A conditional trophic cascade: Birds benefit faster growing trees with strong links between predators and plants

William T. Bridgeland, Paul Beier, Thomas E Kolb, Thomas G Whitham

Research output: Contribution to journalArticle

42 Citations (Scopus)

Abstract

Terrestrial systems are thought to be organized predominantly from the bottom-up, but there is a growing literature documenting top-down trophic cascades under certain ecological conditions. We conducted an experiment to examine how arthropod community structure on a foundation riparian tree mediates the ability of insectivorous birds to influence tree growth. We built whole-tree bird exclosures around 35 mature cottonwood (Populus spp.) trees at two sites in northern Utah, USA, to measure the effect of bird predation on arthropod herbivore and predator species richness, abundance, and biomass, and on tree performance. We maintained bird exclosures over two growing seasons and conducted nondestructive arthropod surveys that recorded 63 652 arthropods of 689 morphospecies representing 19 orders. Five major patterns emerged: (1) We found a significant trophic cascade (18% reduction in trunk growth when birds were excluded) only at one site in one year. (2) The significant trophic cascade was associated with higher precipitation, tree growth, and arthropod abundance, richness, and biomass than other site-year combinations. (3) The trophic cascade was weak or not evident when tree growth and insect populations were low apparently due to drought. (4) Concurrent with the stronger trophic cascade, bird predation significantly reduced total arthropod abundance, richness, and biomass. Arthropod biomass was 67% greater on trees without bird prédation. This pattern was driven largely by two herbivore groups (folivores and non-aphid sap-feeders) suggesting that birds targeted these groups. (5) Three species of folivores (Orthoptera: Melanoplus spp.) were strong links between birds and trees and were only present in the site and the year in which the stronger trophic cascade occurred. Our results suggest that this trophic system is predominately bottom-up driven, but under certain conditions the influence of top predators can stimulate whole tree growth. When the most limiting factor for tree growth switched from water availability to herbivory, the avian predators gained the potential to reduce herbivory. This potential could be realized when strong links between the birds and plant, i.e., species that were both abundant herbivores and preferred prey, were present.

Original languageEnglish (US)
Pages (from-to)73-84
Number of pages12
JournalEcology
Volume91
Issue number1
DOIs
StatePublished - Jan 2010

Fingerprint

trophic cascade
predator
bird
predators
arthropod
birds
herbivores
tree growth
arthropods
herbivore
biomass
herbivory
Melanoplus
insect surveys
predation
arthropod communities
Populus
Orthoptera
sap
tree trunk

Keywords

  • Bird predation
  • Bottom-up
  • Community efjects
  • Foundation species
  • Herbivory
  • Limiting factor
  • Populus
  • Predator removal
  • Strong interactors
  • Top-down
  • Trophic cascade

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics

Cite this

A conditional trophic cascade : Birds benefit faster growing trees with strong links between predators and plants. / Bridgeland, William T.; Beier, Paul; Kolb, Thomas E; Whitham, Thomas G.

In: Ecology, Vol. 91, No. 1, 01.2010, p. 73-84.

Research output: Contribution to journalArticle

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