Dynamics of Population Growth

Population Dynamics and Growth

• Population dynamics are crucial for understanding environmental quality and biodiversity. Organisms impact their environment, affecting water, ecosystems, and species viability.
• Population growth can be extremely rapid. Favorable environments and lack of predation allow species, like invasive carp and houseflies, to reproduce at astonishing rates.
• A single housefly can produce trillions of offspring in just ten years under unrestricted conditions.
• Biological reproduction is always constrained by factors like predation, competition,resource scarcity, disease, and accidents.

Describing Population Growth

• Ecologists use symbols (N, r, t) to describe population growth factors for simplicity and efficiency.
• Population growth depends, without constraints, on initial population size and reproductive rate.
• Exponential growth rate describes population size as a function of growth rate over time.

Exponential Growth

• Exponential growth occurs when a population has no constraints – no predators, abundant food.

Carrying Capacity

• All environments have a limited capacity to support a species. Carrying capacity (K) is the maximum population size that can be sustained.
• Populations initially grow exponentially, reaching and probably exceeding the carrying capacity, and experiencing crashes due to resource limitations.
• Oscillations around carrying capacity are possible. This can alter carrying capacities across an entire food web.

Logistic Growth

• Logistic growth is a density-dependent process. Growth slows as population density increases.
• Factors that slow growth rate include overcrowding-related effects (disease, stress, predation), less food, and lower fertility.
• Density-independent factors, like droughts, fire, and habitat destruction, also affect populations.

R-selected and K-selected Species

• R-selected species (i.e., exponential growth pattern) are "weedy" species.

  • Often occupy low trophic levels or are pioneers in new habitats.
  • Tolerate fluctuating environmental conditions.
  • Reproduce rapidly, mature early, and produce large numbers of offspring.
  • Offer little parental care.
  • Examples include many marine invertebrates, parasites, insects, rodents, and annual plants.

• K-selected species (approach carrying capacity) are typically larger and live longer.

  • Mature slowly, reproduce slowly, and have few offspring per generation.
  • Live longer with few natural predators.
  • Examples include elephants.

• Many species exhibit a mix of both growth patterns; their life history strategies vary greatly.