7/12/2011
Population Biology Concepts
y Population Ecology
y Carrying Capacity (K)
Day 1: Population Biology
D P
l ti Bi l
y Reproductive Strategies
y Survivorship
Population Ecology
y Population ecology plays a large role in POPULATION VIABILITY ANALYSIS (PVA)
Factors Affecting PVA
Increase Viability
Decrease Viability
y Favorable environment
y High natality
y The goal of PVA is to predict the long‐term probability of a species persisting in a given habitat.
y Generalized niche
G
li d i h
y Satisfactory habitat
y Predatory defense mech.
y Resistance to disease
y Ability to migrate
y Adaptability
y Sufficient Food Supplies
Factors Affecting PVA
Increase Viability
Decrease Viability
y Favorable environment
y Unfavorable environment
y High natality
y Low natality
y Generalized niche
G
li d i h
y Specialized niche
S i li d i h
y Satisfactory habitat
y Unsatisfactory habitat
y Predatory defense mech.
y Unsuitable predatory defense
y Resistance to disease
y Little resistance to disease
y Ability to migrate
y Unable to migrate
y Adaptability
y Inflexible (not adaptable)
y Sufficient Food Supplies
y Deficient food supply
Carrying Capacity
y Time for a short game.
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7/12/2011
Carrying Capacity
Carrying Capacity
y Carrying capacity refers to the number of organisms a y Biotic Potential is the maximum rate at which a given area can sustain.
y Factors that help regulate population include:
F
h h l l l i i l d
population can grow.
y What factors likely influence biotic potential?
Wh f
lik l i fl
bi i i l?
y Food availability, space, O2 content in waters
y Nutrient levels in soils, amount of sunlight
Carrying capacity
Carrying Capacity
y When left with unlimited resources, populations grow y No population is truly unlimited though
exponentially
Carrying Capacity
Carrying Capacity
y Values fluctuate over time, hovering around the carrying capacity
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Growth Rates
Growth Rates
y The “Rule of 70” tells us that:
y Population as a system… what factors affect population size?
y If a population is growing at a rate of x%
y Then it takes approximately 70/x years for the population to double
Growth Rates
Growth Rates
y Population as a system… what factors affect population y Population as a system… what factors affect population size?
size?
y Population Size (P) can be calculated as:
P
l i Si (P) b l l d y Population Size (P) can be calculated as:
P
l i Si (P) b l l d P=Original Size + Births – Deaths + immigration ‐
emmigration
P=Original Size + Births – Deaths + immigration –
emmigration
y Net growth rate is a slope: New / Old Reproductive Strategies
Reproductive Strategies
y Organisms have adapted either to:
y Maximize growth rates in environments that lack limits
y Maintain population size at close to the carrying capacity in stable environments
r‐strategists
y Species with high reproductive rates are r‐strategists
y
y
y
y
y Species that reproduce later in life with fewer offspring are k‐strategists
y
y
y
y
Mature rapidly
Short lived
Tend to be prey
Have many offspring and overproduce
Low parental care
Are generally not endangered
Tend to be small
Population size limited by density
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Reproductive Strategies
r‐strategists
k‐strategists
y
y
y
y
y Mature slowly
y
y
y
y
Mature rapidly
Short lived
Tend to be prey
Have many offspring and overproduce
Low parental care
Are generally not endangered
Tend to be small
Population size limited by density
y Long lived
Survivorship Curves
y Survivorship curves show age distribution characteristics of species, reproductive strategies, and life history
y Tend to be both prdeator
T d t b b th d t and d prey
y Have few offspring
y High parental care
y Reproductive success is measured by how many organisms are able to mature and reproduce
y Population size stabilizes near carrying capacity
y Tend to be large
Survivorship Curves
Survivorship Curves
y Type 1: Late Loss y Reproduction occurs early in life
y Most deaths occur at the M d h h limit of lifespan
y Low mortality at birth
Survivorship Curves
Survivorship Curves
y Type 2: Constant Loss y Type 3: Early Loss
y Death rates uniform
y Typical of species that y Predation affects all ages
have many offspring
y Typical of organisms that y Species that reproduce S i h d reach adulthood quickly
for most of their lifetime
y Death is prevalent for younger members of species and declines with age
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