Interactions in Communities

1. Predator/Prey: one organism kills another for food

Predator populations are affected by the size of the prey population, and vice versa.

Why do animals compete?

2. Competition occurs when two organisms fight for the same limited resource. –Intraspecific competition –Interspecific competition

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. Male big horn sheep butt heads violently in competition for mates.

7 3. Symbiosis 2 species living closely connected to one another2 species living closely connected to one another 1. Mutualism 2. Commensalism 3. Parasitism 2. Commensalism 3. Parasitism

8 Mutualism Both species benefit. Ex: CLOWNFISH AND SEA ANEMONE

9 Commensalism Ex: Whale and BarnacleEx: Whale and Barnacle One member benefits and the other is not helped or harmed. 30

Parasitism one organism benefits and the other is harmed

Types of Symbiosis InteractionSpecies ASpecies B MutualismBenefit (+) CommensalismBenefit (+)No Effect (0) ParasitismBenefit (+) Harm ( - )

More about Parasitism –One organism feeds on another organism called the host –Host is almost always larger than the parasite –Parasites often live on or in host –Host usually harmed but not killed

Riverblindness: Parasitic worm transmitted by blackfly

Isopod parasitizing a fish tongue

IV. Herbivory  Herbivores don’t often kills plants  Plant defenses  thorns/spines  chemical compounds that taste bad, kill, or make herbivores sick

5. Coevolution: back and forth evolutionary adjustment between two species that interact

What is the difference between a habitat and a niche? A habitat is the area in which an organism lives. (where) A niche includes the role that the organism plays in the environment. (how)

Are the following part of the habitat or niche? a) Lions eat zebras b) Lions hunt in groups c) Lions live in the savanna d) Lions live near a watering hole e) Lions are most active just after dusk f) Lions reproduce starting at age 4

Fundamental niche : entire range of conditions where an organism could survive. Realized niche: the actual niche that a species occupies.

Competition between two species of barnacles.

growth rate Location in intertidal zone lowhighmiddle The realized niche of each barnacle Balanus realized niche Chthamalus realized niche Balanus and Chthamalus

growth rate Location in intertidal zone lowhighmiddle Chthamalus alone Balanus alone The fundamental niche of each barnacle. Balanus fundamental niche Chthamalus fundamental niche

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?

predict the outcome of interspecific competition Competitive exclusion occurs when one species eliminates another through competition.. Two species of Paramecia P. caudatum P. aurelia Gause (1934)

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.