DOI: 10.5061/dryad.kh1893259
title: Bryophyte microecosystem experiment

description: Ecosystems face multiple, potentially interacting, anthropogenic pressures
 that can modify biodiversity and ecosystem functioning. Using a
 bryophyte-microarthropod microecosystem we tested the combined effects of
 habitat loss, episodic heat-shocks and an introduced non-native apex
 predator on ecosystem function (chlorophyll fluorescence as an indicator
 of photosystem II function) and microarthropod communities (abundance and
 body size). Photosynthetic function was degraded by the sequence of
 heat-shock episodes, but unaffected by microecosystem patch size or
 top-down pressure from the introduced predator. In small microecosystem
 patches without the non-native predator, Acari abundance decreased with
 heat-shock frequency, while Collembola abundance increased. These trends
 disappeared in larger microecosystem patches or when predators were
 introduced, although Acari abundance was lower in large patches that
 underwent heat shocks and were exposed to the predator. Mean assemblage
 body length (Collembola) was reduced independently in small microecosystem
 patches and with greater heat-shock frequency. Our experimental simulation
 of episodic heat waves, habitat loss and non-native predation pressure in
 microecosystems produced evidence of individual and potentially
 synergistic and antagonistic effects on ecosystem function and
 microarthropod communities. Such complex outcomes of interactions between
 multiple stressors need to be considered when assessing anthropogenic
 risks for biota and ecosystem functioning.
description: 96 experimental replicates comprising a bryophyte microecosystem
 supporting Acari and Collembola communities [40, 41] were randomly excised
 (21 June 2017) using domestic steel circular cookie cutters (110 mm or 50
 mm diameter giving microcosms of 95 cm<sup>2 </sup>and 20
 cm<sup>2</sup>, respectively) from a large, continuous
 bryophyte sward (<i>Mnium hornum</i> Hedw. + rare occurrences
 of <i>Polytrichastrum formosum</i> (Hedw.) G.L. Smith;
 <i>Hypnum andoi</i> A.J.E. Smith) on a brown earth soil in a
 woodland (Bush Estate, Scotland, U.K. 55.861111, -3.205833). The
 microecosystem experiment was carried out at CEH Edinburgh (55.861111,
 -3.205833) over 8 weeks (21/06/2017-11/08/2017). We employed a randomised
 factorial blocked design with three treatments: 1) microecosystem size (95
 cm<sup>2</sup>, n = 48; 20 cm<sup>2</sup>, n =
 48); 2) frequency of heat-shock episodes (‘un-stressed’ controls: n = 32;
 2 episodes: n = 32; 3 episodes: n = 32); and 3) addition of an apex
 predator (Dalotia coriaria -Coleptera present n= 48 or control, n = 48).
 We challenged the microecosystem replicates with experimental episodic
 heat shocks (see below) to simulate short duration heat waves. Replicates
 were randomly assigned to acute heat-shock episodes of two hours duration
 on two or three occasions during the experiment or to a control (no
 heat-shock applied). Experimental heat-shock treatment was applied by
 temporarily and carefully exposing replicate microecosystems for two hours
 beneath 40W light bulbs set within racks of 54 Tullgren extraction funnels
 (Burkard Scientific Ltd). The 96 microecosystems randomly to eight blocks
 (large plastic trays 100 cm x 50 cm x 16 cm) ensuring each contained a
 full replicate of the treatment combinations. Following the 24hr
 destructive harvest at the end of the experiment, we sorted and counted
 all invertebrates collected to the level of taxonomic subclass (Acari,
 Collembola) to provide an estimate of community size (total abundance and
 density per cm<sup>2</sup>).We also measured the body length
 (frons to end of abdomen) of sub-samples of Collembola individuals
 extracted from each large or small microecosystem following application of
 each heat-shock (t1/t2/t3) treatment. Moss community chlorophyll
 fluorescence (<i>Fv/Fm</i>) , as an indicator of
 photosynthetic capacity (photosystem II function) was measured using a
 Continuous Excitation Chlorophyll Fluorimeter (HandyPEA, Hansatech
 Instruments Ltd, UK) on randomly selected bryophyte leaves from each
 microecosystem.
description: Data relates to the open access paper in Proceedings of the Royal
 Society B (under revision).