Higher biodiversity is required to sustain multiple ecosystem processes across temperature regimes

Abstract

Biodiversity loss is occurring rapidly worldwide, yet it is uncertain whether few or many species are required to sustain ecosystem functioning in the face of environmental change. The importance of biodiversity might be enhanced when multiple ecosystem processes (termed multifunctionality) and environmental contexts are considered, yet no studies have quantified this explicitly to date. We measured five key processes and their combined multifunctionality at three temperatures (5, 10 and 15 °C) in freshwater aquaria containing different animal assemblages (1-4 benthic macroinvertebrate species). For single processes, biodiversity effects were weak and were best predicted by additive-based models, i.e. polyculture performances represented the sum of their monoculture parts. There were, however, significant effects of biodiversity on multifunctionality at the low and the high (but not the intermediate) temperature. Variation in the contribution of species to processes across temperatures meant that greater biodiversity was required to sustain multifunctionality across different temperatures than was the case for single processes. This suggests that previous studies might have underestimated the importance of biodiversity in sustaining ecosystem functioning in a changing environment.

Keywords: ecosystem functioning; environmental warming; functional redundancy; multifunctionality; species richness.

Figure 1

Relationships between fitted values for model ‘Type × Temperature’ and observed rates of ecosystem processes (a–e). Circles, squares and triangle symbols correspond to 5, 10 and 15 °C temperature treatments respectively. Solid lines represent 1: 1 fits and dashed lines prediction intervals (± 2 SD). Coefficient of variation values (r²) are given for the variation explained by the model in the analysis (Table S1).

Figure 2

Relationships between species richness and multifunctionality at different environmental temperatures. Panels a–c show relationships for multifunctionality thresholds of 25%, 50% and 75% of maximum observed process rates (R_max) with temperature. Panels d–f show the slope of the relationship between species richness and multifunctionality at multiple threshold values (1–83% of R_max) for different temperatures. The 95% confidence intervals (indicated in grey) around the estimated slopes (filled data points) indicate whether the intervals contain zero, giving a test of the threshold values at which diversity has no effect on multifunctionality. T_min and T_max are the slopes with the lowest and highest threshold that is different from zero, respectively. T_mde is the threshold with the steepest slope and R_mde shows the maximum slope estimated at T_mde.