What are the 2 main kinds of models in ecology?
mechanistic models
aim to explain processes underlying observed patterns
empirical model
show relationships between observed data - eg. popualtion size as a function of rainfall
What is the fundemental equation of population dynamics?
Nt+1 = Nt(Bt - Dt +It - Et)
^ population growth
if r>0 = exponential growth
How do you model population growth?
dN/dt = rate of change of N N= current popualtion r= average number of surviving offspring each individual has/ intrinsic growth rate dN/dt = rN r>0 for species not dying out
What factors can stop exponential growth?
weather and environmental variation lack of food nutrients and water lack of space/light disease/parasites predation
What are limiting factors?
stop populations increasing exponentially by reducing growth rate
What are regulating factors?
subset of limiting factors that bring populations back to equilibrium
- doesnt only limit populations by causing lower of negative growth when large
- also allows recovery when rate
- can be hard to show that a factor is regulatory but without regulation factors would not persist.
What is density dependence?
in order to regulate a population factors must act in a density dependent manner.
as density increases per capita growth rate goes down and individual death probablity goes up.
What is the simplistic model of population growth rate?
Change in N = rN
r = intrinsic growth rate
What is the carry capacity?
density at which rates equal equilibrium population size
What are the main things that affect growth rate in different organisms?
insects = 0% because of space. 37% parasites.
small mammals = 67% due to space, 24% due to food
large mammals = 99% due to food
marine mammals = 0% social
mammals = 0% affected by parasites.
