Geoscience Reference
In-Depth Information
unicellular algae) or merely damage it (as in the case of herbivorous
urchins only preying on a small part of benthic macroalgae).
(4) Filtering: A consumer that actively or passively filters their prey species
out of the water column, that is, a suspension feeder.
A second set of traits that encompasses four main prey types, which are:
(1) Herbivore: A consumer that feeds on plant material only.
(2) Carnivore: A consumer that feeds on other animals only.
(3) Omnivore: A consumer that feeds on both animals and plants, as well as
dead and alive material and therefore on more than one trophic level.
(4) Detritivore: A consumer that feeds on dead animals and plants and/or
dissolved organic matter only.
The third trait set deals with mobility and habitat measures and distin-
guishes the various mechanisms for maintaining position and moving around
in the marine environment. Each species was assigned to a mobility category
according to whether it is (1) a 'sessile or passive floater', (2) a 'crawler', (3) a
'facultative swimmer', or (4) an 'obligate swimmer'.
The fourth and last trait set describes the physical position of a species within
the environment. The species are described as (1) benthic, if the species lives on
the seafloor; (2) pelagic, if the species lives close to the surface; (3) benthopela-
gic, if it moves between and links both environments; or (4) land-based, if the
consumer is not aquatic but feeds predominantly in the marine realm.
Applying these classifications, we derived 11 groups, (bearing in mind that
not all combinations are possible): carnivorous benthic predators (e.g. most
fish species and nemertines), carnivorous benthic suspension feeders (e.g. the
hydrozoan Tubularia ralphii or copepods,
Orejas, 2001
), carnivorous pelagic
predators (e.g. squids and fishes), carnivorous land-based predators (e.g. the
Leopard seal), detritivorous/herbivorous grazers (e.g. most sea urchins),
herbivorous/detritivorous benthic suspension feeders (e.g. all Porifera),
omnivorous benthic predators (e.g. amphipods), omnivorous benthic
predator/scavengers (e.g. most seastars), omnivorous benthopelagic preda-
tors (e.g. fishes), omnivorous land-based predators/scavengers (e.g. seabirds)
and omnivorous pelagic predators (e.g. omnivorous copepods).
C. Food Web Parameters
Many summarizing indices or food web metrics have been proposed previ-
ously to allow for comparisons between different food webs across ecosys-
tems (e.g.
Cohen et al., 1993; Jonsson et al., 2005; Pimm, 1982; Pimm et al.,
1991
). Conventional descriptors of food webs are based on the number of
