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Little bodies, big roles: Invertebrates are important to ecosystem functionality

Date: October 19, 2018

Without invertebrates, ecosystem functionality declines


Background

Removing both large- and small-bodied animals from an ecosystem has potentially wide-reaching impacts on the functionality of that system. By analyzing the degree of ecosystem coupling (the overall strength of correlation-based associations between above- and belowground plant, animal, and microbial communities) and of communities with their surrounding physicochemical environment, we can gain a better understanding of the consequences of losing interactions between multispecies communities and their environment. Visually and analytically, ecosystem coupling can be represented as a network in which individual species are substituted with multispecies communities (e.g., microbes, plants, and nematodes). Under undisturbed conditions we would expect that the communities are more strongly connected with one another and their abiotic environment than under disturbed conditions.

We carried out a 5-year field experiment in subalpine grasslands in which we progressively excluded large, medium, and small mammalian vertebrates, and, ultimately, all aboveground dwelling invertebrates with size-selective fences. We predicted that the loss of large animals would reduce ecosystem coupling more than a subsequent loss of smaller animals.

The field experiment encompassed 18 size-selective exclosure setups distributed across two clearly differentiated vegetation types in the Swiss National Park (nine in short-grass, nine in tall-grass vegetation). Each exclosure setup contained four treatment plots that progressively excluded large, medium, and small-sized mammals and aboveground dwelling invertebrates. Next to each exclosure (>5m away) a reference plot provided access to all animals. We considered six ecosystem functions and process rates: soil net nitrogen (N) mineralization, soil respiration, plant tissue N content, plant species richness, root biomass, and microbial biomass carbon, and calculated ecosystem multifunctionality based on the multiple threshold approach.

A grid depicting the exclusion conditions: zero exclusion, all mammal exclusion, large mammal exclusion, large and medium mammal exclusion, and all mammal and invertebrate exclusion.
Size-selective fences to progressively exclude vertebrates and invertebrates. Nine exclosure setups were established in each of the two different vegetation types; short-grass and tall-grass vegetation.

Key Findings

  • Exclusion of all mammals results in the greatest level of ecosystem coupling. Under this condition, there was increased interaction between the remaining biological communities and the abiotic environment. The ecosystem continued to function successfully, though these functions changed from what it had been.
  • Exclusion of all mammals and aboveground-dwelling invertebrates led to poorly coupled ecosystems. Under this condition, there was decreased interaction between remaining biological communities (between plants and soil bacteria), as well as decreased interactions between communities and the abiotic environment (between plants and soil nutrients). There was a weakening in above- and belowground networks.
  • Fewer community interactions result in an unstable ecosystem.
  • There is an increasing importance of invertebrate communities for maintaining ecosystems in an increasingly defaunated world. 

Featured Publications

Risch, A. C. ; Ochoa-Hueso, R. ; van der Putten, W. H. ; Bump, J. K. ; Busse, M. D. ; Frey, B. ; Gwiazdowicz, D. J. ; Page-Dumroese, Deborah S. ; Vandegehuchte, M. L. ; Zimmermann, S. ; Schutz, M. , 2018


Principal Investigators: 
Principal Investigators - External: 
A.C. Risch
R. Ochoa-Hueso
W.H. van der Putten
J.K. Bump
M.D. Busse
B. Frey
D.J. Gwiazdowicz
M.L. Vandegehuchte
S. Zimmermann
M. Schütz