Geoscience Reference
In-Depth Information
The average body mass of the species populations was either directly
measured (
90%) or in case of marine mammals and seabirds taken from
published accounts (
Brose et al., 2005a
).
>
B. Functional Consumer Classification of the
Weddell Sea Food Web
Although characterising the relationship between ecosystem functioning and
biodiversity is a challenging task, it is widely accepted that functional diversity
of organisms sustains ecosystem functioning (e.g. Loreau et al., 2001;
Reiss
et al., 2009; Schulze andMooney, 1993
). This, however, raises the fundamental
issue of how best to classify a functional species and how to assign functional
traits. That is, what are the characteristics that determine the effect of a species
on an ecosystem? Categorising different types of predation is one way to
classify the extent to which species interact with each other. Instead of focusing
on what they eat (which is covered by the traditional food web approach of
who-eats-whom), we here classify consumers by feeding mode, and the general
nature of the interaction (i.e. herbivorous, carnivorous or omnivorous) be-
tween predator and prey species. More specifically, we consider the feeding
strategy, habitat, andmobility of the consumer and trophic type/position of the
prey as important characteristics of consumer species. We suggest that these are
useful additions to traditional descriptions of food web structure that will aid in
linking food web structure to ecosystem functioning.
In this chapter, consumer species are grouped into 11 categories based on
four suites of traits: feeding strategy, prey type, motility and habitat. Within
each of these four groupings, four sub-groups were identified, outlined
below.
The four main feeding strategies considered are:
(1) Predator: If the consumer feeds upon the prey species that it has directly
killed, either via an active hunt for prey or via a sit-and-wait strategy for
prey to approach within striking distance, it is considered a predator.
Such a consumer need not consume the entirety of their prey to fall into
this category but only parts of the prey. In contrast, parasites do not
necessarily kill their hosts.
(2) Scavenger: If, in at least some of the feeding interactions that the con-
sumer takes part, the prey species has already been killed by some
previous event, then the consumer is considered a scavenger. As above,
the entire prey item need not to be consumed entirely during the
interaction.
(3) Grazer: A consumer species that feeds by grazing. In the process, they
may either kill their prey species (like zooplankton species preying on
