Chapter 9: Introduction to Population Ecology

Question 1

Distinguish between unitary and modular organisms and give examples of each.

Answer 1

Unitary: form and development are highly determinant, zygote develops into a recognizable form quickly (dogs, cats, humans)
Modular: development unpredictable and depend on environment, zygote develops into module (coral and other colonial animals)

Question 2

How are animal population sizes estimated?

Answer 2

mark/recapture technique: take a random sample and mark them, later return and capture another sample and take note on which ones are marked

Question 3

How are plant population sizes estimated?

Answer 3

sampling quadrants: selecting random plots of varying size and shape and make generalizations based on the information

Question 4

Define random pattern of dispersion

Answer 4

if randomly distributed then distance between each individual is independent of the location of other individuals (RARE)

Question 5

Define Contagious (clumped) pattern of dispersion.

Answer 5

Plots with greater number of individuals than expected, social groups or patches of resources

Question 6

Define regular (uniform) pattern of dispersion

Answer 6

same number of individuals in plots, equally distanced; territorial or chemical barriers (plants)

Question 7

What might a population in nature show a contagious pattern of dispersion?

Answer 7

social groups, ie: prairie dogs

Question 8

What kinds of biotic interactions might a uniform pattern of dispersion suggest?

Answer 8

territorial animals

allelopathy: creation of chemical barriers around plants to prevent growth of others

Question 9

What information is required to construct a dynamic (cohort) life table?

Answer 9

group of individuals born at the same time and followed until death, best type of life table because no assumptions are made

Question 10

What information is required to construct a static life table?

Answer 10

age structure of a given population

Question 11

Give four assumptions that are required for a static life table to be valid.

Answer 11

• each age class is sampled in proportion to it’s numbers in the population
• birth rates and death rates are constant
• population is stable, not increasing or decreasing
• survivors of the one-year age class were the survivors from the year before as if they all belonged to the same cohort

Question 12

What kinds of information might you use to construct a life table for species such as annual plants and insects that do not have overlapping generations?

Answer 12

use stages of development instead of time intervals

Question 13

Why is survivorship normally plotted on a semilogarithmic scale?

Answer 13

interested in per capita rates of change, not absolute

-nx values plotted on logarithmic scale while age (x) is plotted on an arithmetic scale

Question 14

Describe a Type 1 survivorship curve.

Answer 14

low mortality through lifespan followed by a major decline later in life
-humans

Question 15

Describe a Type 2 survivorship curve.

Answer 15

constant mortality

-birds, Connell’s barnacles

Question 16

Describe a Type 3 survivorship curve.

Answer 16

high initial mortality followed b a period of much lower, relatively constant loss
-fish, marine invertebrates, oysters, clams

Question 17

Why do population data typically result in a “J-shaped” mortality curve?

Answer 17

high mortality in juvenile phase, then mortality rate decreases to a minimum after juvenile phase and then rises again with increasing age

Question 18

Why may it be preferable to use a mortality curve instead of a survivorship curve to track the fate of a population over time?

Answer 18

it is independent of the size of the younger age classes; it is more free from bias (less error)

Question 19

How is net reproductive rate (Ro) defined?

Answer 19

the mean number of offspring produced by an individual during its life

Question 20

What does it mean when Ro>1, Ro=1 or Ro<1?

Answer 20

Ro>1: population is increasing
Ro=1: population is exactly replacing itself
Ro<1: population is decreasing

Question 21

What does Ro represent in a population with discrete (no-overlapping) generations?

Answer 21

• average number of offspring produced by an individual during its lifetime
• overall extent by which the population has increased or decreased over that time

Question 22

What does Ro represent in a population with overlapping generations?

Answer 22

ONLY the average number of offspring produced by an individual during its lifetime

Question 23

Why might it be preferable to express population growth rate as an exponential constant (r) rather than as a geometric constant (R)?

Answer 23

when ecologists are more interested in instantaneous rates of population change, or how much a population is changing at any particular moment in time rather than how much a population has changed over a time interval.

Question 24

Give five factors that influence an organism’s intrinsic rate of population growth.

Answer 24

• death rate of an organism under ideal conditions
• fecundity: number of offspring produced by an organism over its lifetime
• length of organism’s reproductive lifespan and ability to conceive
• frequency of reproduction
• age of first reproduction

Question 25

Which of the mentioned factors leads to the greatest increase in r?

Answer 25

-age of first reproduction

producing offspring as early as possible decreases generation time causing greatest increase in r

Question 26

Distinguish between semelparity and iteroparity and give examples.

Answer 26

iteroparity: produce young throughout their reproductive life span; perennials, most animals
semelparity: reproduce once in a lifetime then die; annuals, salmon, mayflies, bamboo

Question 27

In terms of a population, what is meant by a stable age-structure?

Answer 27

the PROPORTION of individuals in each age-class will remain constant over time
-at this point population will grow exponentially