I. Community Interactions

A. Competition B. Predation

Community

association of populations that live & interact in the same place at the same time

Resource

Anything from the environment that meets needs of a particular species

Limiting resource: a resource in scarce supply

Habitat

location where a species lives its life

Ecological niche

Sum of a species' use of biotic and abiotic resources = organism's ecological role 

• An organism's habitat is its "address"  

• The niche is the organism's profession 

Fundamental niche

Niche potentially occupied by the species – broad

Realized niche 

Niche actually occupied by that species – more narrow 

Competition

• two or more individuals attempt to use the same resource 

  • Use by one decreases availability for others 

  • -/- interaction; both participants hurt (lose-lose situation) 

• Need same resource  

competition occurs between

1. Same species intraspecific 

2. Different species interspecific 

Importance of competition 

Considered most important determinant of: 

• # of species in community 

• Size of each population 

  • Requires overlapping niches to operate 

Complete overlapping 

• 2 species with identical ecological niches cannot coexist 

• Competing for same limiting resources  

• One wins, one loses 

partial overlapp

• Can coexist if there are non-overlapping parts of niches 

• Competition exclusion: selection in one competitor due to competition to use different set of resources 

  • Identical ecological niches competing same limiting resources cannot coexists 

  • So what happens when two species tries to occupy the same niche 

    • One can be extirpated (go logically extinct) 

      • Ie: paramecium 

        • Raised separately -> each pop reached K 

        • Grown together -> compete for same resources -> one went extinct 

        • Conclusion -> cannot coexist permanently 

Resource partitioning

Differentiation of niches that allows similar species to coexist

Lizards -> same resources except for perching area (habitats differ!) less direct competition for food

Or they can become better at using specific resources

---> character displacement

Predation

one species, the predator, kills and eats the prey, +/- interaction

Co evolution

results in evolutionary "arms race"

Predator – evolves better prey catching strategies

Prey -

Adaptations by predators for finding and capturing prey: 

Claws, fangs, venom, speed, camouflage & mimicry 

• Ex: thermoreception in rattlesnake 

Adaptations by prey for protection 

• Mechanical defense 

  • Aposematic coloration:  

    • Warning coloration: frogs store poison in skin 

• Chemical defense 

  • Cryptic coloration: Camouflage  

    • colors or markings that blend into physical surroundings 

Batesian mimicry:

A harmless species mimics a harmful one 

Müllerian mimicry

• 2 harmful species mimic each other (MORE of the same) 

• Often used in combination 

  • Example: herds and cryptic coloration in zebras 

Herbivory

• (plant predation) organism eats part of a plant or algae -- +/- nteraction 

• Plants cant escape, but have adaptations to | chance of being eaten 

  • Physical & chemical adaptations 

Symbiosis

intimate, long-term relationship

Parasitism: 

• parasite benefits, host harmed (rarely killed) 

  +/- interaction 

 

Mutualism

both benefit & depend on each other

+/+ interaction

Commensalism 

One species benefits and the other is neither harmed nor helped 

+/0 interaction 

• Ex: cattle egrets and African buffalo 

• Hawks and 18-wheelers