Lecture 4 - Trade-offs Flashcards
‘Organisms are resource transformers’ - Explain this statement
Organisms are able to acquire a resource such as food, ingest it then metabolise and synthesise it. This provides material for growth and repair, reproduction and defence and any additional material can be stored. Heat is given off as a waste product during metabolism and synthesis and resources are finite.
Describe the Nitrogen experiment with Gypsy moths.
The survival and body compositions of starving gypsy moth larvae was observed when they were reared on aspen foliage or an artificial diet of differing nitrogen levels. The larvae reared on 1.5% Nitrogen diet survived nearly 3 days longer than those on the 3.5% N diet. Those reared on the aspen diet, which had varying N levels survived for the shortest time period. The difference in body compositions was what determined the survival length. Larvae reared on 1.5% N diet had a higher percentage carbohydrate and lower percentage protein prior to starvation than the 3.5% larvae. Hence, larger energy reserves of those on 1.5% N may have contributed to their survival. However despite survival rates being lower for higher N concentration their growth rates and pupal weights were higher suggesting a trade off between rapid growth and survival. Large, fast-growing larvae may be more fit when food is abundant, but this advantage may be severely diminished under food stress.
Describe the behaviour of grasshopper when spiders are present.
Grasshoppers switch to a more carbon rich diet when spiders are present, this is because they spend more time and energy trying to escape predation, thus invest more in metabolism and less in growth and reproduction.
Describe an experiment that shows that differences between individuals have a genetic origin.
The Glanville fritillary, a type of butterfly has a gene for the glycolytic enzyme that exist in two forms, two alleles A and C which have different temperature sensitivities. AA individuals have more larvae that survive low temperatures and have a greater pupal size but the clutch size is smaller and the adults do not live as long. AC individuals on the other hand have fewer larvae surviving low temperatures and their pupal sizes are smaller. The clutch sizes are however larger and the adults have longer lifespans.
What symbol represents the finite rate of increase?
λ The finite rate of increase Populations will increase when λ>1 and decrease when λ<1 λ combines the birth of new individuals with the survival of existing individuals.
What symbol represents the Net Reproductive Rate?
Ro
What symbol represents the intrinsic rate of increase?
r The rate at which a population increases in size if there are no density-dependent forces regulating the population is known as the intrinsic rate of increase.
λ = er What does this mean and represent?
This equation allows for growth parameters to be compared as… Geometric: Nt = Noλ^t Exponential: Nt = Noe^rt So e^r = λ, or r = ln(λ)
What equation represents the net reproductive rate?
Ro = ∑ ( lx*bx )
The net reproductive rate is the lifetime reproductive potential of the average female, adjusted for survival. Assuming survival and fertility schedules remain constant over time, if R0 > 1, then the population will grow exponentially. If R0 < 1, the population will shrink exponentially, and if R0 = 1, the population size will not change over time.
What is an lx curve?
An lx curve is a survivorship curve. Survival is plotted against Age.
What is a bx curve?
A bx curve is a fecundity curve. It plots Fecundity against Age.
What is the purpose of the Euler equation?
The value of r, the intrinsic rate of increase can be estimated to within 10% but sometimes a more precise value is required.
The only way to solve this equation is by trial and error. We already know the values of lxbx, and e ≈ 2.7183.
So various values for ‘r’ can be put into the Euler until it equals 1.0. This will tell us the corrected value of r. A spreadsheet can be used for this process.
The value of ‘r’ can then be used to predict the size of the population in the future. The bx and lx values can then be adjusted to observe their effects on population growth or decline. This kind of analysis is used for human populations to predict the effects in changes of medical care.
Do trade offs consider reproduction or survival?
Trade offs often involve reproduction rather than survival so the variation in life history is important.
What is pleiotropy?
Genes that affect more than one trait are called pleiotropic.
What is antagonistic pleiotropy?
Antagonistic pleiotropy is when a gene that affects multiple traits causes an increase in some and decreases in others
