Chapter 16 conceptsCompetition occurs when individuals experience limited resources.The theory of competition is an extension of logistic growth models.The outcome of competition can be altered by abiotic conditions, disturbances, and interactions with other species.123Competition can occur through exploitation or directinterference, or it may be apparent competition.4
Types of competition1Intraspecific competition: competition among individuals of the same species.Negative density dependence is a common type of intraspecific competition, where an increase in a population’s density causes a decline in the growth rate of the population.Interspecific competition: competition among individuals of different species.Interspecific competition can cause the population of one species to decline and eventually die out.
The role of resources1Resource: anything an organism consumes or uses that causes an increase in population growth rate when it becomes more available.Ecological factors that cannot be consumed (e.g., temperature) are not considered resources.Resources for plants can include sunlight, water, and soil nutrients.Resources for animals can include food, water, and space.Example:Mussels and barnacles in the intertidal zone compete for space on rocks.As space decreases, the growth and fecundity of adults declines.
The role of resources1Renewable resources: resources that are constantly regenerated (e.g., seeds, sunlight).Nonrenewable resources: resources that are not regenerated (e.g., space).Renewable resources can originate from inside or outside the ecosystem in which competitors live (e.g., dead leaves fall into streams from the surrounding forest). Resources from outside the system do not respond to the rate of resource consumption.In contrast, competitors can affect the supply of resources and demand for resources that originate within the ecosystem.
Leibig’s law of the minimum1Not all resources limit consumer populations.Leibig’s law of the minimum: law stating that a population increases until the supply of the most limiting resource prevents it from increasing further.Example:Silica is a limiting resource for diatoms, such as Asterionella formosaand Synedra ulna.The two species have different demands of this limiting resource.Asterionella populations reach carrying capacity when they draw silica down to 1μM.Synedra populations reach carrying capacity when silica goes down to 0.4μM.
Leibig’s law of the minimum1When Synedra reaches carrying capacity, the abundance of silica in the environment is not sufficient to support the population of Asterionella.