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Biodiversity, Species Interactions, and Population
ControlCh. 5
Miller & Spoolman, 16th ed.
Your Goal for this lecture
To be able to explain how interactions between organisms help drive natural selection
Big Idea # 1
Species interactions affect the resource use and sizes of other populations in an area
Species Interactions
There are 3 main types of species interactions:CompetitionPredationSymbiosis
Importance of Species InteractionsThese types of interactions have a significant
impact on each population involvedThese interactions are agents of natural
selection - they influence who survives and is able to reproduce
CompetitionCompetition for
resources2 types:
Interspecific - 2 different species compete for the resource
Intraspecific - members of the same species compete for the resource
Brainstorm
Make a list of resources that species might compete for
Morning Buddies
Intraspecific - often fighting involved to “win” the resourceCan be very intense
Interspecific - usually no fighting, just better at getting it Less intense since species have slightly
different niches
Competitive Exclusion PrincipleNo two species can
occupy exactly the same niche because competition for resources would be too intense
One species will be better at getting the resources
The other species must leave, adapt, or die
Solving the Problem
Resource PartitioningTwo species evolve
adaptations that allow them to use the same resource in different ways, at different times, or in different places in order to minimize competition
How about humans? Are humans subject to the Principle of
Competitive Exclusion? Defend your answer Yes! Our use of resources directly competes with other
organisms, and forces them to leave the area or go extinct in that area (adaptation not possible since we change environment so quickly)
Kicked out of class buddies
Predation All consumers feed on
other organisms Herbivores feed on live
plantsCarnivores feed on
animalsOmnivores feed on both
Predator-Prey RelationshipsChanges in 1 population leads to changes in
other populations
How do changes in population size affect ecosystems?
A change in the size of one population will affect the size of other populations
J-curveExponential Pattern of Growth
Intrinsic Pattern of GrowthS-curve
Intrinsic Pattern of Growth
• The size of the predator population affects the prey population and vice versa
• Who is controlling the rises and falls of these 2 populations? The Hare or the Lynx?
What is an What is an adaptation or adaptation or strategy that would strategy that would be helpful to a be helpful to a predator?predator?
What is an What is an adaptation or adaptation or strategy that would strategy that would be helpful to a prey be helpful to a prey organism?organism?
Song buddies
Structural advantages Natural Weapons - Fangs, claws Flexible bodies Larger Size
Predator Strategies
Predator StrategiesAmbush-
Stalk a victim • VenomGape & Suck (fish)Keen
eyesight
Predator StrategiesSPEED & CUNNING
• More intelligent than prey
• Run faster than prey• Hunt in packs
Predator Strategies
Camouflage Sit in plain site
Predator Strategies
Chemical warfarevenom
Prey Strategies
Defense Techniques
Inflate
Flee
Fight Back
Stab
Poison
Prey StrategiesStructural advantages
Hard Body Coverings Thorns or SpinesBreak away body partsNatural Weapons
Chemical WarfareBlinding inkPoisonOffensive
Smells and Tastes
Prey Strategies
Camouflage Color ChangeCounter-shadingDisruptive PatternsMimicry
Prey Strategies
Mimicry• Mostly a prey technique
Optical and sonic illusions LOOKS like a predator:
• School of fish; false eyes; frilled neck and inflation
Batesian mimicry- a harmless animal mimics a harmful or unpalatable one
Mullerian mimicy-two or more unpalatable species resemble each other
2 rules about coloration
Small + beautiful = poisonousBeautiful + easy to catch = deadly
Food for thought
Think of a local speciesWhat adaptations does it have
to catch prey or avoid being eaten?
food buddies
Predator Prey relationships
Predator benefitsPrey does not…or does it?Predators
strengthen the population in the long term by preying on the weaker individuals
CoevolutionWhen two species have lived together and
adapted to each other for a long time such that changes in the gene pool of one species leads to changes in the gene pool of the other species
Symbiosis
Symbiosis – when different organism live in close, physical contact with one anotherParasitismMutualismCommensalism
Parasitism
A form of symbiosis in which one organism benefits and the other is hurtLeeches, fleas,
ticks, tapeworms, etc
Parasitism
Simple parasites - fleas, ticks, leechesMove from host to hostOr have only one host their
whole life
Complex parasites - plasmodium (malaria), toxoplasmosisMultiple hostsMultiple life stages
Parasitism and Coevolution
Example: malariaParasite infects red blood cellsRBCs are swept into the spleen every few days
and destroyedParasite evolved to latch onto blood vessel with
a sticky proteinBody recognizes protein as foreign and will
attack itParasite evolves to have many different types
of proteins, so body can never catch up
MutualismA form of
symbiosis in which both organisms benefit
Commensalism
A form of symbiosis in which one organism benefits and the other is not harmed or helped
Example: sharks and remoras
Summarize
Why are population interactions a driving force for natural selection?
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