Biology Study Guide: Species Strategies and Survivorship Curves

Specialist vs. Generalist Species

Differences Between Specialists and Generalists

Specialist Species

• Definition: Specialists have a narrow ecological niche and a smaller range of tolerance.

• Characteristics:

  • More prone to extinction due to specific needs.

  • Have specific food requirements, e.g. bamboo for pandas.

  • Less ability to adapt to new conditions due to specialized needs.

  • Have an advantage in stable environments where conditions do not change significantly.

Generalist Species

• Definition: Generalists have a broad ecological niche and a larger range of tolerance.

• Characteristics:

  • Less prone to extinction and have a higher likelihood of becoming invasive.

  • Possess broad food requirements, allowing them to adapt to various environments.

  • High adaptability with a capacity to survive in fluctuating conditions.

Additional Point

• Characteristics of specialists:

  • Narrow niche, less adaptable, more likely to consume a specific set of resources.

  • Easily affected by environmental changes and conditions.

• Characteristics of generalists:

  • Broad niche, adaptable to many environments, less likely to face extinction.

  • Utilize a variety of resources and have a high range of tolerance.

K-selected & r-selected Species

Characteristics of K-selected and r-selected Species

K-selected Species

• Characteristics:

  • Focus on quality over quantity.

  • Few offspring with a commitment to heavy parental care to ensure their protection.

  • Typically have long life spans, take longer to reach sexual maturity resulting in low biotic potential, and subsequently a slow population growth rate.

  • More likely to be negatively impacted by environmental changes and invasions.

  • Examples include most mammals and birds.

r-selected Species

• Characteristics:

  • Focus on quantity over quality.

  • Produce many offspring with little to no parental care; some species may reproduce only once.

  • Have shorter life spans and reach sexual maturity quickly resulting in high biotic potential and rapid population growth rates.

  • Generally more successful in rapidly changing environmental conditions and more likely to be invasive due to their high reproductive rates.

  • Examples include insects, fish, and some plants.

Comparative Table: Traits of K-selected and r-selected Species

Example Data

• Oysters produce approximately 500 million offspring per year (r-selected).

• Fish (Tuna) produce around 6,000 offspring per year (r-selected).

• Frogs produce about 200 offspring per year (r-selected).

• Hares produce approximately 12 offspring per year (K-selected).

• Large Cats (Puma) produce 2 offspring per year (K-selected).

• Chimpanzees produce about 1 offspring every five years (K-selected).

Implications of K and r selection on Populations

• K-selected Species:

  • Typically have low biotic potential, leading to difficulty in recovering populations after disturbances due to environmental changes.

  • High parental care means that the death of a parent results in the death of offspring as well.

  • Susceptible to competition from invasive species (usually r-selected) that can outcompete them for resources due to their high reproductive rates.

  • Less adaptability to rapid changes in environments leads to a greater risk of extinction.

• r-selected Species:

  • High biotic potential allows quicker recovery after disturbances due to rapid population growth.

  • Low parental care means that the death of parents does not necessarily mean the death of their offspring.

  • These species are often the invasive species due to their ability to maintain larger populations and quicker generational turnovers.

  • Higher chances of adaptation due to larger populations and fast generation times leading to lower extinction risks.

Characteristics of Survivorship Curves

• Survivorship Curve:

  • A line that indicates the survival rate of a cohort over its lifetime, moving from birth to death.

  • A rapid decline in the line indicates a quicker die-off of individuals, while a slow drop represents a longer average lifespan.

Detailed Types of Survivorship Curves

• Type I (mostly K-selected):

  • High survivorship in early life due to significant parental care.

  • High survivorship in middle age attributable to larger size and defensive strategies.

  • A rapid decrease in survivorship is typical in late life.

  • Example: Most mammals.

• Type II:

  • This curve reflects a pattern of steadily decreasing survivorship throughout life.

• Type III (mostly r-selected):

  • Characterized by high mortality rates early in life, attributed to low or no parental care.

  • Very few individuals reach midlife, with a slow decline in survivorship thereafter.

  • Even fewer make it to adulthood, followed by a slow decline in survivorship in old age.

  • Example: Insects, fish, and plants.

Specialist vs. Generalist Species

Specialist Species

• Definition: Have a narrow ecological niche and a smaller range of tolerance.

• Characteristics:

  • More prone to extinction due to specific needs.

  • Specific food requirements, e.g., bamboo for pandas.

  • Less adaptability to new conditions.

  • Advantage in stable environments.

Generalist Species

• Definition: Have a broad ecological niche and a larger range of tolerance.

• Characteristics:

  • Less prone to extinction; higher likelihood of becoming invasive.

  • Broad food requirements, allowing adaptation to various environments.

  • High adaptability to fluctuating conditions.

  • Utilize a variety of resources.

K-selected & r-selected Species

K-selected Species

• Characteristics:

  • Focus: quality over quantity.

  • Few offspring with heavy parental care.

  • Long life spans; slow to reach sexual maturity -> low biotic potential, slow population growth.

  • Negatively impacted by environmental changes and invasions.

  • Examples: Most mammals and birds.

r-selected Species

• Characteristics:

  • Focus: quantity over quality.

  • Many offspring with little/no parental care; some reproduce once.

  • Short life spans; quick to reach sexual maturity -> high biotic potential, rapid population growth.

  • Successful in rapidly changing conditions; often invasive (high reproductive rates).

  • Examples: Insects, fish, and some plants.

Example Data

• Oysters: produce $\approx 500$ million offspring/year (r-selected).

• Fish (Tuna): produce $\approx 6,000$ offspring/year (r-selected).

• Frogs: produce $\approx 200$ offspring/year (r-selected).

• Hares: produce $\approx 12$ offspring/year (K-selected).

• Large Cats (Puma): produce $2$ offspring/year (K-selected).

• Chimpanzees: produce $\approx 1$ offspring every five years (K-selected).

Implications of K and r selection on Populations

• K-selected Species:

  • Low biotic potential complicates population recovery after environmental disturbances.

  • High parental care means offspring death if a parent dies.

  • Susceptible to competition from invasive (often r-selected) species.

  • Less adaptability leads to a greater extinction risk.

• r-selected Species:

  • High biotic potential enables quicker population recovery after disturbances.

  • Low parental care allows offspring survival even if parents die.

  • Often invasive due to high reproductive rates and rapid generational turnover.

  • Higher adaptability and lower extinction risks due to large populations and fast generation times.

Characteristics of Survivorship Curves

• Survivorship Curve: A line indicating the survival rate of a cohort over its lifetime (birth to death).

  • Rapid decline = quicker individual die-off.

  • Slow drop = longer average lifespan.

Detailed Types of Survivorship Curves

• Type I (mostly K-selected):

  • High survivorship in early and middle life (parental care, size/defense).

  • Rapid decrease in survivorship in late life.

  • Example: Most mammals.

• Type II:

  • Steadily decreasing survivorship throughout life.

• Type III (mostly r-selected):

  • High mortality rates early in life (low/no parental care).

  • Few individuals reach midlife or adulthood; very slow decline thereafter.

  • Example: Insects, fish, and plants.