Pt 6 Struggle for existence Flashcards
measuring populations
Challenges in Measuring:
Difficulties in locating individuals, especially elusive or cryptic species.
Defining boundaries of populations (e.g., territorial range of species like mountain lions).
Identifying distinct individuals, especially in species with clones (e.g., plants with genet-ramet systems).
Common Approaches:
Mathematical Models: Utilize assumptions to predict trends when direct measurement is infeasible.
Case Studies:
Island populations for clarity of boundaries.
Controlled environments like labs for precision.
pop growth models
Exponential Growth: Unlimited growth when resources are abundant.
-Formula: Nt=N0e^rt
-Assumes no limiting factors
Logistic growth: accounts for resource limitation
-Formula: dN/dt=rN(1 - N/K)
Key parameters
-K- carrying capacity of the environment
-r: intrinsic rate of growth
life tables and survivorship curves
Life Tables: Track age-specific survival and reproduction.
-Components: lx(survivorship), bx(birth rate)
-Net Reproductive Rate (R0): Sum of lxbx; indicates population replacement rate.
Survivorship Curves:
Type I: High survivorship early; declines with age (e.g., humans).
Type II: Constant mortality rate (e.g., birds).
Type III: High mortality in early life (e.g., plants, fish).
Stochastic vs. Deterministic Models
Deterministic Models:
Predict fixed outcomes based on set parameters.
Example: Standard life tables.
Stochastic Models:
Incorporate variability and chance.
Applications: Extinction risk modeling, conservation biology.
Example: Simulating 1,000 projections to assess population stability.
trade-offs in life histories
Key Constraints:
-Size vs. Number: Example: Plants balancing seed size and quantity.
-Early vs. Late Reproduction:
Early reproduction favors rapid growth but reduces individual output.
Late reproduction allows more resource accumulation, increasing offspring quantity.
Cost of Reproduction: Energy trade-off between parental survival and reproductive effort
human pop growth
Examples: Logistic growth models fitted to human populations.
Key Takeaways:
Human populations often exceed K due to technological and agricultural advancements.
Why is defining population boundaries challenging?
A: Species ranges may overlap, individuals can be elusive, or clonal systems make it hard to distinguish individuals.
How does r change in logistic growth as N approaches K
r decreases as N approaches K, slowing pop growth
What does R0>1 indicate?
A: The population is increasing
Provide an example of a species with a Type III survivorship curve.
A: Oak trees, where many seeds fail to germinate.
What is a life history trade-off?
A: The allocation of limited resources between competing demands, such as reproduction and survival.
Provide an example of a trade-off between size and number of offspring.
A: Plants producing many small seeds (e.g., dandelions) versus fewer large seeds (e.g., acorns).
How does early reproduction affect individual survival?
A: It reduces energy available for growth and maintenance, potentially shortening lifespan.
Why might some species delay reproduction?
A: To accumulate resources and increase reproductive success later in life.
Define intrinsic rate of growth (r).
A: The maximum rate at which a population can grow under ideal conditions.
