Population Ecology (W5) Flashcards
What do resources & conditions do for the hierarchy of ecology?
Set the stage for how all the different levels of hierarchy interact with one another.
Resources?
= things that individuals consume throughout their growth & reproduction.
Conditions?
= physiochemical features of an environment that affect the physiology of individuals.
Egs of Conditions? (2)
• Temperature.
• Salinity (in aquatic environments).
Questions we ask/focus on in population ecology? (2)
• What affects the abundance of a population?
• What affects the distribution of a population?
Applied population ecology definitions? (2)
= the use of population ecology principles to achieve a management goal.
OR
= the manipulation/protection of a population to achieve a goal.
Eg of Manipulative management regime?
Kruger National Park (culled animals & water points).
Custodian management regime?
= protecting an area with a goal that the natural processes that occur there will carry on operating without human interaction.
Eg of Custodian management regime?
North American National Parks.
Types of management approaches? (2)
• Manipulative management regime.
• Custodian management regime.
Goals of applied ecology? (4)
• Conservation.
• Pest control.
• Sustained harvest.
• Monitoring.
Conservation?
= make a population increase.
Eg of Conservation?
Roan & Sable antelope.
Pest control?
= make a population decrease.
Eg of Pest control?
Reducing abundance of rats in the city.
Sustained harvest?
= manage for a continuing yield.
Eg of Sustained harvest?
Harvesting fish from fish stock in a sustainable manner.
Monitoring?
= leave it alone but keep an eye on it.
Eg of Monitoring?
In organisms that are not a problem (manipulative management in a way through surveys).
Manipulative management regime attribute?
Does something to a population’s numbers directly or indirectly by altering the habitat, food, predators or disease.
Custodian management regime attributes? (3)
• Preventative.
• Protective.
• Aimed at minimizing the external influences on the population or its habitat.
How to decide which goal to use? (2)
• Value judgement.
• Technical judgement.
Value judgement (VJ)?
VJ attributes? (2)
• Word “should” indicates opinion.
• Depends on background of the opinion giver.
Egs of people deciding on the goal? (3)
• Ministers.
• Politicians.
• Management board.
Who are the people deciding on the goal?
= people responsible to the people they’re protecting.
Eg of VJ statement?
“Local survival of Acacia trees justifies the proposed reduction of elephants.”
Technical judgement (TJ)?
= judgement that is phrased in a way that makes it testable (practical).
TJ attributes? (2)
• Posed as a testable hypothesis.
• Allows us to learn from our failures & successes.
Egs of people who make technical judgements? (3)
• Managers.
• Scientists.
• Ecologists.
Eg of TJ?
“Elephants must be culled because, otherwise, they will eliminate Acacia trees from an area”.
Population?
= a group of individuals of the same species for which it is meaningful to consider density and distribution, rates of birth and death, sex and age structure, and other demographic parameters.
Population attribute?
The boundaries of the population are defined according to administrative convenience.
How do we characterize a population? (2)
Using:
• Static manners.
• Dynamic manners.
Static manners of characterizing a population? (4)
• Open/closed population.
• Movement in and out of the population.
• Density of population.
• Counts of abundance.
Dynamic manners of characterizing a population? (3)
• Population growth rate.
• Sex structure.
• Age structure.
Open population?
= presence of immigration & emigration.
Closed population?
= absence of immigration & emigration.
Density?
= number of animals per unit area.
Counts of abundance?
= numbers of individuals.
Sex structure?
= proportions of males & females.
Age structure?
= proportions of young & old.
What makes populations change over time? (4)
Levels of:
• Births.
• Immigration.
• Deaths.
• Emigration.
Factors that add to/increase the population number? (2)
• Births.
• Immigration.
Factors that decrease population number? (2)
• Deaths.
• Emigration.
If births & immigration are larger than deaths & emigration, what happens to the population?
If deaths & emigration are larger, what happens to the population?
What happens to the population if births and immigration & deaths and emigration are equal?
Births?
= flow of individuals into the population/added to the population number.
Nt?
= population size.
Nt+1?
= population size in the next time-step.
