Within an ecosystem, no organism exists in total isolation – all organisms interact with both the surrounding environment and other organisms

• The interactions between species in a community can be classified according to their effect on the organisms involved
  

Herbivory

Herbivory is the act of eating only plant matter (e.g. primary consumers are considered herbivores)

• Some herbivores may benefit a plant by only consuming certain parts (e.g. honeybees feed on nectar and enable pollen transfer)
  

• Other herbivores feed to the detriment of the plant (e.g. cows grazing on grass, sea turtles eating seaweed)

Predation

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
  

• Examples include owls hunting mice, lions hunting zebras, wolves hunting deer and dolphins hunting fish

Interspecific Competition

Interspecific competition occurs when different species compete for resources (‘inter’ = between)

• The competition can be direct (e.g. vying for territory) or indirect (e.g. consuming a resource to deplete its availability)
  

• Examples include lions and hyenas competing for prey or pine trees and beech trees competing for light
  

Symbiotic Relationships

Symbiosis describes the close and persistent (long-term) interaction between two different species

• Mutualism – Both species benefit from the interaction (e.g. 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 attaching to whales)
  

• Parasitism – One species benefits to the detriment of the other species (ticks or fleas feed on the blood of their canine host)
  

Pathogenicity

Pathogenicity involves an infectious microorganisms living inside or on a host organism and causing disease

• The infectious agent (pathogen) causes disease by disrupting the homeostatic processes within the host
  

• Examples include Mycobacterium causing tuberculosis in animals or powdery mildew (a fungus) causing foliar disease in plants
  

Species Interactions