Problem 8 - Biology Today and Tomorrow with Physiology

Question

The logistic model of population growth takes into account __________ , but not __________. a. density-dependent factors; density-independent factors b. density-independent factors; density-dependent factors

Step-by-Step Solution

Answer

Answer: (a) density-dependent factors; density-independent factors.

Step 1: Understanding the Logistic Model

The logistic model of population growth describes how populations grow in an environment with limited resources. It takes into account the carrying capacity of the environment, which is the maximum population size that can be sustained indefinitely.

Step 2: Identify Key Terms

In this context, density-dependent factors are those that impact the population based on its size, such as competition and predation, while density-independent factors affect the population regardless of its size and include things like weather and natural disasters.

Step 3: Align Factors with Model

The logistic model takes into account density-dependent factors because it includes the carrying capacity which limits growth as the population size approaches a certain level.

Step 4: Determine Missing Aspects

Conversely, the logistic model does not factor in density-independent influences, which can cause sudden population changes irrespective of its current size.

Step 5: Match with Options

After understanding what each term means and which aspects the logistic model considers, we can see that it considers density-dependent factors and does not consider density-independent factors.

Key Concepts

Density-Dependent Factors

Density-dependent factors are crucial components in understanding population dynamics and the logistic model of population growth. These factors vary in intensity depending on the population size. As population density increases, these factors tend to have a greater impact.

• **Competition**: When resources such as food, water, and space become limited, individuals within the population must compete for them. This can slow down population growth, especially as more individuals vie for the same resources.
• **Predation**: As a population grows, the risk of predation can increase. Predators may find it easier to locate and capture prey when there are more individuals to choose from.
• **Disease and Parasitism**: With higher population densities, diseases can spread more quickly, reducing individual health and potentially lowering the overall population growth rate.

These factors create negative feedback on population growth, aligning with the logistic model where growth slows as populations approach the environment's carrying capacity.

Carrying Capacity

Carrying capacity is a critical concept within the logistic model of population growth. It represents the maximum number of individuals that an environment can support indefinitely without degrading the environment. This is often limited by available resources such as food, water, and shelter. As a population nears its carrying capacity, growth rates tend to slow due to increased competition and other density-dependent factors.

• The logistic growth curve illustrates this with an "S" shape, where population growth is rapid at first but slows as it approaches the carrying capacity.
• At carrying capacity, birth rates equal death rates, and the population size stabilizes.

Understanding carrying capacity is essential for managing natural resources and planning for sustainable growth. It highlights the balance needed between population dynamics and available environmental resources.

Density-Independent Factors

Unlike density-dependent factors, density-independent factors affect a population regardless of its size. These factors can cause sudden and dramatic changes in population numbers.

• **Weather**: Events like hurricanes, droughts, and floods can drastically alter population sizes by destroying habitats or food sources.
• **Natural Disasters**: Earthquakes, volcanic eruptions, and wildfires can instantly reduce populations in affected areas.
• **Human Activities**: Pollution, deforestation, and climate change are human-induced factors that also act independently of population size.

Even if a population is well below its carrying capacity, density-independent factors can severely impact its numbers and growth trajectory. The logistic model does not incorporate these factors, as they are unpredictable and not directly related to population density.