Section 2 – Species Interactions

The Niche and CompetitionAn organism’s niche is affected by both its

tolerance and competitive interactionsHabitat: general place it livesNiche: an organism’s habitat, resource use, and

fundamental role in a communityHabitatFood SourceHow/When it Reproduces Interactions with other Organisms

ToleranceTolerance: the ability to survive and reproduce

under changing environmental conditionsSpecialists: very restricted tolerance ranges

Ex. Panda BearsGeneralists: wide tolerance ranges

Ex. RatsBOTH may not be able to adapt when conditions

change.

CompetitionMultiple organisms seek the same limited

resource.Food, Light, Water, Space

Direct Competition: physically, for territoryIndirect Competition: flowers, for pollinatorsIntraspecific Competition: competitive

interactions among members of the same species

Interspecific Competition: competitive interactions among members of two or more different species

Competitive ExclusionCompetitive Exclusion: if one species is a very

effective competitor, it may exclude another species from resource use entirely

Mussel and Clam Populations in Lake St. ClairLake St. Clair connects Lake Erie and Huron20 native mussel speciesBy 1997, they were all goneWhen Zebra Mussels attack, shellfish cannot open

their shells – they eventually suffocate or starve

Fundamental and Realized Niche

Usually, neither competing species fully excludes the other.

Instead, competing species tend to adjust to each other, minimizing competition.Changing BehaviorUsing only a portion of the resources they are

capable of usingFundamental Niche: full niche of a speciesRealized Niche: a niche restricted by competition

Resource PartitioningResource Partitioning: a process that allows

different species to share common resources If 2 bird species eat the same type of seeds

1 specializes in eating larger seeds1 specializes in eating smaller seeds

OR1 is active in the morning1 is active in the evening

Character DisplacementCharacter Displacement: resource

partitioning can lead to the evolution of physical characteristics among the competing species that reflect their specialized role in the environment

Darwin’s Finches – Galapagos IslandsBirds specialize in eating small seeds = small billsBirds specialize in eating large seeds = large bills

Predation, Parasitism, and Herbivory

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

“-/-” = negative effect on both organismsCompetition

“+/-” = beneficial for one participant, but harmful to the otherPredationParasitismHerbivory

Predation and Population Cycles

Predation: the process by which individuals of one species (the predators) hunt, capture, and feed on individuals of another species (the prey)

Population Cycles INCREASE in Prey Population INCREASE in Predator PopulationDECREASE in Prey PopulationDECREASE in Predator Populationand Repeat

Predation and EvolutionNatural Selection – evolution of better predators

Predators skilled at capturing prey – more successful

Prey – evolution of Defense MechanismsStrong selective pressure – IMMEDIATE DEATH

Coevolution and Evolutionary “Arms Race”

Coevolution: the process by which two species evolve in response to changes in each otherNewt 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 and stronger “weapons” in response to the other

ALL SPECIES ADAPT TO BETTER SURVIVE AND REPRODUCE IN THEIR ENVIRONMENT.

ParasitismParasitism: a relationship between two

organisms from different species in which one organism (the parasite) depends on the other (the host) for nourishment or some other benefitTapewormsTicks

Symbiosis: a long term and physically close relationship between two organisms from different species in which at least one organism benefitsCommensalismMutualismParasitism

HerbivoryHerbivory: the act of feeding on a plantInsects – most common type of herbivoreHervibory usually doesn’t kill the plant

Affects growth and populationNatural Selection has given plants defenses:

Produce Toxic/Distasteful ChemicalsThorns, Spines or Irritating Hairs

In response, herbivores evolve ways to overcome.

MutualismMutualism: (+/+) a relationship between two

organisms from different species in which both organisms benefit

Plant Roots + Fungi = MycorrhizaePlant provides energy, fungus assists in nutrient

absorptionPollination

Pollinators enable sexual reproduction in plantsPollinators receive nectar as a reward

CommensalismCommensalism: (+/0) a relationship between

two organisms from different species in which one benefits and the other is unaffected

Example:Palo Verde trees in the Sonoran Desert

Trees create shade and leaf litter that allow the soil to hold moisture

Soil becomes cooler with more moisture, making it easier for young plants to germinate and grow

Other desert plants grow beneath the “nurse” tree

Section 3

Section 4