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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 8-2Figure 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
Population Dynamics• 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• 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
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.
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 8-4Figure 8-4
POPULATION GROWTH
• NO OR FEW RESOURCE LIMITATIONS
• POPULATION WILL GROW AT A FIXED RATE OF
• 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 BOTTOM HALF
LOGISTIC GROWTH
• S-CURVE: RAPID EXPONENTIAL GROWTH FOLLOWED BY STEADY DECREASE IN POPULATION GROWTH WITH TIME UNTIL POPULATION GROWTH LEVELS OFF
• FIGURE 8-3 WHOLE CURVE
Exceeding Carrying Capacity: • Density-independent
factors: ctrl size without consideration of population size – natural disasters
• Density-dependent factors: do depend on population size – competition, space, predation, disease, parasitism Figure 8-6Figure 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.– Irruptive: populations explode and then crash to a
more stable level.– Cyclic: populations fluctuate in regular cyclic or
boom-and-bust cycles.– Irregular: erratic changes possibly due to chaos or
drastic change.
Types of Population Change Curves in Nature
• Predator-prey cycles – top-down vs. bottom-up control
Figure 8-7Figure 8-7
REPRODUCTIVE PATTERNS• Some species reproduce without having
sex (asexual).– Offspring are exact genetic copies (clones).
• Others reproduce by having sex (sexual).– 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.
Reproductive Patterns:Opportunists and Competitors
• r-strategists - Large number of smaller offspring with little parental care
• K-strategists - fewer, larger offspring with higher invested parental care
Figure 8-9Figure 8-9
Reproductive Patterns
• r-selected species tend to be opportunists while K-selected species tend to be competitors.
Figure 8-10Figure 8-10
Survivorship Curves: Short to Long Lives
• Late loss: live to old age
• Constant loss: die at all ages (birds, lizards, small mammals)
• Early loss: die at young ages
Figure 8-11Figure 8-11