Individual Specialization in the Lionfish

This post was written by QBIC sophomore, Brianna Almeida.

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Layman CA., Allgeier JE.(2012) Characterizing trophic ecology of generalist consumers: a case study of the invasive lionfish in The Bahamas. Marine Ecology Progress Series. 448:131-141

Generalist species are organisms that have a wide range of diet and habitat. As a result, many invasive species are also generalist species. Invasive species are able to colonize new habitat, usually through human activities, and alter the food web by consuming the native species of that habitat. Native or endemic species are usually specialist species which specialize in obtaining one type of food source. This causes competition with endemic predators, resulting in the generalists being the “winner species”. This spread of generalist species is known as biotic homogenization.

Lionfish are an example of an invasive species that has colonized much of the Western Atlantic Ocean and the Gulf of Mexico and are competing with native species. They are ravenous predators with a wide range of prey including 41 species of ray finned fishes and a variety of crustaceans. They are also able to live in a variety of habitats, including mangroves and coral reefs. A study was performed by Craig Layman and Jacob Allgeier (2012) to see if diet varied between lionfish based on local prey varieties in the Bight of Old Robinson, Abaco, Bahamas. This area was ideal to study because it contains a wide variety of habitats. They also wanted to see if lionfish were competing for the same prey as the endemic species. Therefore they compared the diet of the invasive lionfish and the schoolmaster snapper (a common native species).

Photo courtesy of the Layman Lab

            To accomplish these goals, they caught the 2 fish they wished to study and identified the prey in their stomachs and assessed the similarity in their diets. They also identified the carbon (C¹³) and nitrogen (N¹⁵) isotopes in the tissues of the predatory fish and their prey. This was done to compare where each species of fish was located in the food web. This would show what level of predator the fish were and what prey they ate. They also calculated individual diet specialization using the data from the carbon isotopes and the dietary information acquired from the fishes stomachs. Using this data they created a simulation to categorizes how specialized or generalized an individual was. They called this the index of diet generality. Values closer to 0 indicate more diet specialization while values closer to 1 indicate a more generalist diet. The researchers also surveyed the different habitats in the Bight to determine if different varieties of fish were available in different patches of habitat. This was done to determine if the available variety of fish influenced the lionfish diet.

            Using statistical analyses, they found that the lionfish and the schoolmaster snapper did not have a similar diet, with the lionfish favoring small fish and the snapper favoring crustaceans. The carbon and nitrogen isotope values also differed between the 2 species. The snapper had more nitrogen in their tissues as a result of their preference for crustaceans. Also based on the carbon levels of the prey, they found that these levels are associated with the carbon levels of the predator. Using the index of diet generality, they found the lion fish had a higher degree of individual specialization, with a value of 0.34. The snapper had a low degree of individual specialization with only a value of 0.8. Although the population of lionfish are generalists, each individual lionfish has its own specialized diet as a result of the distinct prey varieties between habitats.  This could also be a result of the way lionfish and snapper forage for food. Lionfish are usually faithful to one patch of habitat, while snapper survey large areas when they are foraging. Therefore the snapper have a larger variety of prey to choose from, resulting in their generalist diets. Lionfish may be able to stay in one patch as a result of being an invasive, since native prey do not recognize them as a threat. Snapper on the other hand are recognized and to increase their efficiency, must survey a larger area to eat. The diet of the lionfish is influenced by their available prey. Thus, changes in season and habitat change their diet. Because of their specialization of prey by habitat, lionfish have an important impact on local prey populations. This may alter the food web and effect the availability of prey for native species.