Demography and Life History

Fitness Trade-offs

• An individual has a restricted amount of energy and resources at its disposal, leading to fitness trade-offs, particularly between reproduction and survival.
• Example: Strong survival traits may hinder reproduction capabilities.

Survivorship Curves

• Describes the distribution of a population according to age.
  • Type I: Humans and large mammals, high survival rates in early and middle life, higher mortality in older age.
  • Type II: Birds, constant mortality rate throughout life.
  • Type III: Many fish and insects, high mortality in the early stages of life but those that survive tend to live long.

Reproductive Strategies

• r-selected species:
  • Mature quickly, produce many offspring, have high fecundity, and exhibit less parental care.
  • Shorter lifespan but rapid population growth when environmental conditions are favorable.
• K-selected species:
  • Mature slowly, produce fewer offspring but invest more resources in parental care.
  • Longer lifespan with stable populations near carrying capacity.

Population Growth Patterns

• Exponential Growth:
  • Occurs when resources are unlimited. Growth is J-shaped and continues until environmental resistance limits population size.
• Logistic Growth:
  • Population expansion decreases as resources become scarce, approaching carrying capacity leading to an S-shaped curve.

Density-Dependent Factors

• Growth factors that are affected by population size, usually biotic (e.g., food supply, competition).
• Results in fluctuating population sizes based on the availability of resources.

Density-Independent Factors

• Factors that affect population size regardless of the population density.
  • Examples include natural disasters, which can cause abrupt changes in birth and death rates.

Measuring Population Size and Density

• Methods Used:
  • Quadrant sampling for sessile organisms.
  • Mark-recapture for mobile animals, assuming individuals are mixed perfectly in the population.
  • Formula: M/N = m/n where:
    • M = total number of marked individuals,
    • N = total population size,
    • m = number of marked individuals recaptured,
    • n = total number of individuals recaptured.

Community Ecology

• Interactions in Ecology:
  • Commensalism (+/0): One species benefits while the other is unaffected.
  • Competition (-/-): Both species compete for limited resources, reducing fitness.
  • Mutualism (+/+): Long-term beneficial relationship for both species involved, coevolution often occurs.

Abiotic and Biotic Factors Affecting Distribution

• Abiotic Factors:
  • Climate patterns such as temperature, precipitation, sunlight, and wind.
• Biotic Factors:
  • Influence of organisms in the ecosystem on one another.

Climate Patterns and Their Effects

• Tropics receive more direct sunlight and heat, affecting local climate and biodiversity.
• Atmospheric circulation patterns at the equator can lead to diverse climates further from the equator due to rising warm air and subsequent precipitation patterns.