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Experimentally reducing species abundance indirectly affects food web structure and robustness

Experimentally reducing species abundance indirectly affects food web structure and robustness
Experimentally reducing species abundance indirectly affects food web structure and robustness
1.Studies on the robustness of ecological communities suggest that the loss or reduction in abundance of individual species can lead to secondary and cascading extinctions. However, most such studies have been simulation‐based analyses of the effect of primary extinction on food web structure.

2.In a field experiment we tested the direct and indirect effects of reducing the abundance of a common species, focusing on the diverse and self‐contained assemblage of arthropods associated with an abundant Brazilian shrub, Baccharis dracunculifolia D.C. (Asteraceae).

3.Over a 5‐month period we experimentally reduced the abundance of Baccharopelma dracunculifoliae (Sternorrhyncha: Psyllidae), the commonest galling species associated with B. dracunculifolia, in 15 replicate plots paired with 15 control plots. We investigated direct effects of the manipulation on parasitoids attacking B. dracunculifoliae, as well as indirect effects (mediated via a third species or through the environment) on 10 other galler species and 50 associated parasitoid species.

4.The experimental manipulation significantly increased parasitism on B. dracunculifoliae in the treatment plots, but did not significantly alter either the species richness or abundance of other galler species. Compared to control plots, food webs in manipulated plots had significantly lower values of weighted connectance, interaction evenness and robustness (measured as simulated tolerance to secondary extinction), even when B. dracunculifoliae was excluded from calculations.

5.Parasitoid species were almost entirely specialized to individual galler species, so the observed effects of the manipulation on food web structure could not have propagated via the documented trophic links. Instead, they must have spread either through trophic links not included in the webs (e.g. shared predators) or non‐trophically (e.g. through changes in habitat availability). Our results highlight that the inclusion of both trophic and non‐trophic direct and indirect interactions is essential to understand the structure and dynamics of even apparently discrete ecological communities.
0021-8790
327-336
Barbosa, Milton
ea133eb1-5201-467d-8391-61ae9159e0e3
Fernandes, G. Wilson
65e7bb7f-3276-4468-ab5e-7f714104c8e0
Lewis, Owen T.
7e99b2c2-5a31-4009-9037-9cc5a57bd8be
Morris, Rebecca
f63d9be3-e08f-4251-b6a0-43b312d3997e
Barbosa, Milton
ea133eb1-5201-467d-8391-61ae9159e0e3
Fernandes, G. Wilson
65e7bb7f-3276-4468-ab5e-7f714104c8e0
Lewis, Owen T.
7e99b2c2-5a31-4009-9037-9cc5a57bd8be
Morris, Rebecca
f63d9be3-e08f-4251-b6a0-43b312d3997e

Barbosa, Milton, Fernandes, G. Wilson, Lewis, Owen T. and Morris, Rebecca (2017) Experimentally reducing species abundance indirectly affects food web structure and robustness. Journal of Animal Ecology, 86 (2), 327-336. (doi:10.1111/1365-2656.12626).

Record type: Article

Abstract

1.Studies on the robustness of ecological communities suggest that the loss or reduction in abundance of individual species can lead to secondary and cascading extinctions. However, most such studies have been simulation‐based analyses of the effect of primary extinction on food web structure.

2.In a field experiment we tested the direct and indirect effects of reducing the abundance of a common species, focusing on the diverse and self‐contained assemblage of arthropods associated with an abundant Brazilian shrub, Baccharis dracunculifolia D.C. (Asteraceae).

3.Over a 5‐month period we experimentally reduced the abundance of Baccharopelma dracunculifoliae (Sternorrhyncha: Psyllidae), the commonest galling species associated with B. dracunculifolia, in 15 replicate plots paired with 15 control plots. We investigated direct effects of the manipulation on parasitoids attacking B. dracunculifoliae, as well as indirect effects (mediated via a third species or through the environment) on 10 other galler species and 50 associated parasitoid species.

4.The experimental manipulation significantly increased parasitism on B. dracunculifoliae in the treatment plots, but did not significantly alter either the species richness or abundance of other galler species. Compared to control plots, food webs in manipulated plots had significantly lower values of weighted connectance, interaction evenness and robustness (measured as simulated tolerance to secondary extinction), even when B. dracunculifoliae was excluded from calculations.

5.Parasitoid species were almost entirely specialized to individual galler species, so the observed effects of the manipulation on food web structure could not have propagated via the documented trophic links. Instead, they must have spread either through trophic links not included in the webs (e.g. shared predators) or non‐trophically (e.g. through changes in habitat availability). Our results highlight that the inclusion of both trophic and non‐trophic direct and indirect interactions is essential to understand the structure and dynamics of even apparently discrete ecological communities.

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BARBOSA manuscript authors accepted version 28 11 2016 - Accepted Manuscript
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BARBOSA manuscript Online Supporting Information 28 11 2016 - Other
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More information

Accepted/In Press date: 28 November 2016
e-pub ahead of print date: 21 December 2016
Published date: March 2017
Organisations: Biomedicine, Centre for Biological Sciences

Identifiers

Local EPrints ID: 403734
URI: https://eprints.soton.ac.uk/id/eprint/403734
ISSN: 0021-8790
PURE UUID: 469825db-b203-489c-b869-c5e36313267f
ORCID for Rebecca Morris: ORCID iD orcid.org/0000-0002-0020-5327

Catalogue record

Date deposited: 12 Dec 2016 11:12
Last modified: 16 Aug 2019 04:01

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Contributors

Author: Milton Barbosa
Author: G. Wilson Fernandes
Author: Owen T. Lewis
Author: Rebecca Morris ORCID iD

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