'Natural experiment' demonstrates top-down control of spiders by birds on a landscape level.

The combination of small-scale manipulative experiments and large-scale natural experiments provides a powerful approach for demonstrating the importance of top-down trophic control on the ecosystem scale. The most compelling natural experiments have come from studies examining the landscape-scale l...

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Autores principales:	Haldre Rogers, Janneke Hille Ris Lambers, Ross Miller, Joshua J Tewksbury
Formato:	article
Lenguaje:	EN
Publicado:	Public Library of Science (PLoS) 2012
Materias:	Medicine R Science Q
Acceso en línea:	https://doaj.org/article/73a6eb55886b40c490f8fdb3434ed6bb
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spelling	oai:doaj.org-article:73a6eb55886b40c490f8fdb3434ed6bb2021-11-18T07:06:18Z'Natural experiment' demonstrates top-down control of spiders by birds on a landscape level.1932-620310.1371/journal.pone.0043446https://doaj.org/article/73a6eb55886b40c490f8fdb3434ed6bb2012-01-01T00:00:00Zhttps://www.ncbi.nlm.nih.gov/pmc/articles/pmid/22970126/?tool=EBIhttps://doaj.org/toc/1932-6203The combination of small-scale manipulative experiments and large-scale natural experiments provides a powerful approach for demonstrating the importance of top-down trophic control on the ecosystem scale. The most compelling natural experiments have come from studies examining the landscape-scale loss of apex predators like sea otters, wolves, fish and land crabs. Birds are dominant apex predators in terrestrial systems around the world, yet all studies on their role as predators have come from small-scale experiments; the top-down impact of bird loss on their arthropod prey has yet to be examined at a landscape scale. Here, we use a unique natural experiment, the extirpation of insectivorous birds from nearly all forests on the island of Guam by the invasive brown tree snake, to produce the first assessment of the impacts of bird loss on their prey. We focused on spiders because experimental studies showed a consistent top-down effect of birds on spiders. We conducted spider web surveys in native forest on Guam and three nearby islands with healthy bird populations. Spider web densities on the island of Guam were 40 times greater than densities on islands with birds during the wet season, and 2.3 times greater during the dry season. These results confirm the general trend from manipulative experiments conducted in other systems however, the effect size was much greater in this natural experiment than in most manipulative experiments. In addition, bird loss appears to have removed the seasonality of spider webs and led to larger webs in at least one spider species in the forests of Guam than on nearby islands with birds. We discuss several possible mechanisms for the observed changes. Overall, our results suggest that effect sizes from smaller-scale experimental studies may significantly underestimate the impact of bird loss on spider density as demonstrated by this large-scale natural experiment.Haldre RogersJanneke Hille Ris LambersRoss MillerJoshua J TewksburyPublic Library of Science (PLoS)articleMedicineRScienceQENPLoS ONE, Vol 7, Iss 9, p e43446 (2012)
institution	DOAJ
collection	DOAJ
language	EN
topic	Medicine R Science Q
spellingShingle	Medicine R Science Q Haldre Rogers Janneke Hille Ris Lambers Ross Miller Joshua J Tewksbury 'Natural experiment' demonstrates top-down control of spiders by birds on a landscape level.
description	The combination of small-scale manipulative experiments and large-scale natural experiments provides a powerful approach for demonstrating the importance of top-down trophic control on the ecosystem scale. The most compelling natural experiments have come from studies examining the landscape-scale loss of apex predators like sea otters, wolves, fish and land crabs. Birds are dominant apex predators in terrestrial systems around the world, yet all studies on their role as predators have come from small-scale experiments; the top-down impact of bird loss on their arthropod prey has yet to be examined at a landscape scale. Here, we use a unique natural experiment, the extirpation of insectivorous birds from nearly all forests on the island of Guam by the invasive brown tree snake, to produce the first assessment of the impacts of bird loss on their prey. We focused on spiders because experimental studies showed a consistent top-down effect of birds on spiders. We conducted spider web surveys in native forest on Guam and three nearby islands with healthy bird populations. Spider web densities on the island of Guam were 40 times greater than densities on islands with birds during the wet season, and 2.3 times greater during the dry season. These results confirm the general trend from manipulative experiments conducted in other systems however, the effect size was much greater in this natural experiment than in most manipulative experiments. In addition, bird loss appears to have removed the seasonality of spider webs and led to larger webs in at least one spider species in the forests of Guam than on nearby islands with birds. We discuss several possible mechanisms for the observed changes. Overall, our results suggest that effect sizes from smaller-scale experimental studies may significantly underestimate the impact of bird loss on spider density as demonstrated by this large-scale natural experiment.
format	article
author	Haldre Rogers Janneke Hille Ris Lambers Ross Miller Joshua J Tewksbury
author_facet	Haldre Rogers Janneke Hille Ris Lambers Ross Miller Joshua J Tewksbury
author_sort	Haldre Rogers
title	'Natural experiment' demonstrates top-down control of spiders by birds on a landscape level.
title_short	'Natural experiment' demonstrates top-down control of spiders by birds on a landscape level.
title_full	'Natural experiment' demonstrates top-down control of spiders by birds on a landscape level.
title_fullStr	'Natural experiment' demonstrates top-down control of spiders by birds on a landscape level.
title_full_unstemmed	'Natural experiment' demonstrates top-down control of spiders by birds on a landscape level.
title_sort	'natural experiment' demonstrates top-down control of spiders by birds on a landscape level.
publisher	Public Library of Science (PLoS)
publishDate	2012
url	https://doaj.org/article/73a6eb55886b40c490f8fdb3434ed6bb
work_keys_str_mv	AT haldrerogers naturalexperimentdemonstratestopdowncontrolofspidersbybirdsonalandscapelevel AT jannekehillerislambers naturalexperimentdemonstratestopdowncontrolofspidersbybirdsonalandscapelevel AT rossmiller naturalexperimentdemonstratestopdowncontrolofspidersbybirdsonalandscapelevel AT joshuajtewksbury naturalexperimentdemonstratestopdowncontrolofspidersbybirdsonalandscapelevel
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'Natural experiment' demonstrates top-down control of spiders by birds on a landscape level.

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