Multiple anthropogenic stressors cause ecological surprises in boreal lakes

Abstract

The number of combinations of anthropogenic stressors affecting global change is increasing; however, few studies have empirically tested for their interactive effects on ecosystems. Most importantly, interactions among ecological stressors generate nonadditive effects that cannot be easily predicted based on single-stressor studies. Here, we corroborate findings from an in situ mesocosm experiment with evidence from a wholeecosystem manipulation to demonstrate for the first time that interactions between climate and acidification determine their cumulative impact on the food-web structure of coldwater lakes. Interactions among warming, drought, and acidification, rather than the sum of their individual effects, best explained significant changes in planktonic consumer and producer biomass over a 23-year period. Further, these stressors interactively exerted significant synergistic and antagonistic effects on consumers and producers, respectively. The observed prevalence of long-and short-term ecological surprises involving the cumulative impacts of multiple anthropogenic stressors highlights the high degree of uncertainty surrounding current forecasts of the consequences of global change.

Uncovering emergent interactions in three-way combinations of stressors

“…Empirical studies of ecotoxicology and ecological disturbances have examined the nature of interactions in the laboratory [13][14][15] and in the wild [16,17]. Both synergistic [18][19][20][21][22][23][24][25] and antagonistic [23,[26][27][28][29] interactions have been uncovered in a wide range of organisms, environments and systems that range from gene epistasis [30][31][32] to predator-prey interactions [33].…”

Form, function and physics: the ecology of biogenic stabilisation

“…Sedimentary habitats are subject to multiple stressors of both anthropogenic and climatic origin (Christensen et al 2006;Kenworthy et al 2016), the intensities of which are likely to increase in the coming decades (Halpern et al 2008). The effect of these changes on sediment dynamics remains difficult to predict.…”

“…As natural habitats are subject to daily multiple stressors, the addition of a new perturbation will interact with present conditions often in an unpredictable manner. For example, Christensen et al (2006) conducted long-term observational studies in combination with mesocosm experiments in boreal lake systems. Feedback mechanisms between changing climatic conditions and acidification led to ecological surprises that were unpredictable based upon their additive impact.…”

Untangling interactions: do temperature and habitat fragmentation gradients simultaneously impact biotic relationships?

“…This may perhaps be related to the trophic-level hypothesis [55], whereby there is a loss of biological insurance (i.e. the capacity for diverse communities to be more resilient to perturbations (sensu [56]) as taxonomic, physiological and genetic diversity is reduced towards apex populations [52]). Multiple drivers have been found to exert more negative impacts on these top trophic-level organisms [2].…”

“…Although detection of higher order interactions typically precludes the requirement to analyse lower order interactions [51], here, similar to Christensen et al [52], we used these models comprising individual effects and lower order interactions to help interpret higher order interaction models. Interaction effect sizes (F-values) were subtracted from the sum of main effect sizes producing values representing the difference between additive and interactive effects.…”