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BI2135: Ecology > Community Ecology and Assembly > Flashcards

Community Ecology and Assembly Flashcards

1
Q

What is a community?

A

All organisms living and interacting within an environment or habitat.

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2
Q

What are the aims of studying community ecology?

A

Explaining and predicting the distribution and abundance of species.
Quantifying patterns.
To learn about community dynamics and their response to disturbance.

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3
Q

What are some criticisms of the concept of community ecology?

A

Most research is at a single scale - ‘local community’.

Most studies assume the community is closed.

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4
Q

What is a meta-community?

A

A set of communities linked by dispersal, with multiple interacting species (Leibold et al. 2004).

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5
Q

What do abundance distributions show?

A

The full distribution of commonness/rarity in a community.

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6
Q

What is the general pattern of abundance in a community?

A

Many rare species and a few very common species.

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7
Q

What do evenness and dominance distributions show?

A

How the total abundance is distributed among species. More even = more diverse.

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8
Q

Define the Simpson’s index (D).

A

The probability that 2 individuals drawn at random from a community are the same species.

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9
Q

Define richness, in a biological context.

A

The total number of species in a community.

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10
Q

What is the difficulty with studying richness?

A

Most species in a community have low abundance so may not be sampled.

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11
Q

How can richness studies be made more accurate?

A

You can either estimate the total richness or rarefy the data.

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12
Q

How can you estimate total richness?

A

Plot a graph of number of species vs number of individuals until the curve levels off.

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13
Q

How do you work out richness with a low sample size?

A

You can rarefy the data. Look at the number of individuals and species recorded. Then estimate the population size and multiply by the number of species.

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14
Q

Define composition, in a biological context.

A

Similar to community structure, a combination of species richness and species diversity.

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15
Q

What is the function of the Bray-Curtis dissimilarity metric?

A

It summarises the differences in the abundance of all taxa between each site pair. 0 = identical; 1 = no species in common.

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16
Q

What is an organism’s ecological traits?

A

The roles it plays in the ecological community.

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17
Q

What are the 4 high level processes influencing community assembly?

A

Drift, selection, dispersal and speciation.

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18
Q

Define drift, in terms of community assembly.

A

Random fluctuations in population size, independent of species identity.

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19
Q

What does drift eventually lead to? How does community size affect this?

A

A single species dominating as others drift to extinction. Larger community size results in more generations before extinction.

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20
Q

Why does selection occur in a community?

A

Some species have greater fitness.

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21
Q

Define dispersal.

A

Movement of individuals among locations.

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22
Q

What are the 2 forms of dispersal?

A

Immigration and emigration.

23
Q

What is a key feature of communities that allows for dispersal?

A

Local communities are not independent so show more similar composition and dynamics.

24
Q

How are dispersal and speciation linked?

A

These are the 2 processes that can lead to species being added to a community.

25
Q

What is the relative importance of the 4 high level processes?

A

The ‘niche’ view suggests selection is by far the most important. ‘neutral’ models ignore selection but include speciation, dispersal and drift.

26
Q

How do drift and dispersal differ in terms of scale?

A

Drift has a greater impact at a small scale. Speciation has a greater impact at a large scale.

27
Q

What are the 4 types of community change?

A

Equilibrium/Stationary.
Long term directional change.
Alternative stable states.
Collapse.

28
Q

Describe a community in equilibrium.

A

Biomass and structure are broadly constant. There will be some variation around equilibrium. Can be driven by intrinsic dynamics or by extrinsic disturbance.

29
Q

Describe a community undergoing long term directional change.

A

Consistent environmental change. Includes increases, decreases or turnover. Common during primary and secondary succession.

30
Q

Define turnover.

A

A change in what species or factors are present.

31
Q

Describe a community with alternative stable states.

A

A dramatic shift in community structure/ecosystem often resulting from small environmental changes. Often a large change is needed to reverse it.

32
Q

Describe a community in collapse.

A

Catastrophic biodiversity loess, often irreversible. Can be seen as an alternative stable state.

33
Q

What can be studied to detect community change?

A

Abundance distributions.
Evenness (dominance).
Richness.
Composition.

34
Q

What are the 3 types of community disturbance?

A

Pulse, press and ramp.

35
Q

Define pulse disturbance.

A

Short time discrete events like wildfires or rapid pollution with short-term effects.

36
Q

Define press disturbance.

A

May be rapid but reaches a level that is maintained like urbanisation or dam building.

37
Q

Define ramp disturbance.

A

Steadily increasing disturbance with no set endpoint like climate change or ongoing pollutant release.

38
Q

What are the 4 components that impact the stability of a community?

A

Variability.
Resilience.
Resistance.
‘ecological’ resilience.

39
Q

How does variability impact community stability?

A

Higher variability results in lower stability.

40
Q

What is resilience?

A

The speed at which the community returns to its original state after disturbance.

41
Q

What is resistance?

A

How much the community changes in response to a change in the environment.

42
Q

How do resilience and resistance impact community stability?

A

Higher resilience and resistance results in greater community stability.

43
Q

What is ecological resilience?

A

The magnitude of disturbance needed to shift a community between states.

44
Q

How does community structure affect stability?

A

There is a strong correlation between greater diversity and increased stability.

45
Q

How does diversity impact community-level and population-level stability?

A

Increasing diversity increases community-level stability but decreases population-level stability.

46
Q

What are the 3 stages of invasion?

A

Escaping, establishing, and becoming a pest.

47
Q

What is the escaping stage?

A

Transition from imported to introduced.

48
Q

What is the establishing stage?

A

Transition from imported to introduced.

49
Q

What is a pest?

A

An organism that has a negative economic effect.

50
Q

What is the 10s rule?

A

Each stage of invasion has a 10% chance.

51
Q

Why do cultivated/crop plants colonise more successfully?

A

They are continuously introduced into the wild from agricultural fields.

52
Q

How are biological control agents different to invasive species?

A

These organisms are deliberately introduced.

53
Q

Define propagule pressure.

A

Measures individuals per introduction and introduction frequency to measure introduction effort.

BI2135: Ecology (15 decks)

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