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Reduc­ing num­bers of one car­ni­vore species indi­rectly leads to extinc­tion of others

pub­lished 05 March 2013 | mod­i­fied 05 March 2013
Asian lion bristolzooPre­vi­ous stud­ies have shown that car­ni­vores can have indi­rect pos­i­tive effects on each other, which means that when one species is lost, oth­ers could soon fol­low.

A team from the Uni­ver­sity of Exeter and the Uni­ver­sity of Bern has now found that reduc­ing the num­bers of one species of car­ni­vore can lead to the extinc­tion of oth­ers. Pub­lished online on 28 Feb­ru­ary 2013 in the jour­nal Ecol­ogy Let­ters, the study shows that sim­ply reduc­ing the pop­u­la­tion size of one car­ni­vore can indi­rectly cause another sim­i­lar species to become extinct. The research shows that changes in pop­u­la­tion size, as well as extinc­tion, can cre­ate rip­ple effects across sen­si­tive food webs with far-​reaching con­se­quences for many other ani­mals.

The research shows that species could suf­fer just as much from harm to another species as from being under direct threat them­selves. This adds weight to grow­ing evi­dence that a ‘sin­gle species’ approach to con­ser­va­tion, for exam­ple in fish­eries man­age­ment, is mis­guided. Instead the focus needs to be holis­tic, encom­pass­ing species across an entire ecosystem.

The insect sys­tem is handy for exper­i­men­ta­tion but the same prin­ci­ples apply to any ecosys­tem, from mam­mals in the Serengeti to the fish in our seas. It clearly shows that we should have an ecosystem-​based approach to con­ser­va­tion and to the man­age­ment of fish stocks and other nat­ural resources.
Dr Frank van Veen, co-​author, Uni­ver­sity of Exeter’s Cen­tre for Ecol­ogy and Con­ser­va­tion »

The researchers assem­bled exper­i­men­tal ecosys­tems with three species of par­a­sitic wasps, along with the three types of aphids on which each wasp exclu­sively feeds. They set up four sets of tanks each con­tain­ing the three aphid and three wasp species and allowed the pop­u­la­tions to estab­lish for eight weeks. Over the next 14 weeks (seven insect gen­er­a­tions) the researchers removed a pro­por­tion of the wasps from three of the sets of tanks every day — one species from each set. The fourth set had no wasps removed.

The team found that the par­tial removal of one wasp species led indi­rectly to the extinc­tion of other wasp species. In the absence of one wasp species, the aphid it preyed upon grew in num­bers. All three species of aphid feed on the same plant so increased com­pe­ti­tion for food led to changes in sizes of the aphid pop­u­la­tions. How­ever no aphid species went extinct and so the indi­rect extinc­tions of the wasps were not the result of extinc­tion of their prey. Rather, it is likely that the wasps that went extinct had dif­fi­culty search­ing for suit­able prey among large num­bers of unsuit­able ones.

Lead researcher Dr Frank van Veen from Bio­sciences at the Uni­ver­sity of Exeter’s Cen­tre for Ecol­ogy and Con­ser­va­tion said: “We have shown that the com­plex rip­ple effect of a change in pop­u­la­tion size across food webs is more sen­si­tive than pre­vi­ously thought and that a reduc­tion in the num­bers of one car­ni­vore can lead to the extinc­tion of another car­ni­vore species. We also found evi­dence that the ini­tial indi­rect extinc­tion can itself trig­ger fur­ther ones, poten­tially lead­ing to a cas­cade of extinc­tions, like domi­noes top­pling over.”

The research team has recently been awarded a £470K grant by the Nat­ural Envi­ron­ment Research Coun­cil (NERC) to extend this research at a larger scale.

The above news item is reprinted from mate­ri­als avail­able at Uni­ver­sity of Exeter. Orig­i­nal text may be edited for con­tent and length.
(Source: Uni­ver­sity of Exeter Research News, 28.02.2013)
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