Download Notes - Population Ecology

WARM UP
• What does the capital letter K represent in ecology?
• What does it mean to be a K-selected species?
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
POPULATION ECOLOGY
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Ecology is studied at several levels
• Ecology and evolution are
tightly intertwined
• Biosphere = all living
things on Earth and the
areas they inhabit
• Ecosystem = communities
and the nonliving (abiotic)
material and forces they
interact with
• Community = interacting
species that live in the same
area
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Levels of ecology science
• Population ecology = investigates the quantitative
dynamics of how individuals within a species interact
• Community ecology = focuses on interactions among
species (one-on-one to interrelationships among
communities)
• Ecosystem ecology = studies living and nonliving
components of systems to reveal patterns
- nutrient and energy flow
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Organismal ecology: habitat
• Habitat = the environment in which an organism
lives
- includes living and nonliving elements
- scale-dependent: from square meters to square km
• Habitat use = each organism thrives in certain
habitats, but not in others (non-random patterns)
• Habitat selection = the process by which organisms
actively select habitats in which to live
- availability and quality of habitat are crucial to an
organism’s well-being
- human development conflicts with this process
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Organismal ecology: niche
• Niche = an organism’s use of resources and its
functional role in a community
- habitat use, food selection, role in energy and
nutrient flow
- interactions with other individuals
• Specialists = species with narrow niches and very
specific requirements
- extremely good at what they do, but vulnerable to
change
• Generalists = species with broad niches that can use
a wide array of habitats and resources
- able to weather variable conditions, may not thrive
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Gause’s Principle (aka Competitive
Exclusion Principle)
• No two species can fill the same niche at the same time
• The weaker species will fill the smaller niche, relocate or
become extinct.
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Population ecology
• All populations show
characteristics that help scientists
predict their future dynamics
• Understanding human population
dynamics is central to
environmental science
• Population size = the number of
individual organisms present at a
given time
- numbers can increase,
decrease, cycle, or remain the
same
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Population ecology
• Population density = the number of individuals within a
population per unit area
- high densities make it easier to find mates, but
increases competition, and vulnerability to predation &
disease
- low densities make it harder to find mates, but
individuals benefit from more resources and space
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Population ecology
• Population distribution
(dispersion) = spatial
arrangement of organisms
within an area
- Random – individuals located
haphazardly, with no pattern
- Uniform – individuals are
evenly spaced, can be due to
territoriality
- Clumped – arranged
according to availability of
resources needed to survive
- most common in nature
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Population ecology
• Sex ratio = proportion of males to females
- in monogamous species, a 50/50 sex ratio maximizes
population growth
• Age structure (distribution) = the relative numbers of
organisms of each age within a population
- Age structure diagrams (pyramids) = show the age
structure of populations
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Birth and death rates
• Crude birth/death rates =
rates per 1000 individuals
• Survivorship curves = the
likelihood of death varies
with age
- Type I: More deaths at
older ages
- Type II: Equal number
of deaths at all ages
- Type III: More deaths at
young ages
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Four factors of population change
• Natality = births within the population
• Mortality = deaths within the population
• Immigration = arrival of individuals from outside the
population
• Emigration = departure of individuals from the
population
• Growth rate formula =
- (Crude birth rate + immigration rate) - (Crude death
rate + emigration rate) = Growth rate
- per 1000 individuals per year
- expressed in % - better able to compare populations
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Exponential population growth
• Steady growth rates cause
exponential population
growth
- increases by a fixed percent
- Graphed as a J-shaped
curve
• Exponential growth cannot be
sustained indefinitely
- occurs in nature with a
small population and ideal
conditions
- usually when introduced to
a new environment
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Limiting factors restrain population growth
• Limiting factors = physical, chemical and
biological characteristics that restrain
population growth
- water, space, food, mates, shelter, breeding
sites, temperature, predators, and disease
- interaction of these factors determines
carrying capacity
- may be determined by experiment
• Environmental resistance = All limiting
factors taken together
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Carrying capacity
• Carrying capacity = the
maximum population size
of a species that its
environment can sustain
- An S-shaped logistic
growth curve
- Limiting factors slow
and stop exponential
growth
• Carrying capacity can vary
Humans have raised their carrying capacity by decreasing the
carrying capacity for other species
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Perfect logistic curves aren’t often found
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Population density affects limiting factors
• Density-dependent factors = limiting factors whose
influence is affected by population density
- increased chance of finding mates, but risk of
predation and competition for mates occurs with
increased density
• Density-independent factors = limiting factors whose
influence is not affected by population density
- temperature extremes & catastrophic events such as
floods, fires, and landslides
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Biotic potential and reproductive strategies
vary
• Biotic potential = the ability of an organism to produce
offspring
• Interaction between biotic potential and environmental
resistance helps determine the fate of the population
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Biotic potential and reproductive strategies vary
• K-selected species = animals with long gestation periods
and few offspring
- Have a low biotic potential
- Invest in offspring
- Stabilize at or near carrying capacity (K)
- Good competitors
- Regulated by density-dependent factors
• r-selected species = animals which reproduce quickly &
in quantity
- Have a high biotic potential
- Produce as many off spring as possible/little parental care
- At or below carrying capacity
- Regulated by density-independent factors
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
K-selected vs. r-selected species
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Reproductive Potential
•The maximum number of
offspring that each member of the
population can produce in ideal
conditions
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Biotic Potential
•A species’ maximum rate at which its
population can grow
•Many factors influence biotic potential,
including gestation
time and generation time
•Species with high biotic potential can
recover more quickly from population
declines than species with low biotic
potential
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Biotic Potential
Scorpion Fish
• Mature 3-5 years
• Release 50,000 to
100,000 eggs
• Once fertilized take
12-16 days to hatch
• HIGH BIOTIC
POTENTIAL
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Orangutans
• Females Mature 10
years
• Birth to single babies
once every eight years
• LOW BIOTIC
POTENTIAL
Striking gold in Costa Rica
• Golden toads were
discovered in 1964, in
Monteverde, Costa Rica
• The mountainous cloud
forest has a perfect
climate for amphibians
• Unfortunately, they
became extinct within 25
years
- Due to global
warming’s drying
effect on the forest
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Population changes affect communities
• As population in one species declines, other species may
appear
• Human development now displaces other species and
threatens biodiversity
- As Monteverde dried out, species from lower, drier
habitats appeared
- But, species from the cloud-forest habitats disappeared
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Challenges to protecting biodiversity
• Social and economic factors affect species and
communities
- Nature is viewed as an obstacle to development
- Nature is viewed as only a natural resource
- Human population growth pressures biodiversity
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Preserving biodiversity
• Natural parks and protected areas help preserve
biodiversity
- Often, they are underprotected & underfunded
- Ecotourism brings jobs and money to developing
areas
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings