Chapter 5

Section 2 – Species Interactions

The Niche and Competition

An organism’s niche is affected by both its toleranceand competitive interactions

Habitat: general place it lives

Niche: an organism’s habitat, resource use, andfundamental role in a community

Habitat

Food Source

How/When it Reproduces

Interactions with other Organisms

Tolerance

Tolerance: the ability to survive and reproduce underchanging environmental conditions

Specialists: very restricted tolerance ranges

Ex. Panda Bears

Generalists: wide tolerance ranges

Ex. Rats

BOTH may not be able to adapt when conditionschange.

Competition

Multiple organisms seek the same limited resource.

Food, Light, Water, Space

Direct Competition: physically, for territory

Indirect Competition: flowers, for pollinators

Intraspecific Competition: competitive interactionsamong members of the same species

Interspecific Competition: competitive interactionsamong members of two or more different species

Competitive Exclusion

Competitive Exclusion: if one species is a very effectivecompetitor, it may exclude another species fromresource use entirely

Mussel and Clam Populations in Lake St. Clair

Lake St. Clair connects Lake Erie and Huron

20 native mussel species

By 1997, they were all gone

When Zebra Mussels attack, shellfish cannot open theirshells – they eventually suffocate or starve

Fundamental and RealizedNiche

Usually, neither competing species fully excludes theother.

Instead, competing species tend to adjust to eachother, minimizing competition.

Changing Behavior

Using only a portion of the resources they are capable ofusing

Fundamental Niche: full niche of a species

Realized Niche: a niche restricted by competition

Resource Partitioning

Resource Partitioning: a process that allows differentspecies to share common resources

If 2 bird species eat the same type of seeds

1 specializes in eating larger seeds

1 specializes in eating smaller seeds

OR

1 is active in the morning

1 is active in the evening

Character Displacement

Character Displacement: resource partitioning canlead to the evolution of physical characteristics amongthe competing species that reflect their specialized rolein the environment

Darwin’s Finches – Galapagos Islands

Birds specialize in eating small seeds = small bills

Birds specialize in eating large seeds = large bills

Predation, Parasitism, andHerbivory

“0” = relationship in which there is no effect, or theeffect is neutral

“-/-” = negative effect on both organisms

Competition

“+/-” = beneficial for one participant, but harmful to theother

Predation

Parasitism

Herbivory

Predation and Population Cycles

Predation: the process by which individuals of onespecies (the predators) hunt, capture, and feed onindividuals of another species (the prey)

Population Cycles

INCREASE in Prey Population

INCREASE in Predator Population

DECREASE in Prey Population

DECREASE in Predator Population

and Repeat

Predation and Evolution

Natural Selection – evolution of better predators

Predators skilled at capturing prey – more successful

Prey – evolution of Defense Mechanisms

Strong selective pressure – IMMEDIATE DEATH

Coevolution and Evolutionary“Arms Race”

Coevolution: the process by which two species evolvein response to changes in each other

Newt develops toxins that kills predators

In response, predators evolve immunity to the toxins

In response, newt evolve stronger toxins

Arms Race: each species develops stronger andstronger “weapons” in response to the other

ALL SPECIES ADAPT TO BETTER SURVIVE ANDREPRODUCE IN THEIR ENVIRONMENT.

Parasitism

Parasitism: a relationship between two organismsfrom different species in which one organism (theparasite) depends on the other (the host) fornourishment or some other benefit

Tapeworms

Ticks

Symbiosis: a long term and physically closerelationship between two organisms from differentspecies in which at least one organism benefits

Commensalism

Mutualism

Parasitism