Experimental climate change weakens the insurance effect of biodiversity

Ecosystems are simultaneously affected by biodiversity loss and climate change, but we know little about how these factors interact. We predicted that climate warming and CO2-enrichment should strengthen trophic cascades by reducing the relative efficiency of predation-resistant herbivores, if herbivore consumption rate trades off with predation resistance. This weakens the insurance effect of herbivore diversity. We tested this prediction using experimental ocean warming and acidification in seagrass mesocosms. Meta-analyses of published experiments first indicated that consumption rate trades off with predation resistance. The experiment then showed that three common herbivores together controlled macroalgae and facilitated seagrass dominance, regardless of climate change. When the predation-vulnerable herbivore was excluded in normal conditions, the two resistant herbivores maintained top-down control. Under warming, however, increased algal growth outstripped control by herbivores and the system became algal-dominated. Consequently, climate change can reduce the relative efficiency of resistant herbivores and weaken the insurance effect of biodiversity.

Eklöf J. S., Alsterberg C., Havenhand J. N., Sundbäck K., Wood H. L. & Gamfeldt L., in press. Experimental climate change weakens the insurance effect of biodiversity. Ecology Letters. doi: 10.1111/j.1461-0248.2012.01810.x. Article (subscription required).

1 Response to “Experimental climate change weakens the insurance effect of biodiversity”

  1. 1 Johan Eklöf 11 June 2012 at 19:14

    I just saw that our new paper had been mentioned in this blog (Eklöf et al. 2012, Ecol Lett). I can take the opportunity to describe the effects we saw from ocean acidification in the experiment, which due to space limitation did not receive much focus in the paper abstract. Generally, the effects of OA (-0.35 pH units vs. control) were weak; algal grazers (Gammarus locusta, Littorina littorea and Rissoa sp.) showed no effects of OA. A mixed group of macroalgae (Cladophora, Ulva, Polysiphonia) showed no response to OA. Eelgrass (Zostera marina) benefitted slightly from OA in normal water temperature, most likely because it is CO2-limited. In combination with warming (a known stressor on eelgrass growth), this positive OA effect disappeared completely. Consequently, in relation to effects of changes in grazer diversity and environmental warming, OA effects were weak. The most likely explanation is that because eelgrass beds – like other shallow, vegetated ecosystems – experience diel pH changes that greatly exceed the predicted changes in OA for the next century, most of the organisms are quite tolerant to OA. Another explanation may be that we here looked at the effects of OA in relatively complex and variable systems of interacting organisms (whereas a majority of OA studies use use single-species experiments).

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