Interactions in Ecosystems Chapter 14

Competition occurs when two organisms fight for the same limited resource. Intraspecific competition Interspecific competition What is the difference between these?

Interspecific or intraspecific? Two red squirrels race up a tree to find a hidden pile of nuts. A hyena chases off a vulture to feast on an antelope carcass. Shrubs and grasses on the forest floor compete for sunlight. Brown bears hunting for fish on a river’s edge fight over space.

Fundamental niche : entire range of conditions an organism is potentially able to occupy. Realized niche the part of the fundamental niche that a species occupies.

Competition between two species of barnacles. Is this the realized niche or fundamental niche?

Chthamalus realized niche How can we determine the realized niche of each barnacle? Observe where they grow when allowed to compete. Balanus and Chthamalus growth rate Balanus realized niche Chthamalus realized niche low middle high Location in intertidal zone

Chthamalus fundamental niche How can we determine the fundamental niche of each barnacle? Removal experiments – remove each species and see where the other grows Balanus alone Balanus fundamental niche growth rate Chthamalus alone Chthamalus fundamental niche low middle high Location in intertidal zone

What are the fundamental and realized niches for each species? Streams with only Planaria species A Streams with only Planaria species B Streams with both Planaria species What are the fundamental and realized niches for each species?

interspecific competition Competitive exclusion keeps two species from occupying the same niche. Two species of Paramecia predict the outcome of interspecific competition P. aurelia P. caudatum Gause (1934)

Types of Interactions Interaction Species A Species B Mutualism Benefit (+) Commensalism No Effect (0) Parasitism Benefit (+) Harm (-) Predation Competition Amensalism No Effect (0)

What is symbiosis? How are predators of animals different from predators of plants? What is the difference between ectoparasite and an endoparasite?

A black rhinoceros grazes on the African plains A black rhinoceros grazes on the African plains. As it forages, the rhino disturbs multitudes of insects in the grass, crushing some and inadvertently eating others. Birds known as egrets forage on the ground near the rhino, eating insects flushed out by the hooves. Other birds known as oxpeckers eat ticks from the skin of the rhino.