ΔN attributes? (2)
• Total amount of change from one year to the next.
• Increment.
ΔN formula before BIDEN model?
ΔN = B+I–D–E
where:
• ΔN = increment.
• B = births.
• I = immigration.
• D = deaths.
• E = emigration.
BIDEN model?
= model that assumes that there’s no immigration or emigration (no movement in & out of the area), ie., I-E=0.
ΔN formula according BIDEN model?
ΔN = B–D
Per capita rate?
= average birth or death rate per individual.
ΔN formulas under BIDEN model? (2)
• ΔN = B–D
• ΔN = Nt+1 – Nt
R?
= per capita change in population size.
Why divide births (B) & deaths (D) by the population size (Nt)?
It’s because births & deaths happen to individuals.
b?
= per capita birth rate.
d?
= per capita death rate.
R equations? (2)
• R = b–d
• R = ΔN/Nt
ΔN equations? (4)
• ΔN = B+I–D–E
• ΔN = B – D
• ΔN = Nt+1 – Nt
• ΔN = RNt
ΔN = B+I–D–E?
Before BIDEN model.
ΔN = B–D?
BIDEN model.
ΔN = Nt+1 – Nt?
2nd BIDEN model equation.
ΔN = RNt?
Relates to per capita rates.
λ ?
= finite rate of change.
λ > 1?
Population is increasing.
λ < 1?
Population is decreasing.
λ equations? (2)
• λ = 1+R
• λ = 1+b–d
How did λ = 1+R come about? (4)
ΔN = RNt
Nt+1 – Nt = RNt
Nt+1 = Nt + RNt
Nt+1 = Nt (1+R)
Therefore, λ = 1+R.
How did λ = 1+b–d come about? (4)
Nt+1 – Nt = RNt
Nt+1 – Nt = (b–d) Nt
Nt+1 = Nt + (b–d) Nt
Nt+1 = Nt + (1+b–d)
Therefore, λ = 1+b–d.
Types of population models? (2)
• Discrete population model.
• Continuous population model.
When is the Discrete population model appropriate to use? (2)
• Where estimates of population abundance occur at fixed intervals (eg., annually).
• Where important demographic events happen at fixed intervals.
When is the Continuous population model appropriate to use? (2)
• Populations where there is continuous change.
• No fixed intervals between demographic events.
What could you use for Continuous population models?
Calculus & differential equations.
Discrete models vs Continuous models in terms of Abundance representation?
● Discrete models
= Nt.
● Continuous models
= N.
Discrete models vs Continuous models in terms of Max. growth rate?
● Discrete models
= R.
● Continuous models
= r.
Discrete models vs Continuous models in terms of Increment?
● Discrete models
= ΔN.
● Continuous models
= dN/dt.
Discrete models vs Continuous models in terms of Observed per capita rate of change in the population?
● Discrete models
= ΔN/Nt.
● Continuous models
= dN/Ndt.
Discrete models vs Continuous models in terms of Time change?
● Discrete models
= whole time stops.
● Continuous models
= instantaneous time stops.
Discrete models vs Continuous models in terms of Biology?
● Discrete models
= fixed demographic events.
● Continuous models
= no fixed demographic events (continuous).
Discrete models vs Continuous models in terms of Data?
● Discrete models
= fixed surveys.
● Continuous models
= continuous.
List of differences between Discrete models & Continuous models? (7)
• Abundance.
• Max. growth rate.
• Increment.
• Per capita rate of change.
• Time change.
• Biology.
• Data.
Equation showing relationship between Discrete models & Continuous models?
r = loge (1–R)
r = loge (λ)
Therefore, λ = e^r
Uses of λ = e^r ?(2)
• Helps us predict how population is going to change from one year to the next.
• Helps you get growth rate from an exponential growth graph.
How do you get growth rate from an Exponential growth graph? (3)
● Log the Exponential growth graph to a linear graph.
● r is the slope for the line graph.
● Use equation: e^r = λ.
How do we predict how the population is going to change from one year to the next? (2)
● Over the next year equation:
Nt+1
= Ntλ
= Nt e^r
● Over t number of years equation:
Nt
= No λ^t
= No e^rt
Exponential population growth model attributes? (2)
• Appropriate in new populations placed in empty habitats.
