In nature no species exists in total isolation – all organisms interact with both the abiotic environment and other organisms
- If two species interact directly within a shared environment, they share a positive association (they co-exist)
- If interactions within an environment are mutually detrimental to both species, they share a negative association (do not co-exist)
Positive Associations
1. Predator-Prey Relationships
- Predation is a biological interaction whereby one organism (predator) hunts and feeds on another organism (prey)
- Because the predator relies on the prey as a food source, their population levels are inextricably intertwined
- If the prey population drops (e.g. due to over-feeding), predator numbers will dwindle as intra-specific competition increases
- If the prey population rises, predator numbers will increase as a result of the over-abundance of a food source
Predator-Prey Relationships (Arctic Fox vs Snowshoe Hare)
2. Symbiotic Relationships
- Symbiosis describes the close and persistent (long-term) interaction between two species
- Symbiotic relationships can be obligate (required for survival) or facultative (advantageous without being strictly necessary)
- Symbiotic relationships can be beneficial to either one or both organisms in the partnership:
- Mutualism – Both species benefit from the interaction (anemone protects clownfish, clownfish provides fecal matter for food)
- Commensalism – One species benefits, the other is unaffected (barnacles are transported to plankton-rich waters by whales)
- Parasitism – One species benefits to the detriment of the other species (ticks and fleas feed on the blood of their canine host)
Types of Symbiotic Relationships
Negative Associations
1. Competition
- Competition describes the interaction between two organisms whereby the fitness of one is lowered by the presence of the other
- Competition can be intraspecific (between members of same species) or interspecific (between members of different species)
- Limited supplies of resources (e.g. food, water, territory) usually triggers one of two types of responses:
- Competitive exclusion – One species uses the resources more efficiently, driving the other species to local extinction
- Resource partitioning – Both species alter their use of the environment to divide the resources between them
Competitive Exclusion vs Resource Partitioning
