Population dynamics

Question 1

Population density formula:

Answer 1

Dp = N / A

N = sum of
individuals in the quadrats
A = total
area of the quadrats

Question 2

Estimating population size:

Answer 2

Use the population density of several quadrats.

Example: Density population of daisies in 4 different 1.00 m2 quadrats. The section of the field is 10 000 m2

Quadrat #1: 5
Quadrat #2: 3
Quadrat #3: 2
Quadrat #4: 1

Dp = N / A
= 5 +3 +2 +1 / (4 X 1.00 m2)
= 2. 75 daisies / m2

If the entire study area is similar to the sample area, this density can then be extrapolated to determine the population size

Estimated population size = Dp X total study area
= 2.75 daisies/ m2 X 10 000 m2
= 27 500 daisies

Question 3

Mark recapture

Answer 3

Animals are recaptured, marked with a tag or other, released and then recaptured later.
Example: 20 sparrows are captured and marked and
released. One week later, 50 sparrows are captured, and 10 of these were the marked sparrows
Population size (N) = (number original marked) X ( total individuals in recapture)

(marked individuals in recapture)

= (20 X 50)/10
= 100

Question 4

Population distribution

Answer 4

• Populations are rarely evenly distributed throughout their
  habitat.
• There are 3 distribution patterns for populations: Uniform, random, and clumped

Question 5

Clumped distribution

Answer 5

• Organisms tend to clump around resources, such as a water source
• Also common among species in which individuals gather into groups for positive interactions

Question 6

Uniform distribution

Answer 6

• Where resources are evenly distributed but scarce, population exhibit uniform distribution
• It is usually a consequence of competition between two individuals

Question 7

Random distrubution

Answer 7

• If resources are plentiful and uniformly distributed across an area, populations exhibit random distribution
• There is no need for individuals to defend their share and interactions between individuals are neutral
• These conditions are rarely met
  in nature

Question 8

Distribution patterns are fluid

Answer 8

Example: moose may cluster in small groups near food in the winter, but randomly disperse in the summer

Question 9

Fecundy

Answer 9

• The average number of offspring produced by a female member of a population over her lifetime
• This number varies greatly depending on the organism. Some organisms only reproduce once in the their lifetime, others will reproduce many times. Some organisms produce one baby at a time, others hundreds.
• Fecundity is also affected by the age at which an organism becomes sexually mature. The faster the animal sexually matures, the more offspring they can have

Question 10

Survivorship

Answer 10

-The number or percentage of organisms that typically live to a given age in a given population
- To study this, ecologists study a large group of individuals born at the same time, called a cohort.
- They will monitor this group over its lifetime and record the age of death for each organism.

Question 11

Type 1 survivorship

Answer 11

This pattern is a curve and shows a high rate of juvenile survival and individuals that live until sexual maturity and beyond

Example: Humans. They have a high parental care for their young and even though we produce
fewer young, we have a high level of survivorship

Question 12

Type 2 survivorship

Answer 12

The risk of mortality is constant throughout an individual’s lifetime.

Example: birds

Question 13

Type 3 suvivorship

Answer 13

Most individuals will die as juveniles and only a few members will live long enough to produce offspring, and only a small few will live to old age

Example: Oysters
Female oysters release many eggs into the water, many of which will not be fertilized, and if they do they will most likely be consumed by predators.

Question 14

Measuring population

Answer 14

Δ N = (B + I ) – (D + E)

Δ N = population change
B= birth
I= immigration
D= death
E= emigration

Question 15

Calculating population growth rate

Answer 15

gr = ΔN/Δt

gr= growth rate
ΔN = change in population size
Δt = change in time

Question 16

Calculating per capita growth rate

Answer 16

cgr = Δ N/N

cgr = per capita growth
Δ N= change in the number of individuals
N= original number of individuals

Question 17

Population growth in unlimited
environments

Answer 17

• Conditions: ideal, no predators and resources are unlimited
• Biotic potential: Species have the highest possible growth rate.
  Determined by 5 factors

1. The number of offspring per reproductive cycle
2. The number of offspring that survive long enough to reproduce
3. The age of maturity
4. The number of times the individuals reproduce in a life span
5. The life span of the individual

Question 18

Exponential growth pattern

Answer 18

• A population growing at its biotic potential grows exponentially.
• There is a brief lag phase, followed by a steep increase in the growth curve
• A pattern of a population where organisms reproduce continuously at a constant rate

Question 19

Carrying capacity

Answer 19

• Carrying capacity is not a static condition
• It can change from season to season as conditions change
• Over time the population size fluctuates around the carrying capacity of the habitat in a stable equilibrium
• Populations can crash if resources are depleted faster than they can replenish

Question 20

Life strategies

Answer 20

• Life strategies are strategies employed by organisms that can be correlated to the type of environment in which the organism lives
• Organisms have to make trade-offs to maximize the number of offspring that survive

Question 21

R and K species

Answer 21

Species that have an r-selected strategy live close to their biotic potential (r). In general, these organisms
- Have a short life span
- Become sexually mature at a young age
- Produce large broods of offspring
- Provide little or no parental care to their offspring
Example: insects. They reproduce quickly when resources are favourable, but die in large numbers at the end of the season

Organisms with a K-selected strategy live close to the carrying capacity (K) of their habitats. In general, these organisms:
- Have a relatively long life span
- Become sexually mature later in life
- Produce few offspring per reproduction cycle
- Provide a high level of reproductive care
Example: mammals

Question 22

Density independent factors

Answer 22

An abiotic factors that affects population growth in the same way, regardless of population density.
Examples:
- Natural disaters
- Temp change

Question 23

Density dependent factors

Answer 23

A biotic interaction that varies in its effect on population growth, depending on the density of the populations involved.
- Disease
- Predators
- Water
- Mating

Question 24

Competition

Answer 24

Intraspecific competition: a situation in which
members of the same population complete for resources.

Interspecific competition:
A situations in which two or more populations compete for limited resources

Often one species will out-compete the other

Competitive exclusion principle: two species with overlapping niches cannot coexist, but if their niches are different they can live in the same area, but affecting their population

Question 25

Population cycles

Answer 25

Alternating periods of large and small population sizes. A predator-prey relationship is one way that a population cycle can occur

Sinusoidal growth: a wavelike oscillating growth pattern that is typical of predator-prey interactions

Question 26

Defence mechanisms

Answer 26

Protective coloration: adaptations that help individuals avoid predation; includes camouflage, mimicry, and body colouration used as a warning signal

Interactions between producers and consumers typically results in co-evolution.

Question 27

Parisitism

Answer 27

a symbiotic relationship in which a symbiont lives off and harms the host

Example: is a caterpillar and parasitic wasp eggs.

Question 28

Mutualism

Answer 28

A type of symbiotic relationship in which both species benefit from the relationship

Question 29

Commensalism

Answer 29

A symbiotic relationship in which one partner benefits and the other partner neither benefits nor is harmed

Question 30

Invasive species (introduced species)

Answer 30

• Invasive species are non-native species that relocate to an area and outcompete the native species for resources
• These species usually do not have predators in their new environment, so they reproduce in large numbers

Example: The zebra mussels in the Great Lakes are a thriving invasive species. These mussels out-complete the native species for food and habitat.

Question 31

K-selected species

Answer 31

Humans are K-selected
- Have a small number of offspring
- Reproduce later in life
- Provide parental care

Question 32

Factors that affect growth

Answer 32

Many advances in technology occurred in a relatively short period of time

1700s: humans were able to increase their food supply by improved agricultural methods and domestication of animals

Late 1800s to early 1900s: breakthroughs in medicine enabled peoplem to be successfully treated for once-fatal illnesses

Better shelter protected people from the weather

Improvements in the storage capacity of food helped people survive when food was less plentiful

Question 33

Population pyramids

Answer 33

Triangle shape: predicts a future of explosive growth because a large portion of the population will their reproductive years at the same time. It also indicates a decreased average life span

Rectangular shape: population is not expanding and is stable

Inverted triangle: indicates a population in shrinking. There are a large number of individuals that are past their reproductive years and few individuals in or about to enter their reproductive years

Question 34

Ecological footprint

Answer 34

It is the total amount of land needed to support one person
and it includes six major categories of demand:
1. Cropland
2. Grazing land
3. Fishing grounds
4. Forest land
5. Carbon absorption land
6. Building area

Question 35

Managing growth and resources

Answer 35

Like all populations, humans obtains the necessities for survival from their environment. Unlike other species, for many human their environment is the entire globe. The explosive growth of the human population has created some problems such as:

1. Mercury contamination (toxicity and biomagnification)
2. Deforestation
3. Overharvesting Fish
4. Marine Garbage
5. Limiting biodiversity
6. Overexploitation
7. Invasive species