Geoscience Reference
In-Depth Information
ABSTRACT
Body size exerts a critical influence on predator-prey interactions and is
therefore crucial for understanding the structure and dynamics of food
webs. Currently, predator-prey mass ratio (PPMR) is regarded as the most
promising modelling parameter for capturing the complex patterns of feed-
ing links among species and individuals in a simplified way. While PPMR has
been widely used in food-web modelling, its empirical estimation is more
difficult, with the methodology remaining controversial. This is because
PPMR (i) may be defined at different biological scales, such as from indivi-
duals to communities, and (ii) may also vary with biological factors, such as
species identity and body mass, both of which conflict with the conventional
model assumptions. In this chapter, we analyse recently compiled gut content
data of marine food webs to address the two fundamental issues of scale-
dependence and determinants of PPMR. We consider four definitions of
PPMR: (i) species-averaged PPMR, (ii) link-averaged PPMR, (iii) individu-
al-predator PPMR, and (iv) individual-link PPMR. First, we show that
PPMR values have a complicated scale-dependence characterised by data
elements, such as body mass and sample counts of predators and prey, due to
averaging and sampling effects. We subsequently used AIC to systematically
evaluate how the four types of PPMR are related to predator species identity
and body mass. The results indicate that the model providing the best
explanation for individual-predator and individual-link PPMRs incorpo-
rates both species identity and body mass. Meanwhile, the best model for
species-averaged and link-averaged PPMRs was unclear, with different mod-
els being selected across sampling sites. These results imply that the size-
based community-spectrum models describing individual-level interactions
should include taxonomic dissimilarities. Based on the present study, we
suggest that future research regarding PPMR must account for scale depen-
dence and associated determinants to improve its utility as a widely applica-
ble tool.
I. INTRODUCTION
A. Size Matters to Food Webs
Body size is regarded as a key parameter towards understanding ecological
systems at multiple biological levels (
Hildrew et al., 2007; Woodward et al.,
2010; Yvon-Durocher et al., 2011b
). Body size characterises individual fitness
and behaviour, and thus should be directly linked with the processes and
patterns occurring at the individual level. Body size exerts a critical influence
on various feeding-related behaviours of individuals, such as predation and
