3/23 Population Ecology Intro

Question 1

What is population ecology?

Answer 1

Population ecology is the study of how and why population size changes over time and the effects that population change has on the population.

Question 2

Population Ecology Vs. Population Genetics

Answer 2

-Population genetics answered how populations change genetically over time, and how new populations may get started.
-Populations may get larger or smaller without genetic change, and genetic change may occur without population size changes.

Question 3

Examples of why we study population ecology?

Answer 3

• understanding how populations change and what causes those changes provided valuable info
• helps us better plan our farms
• helps us maintain local ecosystems to keep our water and air clean

Question 4

How is population ecology “done”?

Answer 4

• A typical problem for conservation biologists is to figure out how many individuals there are in a population and why the population is growing or declining.
• This is answered by monitoring the changes of specific elements of a population (numbers, ages, sex ratio, etc) over time, while keeping track of the factors that affect these elements, and making predictions about and studying the outcomes of population changes.

Question 5

What does the exponential growth curve look like?

Answer 5

When the data for exponential growth is graphed, you get a curve that starts out with a relatively slow increase that quickly turns to a rapid increase in numbers with very little change in time.

Question 6

Exponential growth curve (equation) variables

Answer 6

• b represents an individual’s probability of dividing/giving birth
• d represents individuals’ probability of dying
• r represents b-d, or the instantaneous rate of growth per individual. Rate of growth (r)=b-d, which is typically considered as a maximum r or r (subscript says max)
• N represents population size
• rN represents the rate of population growth

Question 7

Exponential Growth Equation (formally written)

Answer 7

(ΔN/Δt)=rN

Question 8

Exponential Growth Equation Translated (into words)

Answer 8

The change in population size per change in time (rate of growth) equals the rate of population growth for the individual multiplied by the number of individuals in the population.

Question 9

What are the three stages involved Logistic or Sigmoid growth

Answer 9

• Initial exponential growth
• Decelerating growth rates
• Fluctuations around some “average” population size (often called the K or carrying capacity of the environment)

Question 10

Logistic Equation

Answer 10

(ΔN/Δt)=rN((K-N)/K)

Question 11

r meaning in exponential equation vs. r meaning in logistic equation

Answer 11

r is r max for the exponential equation (max individual growth), r is r relative in logistic equation
- r relative = how an individual can reproduce relative to the influence population size has on the individual

Question 12

Is the logistic or exponential model better?

Answer 12

The logistic model comes closer to predicting real populations than the exponential model does. The exponential model does not take into account the limit that resources place on populations.

Question 13

What are different ways to define Carrying Capacity (K)?

Answer 13

• K can be defined as the point at which the population size is in equilibrium with resources.
• K can be defined as the number of individuals of a species that the environment can support.
• K can be defined as the number of individuals that can survive in the environment.

k is not constant, it changes as environmental conditions change

Question 14

Darwin’s Population Idea

Answer 14

almost all species will create more offspring than what the environment can sustain, it is within this larger set of variation that individuals are selected for or against

Question 15

geomettic exponential growth

Answer 15

a very specific type of exponential growth that is a very predictable, stepwise progression in population size over time (doubling)

Question 16

Shortfall of Sigmoid Growth Curve (logistic model) and exponential model

Answer 16

they assume all individuals in the population are the same (that everyone’s r is equal)

Question 17

density independent growth

Answer 17

• part 1 of logistic model (initial exponential growth phase w a steep slope)
• here, the growth of the population is independent of the population’s size and density

Question 18

density independent growth

Answer 18

• part 2 of the logistic model (decelerating positive growth rate, slower growth)
• says growth of the population is based on how big the population already is

Question 19

Why is does the r represent r max in the exponential model but r represents r relative in the logistic model?

Answer 19

• r in exponential model is max bc there are unlimited resources, the population is simply growing as fast as it can
• r in logistic model is relative to the # of individuals in the population, this is due to there being fewer resources

Question 20

population inertia

Answer 20

• the tendency for a population to move beyond some change, and then take awhile to incorporate that change into their dynamic
• think of seatbelt example
• this can be due to pockets of populations

Question 21

Delisting level

Answer 21

the point where control over an animal is handed over to the state, the federal government has no control anymore

Question 22

Management Goal

Answer 22

animal is basically at carrying capacity, government may have to implement ways to actually decrease the species