Unit 4 Lecture 19 Flashcards
Explain the study with the black footed ferrets
- Black footed ferrets are located in Wyoming and primarily ate prairie dogs (pest species to farmers)
- Because of this prairie dogs declined, but as they started to decline, this caused the black footed ferrets to decline (nearly went extinct)
What do population ecologists do?
They want to be able to describe this dynamic of population growth (i.e. formulate a model) and predict what will happen to the population in the future
How do you find the rate of population growth between two years?
Take Nt+1/t
How do you find the annual population growth rate?
Nt+1 (population size at the next year) / Nt (population at size t) = lambda
How do you solve for the population size at a time next year?
Nt+1 = 𝜆𝑁𝑡
When a population grows with a constant 𝜆 for multiple step what equation do you use?
Nt = N0𝜆^t
n0: initial population size
nt: population size at time t
If 𝜆>1 why would the graph be curved linear and not linear?
Because our initial population size is low, even with a high rate of increase, our population size is going to grow slowly until it reaches a certain point then it’ll grow rapidly
If lambda ‘𝜆’ is constant, then we get a _____ population growth
Geometric: initially growing slowly, but as population size grows is speeds up
- Use this when we measure in discrete time steps
What is the main difference between exponential growth and geometric growth?
In exponential growth, we are no longer talking about time in discrete time intervals
- Nt = N0 λt
- Nt+1 = λNt
When do we use each of these
- Use the top one when finding the population size at time t+1
- When a constant 𝜆 in multiple steps use this to find population at time t
Geometric and exponential growth happens when?
When we have a constant population growth rate
Explain exponential population growth?
Is the same as geometric growth, but for case where reproduction occurs continuously
dN/dt = rN
- dN/dt: Change in N over change in time
- r: exponential growth rate
During what specific times should you use geometric population growth?
When we have organisms that have a very defined breeding time during the year; you can also have organisms that’ll d their reproduction then die
You should use geometric population growth for these scenarios because breeding happens during a very discrete time/time steps
Give an example of when we use exponential growth in organisms
Humans; we are fertile once a month and at different times
Whats another equation do we use for exponential growth?
Nt = N0e^rt
Show the connection between the geometric growth equation and the exponential growth equation
1. Nt = N0 λ^t
2. Nt = N0 e^rt
- λ = e^r
- r = ln(λ)
The defining feature of geometric/exponential population growth is what?
Population growth rate is constant across time
- when the population grows whether geometric or exponential growth rate (λ or r) is constant
When does dN/dt increases when?
There’s a larger population size
When population growth rate is constant its a _______ on a log scale
straight line; because geometric/exponential growth is multiplicative
What is population regulation?
There is a limit to population growth, this idea is population regulation
What are density-independent factors?
Effects on birth and death rates are independent of the number of individuals in the population like:
- Drought
- Extreme weather
- Flood
- Pollution
Give an example of density-independence in a study with thrips
Guys in Australia went out into their rose garden and counted the number of thrips on their roses for several years. They then looked to see what factor correlated with the number of thrips per year
- The main reason for population size to be fluctuating was due to weather changes across years
What are density-dependent factors?
Birth, death, and dispersal rates change as the density of the population changes
- most often there is a negative density dependence (deaths increase when population is crowded)
As density of a population increases, birth rates _____ and death rates ______ and emigration _______
- decrease
- increase
- increase
What factors might cause a negative density dependence?
Disease and Fewer resources per capita
- things that cause negative density dependence are things that CHANGE as a function of the population size
- As population size increases, this could cause diseases to spread easier
Explain the study with the sparrow
There was a graph of the number of independent young per female as a function of number of breeding females recorded over a bunch of years
- In long sparrows, the number of eggs laid per female decreased with density, as did the number of young that survived
- Limited food supply at high density
Explain the study with the owl/bird
There was a graph of the number of independent young per female as a function of number of breeding females recorded over a bunch of years
- In long sparrows, the number of eggs laid per female decreased with density, as did the number of young that survived
- Limited food supply at high density
What is density dependent mortality?
When density-dependence can reduce birth rate AND death rate
What is carrying capacity (K)?
Maximum population size that can be supported indefinitely by the environment
Under logistic growth what happens?
Population increases rapidly looking like geometric or exponential growth but then stabilizes
- What we are plotting for is the number of individuals under a function of time
Carrying capacity can be determine by the amount of what?
Resource
Carrying capacity is where birth rate is:
1. > death rate
2. < death rate
3. = death rate
3.
Carrying capacity is where per-capita growth rate is ___ or when R passes the _____
- 0
- x axis
What is the logistic equation?
dN/dt = rmax N(1-n/k)
As Logistic growth –> growth rate
- Declines through time
- Declines linearly with population size N
When N is small relative to K N«K then…
N/K = 0 or 1-N/K = 1
So dN/dt = rN
When N is close to K (N=K)
dN/dt = 0
N/K = 1
1- N/K = 0
Overall population growth rate (dN/dt) is the ________
Slope of the tangent line
K is where dN/dt = what
0
