Density-Dependent Limiting Factors

Population Dynamics

• Population growth is controlled by two types of factors: density-dependent and density-independent factors.
• Density-dependent factors include:
  • Competition for resources such as food, water, sunlight, and space
  • Predation: the interaction between two different organisms where one captures and feeds on the other
  • Parasitism and disease: the interaction between two organisms where one feeds on the other, often weakening the host
  • Shortages of food, water, and nesting sites
• Density-dependent factors affect population growth as the population size increases, leading to competition for resources and increased predation, parasitism, and disease.

Predator-Prey Relationship

• The predator-prey relationship is a key density-dependent factor that controls population size.
• As the prey population increases, the predator population also increases, leading to a decrease in the prey population.
• As the prey population decreases, the predator population also decreases due to lack of food.

Parasitism and Disease

• Parasitism is a type of density-dependent factor where one organism feeds on another, often weakening the host.
• Disease can also affect population growth, especially as the population density increases.

Life History Traits

• Life history traits refer to the characteristics that affect an organism's schedule of reproduction and survival.
• There are two types of reproduction:
  • Big-bang reproduction: an organism produces all of its offspring in a single event.
  • Repeated reproduction: an organism produces a few offspring each year for several years.
• The type of reproduction an organism uses depends on its life history traits, such as the survival rate of its offspring.

Carrying Capacity

• The carrying capacity is the number of individuals the environment can support over a long period of time.
• As the population grows, it may exceed the carrying capacity, leading to a decrease in population size due to the lack of resources.
• Logistic growth is a model of population growth that takes into account the carrying capacity of the environment.

Logistic Growth

• Logistic growth is a model of population growth that slows down as the population approaches the carrying capacity.
• The graph of logistic growth looks like a stretched out "S" shape.
• When the population is at the carrying capacity, the birth rate equals the death rate, and growth stops.

Density-Independent Factors

• Density-independent factors affect all populations in similar ways, regardless of the size of the population.
• Examples of density-independent factors include:
  • Unusual weather or natural disasters
  • Human activities such as deforestation or damming of a river
• These factors can cause a population to crash or decline suddenly.

Population Growth Rate

• The population growth rate is the amount by which a population's size changes in a given time.
• If the birth rate is greater than the death rate, the population will increase.
• If the birth rate is equal to the death rate, the population will remain stable.
• If the death rate is greater than the birth rate, the population will decrease.

Migration

• Migration is the movement of individuals into and out of a population.
• It can affect population growth rate and size.

Age Structure

• Age structure refers to the distribution of individuals among different ages in a population.
• The age structure of a population can affect its growth rate and size.
• Age-structure diagrams are used to predict the future growth of a population.