Transcript Population Growth and Controls

Population Controls and
Community Succession
• How biotic potential and environmental
resistance control population dynamics.
• The mechanisms of population equilibrium.
• Problems with introduced species
• How disturbance initiates community
succession and leads to enhanced
biodiversity.
• The resilience of ecosystems subject to
disturbance.
Population Equilibrium
Births
Biotic
Potential
Deaths
Environmental
Resistance
A balance between births and deaths.
What if a natural catastrophe suddenly occurred?
Population Growth Curves
No natural enemies.
Maximum level
supported without
degradation =
After the J-crash?
• J repeat
• Establish S
• Local Extinction
Population Dynamics
• Biotic potential: reproductive capacity;
factors contributing to an increase in
population size and/or distribution.
– Reproductive rate
– Migration or dispersal
– Defenses
– Coping strategies
– Reproductive strategy
Reproductive strategies:
Many offspring with
low parental care
Few offspring with
high parental care
Population Growth Control
• Environmental resistance: combination of biotic
and abiotic factors that limit population increase.
– Density-independent: effect does not vary with
population density
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adverse weather
habitat loss
toxic pollutant
climate change
– Density-dependent: effect varies with population
density
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infectious disease
parasites
predators
competition
Biotic Potential Vs.
Environmental Resistance
Population Dynamics
• Recruitment: portion that survives to
reproductive age.
• Replacement Level = Adult Mortality
• Dynamic Balance (fluctuate around a level that
never exceed the carrying capacity; equilibrium)
• Critical Number (Below which extinction results.)
• Threatened versus endangered species
What are the Mechanisms of
Population Equilibrium?
• Natural Enemies
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Predator-Prey
Host-Parasite
Predation on Animals
Plant-Herbivore
Dynamics
• Competition
• Between Plants
• Animal Territoriality
Predator-prey Balance:
Wolves and Moose of Isle Royale
Herbivore-Plant Dynamics
• Absence of natural
enemies like predators
allows a herbivore
population to exceed
carrying capacity which
results in overgrazing of
the habitat.
• Again, the population
succumbs to disease
and crashes; it may or
may not recover.
The Third Principle of
Ecosystem Sustainability
• The size of the
consumer population
is maintained so that
overgrazing or other
overuse does not
occur.
• Primary producers
maintain substantial
standing biomass.
Sheep have overgrazed this western landscape. What would happen if
coyotes were reintroduced and the shepard stopped paying veterinarian bills?
Competition Between Plants
• Plants appear to use the
same resources.
• If used in the same way
(“niche overlap”) the most
competitive will drive the
other to extinction
(“competitive exclusion”).
• How do plants coexist to
maintain biodiversity?
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Microclimates
Specialized adaptations
Mutualism
Balanced herbivory
Balanced Herbivory
• In a new habitat with ample resources, a plant population
experiences exponential growth creating a monoculture.
• A host-specific pest flourishes and causes plant dieoff.
• Resources become free for another plant species.
• A series of these events for different plant species leads
to reduced competition and diverse plant community.
Competition Between Animals
• Interspecific (between different species)
– Niche diversity
– Habitat partitioning
• Territoriality: defense of a resource against
individuals of the same species.
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Intraspecific
Fish, birds, and mammals
Priority use of resources.
The most fit will parent the next generation.
Tipping the Balance:
Introduced Species
• Rabbits in Australia
• Domestic cats on
islands
• Zebra mussels in the
Great Lakes
Why have these introductions resulted in a degradation of
the ecosystems? (Think in terms of environmental
resistance and biotic potential.)
Assignment #4
Population Equilibrium Mechanisms
• Plant-herbivore dynamics, territoriality, and predator-prey
relationships exist in all types of urban, suburban and
rural environments.
• Spend time in the woods on campus, a garden, your
backyard, or a local county park (get outdoors) and look
for population interactions.
• Find, observe, and record as many examples of plantherbivore (pest) dynamics, plant competition, animal
territoriality, and predator-prey relationships as you can
over two hours.
• In your journal, each example should be labeled (plantherbivore dynamics, territoriality, predator-prey
relationships, etc.) and described.
• Also explain how each of these population equilibrium
mechanisms influences population dynamics and
ecological succession.