Density-dependent growth describes how a population's growth rate changes in response to its own density. In established populations, as density increases, resource scarcity and competition intensify, slowing growth. This contrasts with density-independent growth, where population growth is unaffected by density, often occurring in new habitats with abundant resources. A key concept is carrying capacity, the maximum population size a habitat can sustainably support. Once a population reaches its carrying capacity, density-dependent factors limit further growth.
Understanding Density-Dependent Growth
Density-dependent growth is influenced by factors that become more impactful as population density increases. These factors include:
- Competition: Increased competition for resources like food, water, and shelter leads to reduced individual growth and survival.
- Predation: Higher population densities can make prey easier to find for predators, increasing mortality rates.
- Disease: Crowded conditions facilitate the spread of diseases, leading to increased mortality.
- Waste Accumulation: Higher densities lead to greater waste accumulation, which can negatively impact the environment and the population's health.
Examples of Density-Dependent Growth
- Fisheries: Studies on Eastern Baltic cod illustrate how selective fishing, aiming for higher yields, can negatively impact density-dependent growth, ultimately harming the stock's sustainability. (Nature)
- Salmon: Research on Atlantic salmon shows a strong correlation between young-of-the-year population density and growth rate; higher densities lead to slower growth. (Wiley Online Library)
- Cell Cultures: The growth of Myxococcus xanthus bacteria demonstrates cooperative growth above a certain cell density on a casein medium. (PubMed)
- Herring: A model predicts the size of Norwegian spring-spawning herring based on herring density, highlighting the importance of density in determining growth. (DOI)
Density-Dependent vs. Density-Independent Growth
It's crucial to distinguish density-dependent growth from density-independent growth. While density-dependent growth is controlled by factors related to population density, density-independent growth is affected by factors such as weather events, natural disasters, or human interventions that are not directly linked to population density. (Northern Arizona University, University of Minnesota)
