Download Chapter 5 notes - Duluth High School

Biodiversity,
Species
Interactions,
and Population
Control
Chapter 5
How Do Species Interact?
Five types of interactions between
species that share limited resources
– Interspecific Competition
– Predation
– Parasitism
– Mutualism
– Commensalism
They have an impact on resources use
and population size of species in an
ecosystem. (sustainability!!)
Most Species Compete with One
Another for Certain Resources
• Competition-for limited resources
• Most competition involves one species
becoming more efficient at obtaining
resources than another species.
Greater the overlap
=more competition
Competitive Exclusion Principle
Gause’s Law (Gause’s Principle)
• Some species share their niche, but no two
species can occupy exactly the same
niche for very long.
• This causes both species to have limited
resources.
• One (or both) species must change their
niche (if possible)
P. Caudatum are
outcompeted, they
die.
Most Consumer Species Feed on Live
Organisms of Other Species
• Predators may
capture prey by
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Walking
Swimming
Flying
Pursuit and ambush
Camouflage
Chemical warfare
• Prey may avoid capture
by
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Camouflage
Chemical warfare
Warning coloration
Mimicry
Deceptive looks
Deceptive behavior
Some Ways Prey Species Avoid
Their Predators
Predator and Prey Species Can
Drive Each Other’s Evolution
• Predator and prey populations exert intense
natural selection pressures on one another
• Prey develop traits that make them harder to
catch...predators face selection pressures that
favor traits to catch prey
Coevolution: Populations of two species
interact and exert selective pressure forcing
species to adapt. EX: Caribbean crab/snail and
bats/moths
• Remember, coevolution is an example of
populations responding to changes in
environmental conditions.
• Species cannot design strategies to
increase their chances of survival.
»
Some Species Feed off Other Species
by Living on or in Them
• PARASITISM
• EX: tapeworms, mosquitoes,
mistletoe plants,
sea lampreys, ticks,
and cowbirds
• Parasite-host interaction
may lead to coevolution- nature’s way of
controlling populations and biodiversity
Parasitism
Tree with Parasitic Mistletoe
Trout with Blood-Sucking
Sea Lampreys
In Some Interactions, Both Species
Benefit
• Mutualism
• Nutrition and protection relationship
• Gut inhabitant mutualism
In Some Interactions, One Species
Benefits and the Other Is Not Harmed
• Commensalism
• Epiphytes(take no nutrients
from the tree EX: mosses, ferns,
orchids)
• Birds nesting in trees
Bromeliad on Tree
How Can Natural Selection Reduce
Competition between Species?
• Resource partitioning
• Reduce niche overlap
• Use shared resources
at different
– Times
– Places
– Ways
Sharing the Wealth:
Resource Partitioning
Specialist
Species of
Honeycreepers
What Limits the Growth of Populations?
• Populations differ in
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Distribution
Numbers
Age structure
Density
• Population dynamics: how populations change in
response to changes in environmental conditions.
• Changes in population characteristics due to:
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Temperature
Presence of disease organisms or harmful chemicals
Resource availability
Arrival or disappearance of competing species
Most Populations Live Together in
Clumps or Patches
• Look at how populations are distributed or
dispersed
– Clumping
– Uniform dispersion
– Random dispersion-pretty rare
Dispersion Patterns
• Random
(smaller
plants)
• Clumping
(flocks)
• Uniform
(trees)
Why clumping?
– Species tend to cluster where resources
are available
– Groups have a better chance of finding
clumped resources
– Protects some animals from predators
– Packs allow some to get prey
– Temporary groups for mating and caring
for young
Populations
• Can Grow, Shrink, or Remain Stable
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Births
Deaths
Immigration
emigration
• Age structure: proportion of individuals at
various ages
– Pre-reproductive age
– Reproductive age
– Post-reproductive age
No Population Can Grow Indefinitely
• Biotic potential -capacity for population growth
under ideal conditions
– Low…Large animals like elephants
– High… Small organisms like insects
• Intrinsic rate of increase (r)- population growth with
unlimited resources
• Individuals in populations with high r
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Reproduce early in life
Have short generation times
Can reproduce many times
Have many offspring each time they reproduce
Limiting Factors
• Size of populations limited by
– Light
– Water
– Space
– Nutrients
– Exposure to too many competitors,
predators or infectious diseases
There are always limits to population
growth in nature….Sustainability!!!
• Environmental resistance: combination
of all factors that limit the growth of a
population
• Carrying capacity (K)= Biotic Potential
+ Environmental resistance
• Exponential growth-J Curve
• Logistic growth-S Curve
Limiting factors!!
