The word predator often invokes a vision of a fierce and cruel animal the world would be better without. However, predation is a major ecological process controlling both the structure and function of communities. Predation affects the distribution and abundance of species, the strength and direction of energy flow within a system and the diversity and composition of communities. Predators play an essential role in evolution. Traits that decrease the likelihood of being predated and traits that increase the efficacy of the predating are under strong selection. This process has resulted in a vast array of prey defences and predator counter-defences. Also, according to recent studies of the fossil record, predation has played a central role in determining the history of life on earth. Thus, predators are not to be viewed as cold-blooded killers; instead, predation is a critical process for maintaining species diversity in both ecological and evolutionary time.

Key Concepts

• Predators are animals which actively catch and consume other animals.
  
• Predators may be limited in the type of prey they consume; these limitations may be extrinsic, due to factors such as prey abundance, or they may be intrinsic, where the predators’ physiological, reproductive or ecological requirements result in specialization on certain types of prey.
  
• Predation is a crucial ecological force because it moves energy through the system.
  
• Mathematical models and empirical research illustrate how predators and their prey coexist and should cycle through time.
  
• Prey species evolve defences that reduce their vulnerability to predators whereas predators evolve adaptations to counter the defences of the prey.
  
• Predator–prey interactions structured ancient, fossil ecosystems and played a role in determining the history of life on earth.