Lecture 6: Competition and Facilitation

Forms of species interactions

• Predation

• Parasitism

• Mutualism (symbiosis)

• Commensalism (facilitation)

• Competition

What are the different types of facilitation relationships?

1. Obligatory relationship → dependent species completely relies on the other for survival

2. Facultative relationship → dependent species does NOT rely on the for survival.

Types of competition

1. Intraspecific competition → between individuals of the same species for a limited resource

2. Interspecific competition → between individuals of different species for a limited resource

i. Exploitation → use of resource by one individual makes that resource less available for others

• Consumptive (all eaten) vs. pre-emptive (actively taking up the resource)

ii. Interference competition → direct interaction of individualsthrough various types of behaviours. Eg. territoriality.

Conditions for competition

1. Must have an effect on fitness (reproduction, growth, or survival)

2. Resources in short supply for species to affect each other

3. Influence amount of resources available or species ability to obtain the resource

4. Can have both exploitation and interference competition

5. Can cause competitive exclusion

Competitive Exclusion and Hypothesis

species can coexist if adaptations arise to effectively partition resources

“Two species cannot live in the same niche, and if they try to, one will be excluded”

Habitat Selection

• Theory of optimal foraging → resources not limiting, species should concentrate their feeding on the best type of food or habitat

• Theory of habitat selection → resources are limiting, species should contract their niches as a result of interspecific competition

How do we measure competition?

1. Theoretical/graphical models → coefficient of competition (d), Lotka-Volterra equations

2. Experiments → manipulative experiments, using deer mouse vs. voles.

• Removal Experiment → actively removing one competitor from plot or area and seeing how the other species reacts

• Press Experiment → presense/absence experiment, long-term areas (one abundant, one lacking), mainly observing

Theoretical/ graphical models

Outcomes/interpretation of the experiments

Outcomes/interpretations:

• Indirect competition → when one species is competing with another. An intermediate species

• Apparent competition → Changes of population in species 1 affect population of species 2 by influencing predator population