Ecology slides - (Lecture 10)

Competition

• Competition occurs when individuals (of the same or different species) share the use of a resource that limits the growth, survival, or reproduction of each

  • LIMITED RESOURCE*

• Intraspecific - = between members of a single species

• Interspecific - = between members of different species

• Is Negative - Negative (-/-)

  • There may be a “winner,” but in reality both lose or give up something (ex. energy, time) as a result of the need to compete

  • Competition generates a negative effect on the organism relative to the organism on its own (i.e., if it had unlimited access) even if it “wins”

Exploitation competition

• Organisms compete through the consumption of a limited resource (food, space, breeding grounds)

• An INDIRECT form of competition

  • One organism's use of the resource reduces its availability for others

  • Ex: Pollinator A takes pollen, reducing the supply for Pollinator B

Interference competition

• Individuals interact DIRECTLY with one another (fighting, aggression) to obtain a limited resource

Big picture lab hypothesis

Species interactions affect the growth of plants, either positively or negatively

Null hypothesis

• We can make the counter-claim that interactions cause no effects on growth

• We cannot prove or disprove the null hypothesis absolutely, but we can decide to discard it if it is not significantly supported by our results, and then we can accept an alternative hypothesis

“Species interactions have no effect on growth.”

• That is, no differences exist. This does NOT mean that no interactions occur; it just means that the effects within and between species cannot be distinguished.

Specific / Alternative hypothesis

The average length and weight of species A is significantly different in mixtures than in monoculture

de Wit Replacement Series

• Experimental design technique to examine resource use and productivity between competing species

• Interspecific vs. Intraspecific competition

• Monocultures paired with mixed cultures

Principle of competitive exclusion

• Belief that no two species can coexist utilizing the exact same resource

Theory of limiting similarity

• Species that are too similar cannot coexist

Species may not be excluded by competition if…

1. Intraspecific competition (competition between members of a single species) is more severe than interspecific competition (competition between members of different species)

2. Other factors (i.e., predators or weather) negatively affect the superior competitor

   1. Such factors might allow more species to coexist than would be expected based on competition alone

Commensalism

• One species gains from an interaction while another neither gains nor loses

Facultative mutualism

• Both species gain but neither is completely dependent upon one another for survival

Obligate mutualism

• Each species requires the other to survive

We assume reduction in plant size reflects…

• Reduction in fitness

  ---

• Superior competitor should be taller and more robust in the mixture than in the equal density monoculture

• Both species may be positively affected when the two species are grown together in a mixture, or one species may be unaffected while the second species grows better than it would in a monoculture.

Underyielding

• If competition adversely affects one or both species, total yield may be lower in a mixture than in a monoculture

Niche partitioning

• Total yield may be greater in a mixture, and this could reflect either positive interactions between species

Over-yielding

• Interspecific competition is less severe than intraspecific competition because the two species use different resources

• Different crop species are grown together may lead to increased food production.

Pseudo-replication

• All the individuals are exposed to the same experimental conditions, but this is not replication of those experimental conditions

t-test

• Produces a p-value which gives you a basis of comparison for the difference between two means

• Significant changes (p < 0.05)