Lecture 17: Population Ecology Flashcards
population density
number of individuals / area
Why do we care about population size?
- natural resources management
- helps us predict future populations
- health (viral particles are populations we want to keep tabs on, more cells = more severe disease symptoms)
Modern malthus
Paul Ehrlich
- argued that explosive growth of human population would have catastrophic social and environmental consequences
Continuous reproduction
Organisms with no “mating season” like humans. Growth is continuous. Best modelled by differential equations. Also called continuous-time (tiny time steps).
episodic reproduction
Organisms with distinct mating seasons like birds. Discrete time best modelled by difference equations or discrete-time (time units are days, years, whatever).
What do D, B, E, and I stand for?
Deaths, births, emigration, and immigration in one time step
- D+E = decline
- B + I = growth
How are most models simplified?
Only modelling birth and death and converting changes to per capita rates (assumes no immigration or emigration)
Lamda
multiplicative factor by which the population changes over one time unit = finite rate of increase
Natural log of lamda will give you….
r, the intrinsic rate of growth
No species has ever sustained lambda at which values?
Below 1 -> eventual extinction
Above 1 -> population explosion
WHy is exponential growth bad?
Implies species can grow to infinity
Growth constants
r or lambda
Logistic growth
sigmoid curve, eventually population reaches carrying capacity. Growth slows as density dependent factors kick in.
Where is growth fastest on a sigmoid curve?
At the inflection point (about halfway between the starting pop and carrying capacity)
Can you have logistic trajectories that aren’t s shaped?
Yes, if the population is starting from higher numbers and has a growth rate that’s less than one, the curve could decrease.
