Lecture 20: Population Distributions

Question 1

Population

Answer 1

A group of individuals of the same species occupying a specific area. Spatially distinct from other groups.

Question 2

Why study populations?

Answer 2

It is the heart of ecology – the distribution and abundance of organisms.

Important for discussing biodiversity and conservation.

Question 3

Fundamental Niche

Answer 3

Range of abiotic conditions where a species CAN persist (survive, grow, reproduce).

Question 4

Realized Niche

Answer 4

Range of abiotic & biotic conditions where a species DOES persist.

Question 5

Which is always greater: a fundamental or realized niche?

Answer 5

Fundamental.

Question 6

What are the five characteristics of population distributions?

Answer 6

1. Geographic Range (Total area covered by a species)
2. Abundance (# ind. in an area)
3. Density (# ind./unit of area)
4. Dispersion (movement in an area)
5. Dispersal (movement between areas)

Question 7

Regarding dispersion, what are the three main ways individuals organize themselves in an area?

Answer 7

1. Clustering: Aggregating in tight groups
2. Even Spacing: Even distance between neighbors. Reduces competition. Aids in defense.
3. Random: Position of each individual is dependent of the others

Question 8

What are three strategies used to estimate population sizes, abundances, and distributions?

Answer 8

1. Sampling quadrants: Count all individuals, extrapolate to estimate pop. size.
2. Linear transects: Count # of individuals along a line.
3. Mark-recapture: mark some individuals, release, recapture, estimate.

Question 9

What are the steps to mark-recapture studies?

Answer 9

1. Catch individuals and mark them (M)
2. Release marked individuals
3. Wait x time
4. Capture more (C) and count how many of those are marked (R)
5. Estimate population size (N) using equations.

Question 10

What are the assumptions made when using the mark-recapture approach?

Answer 10

1. Individuals are captured at random
2. Marking and recapturing does not alter behavior or survivorship
3. Population size doesn’t change during the waiting period

Question 11

What is the general trend with body size and population density?

Answer 11

As body size increases, population density decreases.

Question 12

Ideal free distribution

Answer 12

When all individuals distribute themselves across habitats in a way that they all have the same per capita benefit

Question 13

What does ideal free distribution assume?

Answer 13

1. All individuals can tell a high-quality patch from a low-quality patch
2. All individuals can move freely among patches and are completely equal

Question 14

As more individuals move to a high-quality patch, what might some individuals do to maintain equal per-capita benefit?

Answer 14

They may move to the lower-quality patch to reduce competition

Question 15

mark-recapture studies – Canada Goose example

a) catch some geese and mark them (M); e.g., 70 geese

b) release the marked individuals

c) wait some period of time (allowing marked individuals to mix
randomly with the rest of the population)

d) capture 200 individuals (C = 200); R = 35 (previously marked,
recaptured)

e) use the following equation to estimate the population size (N)

Answer 15

estimated population size = 400