populations, epidemics and natural selection

hypothetico-deductive model of science : what does each letter stand for?

O - oranges

H - Hate

M - Mould

E - Every

N - Night

O - OBSERVATION

H - HYPOTHESIS

M - MODEL

E =EXPERIMENT TO TEST THE MODEL

N = NEW HYPOTHESES

3 explanations for hare populations fluctuating with lynx (their predator)

• bottom up : food supplies have been exhausted because of the high population of hares —? could starve/die

• top down : predation or disease dominates, even with plenty of food

• social behaviour : social interactions involving territoriality or possibly infanticide

what causes the predator-prey cycle?

external factors, such as solar radiation

assumptions of the LOKTA-VOLTERRA model

• the prey population has ample food

• the predator food supply depends entirely on the size of the prey population

• the rate of change of population is proportional to its size (e.g reproductive rates are independent of population density)

• environment is fixed

• predators have limitless appetite

how does chronic stress affect hare (or prey in general)’s reproductive rate

• stress : defined physiologically by the blood cortisol level, can affect feeding, reproduction and the immune system

• higher, predator-induced glucocorticoid concentrations in individual hare females can cause a decline in number of offspring and quality (eg body mass)

what type of species is a hare

keystone species : changes in populations of their species can have consequences for others within their ecosystem

evolution

the heritable change in phenotype, due to genetic transmission of information across generations (or environment)

how may chronic stress arise in hares/ prey

• signs of predator abundance : odor, visual sightings, unsuccessful chases)

• interactions between other hares/prey

• measured by faecal cortisol

lokta volterra model predictions

for a hare-lynx population, the predator cycle lags behind the prey cycle