Community structure

1
Lecture 18

• Community structure

2
Ecological communities are often highly complex
3
Last Lecture

• We examined patterns in species diversity
• Learned how to measure diversity
• We saw that interpreting patterns can be difficult

4
The same number of species

• Can be arranged into communities that differ in
  how they are structured

5
Food webs
B
A
B
C
A
C
D
D
6
Food webs
A
A
B
C
B
C
D
D
7
Food web structure can influence

• Community stability
• Processes like biomagnification are influenced by
  food chain length

8
Food webs
B

• We use different measurements to describe food
  webs
• Number of trophic levels is the simplest
• This food web has 3

C
A
D
9
Why are food webs short?

• Most food chains (webs) are short
• Human ? Walleye ? Yellow Perch ? Golden shiner ?
  Zooplankton ? Phytoplankton
• Six species (five links)

10
Why are food webs short?

• Energy flow
• Not enough energy left beyond level 5 or 6

11
Food webs

• With short interconnected food chains may also be
  more stable

12
Food webs stability
B
A
B
C
A
C
D
E
D
E
13
If C is removed
A
B
D
D
E
E
14
Remove C
B
A
E
D
15
Food webs stability
B
A
E
D
16
Food webs are short

• Because of energy constraints
• And because short interconnected food chains are
  more stable