Geoscience Reference
In-Depth Information
PPMR has been measured in pattern-oriented approaches based on em-
pirical data obtained from natural ecosystems (
Barnes et al., 2008; Brose
et al., 2006a; Woodward and Warren, 2007
). It is therefore difficult to
understand fully the factors that mediate predator-prey size relationships.
On the other hand, looking back over the history of ecology, we easily find a
large amount of process-oriented work on predator-prey interactions (e.g.
functional responses and strength distribution) and associated ecological
consequences (e.g. system stability and species coexistence). In particular, it
has recently been acknowledged that weak interactions and optimal foraging
have stabilising effects on food webs (e.g.
Kondoh, 2003; McCann et al.,
1998
). These studies have either explicitly or implicitly assumed that different
species would behave differently for predation and predation avoidance,
which is in sharp contrast to the conventional view that PPMR is common
among all species. To bridge the gap between pattern-oriented and process-
oriented approaches, it is necessary to obtain a more detailed evaluation on
the role of body size and species identity in predation processes. Indeed,
empiricists are now becoming more interested in these issues.
The functional response is a key concept to explain predator-prey inter-
actions and its dynamic consequences on food webs. Traditionally, the
concept has ignored the effects of body size, simply representing how the
foraging efficiency of a predator individual varies with prey density, where
species identity is a matter. Now, it is expected that the functional response is
affected by the body sizes of interacting predators and prey. Several experi-
ments have tested the possibility for various predator and prey taxa. For
example,
Elliot (2005)
showed that different size classes of Trichoptera
individuals have different forms of functional response for Chironomidae
larvae. Further,
Moss and Beauchamp (2007)
used different species of sal-
monid fish to illustrate that size-dependent functional responses are species
specific. Some researchers have examined more closely how functional
response parameters, such as attack rate and handling time, are related to
predator and prey body sizes and species identities (e.g.
Aljetlawi et al., 2004;
Vucic-Pestic et al., 2010
). Recently,
Rall et al. (2011)
used AIC to show a
combined functional response for terrestrial arthropods, showing that both
body mass and taxonomic effects performed better than a species-specific
functional response (which does not account for intraspecific body-size
variations of predators) or an allometric functional response (which does
not account for taxonomic dissimilarities). Collectively, existing studies have
established that the strength of predator-prey interactions typically depend
on population abundances, species identities, and the body masses of inter-
acting predators and prey. This seems robust to taxonomic groups, including
fish, being consistent with our findings of the gut content data of marine
food webs.