• Used where populations have been reduced, either by disease or harvest.
Why do we want the simplest model that adequately explains the patterns?
In order to understand a natural phenomenon.
What happens if a model is not simple?
Adds unnecessary complexity & confusion.
If simple model doesn’t match the patterns we observe in the real world?
Add complexity only where necessary.
Problem with Exponential population growth model?
Doesn’t depict that in the real world there are limited resources.
How might high density affect the growth rate of a population? (4)
High density leads to:
• decrease in per capita food availability,
• increase in intraspecific competition,
• decrease in reproduction or survival,
• decrease in population growth rate.
Vital rates?
= involve change in either birth or death rates.
Graph 1/3 of vital rates graphs attributes? (3)
• Birth rate decreases.
• Death rate increases.
• ED or K is vertical dotted line where they cross/meet.
Graph 2/3 of vital rates graphs attributes? (3)
• Birth rate decreases.
• Death rate stays constant.
• ED or K is vertical dotted line where they cross/meet.
Graph 3/3 of vital rates graphs attributes? (3)
• Birth rate stays constant.
• Death rate increases.
• ED or K is vertical dotted line where they cross/meet.
Density dependence?
= there is a relationship between density & some vital rate (eg. births, deaths, i, e, R).
Types of density dependence? (2)
• Negative density dependence.
• Positive density dependence.
Negative density dependence?
= relationship between density & vital rate reduces growth rate.
Positive density dependence?
= relationship between density & vital rate increases growth rate.
Negative density dependence = …?
Decreases R.
Positive density dependence = …?
Increases R.
What mechanisms could cause these relationships (density dependence)? (3)
• Predation pressure.
• Disease pressure.
• Space for settlement.
Explain Predation pressure mechanism? (3)
High abundance of prey, More predators, High predation pressure.
Explain Disease pressure mechanism? (3)
High abundance of individuals, High rates of contact, High transmission of disease.
Explain Space for settlement mechanism? (5)
High abundance needing space, High competition, Low reproduction, Low survivability, Decreased population growth.
Predation pressure?
= where a higher abundance of individuals attracts more predators & more predation pressure.
Types of competition? (3)
• Exploitation competition.
• Interference competition.
• Intraspecific competition.
Exploitation competition?
= removal of resources such that others cannot use them.
Interference competition?
= behavioural exclusion from an area & the resources it contains (eg. territories).
Types of density growths? (2)
• Density dependent growth.
• Density independent growth.
Density independent growth?
= no relationship between density & growth rate.
Density dependent growth?
= relationship between density & growth rate.
Graph 1/2 for Density independent growth attributes? (4)
• x-axis = t.
• y-axis = N.
• Exponential growth/increase.
• Equation: dN/dt = rN.
Graph 2/2 for Density independent growth attributes? (4)
• x-axis = N.
• y-axis = dN/Ndt
• Constant horizontal line (r).
• Equation: dN/dt = rN.
ED stands for?
Equilibrium Density.
ED is AKA?
K.
ED or K?
= carrying capacity.
Graph 1/2 for Density dependent growth attributes? (5)
• x-axis = N.
• y-axis = dN/Ndt.
• Decreasing line graph.
• r is at top of line on y-axis.
• ED is at bottom of line on x-axis.
Graph 2/2 for Density independent growth attributes? (4)
• x-axis = t.
• y-axis = N.
• ED is the horizontal dotted line on y-axis.
• S-shaped.
Interpretation of Graph 1/2 for Density dependent growth attributes? (3)
• As N increases,
• Resources per individual decrease (due to competition),
• Per capita growth rate decreases until it reaches zero growth.
Line general equation?
y = a + bx
Slope of a line general equation from line graph equation?
b = rise/run = Δy/Δx
Slope equation for Graph 1/2 for Density dependent growth?
b = -r/K
Types of graph models that we talk about? (2)
• Exponential population growth model.
• Logistic population growth model.
