L3: Communities and ecosystems

Question 1

What is a community?

Answer 1

An assemblage of organisms that live in a particular habitat and interacts with one another.

Question 2

Why is the community concept sometimes tricky?

Answer 2

It’s a human need to classify the landscape– when we look at plants, animals, bacteria, etc. we try to assemblage all of the species in a specified place altogether and try to understand how they interact.

Question 3

What is community typically spatially defined by?

Answer 3

habitats—local conditions of soil, geology, drainage, topography, etc.

May be characterized by taxa that are specially adapted to the conditions

Question 4

What is a classic example of analysing distributions of marine communities?

Answer 4

• Taking into consideration depth and how different populations of species are distributed in different zones.
• Limiting factors are the availability of light and access to solid surfaces (feeding/ growing)
• Benthic (occurring at the bottom of a body of water) or Pelagic (living in the water column of the open ocean).

Question 5

What is an ecosystem?

Answer 5

The set of biotic and abiotic (e.g. water, heat solar radiation, minerals) components in a given environment.

Question 6

Ecosystem concept

Answer 6

Communities envisioned with respect to roles such as nutrient cycling, energy capture, regulation of other processes (such as hydrology) – depicted as components and flows and amenable to modelling.

Question 7

How are these niches from different species organised?

Answer 7

1) Spatial patterns

2) Temporal patterns

Question 8

Clement’s view of a community

Describe a close community

Answer 8

Believed in ‘organismlistic’ approach, organisms form populations and have an association with each other. Compared a plant community to organs within a body ‘working together’

A community was highly predictable and deterministic

Question 9

Gleasonian view of open community

No change in the whole community together

Answer 9

‘Individualistic’ organisms occur together because of a combination of similar tolerances for environmental factors and historical chance events.

Question 10

What is an ecotone?

Answer 10

Edge between two habitat types. Often share mix species.
Example from Oregon serpentine/nonserpentine soils
Soil conditions may cause community boundaries. Replacement of plant sp. And changes in concentration of elements in the soil.

Question 11

Resistance to climate change can be defined as what?

Answer 11

The ability of a community to maintain its composition and biomass in response to environmental stress, could be explained by reference to the functional composition and successional status of the grasslands.

Question 12

What hypothesis did Whittakers results support?

Answer 12

(Whittaker, 1967)

Species are distributed as if they were independent of one another.

NO abrupt replacement/ NO discrete communities.

Question 13

What is an ecotone?

Answer 13

Edge between two habitat types. Often share mix species.

Question 14

What was the big debate between community ecologies?

Answer 14

Clement’s view of community

vs

Gleasonian’s view of community

Question 15

What are the two different views on community structure? Which one is more favoured?

Answer 15

(emerged in 1920-1930)
1. Integrated Hypotheses (Clements)

2. Individualistic hypothesis (Gleason)«< more favored due to community change continuously with each species more or less independently distributed

Question 16

Individualistic hypothesis (Gleason)

Answer 16

Proposes that communities are loosely organized associations of independently distributed species with the same abiotic requirements

• Predicts that each species is distributed according to its tolerance ranges for abiotic factors

Question 17

Integrated Hypotheses (Clements)

Answer 17

A community is an assemblage of closely linked species, locked into association by mandatory biotic interactions

• Predicts that the presence or absence of particular species depends on the presence or absence of other species
• One should see sharp ecotones between distinct communities with little overlap in the species present in alternative communities

Question 18

How did Margaret Davis study pollen?

Answer 18

Some of the pollen produced by plants that live near a lake falls on the lake surface, sinks, and becomes trapped in lake sediments.

As the sediment builds up over the centuries, this pollen is preserved and forms a historical record of the kinds of plants that lived nearby.

As the lakeside vegetation changes, the mix of pollen preserved in the lake’s sediments also changes.

Question 19

What do the studies of Margaret Davis tell us about the composition of forests in the Appalachian Mountains during the past 12,000 years (see figure 1.8)? Based on this research, what predictions might you make about the future composition of these forests?

Answer 19

• Spruce has been consistent throughout, though lessening in ratio. There have been different periods in time in which a new species comes to the areas tested.
• If no new species are introduced then they current tree species will continue to compete, and beech is not a strong competitor

Question 20

Why understanding communities is relevant?

Answer 20

Community is an intrinsic concept when talking about drivers of change.

If it is changing fast/ slow, if there are species changing in the same way? All this leads to tipping points.