Allelopathy and herbivory
This presentation is the property of its rightful owner.
Sponsored Links
1 / 25

Allelopathy and herbivory PowerPoint PPT Presentation


  • 93 Views
  • Uploaded on
  • Presentation posted in: General

Allelopathy and herbivory. Additional readings: Hawkes CV, Sullivan JJ . 2001. The impact of herbivory on plants in different resource conditions: A meta-analysis. Ecology 82 :2045-2058. Seminars. Outline. Amensalism What is allelopathy and how is it inferred? “plus-minus” interactions

Download Presentation

Allelopathy and herbivory

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Allelopathy and herbivory

Allelopathy and herbivory

Additional readings:

  • Hawkes CV, Sullivan JJ . 2001. The impact of herbivory on plants in different resource conditions: A meta-analysis. Ecology 82:2045-2058.


Seminars

Seminars


Outline

Outline

  • Amensalism

  • What is allelopathy and how is it inferred?

  • “plus-minus” interactions

  • Herbivory and importance in range and forest

  • Trophic relationships: top down VS bottom up

  • Effects of herbivory

    • Aspects of herbivory in range and forest

    • Herbivore functional responses

    • Sublethal effects and compensation (example)


Allelopathy

Allelopathy

  • Could be considered “interference competition” for plants...

  • Definition:

  • Often mentioned, but hard to prove. Why?


Allelopathy1

Allelopathy

  • Inferred by:

    • Spatial pattern/arrangement of plant community

    • Presence of chemicals in leaves, roots and/or soil

    • Demonstration that chemicals cause decline in growth or survival of surrounding vegetation


Allelopathy2

Allelopathy

  • Difficult to prove because:

    • Low [chemicals] in the field

    • Mediated by 3rdparty (e.g. microbes and litter)

    • Trophic interactions similar to apparent competition: shrub harbours seed predator – causes “allelopathic” spatial arrangement.


Allelopathy3

Allelopathy

  • Recent work on Centauria maculata (spotted knapweed) provides good evidence for allelochemicals.

  • Knapweed is an important rangeland weed; what are implications of allelopathy?


Amensalism

Amensalism

  • Negative to one species, inconsequential to other.

  • Often is actually very asymmetric competition/pathogenesis

  • Example: allelopathy


Plus minus relationships

“Plus-Minus” relationships

  • Include disease, parasitism, predation and herbivory.

  • Effects on population (or biomass) can be modelled using Lotka-Volterra equations to predict population of prey and predators.

    dV/dt=V[b-aP]=f1(V,P)

    dP/dt=V[kaV-d]=f2(V,P)

    Where: V=#prey, P=#predators, b=prey growth rate, a=prey consumption rate by predator, k=rate of increase of predator per unit prey, and d=predator death rate


Functional response

Functional response

  • Relationship of predator (herbivore) consumption of prey (plants) to density of prey (plants)

  • 3 types – unsaturating (I), saturating(II), and sigmoidal (III)

  • Type of functional response has implications for community structure and stability

  • Discuss further in lab…


Herbivory

Herbivory

  • What is the importance of herbivory?

    • Small amount of biomass removed: 10%

      • Tundra/alpine 3%

      • Forest 4%

      • Grassland 10-15%

      • Rangeland/grazing systems 30-60%

    • “world is green” hypothesis (who?): there is more plant biomass than herbivores can eat.

    • Why? Trophic interactions.

      • Top down control (predators)

      • Bottom up control (plant forage quality)


Herbivory1

Herbivory

  • But – trophic cascade models too simplistic; herbivory has more dramatic effects than they predict...

    • Defensive compounds (coevolution)

    • Community composition

    • Productivity

    • Seedling survival and demography

    • Seed predation


Herbivory2

Herbivory

  • What are some of the effects of herbivores on plants and plant communities?


Effects and issues

Effects and issues

  • Mortality of seedlings

  • Insects VS vertebrates

  • Herbivore outbreaks (insects especially)

  • Sublethal effects and herbivory escape

  • Compensatory growth and overcompensation

  • Productivity

  • Herbivore functional responses

  • Resistance/defence


Forests

Forests

  • Mortality of seedlings

  • Insects

  • Outbreaks (insects especially)

  • Sublethal effects and herbivory escape

  • Defensive compounds?


