Community ecology - Week 20

Question 1

How did Tansley (1935) describe the necessities for an ecosystem?

Answer 1

• Self contained unit
• Biological community + abiotic environment
• Trophic level and energy flows (autotrophs to top preditors)
• Biogeochemical cycles (nutrients, nitrogen, phosphorous)

Question 2

What does the following mean?

Intraspecific?
Interspecific?
Direct interaction?
Indirect interaction?

Answer 2

Intraspecific? Interactions of same species

Interspecific? Interaction of different species

Direct interaction? Physical touch, consumption

Indirect interaction? No touch, shared resource

Question 3

What are the effects of each of these interactions?

Mutualism?
Commensalism?
Compitition?
Antagonism?

Answer 3

Mutualism? +/+ both species benefit
- one of both species cannot survive without the other

Commensalism? +/0 one species benefits, other is not affected
- close interactions, shark and remora

Competition? -/- each species affected negatively
- both competing for same limited resource

Antagonism? +/- one species benefit, other disadvantaged

Question 4

What are these different types of competition?

Interference?
Exploitation?
Apparent?

Answer 4

Interference? direct, between individuals if interfere with another foraging, survival, reproduction. Survival of the fittest. K species

Exploitation? indirect, use of resources depletes amount available for others. R species

Apparent? indirect between 2 species. C could predate A n B so A n B indirectly affect each other

Question 5

What is bottom-up control?

What is top-down control?

What is antagonism?

Answer 5

with limited resources population decline with competition to access limited resource, food at bottom of chain dictating preditors at top of chain

preditors at top of chain affecting what is eaten at bottom of chain

predation, parasitism, herbivory, cannabalism

Question 6

What is preditor-mediated co-existance?

Answer 6

Preditors can increase/ decrease the number of species in a community.
Species could be reduced by predators, increasing biodiversity allowing more species to co-exsist

Question 7

What is a predator/ prey cycle and what can affect this?

Answer 7

Regular increase/ decrease in population of predators and prey.

Extrinsic factors
Intrinisic factors

Question 8

What is a food web?

Answer 8

Who eats who

Representation of feeding relationships in a community

Question 9

How to work out connectance, the measure of complexity?

Answer 9

Actual number of interactions
/
Possible number of interspecific interactions

Question 10

Why are food chains so short?

Answer 10

Energy flow hypothesis, only 30% energy consumed at trophic level in available as food for the next

Dynamic fragility, longer chain = severe population fluctuations, top predators more likely to go extinct

Contrants of predator design/ behaviour, can’t beat a bear in a fight

Question 11

If you remove a species what can happen?

Answer 11

Disasterous effects

Sometimes, another species can fill their role, nature can heal itself

Question 12

What are some island ecological characteristics?

Island biogeography theory?

Answer 12

High conservation status, continental and oceanic remote, evolutionary hot houses, badly damaged (tourism alien species), vulnerable to chance events, huge scope for restoration

Ecosystem isolated by being surrounded by different ecosystems

Question 13

What are the two main causes of fragmentation?

One way to reduce the impact of fragmentation?

Answer 13

Reduced area

Edge effect, edge environment is different to center, light, wind, water etc

• More land subject to edge effect if habitat divided into fragments
• Preditors, large species, habitat specialists may all go extinct

Wildlife corridors, expensive, biggest benefit to preditors