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Animal water balance drives top-down effects in a riparian forest-implications for terrestrial trophic cascades.

ABSTRACT: Despite the clear importance of water balance to the evolution of terrestrial life, much remains unknown about the effects of animal water balance on food webs. Based on recent research suggesting animal water imbalance can increase trophic interaction strengths in cages, we hypothesized that water availability could drive top-down effects in open environments, influencing the occurrence of trophic cascades. We manipulated large spider abundance and water availability in 20 × 20 m open-air plots in a streamside forest in Arizona, USA, and measured changes in cricket and small spider abundance and leaf damage. As expected, large spiders reduced both cricket abundance and herbivory under ambient, dry conditions, but not where free water was added. When water was added (free or within moist leaves), cricket abundance was unaffected by large spiders, but spiders still altered herbivory, suggesting behavioural effects. Moreover, we found threshold-type increases in herbivory at moderately low soil moisture (between 5.5% and 7% by volume), suggesting the possibility that water balance may commonly influence top-down effects. Overall, our results point towards animal water balance as an important driver of direct and indirect species interactions and food web dynamics in terrestrial ecosystems.

SUBMITTER: McCluney KE

PROVIDER: S-EPMC5013762 | biostudies-literature | 2016 Aug

REPOSITORIES: biostudies-literature

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Animal water balance drives top-down effects in a riparian forest-implications for terrestrial trophic cascades.

McCluney Kevin E KE Sabo John L JL

Proceedings. Biological sciences 20160801 1836

Despite the clear importance of water balance to the evolution of terrestrial life, much remains unknown about the effects of animal water balance on food webs. Based on recent research suggesting animal water imbalance can increase trophic interaction strengths in cages, we hypothesized that water availability could drive top-down effects in open environments, influencing the occurrence of trophic cascades. We manipulated large spider abundance and water availability in 20 × 20 m open-air plots ...[more]

PMID: 27534953

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Project description:Learning is a behavioural change based on memory of previous experiences and a ubiquitous phenomenon in animals. Learning effects are commonly life-stage- and age-specific. In many animals, early life experiences lead to pervasive and persistent behavioural changes.There is broad consensus that learning has far-reaching implications to biological control. Proximate and ultimate factors of individual learning by parasitoids and true predators are relatively well understood, yet the consequences of learning to higher organizational levels, populations and communities, and top-down trophic cascades are unexplored.We addressed this issue using a tri-trophic system consisting of predatory mites Amblyseius swirskii, Western flower thrips Frankliniella occidentalis and whole common bean plants, Phaseolus vulgaris. F. occidentalis are notorious horticultural pests that are difficult to control. Therefore, practitioners have much to gain by optimizing biological control of thrips.Previous studies have shown that early life experience of thrips by A. swirskii improves foraging on thrips later in life due to decreased prey recognition times and increased predation rates, together enhancing predator fecundity. Here, we hypothesized that early learning by A. swirskii enhances biological control of thrips via immediate and cascading effects. We predicted that release of thrips-experienced predators enhances predator population growth and thrips suppression and reduces plant damage as compared to release of thrips-naïve predators.The behavioural changes brought about by early learning cascaded up to the population and community levels. Thrips-experienced predators caused favourable immediate and cascading effects that could not be compensated for in populations founded by thrips-naïve predators. Populations founded by thrips-experienced predators grew faster, reached higher abundances, were more efficacious in suppressing an emerging thrips population and kept plant damage at lower levels than populations founded by thrips-naïve predators. Plant fecundity correlated negatively with thrips abundance and positively with predatory mite abundance. Improved biological control was mainly due to thrips-experienced founders providing for a head-start in predator population growth and thrips suppression. Synthesis and applications. Our study suggests that learned natural enemies have high potential to optimize augmentative biological control on a larger scale due to favourably modulating organizational upward and trophic top-down cascades.

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Animal water balance drives top-down effects in a riparian forest-implications for terrestrial trophic cascades.

Publications

Animal water balance drives top-down effects in a riparian forest-implications for terrestrial trophic cascades.

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