Plant Ecology - Chapter 10

1
Plant Ecology - Chapter 10

• Competition

2
Competition

• Reduction in fitness due to shared use of a
  resource that is in limited supply
• Intraspecific
• Interspecific

3
Competition

• - / - both parties lose
• 0 / - or / - asymmetric competition - largest
  individuals have disproportionate negative
  effects on their smaller neighbors

4
Competition

• Small head start may confer a large size
  advantage - competitive dominance over
  later-emerging plants
• Self-thinning - higher early mortality in smaller
  or weaker individuals in overly dense plantings

5
Competition

• Competing for light, water and mineral nutrients
  from the soil, space to grow and acquire
  resources, access to mates
• Competitive interactions experienced by a plant
  occur very locally

6
Competition

• Immediate density most important - average
  density essentially irrelevant
• Effects of neighbors decrease sharply with
  distance

7
Competition

• Winning the competition for light may affect all
  other competition

8
Competition

• Tall plants may intercept light, but small plants
  may intercept water, soil nutrients
• Asymmetric, but larger plants usually have much
  greater effects

9
Competition

• Trade-offs and strategies
• Winning competition for one resource may
  compromise ability to win comp. for another
  (light vs. nutrients)
• Outcome may change as resource availability
  changes

10
Allelopathy - Allelochemicals

• Chemical warfare among neighboring plants
• Release toxins into soil to reduce growth or kill
  adjacent plants
• Sure way to gain competitive advantage
• Knapweed on rangelands - little effect on
  Eurasian plants, strong effects on N. Amer. plants

11
Facilitation

• Positive effects on neighbors rather than
  negative (opposite of competition?)
• May be particularly common under conditions of
  high abiotic stress, or high herbivory

12
Facilitation-nurse plants

• Mature nurse plant may facilitate germination,
  establishment, growth of juvenile plant of a
  different growth form
• Particularly common in deserts, e.g. columnar
  cactus established with help of nurse shrub

13
Facilitation-CMNs

• Common mycorrhizal networks - extensive
  connections linking many plants of differing age,
  species
• May facilitate seedling and sapling survival and
  growth by way of nutrient and water transfers
  among plants
• Mature helping juvenile

14
Competition Models

• Lotka-Volterra model not very useful for plants,
  since plants dont experience the average effects
  of density the same way animals do
• Two different groups of models developed for
  plants

15
Competition Models

• Equilibrium models - how different the niches of
  species need to be to prevent competitive
  exclusion at equilibrium

16
Competition Models

• Nonequilibrium models - emphasize importance of
  resource variation (in time, space) and
  competition affecting coexistence

17
Competition Debate

• Are there predictable competitive hierarchies
  across different communities?

18
Competition Debate

• Is competition more intense in high-productivity
  than low-productivity environments?

19
Competition Debate

• How important is competition compared to other
  forces in determining species distributions and
  community composition?

20
Competition Debate

• No general consensus on any of these yet