-selected’ populations have?
Reproduce rapidly
Use resources wastefully
Success replies upon finding new resources elsewhere
What features do ‘K-selected’ populations have?
Breed slower
Use resources more efficiently
What are the pros of r-selected populations?
Large progenies
High dispersal
Unlimited enviro
Low competition
What are the cons of r-selected populations?
Short life time
High predation
What are the cons of K- selected species?
Slow to mature
Competitive enviros
High mortality risk
High parental care
