The simultaneous inference of zooplanktivorous fish and macrophyte density from sub‐fossil cladoceran assemblages: a multivariate regression tree approach

Abstract

1. Quantitative palaeolimnology has traditionally sought to quantify species-environment relationships to use alterations in biological assemblages to reflect past environmental change. Transfer functions have used regression techniques, such as weighted averaging, to define taxon optima and tolerance for a single chemical or biological variable. 2. Cladoceran assemblages and their sub-fossil remains in shallow lakes are shaped by a combination of interacting factors. Partial constrained ordination of sub-fossil cladoceran assemblages from 39 shallow lakes (29 in Norfolk, U.K. and 10 in Denmark) indicated that both zooplanktivorous fish (ZF) density and submerged macrophyte abundance significantly influenced community composition. These dual structuring forces precluded the use of a transfer function as one of the key assumptions of this approach was not met, namely that environmental variables apart from the variable being modelled have negligible influence on species distribution or that there is a linear relationship between the two. Separate transfer functions for ZF and macrophyte abundance were developed but had poor performance diagnostics with low bootstrapped r 2 , high root mean square error of prediction (RMSEP) and large bias. 3. To obviate the problem of multiple structuring forces a multivariate regression tree (MRT) was employed, which allows for more than one explanatory variable within a model. The MRT analysis defined six groups with discrete ranges of ZF and macrophyte densities. The technique identified critical values or 'break points' in ZF and macrophyte abundances which result in significant alterations in the sub-fossil cladoceran assemblage. In addition, the MRT groups had different summer mean values for chlorophyll-a, Secchi depth, total phosphorus and nitrate-nitrogen. 4. The predictive abilities of the model were assessed by comparing the observed versus predicted MRT group membership. In general group membership was reliably predicted, suggesting sub-fossil cladoceran assemblages reliably reflect ZF and macrophyte density in shallow lakes. For a relatively small number of sites there were differences between the observed and predicted MRT group membership. These failures of prediction may result, at least in part, from the disparity of the time Correspondence: Thomas Davidson, Environmental period represented by the environmental data and the surface sediment cladoceran assemblage.

Intra-lake heterogeneity of sedimentary cladoceran (Crustacea) assemblages forced by local hydrology

“…2), its littoral affinities in the lake may have been driven by these food-rich vegetative habitats because it is shown to aggregate at food-rich habitats among macrophytes (Cerbin et al, 2003). However, since top-down control of fish on cladoceran zooplankton is well established and also more important in shallow sites (Jeppesen et al, 1997(Jeppesen et al, , 2003, and the coupling effects of fish and aquatic macrophytes in structuring cladoceran communities are well known (Jeppesen et al, 1997;Davidson et al, 2007Davidson et al, , 2010a, fish predation and presence of macrophytes most likely had high influence in structuring the intra-lake distribution of cladoceran zooplankton in Lake PieniKauro. In addition to horizontal migration from pelagial into littoral macrophyte stands occurring as a means to avoid fish predation (Burks et al, 2002), 'shore avoidance' behavior of large-bodied zooplankton acts as an efficient mechanism to avoid high predation risk in near-shore habitats (Gliwicz & Rykowska, 1992).…”

“…In addition, cladocerans are not a homogenous group in respect to their habitats, feeding, or positions in the foodwebs, and several other chemical and physical Table 2 Distribution of most abundant body parts (C = carapace, H = headshield, P = postabdomen, E = ephippium) of the common chydorid species (shown in Fig. 2) encountered in Lake Pieni-Kauro and River Saavanjoki along the water depth gradient from the shallowest (1) (Korhola, 1999;Jeppesen et al, 2001;Amsinck et al, 2005;Sweetman & Smol, 2006;DeSellas et al, 2008;Davidson et al, 2010a). The ordinations specified some habitat affinities (Figs.…”

Topical advances and recent studies in paleolimnological research

“…Recent studies have presented innovative ways of addressing the fact that multiple rather than single structuring forces tend to influence changes in lake communities. Davidson et al (2010a) showed that both submerged macrophyte abundance and zooplanktivorous fish influence cladoceran communities in shallow lakes of the UK and Denmark, and they developed a multivariate regression tree model that incorporated both explanatory variables. They observed six break points at which fish density and macrophyte abundance influenced significant changes in sub-fossil cladoceran assemblages.…”

The usefulness of subfossil Cladocera remains in Younger Dryas climatic reconstructions in central Poland

“…Size-selective predation on larger cladoceran species could increase the relative abundance of some planktonic species. For example, the rise of Bosmina longirostris in concert with the density of zooplanktivorous fish could also result in an absence of Daphnia pulex (Davidson et al 2010). However, changes associated with size-selective predation of larger species (e.g., Daphnia spp.)…”

“…sphaericus; a slight increase in zooplanktivorous fish density may have resulted in the absence of these taxa. These cladocerans are abundant in temperate lakes and mires and are strongly associated with the presence of aquatic macrophytes at lower fish densities (Davidson et al 2010). However, their T July optima are similar to those of small-bodied Bosminidae, ca.…”