Download Chapter 8 - Cherokee County Schools

Chapter 8
Population Ecology
WHAT IS A KEYSTONE?
• THE TOP BLOCK
IN AN ARCHWAY
• REMOVE
KEYSTONE
• ARCHWAY
COLLAPSES
KEYSTONE SPECIES
• PLAY CRITICAL ECOLOGICAL ROLE
IN HELPING SUSTAIN A
COMMMUNITY
• EX. POLLINATORS, TOP
PREDATORS (WOLF, LEOPARD,
LION, ALLIGATOR, SOME SHARKS)
DUNG BEETLES, SEA STARS,
SOUTHERN SEA OTTER
KEYSTONE SPECIES
• LOSS OF KEYSTONE SPECIES CAN
LEAD TO POPULATION CRASHES
AND EXTINCTION OF OTHER
SPECIES IN COMMUNITY THAT
DEPENDS ON THE K.SPECIES FOR
CERTAIN SERVICES/ROLES;
POPULATION DYNAMICS AND
CARRYING CAPACITY
• 3 Types of Population dispersal:
• 1) Clumped
• 2) Uniform
3) Random
Figure 8-2
THE WORLD IS MOSTLY
CLUMPY
• HERDS, FLOCKS, SCHOOLS, PACKS
• RESOURCES SPECIES NEEDS VARIES GREATLY
IN AVAILABILITY FROM PLACE TO PLACE;
• CAN PROVIDE BETTER PROTECTION FROM
PREDATORS & POPULATION DECLINE
• BETTER CHANCE FOR FOOD, MATING & CARING
FOR YOUNG
POPULATION DYNAMICS
• MOSTLY REPRODUCTIVE AGE –
POPULATION INCREASE
• MOSTLY POSTREPRODUCTIVE AGE –
POPULATION DECREASE
• EVEN DISTRIBUTION PRE & POST –
POPULATION IS STABLE
• NO POPULATION CAN INCREASE ITS SIZE
INDEFINITELY
Changes in Population Size:
Entrances and Exits
• Rule of 70: To calculate doubling time for a
population in years, divide 70 by the percent
growth rate
Age Structure: Young Populations
Can Grow Fast
• How fast a population
grows or declines depends
on its age structure.
– Prereproductive age: not
mature enough to
reproduce.
– Reproductive age: those
capable of reproduction.
– Postreproductive age:
those too old to reproduce.
Population Dynamics
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•
•
•
•
•
•
Depends on: size, density, dispersion, age distribution
Biotic potential = capacity for growth
Intrinsic rate of increase (r) – rate population grows if resources unlimited
High r 1) reproduce early, 2) short generation times, 3) long reproductive life,
& 4) have many offspring
Environmental Resistance – all factors acting to limit growth of a population
Carrying capacity (k) – Biotic potential + environmental resistance
Limiting Factors – light, water, space, nutrients, competition, predators, disease
(environmental resistance)
CARRYING CAPACITY (K)
• THE MAXIMUM POPULATION OF A
GIVEN SPECIES THAT A
PARTICULAR HABITAT CAN
SUSTAIN INDEFINITELY WITHOUT
DEGRADING THE HABITAT
• GROWTH RATE DECREASES AS
POPULATION SIZE NEARS K
Biotic Potential vs. Environmental
Resistance
• No population can increase
its size indefinitely.
– Intrinsic rate of increase
(r) -rate at which a
population would grow if it
had unlimited resources
(biotic potential).
