Survivorship 3.1–3.3
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Generalist vs. Specialist Species
Generalist Species
Definition: Organisms with a broad niche (wide range of tolerance).
Diet & Habitat: Can use a variety of resources and live in many different environments.
Advantages:
Do well when environments are changing.
Flexible in food choice and living conditions.
Examples: Raccoons, cockroaches, rats, deer, humans.
Specialist Species
Definition: Organisms with a narrow niche (limited tolerance).
Diet & Habitat: Depend on specific resources or habitats.
Advantages:
Do well in stable, constant environments where their specific needs are consistently met.
Disadvantages:
Struggle if the environment changes or if resources disappear.
Examples: Pandas (bamboo diet), koalas (eucalyptus diet), spotted owls.
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Population Growth & Reproductive Strategies
K-Selected Species (K = carrying capacity)
Habitat: Stable, predictable environments.
Reproduction:
Produce few offspring.
Long gestation and developmental periods.
High parental care → higher survival chances for young.
Survivorship curve type: Type I (late loss).
Examples: Humans, elephants, whales, primates.
Traits summary: “Quality over quantity.”
r-Selected Species (r = growth rate)
Habitat: Disturbed or unpredictable environments.
Reproduction:
Produce many offspring.
Little to no parental care.
Most die early; only a few survive to adulthood.
Survivorship curve type: Type III (early loss).
Examples: Insects, weeds, fish, amphibians.
Traits summary: “Quantity over quality.”
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Invasive Species
Definition: Non-native (introduced) organisms that spread rapidly and cause harm.
Other names: Alien, non-indigenous, exotic species.
Impact:
Harm ecosystems, biodiversity, and economies.
Can outcompete native species for resources.
Disrupt food webs and habitat balance.
Often lack natural predators, parasites, or diseases in the new environment, contributing to their rapid spread.
Typical traits:
Usually r-selected species → reproduce quickly, adaptable, little care for offspring.
Effect on other species:
K-selected species → heavily impacted because they can’t adapt quickly.
r-selected species → less affected, often compete well.
Examples: Zebra mussels, cane toads, kudzu vine, lionfish.
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Survivorship Curves
Definition: Graph showing the proportion of individuals surviving at different ages in a population.
Types of Curves
Type I (Late Loss)
Most survive into adulthood; mortality increases at old age.
High parental investment → young survive.
Typical of K-selected species.
Examples: Humans, elephants, whales.
Type II (Constant Loss)
Mortality risk is constant throughout life.
Equal chance of dying at any age.
Examples: Songbirds, rodents, reptiles.
Type III (Early Loss)
Very high death rate early in life.
Few survive to adulthood, but those who do live long.
Typical of r-selected species.
Examples: Fish, insects, plants (trees release thousands of seeds, few grow).
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Example Case: Sea Otters & Kelp Forests
Sea otters live in kelp forests (Pacific coast).
Hunted to near extinction in early 1900s for fur.
Recovery began after listing as endangered in 1977.
Ecological role:
Keystone species → control sea urchin populations.
Prevent overgrazing of kelp.
Show how species survival impacts entire ecosystems.
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Key Takeaways for Quiz
Generalists = broad niche, thrive in changing environments.
Specialists = narrow niche, thrive in stable environments.
K-selected = few offspring, high care, Type I survivorship.
r-selected = many offspring, low care, Type III survivorship.
Invasive species are usually r-selected and harm K-selected species.
Survivorship curves: Type I (late loss), Type II (constant), Type III (early loss).