Complementarity in marine biodiversity manipulations: Reconciling divergent evidence from field and mesocosm experiments

Abstract

Mounting concern over the loss of marine biodiversity has increased the urgency of understanding its consequences. This urgency spurred the publication of many short-term studies, which often report weak effects of diversity (species richness) driven by the presence of key species (the sampling effect). Longer-term field experiments are slowly accumulating, and they more often report strong diversity effects driven by species complementarity, calling into question the generality of earlier findings. However, differences among study systems in which short-and long-term studies are conducted currently limit our ability to assess whether these differences are simply due to biological or environmental differences among systems. In this paper, we compared the effect of intertidal seaweed species richness on biomass accumulation in mesocosms and field experiments using the same pool of species. We found that seaweed species richness increased biomass accumulation in field experiments in both short (2-month) and long (3-year) experiments, although effects were stronger in the longterm experiment. In contrast, richness had no effect in mesocosm experiments, where biomass accumulation was completely a function of species identity. We argue that the short-term experiments, like many published experiments on the topic, detect only a subset of possible mechanisms that operate in the field over the longer term because they lack sufficient environmental heterogeneity to allow expression of niche differences, and they are of insufficient length to capture population-level responses, such as recruitment. Many published experiments, therefore, likely underestimate the strength of diversity on ecosystem processes in natural ecosystems. diversity-ecosystem function ͉ seaweed ͉ species identity ͉ intertidal ͉ algae

The relative importance of species diversity and functional group diversity on carbon uptake in phytoplankton communities

“…Although we do not know if this happened in those experimental communities, it corresponds well with the complementarity effect being negative on average. A common hypothesis states that in experimental studies, namely in highly controlled laboratory experiments, monocultures often perform better than mixtures just due to the simplified environment (Duffy 2009;Powder and Cardinale 2009) or the relatively short experimental period (Cardinale et al 2007;Stachowicz et al 2008). This would even point toward a possible underestimation of diversity effects such as resource-use complementarity in mesocosm experiments, as compared with real-world ecosystems.…”

Integrating Different Organizational Levels in Benthic Biodiversity – Ecosystem Functioning (BEF) Studies

“…As the experiment of, e.g., , very elegantly shows, disturbance may dampen strong single-species effects. It is more probable that changing environmental conditions allow resource partitioning among species, and that under natural conditions, such disproportionate key species effects are greatly reduced allowing stronger diversity effects per se (Stachowicz et al, 2008). Moreover, there are many possibilities to include more organisms, species and/or trophic levels and functional groups in an extended version of our setup.…”

“…Although short-term experiments are valuable in estimating the effects of species richness and identity on ecosystem processes, they are likely to be unable to capture seasonal environmental heterogeneity and population responses. Therefore, they are likely to underestimate the influence of diversity on ecosystem processes in natural ecosystems (Stachowicz et al, 2008).…”

Biodiversity: Rack and field

“…In 2008, they compared the effect of seaweed species richness on biomass in field plots on Pacific shores and in experimental tidal beds 9 . They found that more species meant a higher rate of biomass accumulation in the field, but not in the experimental chamber.…”