Biotic and abiotic factors are key elements that regulate population size by influencing birth and death rates, ultimately determining the carrying capacity of an ecosystem. These factors can be density-dependent or density- independent, and they interact to control how populations grow and stabilize over time.
Abiotic Factors
Abiotic factors are non-living physical and chemical components of the environment that limit population size. These include temperature, water availability, light intensity, soil pH, mineral content, oxygen levels, and shelter. For example, extreme temperatures can slow metabolic reactions or make environments uninhabitable, directly reducing the number of individuals an ecosystem can support. Similarly, insufficient light limits photosynthesis in plants, decreasing primary productivity and thereby affecting entire food webs. Water scarcity or poor moisture levels can restrict plant growth and animal survival, especially in arid regions. Natural disasters such as hurricanes, earthquakes, and wildfires are density-independent abiotic factors that can drastically reduce population sizes regardless of how dense the population is.
Biotic Factors
Biotic factors involve living components of an ecosystem and their interactions, such as competition, predation, disease, parasitism, and food availability. Competition for limited resources like food, water, and nesting sites increases with population density and can reduce reproductive success and survival rates. Predation controls prey populations while also being regulated by prey availability, creating dynamic population cycles. Disease spreads more easily in dense populations, making it a density-dependent limiting factor that can lead to significant mortality. Parasites similarly weaken hosts and reduce fitness, especially when host populations are large and crowded. The availability of food—whether plant or animal—is a critical biotic factor; insufficient food leads to starvation and reduced reproduction, ultimately curbing population growth.
Interaction and Carrying Capacity
Both biotic and abiotic factors collectively determine the carrying capacity (K) of an environment—the maximum population size that can be sustained indefinitely. When populations exceed this threshold, limiting factors intensify, causing growth to slow and eventually stabilize or decline. For instance, while abiotic conditions set the baseline for what species can survive in a given area, biotic interactions fine-tune population levels through complex ecological relationships. According to Liebig’s law of the minimum, population growth is constrained by the resource that is most scarce relative to demand, whether it's a nutrient, water, or space
