1.2: Understanding characteristics of populations

Question 1

Why did the number of monarchs declined?

Answer 1

due to the logging in Mexico
use of pesticide
loss of breeding habitat in eastern North America

Question 2

Define population

Answer 2

Is a group of individual organisms of the same species that live together in the same geographic area.

Question 3

Biologists describe populations in two ways:

Answer 3

Population density
Population dispersion

Question 4

What does a population density describe?

Answer 4

It describes how many individuals are there in a given area

Question 5

What does a population dispersion describe?

Answer 5

It describes how the individuals are distributed over the area

Question 6

Define a population density

Answer 6

number of individuals per unit area

Question 7

Formula for population density

Answer 7

D= N/S (N= number of individuals; S= space occupied)

Question 8

What is a crude density? How is it helpful?

Answer 8

Its a simple measure of density and is helpful if the entire habitat included in the calculation is useable habitat for population.

Question 9

Define ecological space (Se)

Answer 9

The size of the area that is actually usable by a species

Question 10

Function for ecological density

Answer 10

De = N/Se

Question 11

Why does clumped dispersion occur in animals?

Answer 11

• protection
• exploitation of a resource

Question 12

Why does clumped dispersion occur in plants?

Answer 12

because of asexual reproduction

Question 13

When does uniform dispersion occur in animals?

Answer 13

• defending a small territory

Question 14

When does uniform dispersion occur in plants?

Answer 14

when a plant is using all of its resources around it

Question 15

When does random dispersion occur?

Answer 15

When individuals are not affected by each other

Question 16

Where does random dispersion occur in plants

Answer 16

rainforest trees and microscopic marine organisms for example algae

Question 17

Several sampling methods can be used depending on:

Answer 17

how large the population is
the way that it is dispersed
how difficult it is to see

Question 18

What is Quadrat sampling used for?

Answer 18

is used for counting abundant organisms, like plants, or organisms living beneath the soil, like earthworms, that do not move much and can easily be seen.

Question 19

Quadrat sampling steps

Answer 19

1. An area in which a population is being studied is mapped out.
2. A grid is drawn over the map.
3. Grid squares within the mapped area are chosen at random to be sampled.
4. The actual sampling area on the ground is defined using a square made of wooden sticks or plastic pipes, called a quadrat. In surveys of small plants, or soil-inhabiting organisms like worms, the quadrat is usually 1m2 in size.

Question 20

Calculating the average value per quadrat

Answer 20

• First, all of the individuals found within a quadrat are counted.
• This process is repeated several times over the grid.
• The counts within each quadrat are summed up and the average value per quadrat is calculated.
• Because the locations of the quadrats are chosen at random, the average count per quadrat should give a good estimate of the average count per square meter for the entire area.

Question 21

Average count per quadrat

Answer 21

Average count per quadrat= Total of milkweed Individuals in all quadrants/Number of quadrats

Question 22

Describe the limitations of Quadrat Sampling method

Answer 22

• the quadrats sampled are representative of the area; if not, then the estimate may be either too high or too low.
• the organism has a heavily clumped dispersion; if so, the quadrats may have missed the clumps just by chance, making the population estimate too low. Or, too many clumps may have been sampled just by chance, and so the estimate will be too high. Taking more samples will help limit the chances that clumps are either overlooked or overrepresented in the study.

Question 23

Mark and recapture sampling procedure

Answer 23

1. To estimate population size, a sample of individuals is taken from the population and marked in some way.
2. Marked individuals are then returned to the population.
3. After a short time, a second sample is taken.
4. The ratio of the number of marked individuals in the second sample (called recaptures) to the unmarked ones gives an estimate of population size.

Question 24

Thus the mark and recapture formula to estimate the population size is:

Answer 24

Total Population (N)= Total # marked (M) x Size of second sample (n)/ # of recaptures (m)

Question 25

Limitations of the mark and recapture method

Answer 25

• the proportion of marked and unmarked individuals between the first capture and the second sample does not change. This can only happen if the population has no immigration or emigration, and if the length of time between samples is short enough for no births or deaths to occur.
• the marked individuals have the same chance of getting caught in the second sample as any of the unmarked ones. This means that marking should not affect their survival or their chance of being recaptured.

Question 26

Define survivorship pattern or curve.

Answer 26

The pattern of how mortality rates change with age

Question 27

Describe species with a type I survivorship curve

Answer 27

have relatively few offspring, but each one has a high probability of living to the maximum age. Mortality rates are low and constant for most of their life, but then increase rapidly as they approach the maximum age.

Question 28

Describe species with a type II survivorship curve

Answer 28

These species have a constant mortality rate throughout their life, so young and old have an equal chance of surviving. (for example bees)

Question 29

Describe species with a type III survivorship curve

Answer 29

These species show a high mortality rate when they are young, but this declines as they grow older. Species with this type of survivorship curve tend to produce many offspring in their lifetime, to compensate for the high early mortality rates

Question 30

The number of offspring an individual can produce over its lifetime is called its

Answer 30

fecundity

Question 31

Species with type II and III survivorships have ________ fecundity, whereas those with type I survivorship have _______ fecundity

Answer 31

high/low

Question 32

In addition to fecundity, a population’s ability to reproduce is strongly dependent on its

Answer 32

age structure