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Extinc­tion can spread from preda­tor to preda­tor, researchers have found

pub­lished 13 Novem­ber 2015 | mod­i­fied 13 Novem­ber 2015

parasitic wasps field studyThe extinc­tion of one car­ni­vore species can trig­ger the demise of fel­low preda­tors, con­ser­va­tion biol­o­gists at the Uni­ver­sity of Exeter have confirmed.

A ground-​breaking study pub­lished online on 12 Novem­ber in Cur­rent Biol­ogy has backed up the­o­ries and pre­vi­ous lab­o­ra­tory research demon­strat­ing the phe­nom­e­non of hor­i­zon­tal extinc­tion cas­cades, where extinc­tions of car­ni­vore species can have a rip­ple effect across species trig­ger­ing fur­ther unex­pected extinc­tions of other carnivores.

If we want to pro­tect an endan­gered car­ni­vore species, for exam­ple, we might need to pro­tect other preda­tors around it, which is quite an impor­tant message
Dr Sanders, lead author, asso­ciate research fel­low, Cen­tre for Ecol­ogy and Con­ser­va­tion, Uni­ver­sity of Exeter »

The researchers believe their find­ings pro­vide an impor­tant mes­sage for those work­ing in con­ser­va­tion. Rather than focus on the con­ser­va­tion of a sin­gle species, researchers sug­gest adopt­ing a whole sys­tem approach that also includes fel­low predators.

Using insects, the research team Frank van Veen, Dirk Sanders and Rachel Kehoe from the Cen­tre for Ecol­ogy and Con­ser­va­tion at the University’s Pen­ryn cam­pus set up exper­i­men­tal com­mu­ni­ties with com­plex food webs in 40 four-​square metre out­door field-​cages which they observed over a spring and sum­mer sea­son. These com­mu­ni­ties con­sisted of sev­eral species of aphids and their nat­ural ene­mies, par­a­sitoid wasps.

They found that remov­ing one wasp species led to an increased rate of extinc­tion in other species of wasp, an effect that was trans­mit­ted through changes in den­sity of the aphid species.

The study found that once one wasp species was removed its aphid-​prey grew in num­bers, crowd­ing out the other aphids and mak­ing it dif­fi­cult for the other wasp species to locate their par­tic­u­lar food resource, even­tu­ally lead­ing to their extinction.

This is a unique exper­i­ment. Usu­ally these research ques­tions are tack­led with the­o­ret­i­cal approaches and researchers focus on extinc­tions after the loss of food species. This is the first time any­one has looked at mech­a­nisms of hor­i­zon­tal extinc­tion cas­cades in a nat­ural large field exper­i­ment,” said Dr Sanders.

Such extinc­tion cas­cades are seen as a major threat to bio­di­ver­sity but it is very hard to get data about this hap­pen­ing in nature, due to the many dif­fer­ent influ­ences. Know­ing how such extinc­tion cas­cades can hap­pen gives us a bet­ter under­stand­ing and helps us to pre­dict when they might hap­pen. If we want to pro­tect an endan­gered car­ni­vore species, for exam­ple, we might need to pro­tect other preda­tors around it, which is quite an impor­tant message.”

(Source: Uni­ver­sity of Exeter news release, 12.11.2015)

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