Resource-niche complementarity and autotrophic compensation determines ecosystem-level responses to increased cladoceran species richness

Abstract

This study examines the relationship between cladoceran species richness and ecosystem functioning. I conducted an experiment in which four cladocerans, Daphnia. magna, D. longispina, D. pulex and Chydorus sphaericus, were cultured in microcosms using different species combinations and levels of species richness. The results demonstrate that even within this closely related group of organisms the effects on ecosystem-level variables, such as total algae and zooplankton biomass, per capita productivity, and nutrient concentrations, as well as phytoplankton community structure, were highly variable between different combinations of these species. Since only four species where involved in this study, species-specific effects dominated the general relationship between species richness and ecosystem functioning. Particular combinations of species resulted in effects that indicated more efficient grazing. These effects, which were most pronounced in combinations including both D. magna and C. sphaericus, were manifested as an indirect effect as the prey community shifted towards grazing-resistant species. As a result, the productivity of the prey community decreased, because phytoplankton species with lower per capita productivity became more dominant. I suggest that the primary mechanism that caused this significant effect was complementarity in prey-size use of D. magna and C. sphaericus. In terms of prey-size range, D. pulex and D. longispina were redundant when D. magna was present and were quickly out-competed by the latter despite higher per capita filtering efficiency. The results show that different mechanisms are important for different combinations of species. Furthermore, the ability of the prey community to respond to changes of consumer species composition is an important factor in experiments in which consumer species richness is experimentally manipulated.

Food-web constraints on biodiversity–ecosystem functioning relationships

“…However, trophic cascades lead also to variations in plant species evenness (32), which affects plant biomass and productivity. Second, food-web connectivity, which is determined by the degree of generalization or specialization of consumers, also has a significant influence on the relationship between biodiversity and ecosystem functioning through changes in resource-use complementarity (33) and species abundances due to direct and indirect effects (34). A more complex food web does not lead in this model to synergistic effects of species richness on productivity, as suggested recently (18).…”

Resistant Microbial Cooccurrence Patterns Inferred by Network Topology

“…While it can be argued that bacterial communities feature a sufficiently high functional redundancy to fill any temporarily vacated niche over time, this may not be evident for phytoplankton and zooplankton. Previous results demonstrate that despite functional redundancy among zooplankton species, the effects of ecosystem-level variables, such as phytoplankton community structure, can be highly variable for different species combinations even within closely related organisms (43). Thus, taxa at different trophic levels may not be equal in terms of functional redundancy.…”

Biodiversity and ecosystem functioning: A complex adaptive systems approach

“…The research was funded by grants from the Swedish research council. er et al 1999;Petchey and Gaston 2002), (2) what the processes relating regional to local species abundances are, i.e., metacommunity/ecosystem dynamics (Bond and Chase 2002;Loreau et al 2003;Leibold and Norberg 2004) and species area relationships (Plotkin et al 2000;Hubbel 2001) (3) how species sorting processes affect local trait distributions (Chase and Leibold 2003), and (4) how trait distributions in the community, i.e., dominant and subdominant traits, relate to ecosystem functioning (Norberg at al. 2001).…”

“…If such traits correlate to the fitness of individuals, there exists a tradeoff gradient on which selection can act (Fisher 1958). This notion can be extended to interspecies comparisons of traits (Grime et al 1997;Reynolds 1997;Norberg et al 2001). If traits correlate with specific growth rate, we can think of them as interspecies tradeoff relationships.…”

“…In many experiments an initial sampling effect was evident because of the way the experiment was set up, but over time as competition takes place complementarity effects become more pronounced (Pacala and Tilman 2003). Furthermore, some traits relate the efficiency to environmental parameters such as temperature or pH (Norberg et al 2001). Functional groups, commonly used as the unit of ecosystem networks, are here defined as a group of species having similar resource requirements (i.e., sharing essential resources) and thus potentially competing for them (Steneck 2001).…”