Realism of model ecosystems: an evaluation of physicochemistry and macroinvertebrate assemblages in artificial streams

Abstract

Ecological realism is an important yet rarely reported feature of model ecosystems. In this case study, we assess the realism of four outdoor artificial stream mesocosms (4 m 2 ) bordering a chalk river in southern England. Comparisons of physiochemical conditions and benthic macroinvertebrate assemblages were made between the mesocosm units and the parent water body, a side arm of the River Frome. Physicochemistry of the mesocosm replicates was similar to that of the source stream, with congruent temporal variation evident between the real system and each of the models. The high realism of the mesocosms was explained by the outdoor location and close physical proximity of the array to the source stream, and the short mesocosm residence time of water sourced from the parent feeder system. Mesocosms supported a diverse array of benthic macroinvertebrates (60 families from 14 taxonomic orders), including all macroinvertebrate families in the source stream. Individual mesocosms contained a mean of 89% of source stream biota. We conclude that once-through mesocosms can be satisfactory analogues of natural systems, particularly where model and natural scales overlap.

Effects of flow events and nutrient addition on stream periphyton and macroinvertebrates: an experimental study using flumes

“…We therefore believe that diversity in experimental flumes maybe generally lower than in natural stream ecosystems, such as was the case in our experiments. Also Ledger et al (2009) reported less taxa in the flumes than in the stream. This should mean that many flume experiments may lack "ecological realism" (Ledger et al, 2009).…”

“…Also Ledger et al (2009) reported less taxa in the flumes than in the stream. This should mean that many flume experiments may lack "ecological realism" (Ledger et al, 2009). Experiments are necessary in order to deduce causal relationships, since these cannot be inferred from correlative field data.…”

“…However, biodiversity affects stream functioning through interspecific facilitation (Cardinale et al, 2002), and a higher biodiversity is generally assumed to stabilize ecosystem functions in response to disturbances and variation in abiotic conditions (Hooper et al, 2005). However, despite their widespread use in aquatic environments, few publications using flume experiments report the natural diversity of the analyzed organism groups in the nearby lotic ecosystem, and compared it with the diversity in the experimental flumes (but see Ledger et al, 2009). Although we do admit that the number of macroinvertebrate taxa in our flumes may have been enhanced, for example by adding standard loads from kick-net sampling in the Sagelva stream, our experimental design generally is similar to other flume experiments (e.g.…”

Biodiversity, Species Interactions and Ecological Networks in a Fragmented World

“…18). These model systems reflected the abiotic conditions, biodiversity and food web properties of natural streams Harris et al, 2007;Ledger et al, 2009). The results of this fragmentation experiment revealed some dramatic impacts on the food webs: consistent with the higher trophic rank hypothesis (e.g.…”

“…Besides food webs, several examples from other multitrophic systems give an indication of how antagonistic host-parasitoid networks may be affected by fragmentation (Cronin, 2004;Kruess, 2003;Thies et al, 2005 Figure 18 Impacts of habitat fragmentation caused by drought in experimental stream food webs: results from a long-term field experiment in artificial streams Ledger et al, 2008Ledger et al, , 2009Ledger et al, , 2011. Drought can have patchy effects in river networks and individual stream channels can be viewed as fragmented patches in the wider riverscape.…”