When choosing prey, a predator will first consider the abundance or search time, of more profitable prey items compared to less profitable.
When prey abundance is low predators will become generalists in their foraging strategy, consuming more and less profitable prey. However, when more profitable prey is more abundant, predators will become specialists – consuming only the most profitable prey irrespective of the abundance of the less profitable. This is due to the potential energy lost whilst handling less profitable prey being greater than the energy gained by consuming it.
Consequently, the ratio of the handling time of an item in proportion to the energy gained by consuming it is also considered. For example, considering crab predation of mussels, although large mussels have a higher energy content, they also require more time to open. Conversely, in spite of small mussels requiring less time to be opened, they have a lower energy content. Crabs will consequently choose a mussel that balances the handling time and its energy content to maximise energy consumed.
A predator will, therefore, consider the abundance of prey versus its search time, the handling time and energy content when choosing a prey item.
Figure 1- A blue crab handling a ribbed mussel
‘Blue Crab (Callinectes sapidus) with ribbed mussel (Geukensia dimissa)’, 2011, Graphic, Ryan Moody https://www.flickr.com/photos/littoraria/5553568532 Accessed 23/12/18
Generalist – A predator who eats many types of prey, and switches between these type of prey based on prey abundance.
Handling Time – Time taken from a predator picking up a prey item to swallowing it.
Less Profitable Prey – Prey whose energy content is greater than the energy spent to search for and handle.
Profitable prey – Prey whose energy content is greater than the energy spent to search for and handle.
Search Time – The time taken for a predator to find a prey item.
Specialist – A predator who eats only a specific type of prey.