Population Dynamics Overview

Population Dynamics

• Populations are groups of individuals of the same species that live in the same area and interact with each other.
• Population size is influenced by birth rate, death rate, immigration, and emigration.
• Population growth models describe how populations change over time.
  • Exponential growth occurs when resources are unlimited and the birth rate exceeds the death rate.
  • Logistic growth models take into account environmental limitations (carrying capacity).
  • The carrying capacity (K) represents the maximum population size that an environment can sustain.
• Density-dependent factors affect population growth as population density increases. Examples include competition for resources, predation, disease, and stress.
• Density-independent factors affect population growth regardless of population size. Examples include natural disasters and harsh weather.
• Factors influencing population growth include: biotic factors (predation, competition, disease), and abiotic factors (climate, temperature, rainfall).
• Population fluctuations are common and can be regular or erratic, affected by environmental changes, and often related to resource availability.

Community Dynamics

• Communities are groups of interacting populations of different species in a given area.
• Species richness refers to the number of different species in a community.
• Species diversity encompasses both species richness and the relative abundance of each species.
• Interspecific interactions involve relationships between different species.
  • Competition occurs when two or more species use the same limited resource.
  • Predation occurs when one species (predator) hunts and kills another (prey).
  • Symbiosis encompasses relationships where two or more species live in close proximity.
    • Mutualism benefits both species.
    • Commensalism benefits one species and has no effect on the other.
    • Parasitism benefits one species (parasite) at the expense of another (host).
• Keystone species are species whose presence significantly influences the structure and function of a community, even if they have relatively low abundance in the community.
• Community structure refers to the organization of species in a community, such as trophic levels and species interactions.
• Succession is the process of gradual change in species composition in a community over time.
  • Primary succession begins in areas without soil, often after volcanic eruptions, and involves the colonization of pioneer species.
  • Secondary succession occurs in areas that have been disturbed but still contain soil, often after wildfires or floods. It typically proceeds more quickly than primary succession.
• Disturbances, such as fire, floods, and storms, significantly influence community structure and can even trigger succession.
• Some communities are more resilient to disturbances than others, depending on factors like species diversity, and the presence of keystone species.
• Factors influencing community structure and function include species interactions, the availability of resources, and environmental conditions.

Population-Community Interactions

• Changes in one population can influence the dynamics of interacting populations within a community.
• Predation can influence prey populations and vice-versa.
• Competition for resources can influence the relative abundance of different species.
• Symbiotic relationships can have important effects on population dynamics and the efficiency of resource use within a given community.
• Community structure can affect the populations within the community.
• Changing conditions in a community can lead to the local extinction of certain species and the evolution of others.