When a Population Exceeds Its Habitat’s
Carrying Capacity, Its Population Can Crash
• Carrying capacity: not fixed…can change during
seasons or years
• Reproductive time lag may lead to overshoot
– Dieback (crash)-time needed for birth rate to
fall and death rate to rise in response to
resource overconsumption
• Damage may reduce area’s carrying capacity.
Ex overgrazing
Exponential Growth, Overshoot, and
Population Crash of a Reindeer
Moose and Wolf Population
• http://vicksta.com/wolf%20and%20moose
%20graph7.html
Different Reproductive Patterns
• r-Selected species, opportunists
– Capacity for high rate of population
increase
– ex. Small, lots of offspring, no parental care
• K-selected species, competitors
– Reproduce later in life, small # of offspring,
long life span
– Large mammals, birds of prey
Positions of r- and K-Selected Species on the
S-Shaped Population Growth Curve
GROSS!!!!
Genetic Diversity Can Affect the Size
of Small Isolated Populations
• Founder effect -colonize new habitat, limits genetic diversity
• Demographic bottleneck- only a few survive a catastrophe
ex. fire
• Genetic drift- certain individual breeding more than others
and genes dominate gene pool
• Inbreeding- increases frequency of defective gens
Minimum viable population size- # of individuals needed for
long term survival of the population
Population Density Can Affect
Population Size
• Density-dependent population controls
– Predation
– Parasitism
– Infectious disease
– Competition for resources
• Density-Independent
Patterns of Variation in
Population Size
• Stable- slight fluctuations in carrying capacity
• Irruptive- High peak then crash to stable
lower level (ex: seasonal changes-die in
winter)
• Cyclic fluctuations (boom-and-bust cycles)
regular cycles of population
– Top-down population regulation
– Bottom-up population regulation
• Irregular – severe weather?
Cyclic fluctuations for the
Snowshoe Hare and Canada Lynx
Humans Are Not Exempt from
Nature’s Population Controls
• Ireland
– Potato crop in 1845, 1 million people died, 3 million
migrated
• Bubonic plague (Cats of Borneo!!)
– Fourteenth century, 25 million killed
• AIDS
– Global epidemic, 25 million killed between 1981 and
2007
Counting Populations
• See interactive of mark and recapture of
butterflies (Miller ppt)
• Random sampling
Communities and Ecosystems Change over
Time: Ecological Succession
• Natural ecological restoration
– Primary succession
– Secondary succession
Some Ecosystems Start from
Scratch: Primary Succession
• No soil in a terrestrial system
• No bottom sediment in an aquatic system
• Early successional plant species, pioneer
• Midsuccessional plant species
• Late successional plant species
Primary
Ecological
Succession
Secondary Succession
• Some soil remains in a terrestrial system
• Some bottom sediment remains in an
aquatic system
• Ecosystem has been
– Disturbed
– Removed
– Destroyed
Some Ecosystems Do Not Have to Start
from Scratch: Secondary Succession
• Primary and secondary succession
– Tend to increase biodiversity
– Increase species richness and interactions among
species
• Primary and secondary succession can be
interrupted by
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Fires
Hurricanes
Clear-cutting of forests
Plowing of grasslands
Invasion by nonnative species
Natural
Ecological
Restoration of
Disturbed
Land
Secondary Succession
Succession Doesn’t Follow a
Predictable Path
• Traditional view
– Balance of nature and a climax community
• Current view
– Ever-changing mosaic of patches of
vegetation
– Mature late-successional ecosystems
• State of continual disturbance and change
Living Systems Are Sustained
through Constant Change
• Inertia, persistence
– Ability of a living system to survive moderate
disturbances
• Resilience
– Ability of a living system to be restored through
secondary succession after a moderate disturbance
• Tipping point
Core Case Study: Southern Sea Otters:
Are They Back from the Brink of
Extinction?
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Habitat
Hunted: early 1900s
Partial recovery
Why care about sea otters?
– Ethics
– Keystone species
– Tourism dollars
Southern Sea Otter
Why Are Protected Sea Otters Making
a Slow Comeback?
• Low biotic potential
• Prey for orcas
• Cat parasites
• Thorny-headed worms
• Toxic algae blooms
• PCBs and other toxins
• Oil spills
Population Size of Southern Sea Otters
Off the Coast of So. California (U.S.)
Video: Kelp forest (Channel Islands)
Video: Otter feeding