Rangelands

Rangelands

  • Productivity

  • Compensation/overcompensation

  • Herbivore functional responses

  • Toxicity and herbivore resistance

  • Selectivity/preference

  • Diversity and coexistence


Herbivore selectivity

Herbivore selectivity

  • Plant stress VS plant vigour hypotheses:

    • Herbivores attack already stressed plants

    • Herbivores favour plants in high resource areas and with larger “plant modules”

    • Evidence for both

    • Also influenced by herbivore defenses

  • Can alter species composition and lead to coexistence IF favoured species is best competitor

  • Differs among herbivore species, therefore management of different species can change community composition


Compensation

Compensation

  • Response of plants to defoliation can vary widely: positive, negative or neutral

  • “Compensation” means plant growth increases after herbivory to compensate for lost tissue

  • “Overcompensation” much discussed: this means plants are stimulated to grow MORE after grazing/browsing.

  • Is overcompensation possible?

  • Is compensation over extended periods possible?


Sublethal effects of herbivory

Sublethal effects of herbivory

  • Herbivores don’t often cause mortality of adult plants.

  • Can affect plants in other ways:

    • Reduced seed set/fruit abortion

    • Reduced size/growth rate

    • Change in architecture

    • Delay or prevention of maturity

    • These may all affect plant fitness (contribution to next generation)

  • Example: population consequences of herbivory on three Australian native plants. Allcock and Hik 2004. Oecologia 138:231-241.


Grazing experiment

Grazing experiment

  • Three groups of grazing animals: domestic stock (sheep and cattle), native macropods (kangaroos and wallabies), and introduced rabbits.

  • Four treatments: control, stock fence, kangaroo fence, rabbit fence.

  • Two habitats: woodland (intact Eucalyptus canopy) and grassland (cleared “native” pasture)

  • Three target species: kangaroo grass (Themeda australis), cypress pine (Callitris glaucophylla) and white box (Eucalyptus albens)


Grazing experiment1

Grazing experiment

  • Plants placed in experimental plots in April 1998

  • Monitored until April 2001.

  • Generalized linear modelling used to analyze factors affecting survival (habitat, grazing animals, competition)

  • Survival and growth data used to parameterize stage-based population models for trees.


Life history transition diagram

“Life history” transition diagram

  • Transitions between 5 size (height) classes for trees; final stage is “escape from herbivory”.

  • Models created for each habitat and treatment combination.


Allelopathy and herbivory

P

35

P

25

P

P

15

P

14

24

P

13

P

P

P

S

P

S

S

S

S

23

34

45

12

3

5

1

2

4

P

P

P

P

P

22

33

44

55

54

P

P

P

P

21

18

11

43

P

P

P

51

52

53

P

42

P

41

P

31

S

S

S

S

S

S

S

S

S

S

Matrix Two

1

2

3

4

5

Matrix One

1

2

3

4

5

P

P

P

P

P

S

[<25 cm]

0

P

0 0 0

S

[<25 cm]

11

21

31

41

51

1

21

1

P

P

P

P

P

S

[25

-

49 cm]

0 P

0 0 0

S

[25

-

49 cm]

12

22

32

42

52

2

22

2

P

P

P

P

P

S

[50

-

74 cm]

0 P

0

0 0

S

[50

-

74 cm]

13

23

33

43

53

3

23

3

P

P

P

P

P

S

[75

-

100 cm]

0 P

0 0 0

S

[75

-

100 cm]

14

24

34

44

54

4

24

4

P

P

P

P

P

S

[ >100 cm]

0 P

0 0 0

S

[ >100 cm]

15

25

35

45

55

5

25

5


Results

Results

  • Different herbivore species affected different plant species (rabbits/kangaroos – cypress; stock – Eucalyptus)

  • Plants in productive environment better able to compensate (more rapid growth)

  • High herbivory rate in unfenced low productivity habitats prevented “escape”.

  • This could have population consequences even though mortality was fairly low.

  • Interaction between competition and herbivory…tradeoff.


  • Login