Biotic Interaction Part IV

Case Study (Organism)

Anolis Lizards in Greater Antilles

Case Study (Role of Competition)

Over 150 species of Anolis lizards inhabit Caribbean islands

Case Study (Ectomorphs)

Diversified into 4-6 types of ectomorphsEcomor each adapted to particular microhabitats.

Ecomorphs

Local variety of species whose appearance is determined by ecological environment.

Specialization reduces 

Interspecific competition by allowing species to exploit different resources 

Convergent Evolution due to

past competition, “The Ghost of Competition Past”.

Case Study (Role of Predation) (example) 

Influence Anolis behavior/morphology 

• Ex: Predatory curly tailed lizard (Leiocephalus carinatus) in Bahamas led to changed in habitat use/behavior of other Anolis to avoid predation. 

Anolis (Population Effect)

When curly-tailed lizard was introduced, population of trunk-ground Anolis species declined, ‘direct top-down control.

Anolis and curly tailed lizards (Community Level Effect)

• Reduction of abundance of some species

• Forcing other species to alter niche (Some species more upper levels to veg) 

• Changing competition patterns in higher level veg zone. 

Field Studies show

The effect of competition on community structure (eg, distribution of 2 species of cattails)

Cattail example of competition

When growing alone T. angustifolia could extend distribution into shallow water, T. latifolia is able to do that.

Resulting in Angustifolia is excluded from shallow water sites. 

Competitive Exclusion principle and Lotka-Volterra model of competition suggests

Coexistence of similar competition is possible but k of the species need to be low.

2 simple ways of divergence

1) Character Displacement

2) Resource partitioning among the species

Character Displacement Occurs When

Morphological differences among similar species are magnified in regions where they co-occur, but diminished or absent when distribution don’t overlap.

Resource Partitioning 

Another way to reduce interspecific competition or prevent exclusion specie from community (eg. Anolis Lizards in Greater Antilles) 

Ghost of Competition Past

Connell 1980

Resource Partitioning (different forms)

• Based on specific characteristics of resource (eg; type, size)

• Based on spatial distribution of resource - spatial resource partitioning or microhabitat resource partitioning

• Based on when is the resource used (temporal resource partitioning) 

• Based on abiotic conditions (abiotic resource partitioning) 

Disturbance, predation and herbivory: similar effects on community structure

• Disturbance - Sometimes defined as ‘total or partial removal of veg’

• Predation - seen as mode of disturbance 

• Herbivory 

Joseph Connells 1978 study

Communities tend to have low species diversity in the absence of disturbances

(ex: tropical rainforests, coral reefs are subject to frequent disturbances. 

Intermediate disturbance Hypothesis (J. Connel 1978)

Species richness highest at intermediate levels (intensity or frequency) of disturbance

Intermediate Disturbance (1979)

(W. Sousa) Classified intertidal boulders into groups of small, intermediate/large depending on force of wave that required to move them

Results: Intermediate sized rocks had more diverse algae community. 

Example of Rabbits and grazing pressure 

Examined relationship between grazing intensity by rabbits and species diversity of plants 

Found thatplant species richness was highest under mederate grazing pressure. 

Paine (1969) 

Experimental remove (predator removal) of rocky intertidal carnivore, the starfish. 

Removed: 

1) Intertidal community 

2) Removed of pisaster (predator) 

3) Control sit (presence of pisaster) 

Starfish (learned from experiment)

Is specialist predator that has preference of Mytilus. By feeding on Mytilus, starfish control abundance of this species.

Keystone Species

Some species have disproportionately large effect on community structure.

• Shown by Paine

• Removal of species leads to change in community composition

Predators and community structure (showed) 

Top predators limit abundance of mesopredators and prevent over exploiting food resources (herbivores or primary producers) 

Non-predator keystone species

Ecosystem engineers (increase habitat diversity)

(ex: Beavers)