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Community Interactions. Communities. Habitat is the environment in which an organism lives. A population's niche is its role in the community How it uses the biotic and abiotic resources of its habitat. Community interactions.
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Communities • Habitat is the environment in which an organism lives. • A population's niche is its role in the community • How it uses the biotic and abiotic resources of its habitat
Community interactions • There are five main types of relationships among species within communities • Competition • Predation • Parasitism • Commensalism • Mutualism
Community interactions Interspecific competition occurs between two populations if they both require the same limited resource Intraspecific competition occurs between organisms of the same species.
Populations of two species cannot coexist in a community if their niches are nearly identical • The competitive exclusion principle Hightide Chthamalus Balanus Ocean Lowtide Figure 36.2
Competition between species with identical niches has two possible outcomes • One population will eventually eliminate the other • Natural selection may lead to resource partitioning (division)
Predation • Predation is an interaction where one species eats another • consumer = predator • food species = prey
Adaptations are driven by these relationships…COEVOLUTION! • Prey gain protection against predators through a variety of defense mechanisms • 1. Mechanical defenses, such as the quills of a porcupine
Animals are often brightly colored to warn predators • Example: the poison-arrow frog 2. Chemical defenses
Example: gray tree frog 3. Camouflage Figure 36.3C
4. Batesian mimicry occurs when a harmless species mimics a harmful one • mimicry can involve behavior • hawkmoth larva puffs up its head to mimic the head of a snake Figure 36.3D
How does predation affect the community? • Eliminates weaker individuals • keystone predator maintains diversity by reducing numbers of the strongest competitors in a community - Ex. sea star is a keystone predator Figure 36.4A
Predation by killer whales on sea otters, allowing sea urchins to overgraze on kelp • Sea otters represent the keystone species
Parasitism • Parasitism is a form of predation • Parasite, host • Not immediately lethal • Example: mistletoe on oaks, tapeworm in human intestine
Commensalism - one partner benefits and the other is unaffected • Examples • - Algae that grow on the shells of sea turtles • Barnacles that attach to whales • Birds that feed on insects flushed out of the grass by grazing cattle
Mutualism: both partners benefit • Examples: • - Nitrogen-fixing bacteria and legumes • Acacia trees and the ants of the genus Pseudomyrmex Figure 36.5B
Symbiosis • Any long term biological interaction is known as symbiosis or a symbiotic relationship • Some biologists only characterize mutualism and commensalism as symbiosis • Others include parasitism as well • Endosymbiosis is the theory that several eukaryotic organelles are the result of a symbiotic relationship between specialized prokaryotic cells.
Your task… • Community Interaction comic • Pick one of the types of interactions we discussed. (competition, predation, parasitism, mutualism, commensalism) • Draw a comic showing the interaction. • Comic must have at least three panels • No words are necessary, but it must clearly show the type of interaction • Do not write the type of interaction on your comic or your name • When it is finished, bring it to me for a number and further directions.
