Competition Ch' 10

1
Competition (Ch. 10)
Ken Jennings my hero! 74 wins (2004) 2.52
million
2
DeWit Replacement Series

• Note that if a line is above the stability line,
  you will move along it from left to right

Stability line
log output AB
log input AB
3
DeWit Replacement Series

• Note that if a line is above the stability line,
  you will move along it from left to right
• If a line is below the stability line, you will
  move along it from right to left

Stability line
log output AB
log input AB
4
DeWit Replacement Series

• Example results
• Line of slope 1 above stability line
• A is better competitor than B at all input ratios

Stability line
log output AB
log input AB
5
DeWit Replacement Series

• Example results
• Line of slope 1 below stability line
• B is better competitor than A at all input ratios

Stability line
log output AB
log input AB
6
DeWit Replacement Series

• Example results
• Slope lt1
• At low input ratios A wins, at high input ratios
  B wins
• Single stable mixture results

Stability line
log output AB
log input AB
7
DeWit Replacement Series

• Example results
• Slope gt1
• At low input ratios B wins, at high input ratios
  A wins
• Winner depends on input ratio

Stability line
log output AB
log input AB
8
DeWit Replacement Series

• Note that more complicated designs allow changing
  of ratio and density

Replacement Series
Partial Additive Series
Additive Series
Complete Additive Series
9
DeWit Replacement Series

• How helpful are these experiments in explaining
  field situations?
• Not too...
• Example, wild oats (Avena)
• California annual grassland
• Mediterranean climate Green in winter, dry and
  brown in summer

10
DeWit Replacement Series

• Example, wild oats (Avena)
• 2 introduced species present in grassland
• Avena fatua (wild oat left)
• Avena barbata (slender wild oat right)

11
DeWit Replacement Series

• Example, wild oats (Avena)
• Greenhouse DeWit replacement series results
• Outcome (dotted line)
• Single stable mixture at 80 A. fatua20 A.
  barbata

12
DeWit Replacement Series

• Example, wild oats (Avena)
• Field trials in mixed plots gt90 of plots had
  100 of one species or the other!

13
Studying Competition

• Field approach removal experiment
• Remove potential competitor(s) and study response
  of remaining plant(s)
• Example target-neighborhood experiment

14
Target-neighborhood experiment

• Example creosote bush (Larrea tridentata) and
  burrow bush (Ambrosia dumosa)
• Important shrubs in Mojave Desert (low elevation
  hot desert) of California, Arizona, Nevada

15
Target-neighborhood experiment

• Example creosote bush (Larrea tridentata) and
  burrow bush (Ambrosia dumosa)
• Study of competition removed all, Larrea, or
  Ambrosia around single target shrub of each
  species
• Performance of target monitored (water status)

16
Target-neighborhood experiment

• Result showed little Larrea-Larrea competition,
  great Larrea-Ambrosia competition, little
  Ambrosia-Ambrosia competition

17
Danger for removal experiments apparent
competition

• When herbivore effects can mimic those of
  competition
• Example Herbivore eats both A and B
• Increase A, more herbivores, B suffers
• Or, remove A, herbivore leaves, B prospers
• Interaction between A and B mediated by third
  species

18
Other points

• 1) Herbivory can influence competitive outcomes
• Ex, chalk grassland (England)
• Occurs on alkaline soils (chalk substrate)
• Rich mix of a grass and many forbs (herbaceous
  dicots)
• Lab studies showed grass was better competitor
• How forbs persist in field?
• Answer European rabbits (killer rabbits?)

19
Other points

• Rabbits preferred to forage on the grass, giving
  forbs chance to compete
• Twist This discovery had practical consequences
  when myxomatosis decimated rabbit populations in
  1950s and forbs started to disappear
• That had negative consequences for rare
  butterflies whose larvae ate forbs (ex, marsh
  fritillary)
• Note Rabbits were not native to England
  introduced by Normans in 1066, became abundant in
  1700s

The marsh fritillary
20
Other points

• 2) Disturbance timing can affect competition
  outcome

species 1
numbers
species 2
time
21
Other points

• 2) Disturbance timing can affect competition
  outcome
• Can allow coexistence by poor competitor

Frequent disturbances
numbers
species 1
species 2
time
22
Other points

• 3) Phenology can affect competition outcome
• Ex, lab study of 2 species
• When both germinated at same time, species 1 with
  most of biomass (species 2 outcompeted)
• When species 2 germinated 2 weeks earlier, it had
  most of biomass (species 1 outcompeted)

23
Allelopathy

• Type of allelochemic interaction chemicals
  secreted by one organism negatively affect
  another organism
• Allelopathy chemical released by one plant
  species negatively impacts another

24
Allelopathy

• May be viewed as mechanism of interference
  competition among plants.
• Definitely differs from exploitation competition,
  where resources removed from environment
• In allelopathy chemicals are added to environment

25
Plants are leaky

• Many pathways to release of materials
• rainwater leaches materials from leaves/bark
• volatile chemicals released from leaves (aromatic
  plants)
• roots produce exudates
• decay of dead parts liberates chemicals into soil

26
Examples

• Some of these chemicals inhibit other plants
• Example, Salvia (sage) in coastal sage scrub
  (California)

27
Examples

• Example, Salvia (sage) in coastal sage scrub
  (California)
• Releases cineole and camphor from leaves
• Deposited into soil around shrub inhibits
  germination growth of annual plants
• In grassland, bare zones around shrub borders

camphor
28
Examples

• Example, Juglans nigra (black walnut)

29
Examples

• Example, Juglans nigra (black walnut)
• Roots release juglone into soil
• Inhibits growth of roots of some other plant
  species (tomatoes, apples, alfalfa, etc.)

30
Examples

• Example, Ceratiola ericoides (beach rosemary)
• Grows on sandy soils

31
Examples

• Example, Ceratiola ericoides (beach rosemary)
• Releases ceratiolin into soil
• Breaks down into substances that inhibit growth
  of herbaceous plants

32
Allelopathy Problems with proof

• Need to
• 1) Isolate toxin in lab
• 2) Demonstrate toxin effect in lab
• 3) Demonstrate toxin effect in field. Does toxin
  remain in active form and sufficient
  concentration to have suggested effect?
• 3 hard to do. Bacteria etc. in soils rapidly
  degrade many compounds or convert them into
  others
• So allelopathy useful concept, but role difficult
  to prove conclusively

33
Allelopathy Problems with proof

• Other ecological factors herbivory
• Studies of bare areas around sage found herbivore
  activity greatest there
• Cages allowed some grassland species to survive
  despite allelopathy

34
Weeds and allelopathy

• Example, Centaurea maculosa (spotted knapweed)
• Major invasive nonnative weed

35
Weed example

• Example, Centaurea maculosa (spotted knapweed)
• Releases catechin into soil
• When absorbed by roots of other plant species,
  causes wave of cell death to move up roots into
  stems
• Aids invasiveness

catechin