Download Growth rate

Chapter 6-Population and
Community Ecology
Population Abundance and
Distribution
growth rate [ r ]= (rb + ri) - (rd + re)
D = N / area
A population of gray wolves has a growth rate
(r) of 0.2 / year. If the population starts out with
100 individuals, how many would you expect
after 1 year? 2 Years?
Doubling time and the Rule of 70.
To find doubling time of a quantity growing at a given annual
percentage rate, divide percentage into 70.
How long will it take that population of gray wolves to
reach 200?
How do populations occupy space?
Examples: pack of wolves, flock of birds, school
of fish; cluster where resources available, helps
protect from predators, better hunting success.
Examples: common where resources are scarce;
distance between neighboring individuals is
maximized to avoid competition or avoid
territoriality; penguins, creosote bush (terpenes)
Examples: least common; position of each
individual is independent of the other individuals;
occurs in habitats where environmental
conditions and resources are consistent;
dandelions, oyster larvae carried by ocean
currents.
Factors that influence population size (Influence
an individual’s probability of survival and reproduction)
Density Dependent Factors:
depends on the size of the population:
competition, predation, disease
Density Independent Factors: are
not dependent on the size of the
population: fire, drought, hurricane,
pest spraying
Limiting Factor/Limiting Resource: A resource
that a population cannot live without and which
occurs in quantities lower than the population
would require to increase in size.
Carrying Capacity: (K) the population size of
the species that the environment can sustain
indefinitely, given the food, habitat, water and
necessities available in the environment
Growth Models
• Growth rate: Number of offspring an individual
can produce in a given period of time, minus
deaths of the individual or offspring during the
same period of time.
• Intrinsic Growth Rate (r) is the rate at which a
population would grow if it had unlimited
resources.
• Population growth is affected by biotic or intrinsic
factors that are built into the genetic basis of each
species. This is known as biotic potential: the
maximum size a population would get it there
were nothing holding it back.
Exponential Growth Model
• Exponential Growth
Model: Populations
growing at a fixed rate.
When population are
not limited by resources
their growth is very
rapid, as more growths
occur with each step in
time. Represented by a
J-shaped curve
1,000,000 pennies
Logistical Growth Model
• Populations can not
grow at an exponential
rate indefinitely.
Logistic growth:
exponential at first but
slows as population
reaches carrying
capacity. Sigmoid (s
shaped) curve
• Together, biotic
potential and
environmental
resistance determine
carrying capacity (K)
Environmental Resistance +
Biotic Potential =Carrying
Capacity
Variations on the Logistic Growth
Model
• Some populations will
overshoot K, there will
be a lack of resources
and the population will
experience a dieoff/crash.
• Reindeer of St. Paul
Island.
Variations to Logistical growth
Predator-Prey Cycles
• Canada Lynx and
Snowshoe Harerecords estimated
from Hudson Bay Co.
show oscillations of
abundance, with lynx
pop. Peaking 1-2
years after the hare
population
Reproductive Strategies
•
Biotic or Intrinsic factors are specific to each species and include
➢ Age of reproductive maturity
➢ Number of offspring per reproductive event
➢ Number of reproductive events per lifetime
➢ These factors together are referred to as fecundity/fertility.
➢ r strategists (r-selected species)
High intrinsic growth rate because they reproduce often and produce
large number of off spring. Populations do not typically remain near K,
but exhibit rapid growth followed by overshoots and die-offs
➢ K strategists (K-selected species)
Low intrinsic growth rate so pop increases slowly until reach K.
Fluctuations are small
Survivorship Curves
• Late Loss
• Constant Loss
• Early Loss
Late Loss
Constant Loss
Early Loss
Species Interactions
• Competition: Struggle
of individuals to obtain
a limited resource
• Competitive Exclusion
Principle: Two species
competing for same
limited resource cannot
coexist
• Resource Partitioning:
results from
competition, two
species divide a
resources based on
behavior or
morphology.
warblers
Predation: Use of one species by
another species
• True Predators: Kill prey and consume most of
what they kill
• Parasitism: One species (the parasite) feeds on
part of another organism (the host) usually by
living on or in the host. Parasite benefits/host is
harmed.
• Mutualism: two species or a network of species
interact in a way that benefits both.
• Commensalism: an interaction that benefits one
species but has little, if any effect on the other
species
Indicator: Amphibians, Birds,
Butterflies
Habitat Loss,
Increases in UV,
Parasites, Pollution
(pesticides), Climate
change, Overhunting
Butterflies as Indicator
Species
Keystone: American Alligator
Dig holes that hold
freshwater during dry
spells and serve as
refuges for aquatic life
and provide fresh
water
Foundation: create and enhance habitat that
benefit other species
Beaver: build a dam,
create a pond, where
other organisms live.
Bat and bird species
that regenerate
deforested areas and
spread fruit plants in
their droppings.
Theory of Island Biogeography
• Number of types of species influenced by size
and distance from mainland
• Larger habitats have more species-why?
• Closer to other habitat = more species. Why?
Central Park-New York City
Reintroducing Wolves in Yellowstone
• https://www.youtube.com/watch?v=dMGJ9o
ThHbc
• https://www.youtube.com/watch?v=ysa5OBh
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