Population And Community Ecology

Question 1

What is Population Ecology

Answer 1

The study of populations in relation to the environment, including environmental influences on density (increase or decrease) and distribution (clump or spread out), age structure, and population size

Question 2

Population density (2)

Answer 2

• Describes the number of individuals per unit or volume (ocean)
• D = M/V

Question 3

Density-Independent Factors (3)

Answer 3

• Environmental conditions that affect a population regardless of its density
• Usually abiotic (non-living) factors like seasonal weather or natural disasters
• Cannot be controlled but end up changing the density

Question 4

Density-dependent factors

Answer 4

Factors that affect the population growth as a result of density or population surrounding the area

Question 5

Territoriality in relation to density

Answer 5

• May limit density
• Animals that use chemical communication to warn off same species of their boundaries (bad density)
• Animals bunch up together while having a close separation (good density)

Question 6

Health and density

Answer 6

In dense populations, pathogens can spread more rapidly since physical contact between individuals increases

Density can influence health and survival

Question 7

Stress and Density

Answer 7

• Crowded animals show increase in levels of stress as a result they act abnormally;

Stress can cause:
- aggression
- decrease in fertility (hormonal changes)
- reduce the population growth rate

Question 8

Predation and density

Answer 8

With increased predation, the prey population decreases. This in turn, limits the predator population since less food available.With reduced predation the prey population begins to grow and the cycle is repeated

Question 9

Competition and density

Answer 9

Interspecific competition: different species (decrease or increase one) = land, ressources, food

Intraspecific competition: same species = usually mates, or territory

Question 10

Population Models Describe Population Size

Answer 10

The size of a population at any time depends on the balance between individuals being added to the population and individuals being removed from the population: death, birth, immigrations and emigration

Population change = B+I-D-E

Question 11

Population change as a percentage

Answer 11

(B+I-D-E)/n x 100 = %

Question 12

Determining Density in populations

Answer 12

Determining the density of natural populations is difficult and impossible
Techniques are used to estimate:
- Mark and recapture
- Quadrat sampling
- Random sampling

Question 13

Mark and recapture

Answer 13

Formula: (total number capture) x (number marked)/ total number recapture with mark) = estimate size
Basic idea: 1. Capture a small number of individuals 2. Harmless mark them 3. Release them 4. Over the years capture geese and record their numbers

Question 14

Random sampling

Answer 14

Basic idea: 1. Plots the area 2. Chooses random spots 3. Counts population in those specific plots 4. Averages 5. Multiplies to get the estimate

• doesn’t work great with animals that move around

Question 15

Dispersion

Answer 15

Pattern of spacing among individuals within the boundaries of the population

Question 16

The patterns of dispersion

Answer 16

Environmental and social factors influence spacing of individuals in a population

Types:
- clumped
- uniform
- random

Question 17

Clumped dispersion

Answer 17

In a clumped dispersion, individual aggregate in patches (groups), usually influenced by resource availability and behaviour

Benefits: increases the effectiveness of retrieving food, protecting and caring for young and exclude other individuals from territory (defending)

Question 18

Uniform dispersion

Answer 18

In a uniform dispersion, individuals are evenly distributed, may be related by social interactions such as territoriality

Often exhibition of uniform spacing is maintained by aggressive interactions between neighbours but together easier to avoid predators

Question 19

Random dispersion

Answer 19

In a random dispersion, the position of the individuals is independent of the others

Question 20

What is a community?

Answer 20

A biological community is an assemblage of populations of various species living close enough for potential interaction

Question 21

Community interactions

Answer 21

Affect species survival and reproduction

• Competition
• Predation
• Herbivory
• Symbiosis (parasitism, mutualism, commensalism)
• Disease

Question 22

Competition

Answer 22

Occurs when species compete for a resource in short supply

-/-

Question 23

Compétition Exclusion Principle

Answer 23

States that two species competing for the same limiting resources cannot coexist in the same place

Question 24

Predation

Answer 24

Refers to interaction where one species, the predator, kills and eats the other, the prey.

-/+

Question 25

Behavioural defenses to predation

Answer 25

Prey display various defensive adaptations:
- Behavioural defenses include hiding, fleeing, self-defense and alarm calls
- Also morphological and physiological defense adaptations

Question 26

Cryptic Coloration

Answer 26

Cryptic coloration or camouflage makes prey difficult to spot (morphological - colour)

Question 27

Chemical Defense

Answer 27

Physiological adaptation
Animal with effective chemical defense often exhibit bright warning coloration called aposematic coloration

Question 28

Mimicry

Answer 28

A prey may gain significant protection by mimicking the appearance (morphological) or even the smell of another species (physiological) which in turn aids its survival

Question 29

Parasitism

Answer 29

In parasitism, one organism, the parasite, derives nourishment from another organism, the host, which is harmed in the process

-/+

Question 30

Disease

Answer 30

Pathogens, disease-causing agents are typically bacteria, viruses or protists
Reproduction faster than parasites

-/+

Question 31

Mutualism

Answer 31

An interspecific interaction that benefits both species

+/+

Question 32

Commensalism

Answer 32

One species benefits and the other is apparently unaffected

Very rarely seen in nature
+/neutral

Question 33

Species diversity

Answer 33

Species diversity of a community is the variety of organism that make up the community (different species)

It had 2 components:
- species richness
- relative abundance

Question 34

Species richness

Answer 34

Species richness is the total number of different species in the community

Question 35

Relative abundance

Answer 35

Relative abundance is the proportion each species represents of the total individuals in the community

Relative abundance = number of individuals in one species/ total number of individuals x 100 (percentage)

Question 36

Species richness in relation to species evenness

Answer 36

Species Richness - number of species in a community
Species Evenness - relative abundance of each species

If high in one species richness, low in species evenness (vice versa)

Question 37

Keystone species

Answer 37

Keystone species are a species which other species in an ecosystem largely depend. If the keystone species were to be removed, the ecosystem would change drastically

• not necessarily abundant
• exert strong control on a community by their ecological roles

Question 38

Exponential Growth

Answer 38

Ideal environment with unlimited ressources = J-shaped curve on a graph
Always growing

Question 39

Logistic Growth

Answer 39

Population experiences a levelling off from exponential growth due to limiting ressources
- S-shaped
- carrying capacity = k represents the maximum population size that can be supported in an environment

Question 40

Quadrat