– Carrying capacity (K):
maximum population of a
given species that a
particular habitat can sustain
Exponential and Logistic
Population Growth: J-Curves and
S-Curves
– J-curve:
exponential
growth
– S-curve:
logistic growth
Figure 8-4
POPULATION GROWTH
• NO OR FEW RESOURCE
LIMITATIONS
• POPULATION WILL GROW AT A
FIXED RATE SUCH AS
• 1% TO 2% EACH YEAR
EXPONENTIAL GROWTH
• GEOMETRIC
• STARTS SLOWLY
• THEN ACCELERATES AS
POPULATION INCREASES DUE TO
BASE SIZE OF POPULATION
INCREASING
• FIGURE 8-3
LOGISTIC GROWTH
• S-CURVE: RAPID EXPONENTIAL
GROWTH FOLLOWED BY STEADY
DECREASE IN POPULATION
GROWTH WITH TIME UNTIL
POPULATION GROWTH LEVELS OFF
• FIGURE 8-4
EXAMPLE OF
EXPONENTIAL GROWTH
• BROWN TREE SNAKE – NATIVE TO AUSTRALIA,
NEW GUINEA & SOLOMON ISLANDS
• INTRODUCED INTO GUAM IN WWII
• NO NATURAL PREDATORS
• EXPONENTIAL GROWTH (5000 SNAKES/SQUARE
KM)
• WILL EXCEED CARRYING CAPACITY SO
POPULATION WILL DECREASE
• MEANWHILE, DESTROYING NATIVE SPECIES
EXCEEDING CARRYING
CAPACITY
• POPULATION EXCEEDS RESOURCES, MANY
WILL DIE UNLESS THEY MOVE OR SWITCH TO
NEW RESOURCES
• REPRODUCTIVE TIME LAG: PERIOD NEEDED
FOR BIRTH RATE TO FALL & DEATH RATE TO
RISE IN RESPONSE TO RESOURCE
OVERCONSUMPTION
• POPULATION DIEBACK OR CRASH UNLESS
POPULATION MEMBERS MOVE
• ST. PAUL REINDEER POPULATION
St. Paul Reindeer Population
A POPULATION EXCEEDING
CARRYING CAPACITY CAN:
• DAMAGE THE AREA’S RESOURCES
• EX. OVERGRAZING OF RANGELAND
IN WESTERN U.S
• SAGEBRUSH HAS REPLACED
NATIVE GRASSES
EXAMPLES OF HUMAN POPULATIONS
EXCEEDING CARRYING CAPACITY
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•
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•
•
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HUMAN DIEBACK – IRELAND – 1845
POTATO CROP DESTROYED BY A PROTIST, A WATER MOLD;
GENETIC VARIATION OF POTATOES ALSO DECREASED BY
HAVING ONLY 1 MAIN CROP FOR FOOD
1 MILLION DIED
3 MILLION MIGRATED
EASTER ISLAND – POLYNESIANS USED UP ISLAND’S TREES
EXPAND CARRYING
CAPACITY
• SOME SPECIES DEVELOP ADAPTIVE TRAITS
THROUGH NATURAL SELECTION, DECREASING
ENVIRONMENTAL RESISTANCE TO THEIR
POPULATION GROWTH
• CARRYING CAPACITY CAN INCREASE OR
DECREASE SEASONALLY, YEAR-TO-YEAR OR
SPECIES MIGRATE
• EARTH’S CARRYING CAPACITY FOR HUMANS
HAS BEEN EXTENDED THROUGH TECHNOLOGY,
SOCIETY & OTHER CULTURAL CHANGES
POPULATION DENSITY
• # OF INDIVIDUALS IN A POPULATION
FOUND IN A PARTICULAR AREA;
• SOME FACTORS THAT LIMIT
POPULATION GROWTH HAVE A
GREATER EFFECT AS A
POPULATION’S DENSITY
INCREASES
Exceeding Carrying Capacity:
• Density-dependent
factors: do depend on
population size –
competition, living space,
predation, infectious
disease, parasitism
Figure 8-6
Exceeding Carrying Capacity:
• Density-independent
factors: ctrl size without
consideration of
population size – natural
disasters – floods,
hurricanes, severe freeze
in late spring, fire,
pollution, habitat
destruction
Figure 8-6
Types of Population Change
Curves in Nature
• Population sizes may stay the same, increase,
decrease, vary in regular cycles, or change erratically.
– Stable: fluctuates slightly above and below carrying
capacity; undisturbed TRF
– Irruptive: populations explode and then crash to a more
stable level; algae, insects,
– Cyclic: populations fluctuate in regular cyclic or boom-andbust cycles; lemmings, lynx & snowshoe hare;
– Irregular: erratic changes possibly due to chaos or periodic
catastrophic population crashes due to severe winter
weather
Types of Population Change
Curves in Nature
• Predator-prey cycles – top-down (predation) vs.
bottom-up control (scarcity of 1 or more resources)
Figure 8-7
REPRODUCTIVE PATTERNS
• Some species reproduce asexually.
– Offspring are exact genetic copies (clones).
• Others reproduce sexually:
– Genetic material is mixture of two individuals.
– Disadvantages: males do not give birth,
increase chance of genetic errors and
defects, courtship and mating rituals can be
costly.
– Major advantages: genetic diversity, offspring
protection and training;
Reproductive Patterns:Opportunists
r-selected – capacity for high rate of
population increase
• r-strategists - Large
number of smaller
offspring with little or
no parental care or
protection; overcome
massive loss of
offspring by producing
huge numbers;
• Algae, bacteria,
annual plants
(dandelions), most
insects
Figure 8-9
Reproductive Patterns:
Competitors
• K-strategists - fewer, larger
offspring with higher invested
parental care; produce later in
life, small number of offspring
with fairly long life spans
• Populations typically follow a
logistic growth curve – stay at
or near carrying capacity (K);
• Elephants, whales, humans,
TRF trees, saguaro cactus,
• Can be more prone to
extinction
Figure 8-9
Reproductive Patterns
• r-selected species tend to be opportunists
while K-selected species tend to be
Figure 8-10
competitors.
Survivorship Curves: Short to Long Lives
Shows different life expectancies
• Late loss: live to
old age
• Constant loss:
die at all ages
(birds, lizards,
small mammals)
• Early loss: die at
young ages
Figure 8-11