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5-1 How Do Species Interact?
• The interactions between species in an ecosystem affect:• the resource use in an ecosystem and• population sizes of the species in an ecosystem.
Five types of Interactions• Interspecific Competition
• Predation
• Parasitism
• Mutualism
• Commensalism
Five types of Interactions
• Interspecific Competition• Predation
• Parasitism
• Mutualism
• Commensalism
Interspecific Competition• Species compete for limited resources like• Water• Food/Nutrients• Light• Habitat/Space
Five types of Interactions• Interspecific Competition
•Predation• Parasitism
• Mutualism
• Commensalism
Predation• Predators may capture prey by
1. Walking2. Swimming3. Flying4. Pursuit and ambush5. Camouflage6. Chemical warfare
Avoiding Predation• Prey may avoid capture by
1. Run, swim, fly2. Protection: shells, bark, thorns3. Camouflage4. Chemical warfare5. Warning coloration6. Mimicry7. Deceptive looks8. Deceptive behavior
Predator and Prey Interactions Can Drive Each Other’s Evolution
• Intense natural selection pressures between predator and prey populations
• Coevolution• Interact over a long period of time• Example - Bats and moths: echolocation of bats and
sensitive hearing of moths
Five types of Interactions• Interspecific Competition
• Predation
•Parasitism• Mutualism
• Commensalism
Parasitism• Parasitism – species feed off other species or live on
or in them
• Parasite is usually much smaller than the host
• Parasite rarely kills the host
• Parasite-host interaction may lead to coevolution
Five types of Interactions• Interspecific Competition
• Predation
• Parasitism
•Mutualism• Commensalism
Mutualism• Mutualism – both species benefit
• Nutrition and protection relationship• Clownfish and anemone
• Gut inhabitant mutualism• Bacteria in our intestines
• Not cooperation: it’s mutual exploitation
Five types of Interactions• Interspecific Competition
• Predation
• Parasitism
• Mutualism
•Commensalism
Commensalism• Commensalism • One species benefits, one not
harmed
• Bromeliad (air plant) in tree
• Birds nesting in trees
What Limits the Growth of Populations?
• No population can continue to grow indefinitely because of
• limitations on resources and
• competition among species for those resources.
Most Populations Live Together in Clumps or Patches
• Population: group of interbreeding individuals of the same species
• Population distribution 1. Clumping (ex. Flocks of birds)2. Uniform dispersion3. Random dispersion
Most Populations Live Together in Clumps or Patches
• Why clumping?1. Species cluster where resources are available2. Clumps have a better chance of finding resources3. Protects some animals from predators4. Packs allow some to get prey
Population Growth and Decline• Population size governed by• Births• Deaths• Immigration• Emigration
• Population change = (births + immigration) – (deaths + emigration)
Population Growth and Decline• Age structure• Pre-reproductive age “kids”• Reproductive age “adults”• Post-reproductive age “elderly”
• Sizes of each group will drive the growth or decline of population in the future
• Example: A population with 70% of kids will most likely have a population growth spike as those kids become adults
Some Factors Can Limit Population Size
• Range of tolerance• Variations in physical and chemical environment that
impact a population’s ability to survive and reproduce• Temperature, Rain, Nutrients…
Some Factors Can Limit Population Size
• Limiting factor principle• Too much or too little of any physical or chemical
factor can limit or prevent growth of a population, even if all other factors are at or near the optimal range of tolerance
“Population can only grow as much as its scarcest resource!”
No Population Can Grow Indefinitely: J-Curves and S-Curves
• Size of populations controlled by limiting factors:• Light• Water• Space• Nutrients• Exposure to too many competitors, predators or
infectious diseases
No Population Can Grow Indefinitely: J-Curves and S-Curves
• Environmental resistance • All factors that act to limit the growth of a population
• Carrying capacity (K)• Maximum population a given habitat can sustain• Calculated by looking at the limiting factors
No Population Can Grow Indefinitely: J-Curves and S-Curves
• Exponential growth• Starts slowly, then accelerates to carrying capacity
when meets environmental resistance
• Known as “J” curve due to shape• No limiting factors yet
No Population Can Grow Indefinitely: J-Curves and S-Curves (3)
• Logistic growth• Decreased population growth rate as population size
reaches carrying capacity
Yellow line = calculated theoretical carrying capacity
Green = actual population
When a Population Exceeds Its Habitat’s Carrying Capacity, Its Population Can Crash• A population can “briefly” exceed (overshoot) the
area’s carrying capacity due to:
• Reproductive time lag
• If it greatly overshoots the carrying capacity, the result is:
• Population crash and • Damage may reduce area’s new carrying capacity
Species Have Different Reproductive Patterns
• Some species
• Many, usually small, offspring• Little or no parental care• Massive deaths of offspring• Ex. Insects, bacteria, algae
Species Have Different Reproductive Patterns
• Other species
• Reproduce later in life• Small number of offspring with long life spans• Young offspring grow inside mother• Long time to maturity• Protected by parents, and potentially groups• Ex. Humans, Elephants
Under Some Circumstances Population Density Affects Population Size
• Density-dependent population controls• Predation• Parasitism• Infectious disease• Competition for resources
Several Different Types of Population Change Occur in Nature
• Stable
• Irruptive• Population surge, followed by crash
• Cyclic fluctuations, boom-and-bust cycles• Top-down population regulation• Bottom-up population regulation
• Irregular
Humans Are Not Exempt from Nature’s Population Controls
• Ireland• Potato crop in 1845
• Bubonic plague• Fourteenth century
• AIDS• Global epidemic
5-3 How Do Communities and Ecosystems Respond to Changing Environmental
Conditions?• Concept 5-3 The structure and species composition
of communities and ecosystems change in response to changing environmental conditions through a process called ecological succession.
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 or no bottom sediment
in an aquatic system
• Takes hundreds to thousands of years to build up soils/sediments to provide necessary nutrients
• Ex. – Bare rock after a glacier retreats
Some Ecosystems Do Not Have to Start from Scratch
• Secondary Succession• Some soil remains in a terrestrial system or bottom
sediment remains in an aquatic system
• Ecosystem has been• Disturbed• Removed• Destroyed
• Ex – old farmland, forest fires
Some Ecosystems Do Not Have to Start from Scratch: Secondary Succession (2)
• Primary and secondary succession• Tend to increase biodiversity• Increase species richness and interactions among species
• Primary and secondary succession can be interrupted by• Fires• Hurricanes• Clear-cutting of forests• Plowing of grasslands• Invasion by nonnative species
Science Focus: How Do Species Replace One Another in Ecological Succession?
• Facilitation
• Inhibition
• Tolerance
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
• Some systems have one property, but not the other: tropical rainforests
Three Big Ideas
1. Certain interactions among species affect their use of resources and their population sizes.
2. There are always limits to population growth in nature.
3. Changes in environmental conditions cause communities and ecosystems to gradually alter their species composition and population sizes (ecological succession).