To explore possible determinants of feeld PPSR, we tested four statistical models following : (i) a null model, where prey BW is common among all predators (i.e. logten(prey BW) = ?), (ii) a taxonomic model, where prey BW is species-specific (i.e. logten(prey BW) = ? + ? ? (predator species identity)), (iii) an allometric model, where prey BW is size-dependent (i.e. log10(prey BW) = ? + ? ? log10(predator BW)), and (iv) a combined model (i.e. log10(prey BW) = ? + ?1 ? (predator species identity) + ?2 ? log10(predator BW) + ?step three ? (predator species identity) ? log10(predator BW)). Here, BW represented individual weights for individual-link PPSR, whereas the mean measurements were used for the other definitions. Calculating the Akaike information criterion (AIC) by ordinary least-squares regression, we determined the best statistical model for each definition. All analyses (including calculations of parameters ? and ?) were conducted using the software R .
step three. Show
For all the definitions, PPMR generally ranged between 0 and 1 on a log scale, i.e. the predators and prey had similar body sizes of the same order of magnitude (figure 2a). For species-averaged definition, K. deyrolli had larger prey BW than the other species (p < 0.05, figure 2b). For link-averaged definition, A. japonicus and L. japonensis increased their prey size as they grew, whereas K. deyrolli did not (figure 2c). For individual-link definition, all species showed increases in prey BW during growth, but the regression slope of K. deyrolli was significantly lower than the other species (figure 2d). These results indicate that the effects of predator size and species identity were scale-dependent. We plotted contour lines of PPMR (grey lines) in each panel of figure 2b–d. By comparing these contours with the regressions of predator versus prey BW, we can infer how PPMR during growth (also see the electronic supplementary material, S4 for direct comparison of PPMR versus predator size). We found that K. deyrolli clearly increased individual-link PPMR as it grew (i.e. the regression slope was significantly less than 1), whereas the other two predators had slightly R during growth (i.e. the regression slope is greater than 1) (figure 2d). The AIC values showed that species-averaged prey BW was best explained by the allometric model, whereas link-averaged and individual-link prey BWs were best explained by the combined model (table 1; see the electronic supplementary material, S5 for model selection to explain PPMR).
Figure 2. (a) The three definitions of PPMR are shown in box plots. The thick and dashed lines represent the median and mean values, respectively. (b) Species-averaged prey body weight (BW), (c) link-averaged prey BW, and (d) individual-link prey BW are plotted against predator BW on a log–log scale. The open circles with dotted regression, grey squares with dashed regression and black diamonds with solid regression represent A. japonicus, K. deyrolli and L. japonensis, respectively. The grey lines represent contours of PPMR on a log scale. Only significant regressions were shown in (c) and (d). Different superscripts indicate significant differences in regression slope or intercept between species (p < 0.05), and ‘p' columns indicate the significance of the regressions.
4. Conversation
To your knowledge, this is the basic had written just be sure to formally define PPSR whenever predators can also be eat victim larger than by themselves. The knowledge showed that PPSR ranged that have predator size and types title, while the utilization of the averaged systems puzzled this type of consequences (contour 2b–d and you will dining table 1). That it scale dependency is in line with one to in seafood tummy articles datasets . Somewhat, however, our very own results revealed that varieties averaging builds a deceptive image of actual serving relationships whilst it cannot affect PPMR (shape 2a), while earlier studies managed this dilemma according to the meaning dependency out of PPMR [seven,fourteen,15]. Ergo, it’s important to check out the variability while the determinants out of PPSR from the personal level.
Importantly, PPSR will be defined in various implies with respect to the meaning of dimensions [seven,ten,fourteen,15]. Right here, i thought three significance adopting the [eight,ten,14]: (i) ‘species-averaged PPSR’ hence spends suggest looks loads (BW) of predator and sufferer variety, (ii) ‘link-averaged PPSR’ hence uses suggest BW away from predators and victim someone that really consume or try ate by connecting varieties, and you may (iii) ‘individual-link PPSR’ and that uses predator and you can target personal BW for each query experiences. Keep in mind that the last represents the genuine eating dating. I compared sufferer BW among predators that with a standardized major axis (SMA) process to at exactly the same time imagine differences in the 2 axes . To own varieties-averaged PPSR, we just utilized you to definitely-way ANOVA once the SMA was not applicable. It would be good for is private label off predators as a haphazard basis to quit a possible pseudo-duplication issue , but really it was not feasible just like the predators i checked moult and you will shed decorate marks for individual identification; yet not, this would perhaps not affect our very own biggest conclusions. I in addition to evaluated predator–prey size percentages (PPMRs) in proportions-mainly based food-websites studies, with the about three meanings (see the digital secondary thing, S3).
