16. Life Tables and Population Growth Flashcards
What is the importance of age distribution in a population? 4
1• When describing populations rather than individuals we want to know the makeup of the population. 2• One of the most interesting features is the age of different members of the population. 3• This particularly sensitive to ecological influence (both biotic and abiotic factors) 4. baseline levels are useful to know to track changes
What can the ages of plants tell us about their ecology? 3
- ungrazed fields have mostly young plants with a few older ones 2. in grazed areas younger vegetation is eaten as they have less toxic compounds for defence 3. this gives a skewed age distribution is overgrazing
What are life tables and how can we use them? 6
- We can describe the population age structure using life tables. 2• These tabulate the mortality data by age and we can extract some important parameters. 3. Survivorship = number surviving this year / total number born 4. Age-specific mortality = number dying / number surviving 5. the proportion surviving and mortality rate are most important to see over time 6. allows us to see probability of surviving in a particular year
How can we plot the data provided by life tables? 4
1• We can plot this data in a number of ways to investigate the variations between different populations and between different species. 2• For example mortality (aka death rate) can tell us about factors that affect the population such as predation. 3. This can give us a lot of information about the ecology of the animal 4• Survivorship curves tell us about the population strategy of a species.
What are the three idealised survivorship curves? 6
- type 1 - death rate low in young and middle aged, but have fewer offspring and invest more effort into them
- in type three, most die young, but have more offspring that they put little, if any, effort into rasing
- the shape of the curves is affected by environmental factors eg. predation or herbivory
What is an organism’s life history? 3
- An organism’s life history describes the timing of key activities.
- This includes age at death, but also things like age at maturity, inter-birth interval, generation time.
- It also includes other population metrics like litter size.
How is population growth measured in seasonal breeders? 5
Nt+1 is the new population
R0 is the value
Nt is the number
When does geometric growth occur and what does it look like on a graph? 2
- occurs in empty environments with seasonal breeding
How is population growth worked out in continuous breeders? 5
Compare exponential and continuous growth graphs. 3
- All population growth is eventually limited by carrying capacity
What are the limitations of the expotential and geometric growth models? 3
- These growth rate models are only applicable in special cases such as the introduction on a new species into an empty niche.
- In most cases resources are limiting so that there is a maximum population whereas these models keep on growing.
- The logistic growth model is more general.
What factors often limit the carrying capacity of a population? 6
- small mammals and birds often limited by space
- large mammals limited by food
- insects limited by parasites
- removal of disease or prasites can increase a population massively
- limiting factors don’t cause instantaneous death - there is a time lag
- carrying capacity may oscilliate
What is the effect of time lags on the changes to carrying capacity?
- small time lags cause a population wobble, then staiblity again
- big time lags can cause a population crash
- Sometimes the effect of density dependence does not act immediately but takes a certain amount of time.
- For example the incidence of disease or rates of predation usually lag behind the growth of population
- This can be modelled using a variation of the logistic equation:
What life history strategies can organsisms use? 4
- Based on the logistic equation [dN/dt = rN(K-N)/K] we can define r-selection & K-selection.
2• r-selected species have a high growth rate per capita.
3• k-selected species have stable populations that exist at close to the carrying capacity
- some species specialise in one or the other
What traits characterise r and k species? 12
How can the age of large, unnapproachable animals eg, elephants be measures and why is this important?
- elephants must be measured as it is needed for conservation and management purposes
- Can work out age based on height in large animals
- Use laser range finder, work out distace away of elephant and the angle of the top of head to ground, and use this to work out height
- put this agaisnt charts of known ages
