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 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. Resources include food, water, nesting sites Plants compete for sunlight, water, soil nutrients, space

The competitive exclusion principle Populations of two species cannot coexist in a community if their niches are nearly identical High tide Chthamalus Barnacle expt shows two outcomes possible: Remove blue barnacles, brown ones grow down and cover entire rock. Ther4, blues outcompeting brown for low space on rock. Remove brown ones, blue ones do NOT grow up. Ther4, resource (space on rock) has been divided and only brown are adapted to drier upper zones of rock. Balanus Ocean Low tide 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 Predation is severe form of natural selection. Leads to many diverse adaptations designed to escape predation and to make more successful predators. Explains why the most successful parasite is not a fast killer. Examples: mistletoe on oaks, dodder on phosyn plants, fungal hyphae on nematodes

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

2. Chemical defenses Animals are often brightly colored to warn predators Example: the poison-arrow frog Many interesting chemicals from amphibs. Antibiotic megainan, anithestic.

Physical/Chemical Combat

3. Camouflage Example: gray tree frog Figure 36.3C

Camouflage

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

Trickery/Mimicry

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.