There are various relationships between different species, and they greatly affect changes in population size. Let us understand the patterns of major interspecific relationships and their results.
Basic Knowledge
Interspecific competition: A relationship in which organisms compete for the same resources. Competitive exclusion principle(Gause's law)=two species whose niches completely overlap cannot coexist in the same place, and one is excluded. Coexistence becomes possible through niche partitioning(character displacement).
Predator-prey relationship: Lotka-Volterra model=the population sizes of predators and prey fluctuate with a phase difference(prey↑→predators↑→prey↓→predators↓→prey↑).
Symbiotic relationships: Mutualism=both organisms benefit(example: leguminous plants and root nodule bacteria・honeybees and flowers). Commensalism=only one organism benefits(example: remoras and sharks). Parasitism=one organism benefits and the other is harmed(example: malaria parasites and humans). Allelopathy=the suppression of other species by chemical substances.
Explain the competitive exclusion principle using Gause's experiment as an example.
Answer: It is the principle that when two species whose ecological niches completely overlap are placed in the same environment, one of them is always excluded. Gause experimentally showed that when two species of Paramecium(P. aurelia and P. caudatum) were cultured together, P. aurelia competitively excluded P. caudatum.
- Competitive exclusion principle=two species with completely overlapping niches cannot coexist
- Niche partitioning=character displacement makes coexistence possible
- Predator-prey relationship=Lotka-Volterra oscillation model
- Mutualism=both benefit(root nodule bacteria・honeybees)
- Commensalism=only one benefits(remoras)
- Parasitism=one benefits and the other is harmed(malaria parasites)
- Allelopathy=suppression of other species by chemical substances
Points to Note
① The difference between mutualism and parasitism is whether both organisms benefit or one is harmed. ② In predator-prey oscillations, the predator peak lags behind the prey peak. ③ Do not confuse intraspecific competition(between members of the same species) with interspecific competition(between different species).
Practice
- State the competitive exclusion principle and explain the mechanism that avoids it(niche partitioning).
- Give two specific examples of mutualism.
- Explain the relationship between fluctuations in predator and prey populations using the Lotka-Volterra model.