Interspecific interactions

Question 1

Interactions among species

4 points

Answer 1

1. Mutualism
2. Competition (interspecific)
3. Competitive exclusion or coexistence
4. Fundamental and realised niche

Question 2

5 biotic interactions

Answer 2

1. Competition
2. Commensalism (1 benefits 1 neutral)
3. Mutualism (benefit to both)
4. Predation
5. Succession

Question 3

Symbiosis

Answer 3

living together - a close, often long term ecological relationship between 2 or more species

Question 4

Commensalism

Answer 4

one benefits, other is unaffected

e.g algae growing on a turtle shell, or moss on a tree, benefit from the substrate and sunlight

Question 5

Mutualism

Answer 5

both species benefit from association

e.g. rumen bacteria in the stomach of a deer allow the deer to digest cellulose while the bacteria grow in a warm, stable, safe environment

Question 6

Parasitism

Answer 6

benefits for parasite, costs for host

Question 7

Mutualism

Types of benefit

Answer 7

1. Food for at least one party
2. Protection from enemies
3. Provision of favourable environment
4. Provision of ‘service’
   Pollination
   Seed dispersal
   Cleaning

Question 8

Mutualism

Endosymbionts

Answer 8

provide food; gain nutrients and protection (inside organism)

Question 9

Mutualism

Ectosymbionts

Answer 9

provide protection or cleaning; gain substrate, transport, protection, food (outside organism)

Question 10

Mutualism

Answer 10

1. Each partner is acting in a selfish manner

Question 11

Mutualism may be

3 points

Answer 11

Facultative (capable but not restricted) for each partner

Obligate for one and facultative for the other

Obligate for both partners

Question 12

Obligate Mutualism

2 points

Answer 12

1. both species depend on one another to survive.
2. Extinction occurs in the absence of either species

e.g. coral bleaching (loss of Symbiodinium

Question 13

Facultative mutualism

3 points

Answer 13

1. Includes pollination and fruit / seed dispersal
2. Positive interaction with a group of species rather than obligate relationship with a specific species
3. Many fruits and seeds are dispersed by birds

Passage of seed through the gut is sometimes required for the seed to germinate

Birds gain nutrition
Plant gains mobility and initial nutrients

Question 14

Mutualism - example

2 points

Answer 14

Animal guts and their inhabitants

1. Animal gains digestible resources

Ruminants (deer, cattle, antelope)

2. Microbe gains food and stable environment

Bacteria and Protozoa involved
Digest cellulose using cellulase
Obligate anaerobes

Question 15

Interspecific competition

3 points

Answer 15

1. Individuals of the same species have very similar niches
2. Individuals of different species usually have distinct niches
3. If two species’ niches overlap there is interspecific competition

Question 16

Exploitation or interference competition Results in

4 points

Answer 16

1. Increased mortality
2. Slower development
3. Reduced reproduction

4.Leads to
Coexistence or competitive exclusion

Question 17

Competitive exclusion principle (Gause’s law)

3 points

Answer 17

1. Complete competitors cannot coexist
2. Two species with similar ecology, competing for the same resources cannot coexist if other ecological factors are constant
3. One competitor with an adaptive advantage will outcompete the other and eliminate it or force an evolutionary shift to a different niche

Question 18

Resource partitioning

Answer 18

When species divide a niche to avoid competition for resources

Question 19

Character displacement

Answer 19

Competition leading to interspecific divergence

Question 20

Interspecific competition - example

Answer 20

1. Red squirrel, Sciurus vulgaris, is native and more competitive in coniferous woodland
2. Grey squirrel, Sciurus carolinensis, is introduced (1876) and more competitive in deciduous woodland

Question 21

Interspecific competition is often

Answer 21

asymmetric

factors and consequences are not the same for both species

Question 22

How do we determine experimentally whether competition occurs between two species?

Answer 22

1. Removal & exclusion experiments
2. Laboratory experiments

A species may do well grown alone but be driven to extinction in competition with another species

Competition may be mediated by environmental factors

Question 23

Ecological Niche
Fundamental niche
2 points

Answer 23

1. The overall potential of a species

2. The widest range of conditions a population could occupy in the absence of competition

Question 24

Ecological Niche

Realised niche

Answer 24

1. A smaller niche that a population actually occupies due to competition & predation
2. limited by interspecific compertition