Equation for Logistic population growth model?
dN/dt = rN (1– N/K)
Elaborate how we got the Logistic population growth model equation? (6)
• y = a + bx
• dN/Ndt = r + (-r/K)N
• dN/Ndt = Kr/K – Nr/K
• dN/Ndt = (Kr–Nr)/K
• dN/Ndt = r (1–N/K)
Therefore,
• dN/dt = rN (1–N/K)
Large N attributes in terms of Logistic population growth model? (3)
• Little change in population size.
• Little change in dN/Ndt.
• N/K approaches 1, therefore (1–N/K) becomes (1–1) = 0.
Small N attributes in terms of Logistic population growth model? (2)
• N/K approaches 0, therefore (1–N/K) becomes (1–0) = 1.
• Population grows close to exponential rate.
Graphs of Logistic model? (3)
• Observed per capita growth rate.
• Increment (# of individuals added).
• Population size vs Time.
Observed per capita growth rate graph attributes? (7)
• x-axis = N.
• y-axis = dN/Ndt.
• r is at top of line on y-axis.
• K is at bottom of line on x-axis.
• Decreasing line graph.
• Equation for Continuous model.
• Equation for Discrete model.
Observed per capita growth rate graph equation for Continuous model?
dN/Ndt = r (1–N/K)
Observed per capita growth rate graph equation for Discrete model?
ΔN/Nt = R (1–Nt/K)
Increment (# of individuals added) graph attributes? (6)
• x-axis = N.
• y-axis = dN/dt.
• K is at the bottom of “hill” on x-axis.
• Hill looking from bottom, tip of hill then back down.
• Equation for Continuous model.
• Equation for Discrete model.
Increment equation for Continuous model?
dN/dt = rN (1– N/K)
Increment equation for Discrete model?
ΔN = RNt (1–Nt/K)
Population size vs Time graph attributes? (3)
• x-axis = t.
• y-axis = N(t).
• S-shaped graph.
Population size vs Time equation for Continuous model?
N(t) = K/ [1+ e^(a–rt)]
Population size vs Time equation for Discrete model?
Nt+1 = Nt + RNt (1–Nt/K)
Blue circle (at beginning of graphs) on Increment & Population size vs Time graphs attributes? (2)
• Lots of resources.
• Few individuals breeding & adding numbers to the population.
Orange circle (at middle of graphs) on Increment & Population size vs Time graphs attributes? (2)
• Fair number of resources.
• Fair number of individuals breeding (with maximum added individuals).
Green circle (at end/top of graphs) on Increment & Population size vs Time graphs attributes? (2)
• Few resources.
• Lots of individuals breeding (but few numbers being added to population).
Important concepts related to Logistic model? (2)
• Population regulation.
• Population limitation.
Population regulation question?
What processes halt population increase?
Population limitation question?
What factors or process can change the average density.
Egs of Population regulation vs Population limitation? (2)
• Game reserve.
• Animal density in relation to food abundance.
Regulating factors attributes? (3)
• Exert a negative feedback on population growth rate.
• Negative density dependent.
• Causes the return of a population size to an equilibrium (eg. K).
Limiting factors attributes? (4)
• Determine the ED.
• Affect births or deaths.
• Can be density dependent or density independent.
• They are often resources.
Eg of Regulating factor?
Decrease in per capita food reduces survival-intensity of the effect (density dependent).
Eg of limiting factor?
Rainfall affecting food & determining the upper limit of the population (density independent).
As line gets closer to K, what happens? (4)
• Intraspecific competition,
• Leads to low b and high d,
• Density dependent.
• Regulating factor.
Assumptions of the Logistic model? (7)
• Population growth rate is directly affected by density.
• Relationship between growth rate & density is linear.
• No time lag.
• Ignores environmental influences.
• ED or K is constant.
• Population is closed (I–E=0).
• Age structure is not considered.
How to add complexity to models to make them realistic (modification)? (3)
• Non-linear density dependence.
• Time lags.
• Variable environment.
Logistic model assumption addressed in Non-linear density dependence?
“Relationship between growth rate & density is linear”.
Model under Non-linear density dependence?
θ-logistic model (theta).
