Population dynamics Flashcards
Give the ‘fundamental equation for ecology’. Explain all the terms.
N(t+1) = N(t) + bN(t) - dN(t) + (I - EN(t))
N(t) = no. individuals at time t
bN(t) = no. of births at time t
dN(t) = no. of deaths at time t
I - EN(t) = immigration - emigration (net migration) at time t
Define a source population.
One that is increasing, generaly because b>d.
Define a sink population.
One that is decreasing, generally d>b.
What kind of habitat do source populations have?
High quality.
What kind of habitat do sink populations have?
Low quality.
Are most populations open or closed?
Open
What is a pseudo-sink population?
One that appears to be declining but isn’t, e.g. d>b but I>E.
N stands for density. What does this mean?
Number of organisms per unit area, n/A.
What is ‘r’?
Population growth rate.
r = b-d
If r=0, what does this say about the population?
The population stays the same size.
If r<0, what does that say about the population?
The population is shrinking.
If r>0, what does that say about the population?
The population is increasing.
r + 1 = ?
λ
What does λ always imply?
Discrete data.
What is discrete data?
Data that falls into distinct categories.
There are 2 types of mean. What are they?
- Arithmetic mean = SUM the values and divide by how many there are
- Geometric mean = MULTIPLY all their values and divide by how many there are
Which mean is always slightly higher than the other?
The arithmetic mean is higher than the geometric mean.
What kind of time do difference equations refer to, discrete or continuous?
Discrete time, e.g. 1/2/3 years. Time that does not overlap.
Discrete data does not take into account immigration or emigration. True or false?
True.
What kind of time do differential equations refer to, discrete or continuous?
Continuous, time with overlapping generations.
What factors contribute to positive density dependence?
Those that increase density, i.e. increasing birth rate.
What factors contribute to negative density dependence?
Those that decrease density, i.e. increasing death rate.
What does the equation dN/dt mean?
Rate of change in a population.
dN = density dt = time
What causes demographic stochasticity in populations?
Chance events.
What causes environmental stochasticity in populations?
The weather/climate etc.
In populations with environmental stochasticity, does r vary each year?
Yes.
In populations with environmental stochasticity, are events random?
Yes.
In populations with environmental stochasticity, λ is fixed and will not change over time. True or false?
False - λ changes over time as it varies in relation to abiotic factors like temperature and rainfall.
What does dN/dt represent on a graph?
The gradient.
What kind of equation is N(t+1) = λN(t), a difference of differential equation?
A difference equation.
What kind of equation is dN/dt = rN, a difference of differential equation?
A differential equation.
What is the equation for discrete time growth?
Nt+1 = (1 + r)Nt
Why is Nt+1 = (1 + r)Nt the same as Nt+1 = λNt?
Because λ is the same as (1 + r).
