Mads Thomsen Lectures Week 1

Question 1

How do we understand the structure of a community?

Answer 1

By understanding the distribution and abundance of species

• What processes shape the patterns of community structure?
• How does a community respond to the addition or removal of a species?
• Why are communities in some environments more diverse than in others?

Question 2

The species niche expresses community structure

Answer 2

Diagrams: A plot showing the environmental gradient relative to species abundance. The environmental gradient is the different conditions in an environment. The arrows show how much of each species is in each of the sites.

A) Shows the fundamental niche - Adaptations of organisms allow them suceed under certain environmental conditions. But these adaptations may be restrictive under other environmental conditions.

B) Shows the realised niche - The interactions of organisms within their niche. Some organisms are competing for water in the soil which reduces the water and therefore reduces the growth of each other. The performance curve gets narrower indicating competition in the system.

The performance curve in the realised ncihe can sometimes be expanded when there is a mutalism between two organisms.

Question 3

Species composition

Question 4

Definition: Fundamental Niche

Answer 4

The fundamental niche, sometimes referred to as the physiological niche, provides a description of the set of environmental conditions under which a species can persist.

Question 5

Realised Niche

Answer 5

Realized niche is the set of conditions actually used by given animal (pop, species), after interactions with other species (predation and especially competition) have been taken into account.

Question 6

Bird Example of community structure and the niche

Answer 6

• Four birds found in the same area.
• The diagrams show their geographical distribution.
• The dark blue means more abundant.
• You can see that most of the species are most abundant outside their main area of geographical region.
• The species may fluctuate along their ranges so you may find it one year and not the next in that spot.
• The way organisms interact depends on where you find it relative to its range. If it’s near the edges of its range you would expect that it’s a very weak competitor and if you find it near the center of its range you would expect that this is where it is best adapted to the environment and it’s a stronger competitor.

Question 7

The result of species different tolerances and interactions along environmental gradients is Zonation

Answer 7

• Salt marshes have a strong zonation gradient.
• Different environmental conditions along the environmental gradient - Lots of water at one end (can’t do photosyntehsis, sediment, but lots of nutrients) and then the terrestrial environment where there is lots of competition.