θ-logistic model equation?
dN/Ndt = r (r– [N/K]^θ)
θ-logistic model graphs? (3)
• θ < 1.
• θ > 1.
• θ = 1.
θ < 1 graph attributes? (6)
• x-axis = N.
• y-axis = dN/Ndt.
• Concave up relationship (exponential decrease).
• Undercompensatory DD.
• Growth rates decrease but not fast enough to equilibriate.
• Outbreaks.
θ > 1 graph attributes? (6)
• x-axis = N.
• y-axis = dN/Ndt.
• Concave down relationship (cliff).
• Overcompensatory DD.
• Growth rates decrease but way too much to equilibriate.
• Fluctuate at K.
θ = 1 graph attributes? (4)
• x-axis = N.
• y-axis = dN/Ndt.
• Linear relationship (decreasing).
• Exactly compensatory DD.
Eg of θ < 1 graph?
Lemmings.
Eg of θ > 1 graph?
Wildebeest.
Eg of θ = 1 graph?
Warblers.
Why undercompensatory DD?
It’s because changes in births & deaths are not happening fast enough to keep the population from halting increase at the equilibrium density (ED).
Why overcompensatory DD?
It’s because changes in births & deaths happen so fast that it pulls the population down below equilibrium density (ED), resulting in fluctuation at K.
What do Time lags depend on? (2)
• How quickly the population grows (r).
• How long the lag is (L).
Logistic model assumption addressed in Time lags?
“No time lag”.
Time lags graphs? (3)
• rL is small.
• rL is moderate.
• rL is large.
rL is small graph attributes? (6)
• Little change from standard model.
• Either population is growing very slowly (r).
OR
• Little lag between population size & growth rate (L).
• x-axis = t.
• y-axis = N.
• S-shaped/Sigmoid shape.
rL is moderate graph attributes? (5)
• Dampened oscillations until K is reached.
• Moderate growth rate (r).
OR
• Moderate lag between population size & growth rate (L).
• x-axis = t.
• y-axis = N.
rL is large graph attributes? (6)
• Lot of growth rate (r).
OR
• Lot of lag (L).
• Stable limit cycles.
• x-axis = t.
• y-axis = N.
• Fluctuations at K.
DD stands for?
Density dependent.
Logistic model assumption addressed by Variable environment?
“Ignores environmental influences”.
Explain Variable environment graph regarding theoretical vs realistic graph? (3)
● Graph is of birth rate (b) decrease & death rate (d) increase with K being vertical dotted line where they cross/meet.
● Theoretically, the b & d lines are straight however, in reality they are fluctuating as b decreases & d increases.
● Theoretically, K is a vertical dotted line where b & d lines meet/cross but, in reality K is an equilibrium band zone (square/2 vertical dotted lines where b & d cross).
X-axis for b & d graphs?
N.
Y-axis for b & d graphs?
Rate.
What is a fluctuating equilibrium due to/ What causes fluctuating equilibrium? (2)
• K itself fluctuating.
• K relatively constant, but other factors push the population away from K.
Explain discussion:
Have a look at the population growth for wildebeest in the Serengeti.
¹ What is happening to this population before the peak?
² What could be causing the pattern in abundance after the peak?
● Before the peak
= exponential growth.
● After the peak
= population size decreases.
From discussion, why does the population size decrease after the peak? (4)
• Environmental variability.
• Lagged effect.
• Overshoot, then settling at K.
• K is constant, but other factors are pushing population away from K.
dN/dt = rN (1– Nt-L/K) represents…?
Delayed density dependence (seen in L for lag).
dN/dt = rN (1–[N/K]^θ) represents…?
Non-linear density dependence (seen by θ).
dN/dt = rN represents…?
Unlimited resources.
Imagine that a scientist experimentally reduces one population to half its ED. Show a detailed progression of mechanisms by which the reduced population returns to a regulated state? (8) [in order]
• Reduced population size.
• Reduced competition for resources.
• Improved body conditions.
• Improved reproduction & survival.
• Increase in population size.
• Increased competition.
• Reduced body conditions.
• Reduced population growth.
