Experiments with realistic scenarios of species loss from multitrophic ecosystems may improve insight into how biodiversity affects ecosystem functioning. Using 1000 L mesocoms, we examined effects of nonrandom species loss on community structure and ecosystem functioning of experimental food webs based on multitrophic tropical floodplain lagoon ecosystems. Realistic biodiversity scenarios were developed based on long-term field surveys, and experimental assemblages replicated sequential loss of rare species which occurred across all trophic levels of these complex food webs. Response variables represented multiple components of ecosystem functioning, including nutrient cycling, primary and secondary production, organic matter accumulation and whole ecosystem metabolism. Species richness significantly affected ecosystem function, even after statistically controlling for potentially confounding factors such as total biomass and direct trophic interactions. Overall, loss of rare species was generally associated with lower nutrient concentrations, phytoplankton and zooplankton densities, and whole ecosystem metabolism when compared with more diverse assemblages. This pattern was also observed for overall ecosystem multifunctionality, a combined metric representing the ability of an ecosystem to simultaneously maintain multiple functions. One key exception was attributed to time-dependent effects of intraguild predation, which initially increased values for most ecosystem response variables, but resulted in decreases over time likely due to reduced nutrient remineralization by surviving predators. At the same time, loss of species did not result in strong trophic cascades, possibly a result of compensation and complexity of these multitrophic ecosystems along with a dominance of bottom-up effects. Our results indicate that although rare species may comprise minor components of communities, their loss can have profound ecosystem consequences across multiple trophic levels due to a combination of direct and indirect effects in diverse multitrophic ecosystems.
"The M-index is statistically robust (Maestre et al., 2012), is being increasingly used (e.g. Pendleton et al., 2014; Wagg et al., 2014) and is related to other widely used multifunctionality metrics (Byrnes et al., 2014). Multifunctionality measurements may obscure specific responses for the different soil variables measured. "
[Show abstract][Hide abstract] ABSTRACT: The global spread of woody plants into grasslands is predicted to increase over the coming century. While there is general agreement regarding the anthropogenic causes of this phenomenon, its ecological consequences are less certain. We analyzed how woody vegetation of differing cover affects plant diversity (richness and evenness) and multiple ecosystem functions (multifunctionality) in global drylands, and how this changes with aridity.
224 dryland sites from all continents except Antarctica widely differing in their environmental conditions (from arid to dry-subhumid sites) and woody covers (from 0 to 100%).
Using a standardized field survey, we measured the cover, richness and evenness of perennial vegetation. At each site, we measured 14 ecosystem functions related to soil fertility and the build-up of nutrient pools. These functions are critical for maintaining ecosystem function in drylands.
Species richness and ecosystem multifunctionality were strongly influenced by woody vegetation, with both variables peaking at relative woody covers (RWC) of 41-60%. This relationship shifted with aridity. We observed linear positive effects of RWC in dry-subhumid sites. These positive trends shifted to hump-shaped RWC-diversity and multifunctionality relationships under semiarid environments. Finally, hump-shaped (richness, evenness) or linear negative (multifunctionality) effects of RWC were found under the most arid conditions.
Plant diversity and multifunctionality peaked at intermediate levels of woody cover, although this relationship became increasingly positive under wetter environments. This comprehensive study accounts for multiple ecosystem attributes across a range of woody covers and environmental conditions. Our results help us to reconcile contrasting views of woody encroachment found in current literature and can be used to improve predictions of the likely effects of encroachment on biodiversity and ecosystem services.
Global Ecology and Biogeography 09/2014; 23(12). DOI:10.1111/geb.12215 · 6.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We used a functional trait-based approach to assess the impacts of aridity and shrub encroachment on the functional structure of Mediterranean dryland communities (functional diversity (FD) and community-weighted mean trait values (CWM)), and to evaluate how these functional attributes ultimately affect multifunctionality (i.e. the provision of several ecosystem functions simultaneously). Shrub encroachment (the increase in the abundance/cover of shrubs) is a major land cover change that is taking place in grasslands worldwide. Studies conducted on drylands have reported positive or negative impacts of shrub encroachment depending on the functions and the traits of the sprouting or nonsprouting shrub species considered. FD and CWM were equally important as drivers of multifunctionality responses to both
New Phytologist 01/2015; 206(2). DOI:10.1111/nph.13268 · 7.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Species or functional guild loss from upper trophic positions, i.e., trophic downgrading, will likely have important consequences for ecosystem functioning due to cascading direct and indirect effects. Using 1000 l mesocosms, we examined how sequential loss of species occupying upper trophic positions influenced ecosystem functioning of experimental floodplain lagoon food webs. Treatments were developed based on fish assemblage data from long-term field surveys of tropical floodplain lagoons, and response variables represented multiple components of ecosystem functioning. Sequential loss of species occupying upper trophic positions significantly influenced multiple ecosystem responses including changes in fish assemblage structure, nutrient concentrations, and zooplankton density. Although loss of species from specific functional roles is expected to facilitate predictive understanding of ecosystem consequences, we observed complex and dynamic responses to trophic downgrading that did not follow expectations of strong predicted top-down effects. The highly connected food web structure in our system and relative balance between top-down and bottom-up processes likely suppressed cascading effects. Consequences of biodiversity loss in highly connected multitrophic ecosystems may be difficult to predict as ecosystem responses will likely deviate from simplified food chain dynamics or from patterns that emerged from single trophic level studies.
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