Geoscience Reference
In-Depth Information
Table 1
Topological food web properties for four marine food webs
(Taxa
¼
number of taxa, C
¼
connectance (L/S2), L/S
¼
links per species, TL
¼
mean
trophic level, T
¼
% top species, I
¼
% intermediate species, B
¼
% basal species,
Omn
¼
% omnivorous species)
SC /S
TL TI B Omn Reference
Benguela
29
0.24
7.0
3.2
0
93
7
76
Yodzis (1998)
Caribbean Reef 50
0.22
11.1
2.9
0
94
6
86
Opitz (1996)
NE US Shelf
81
0.22
17.8
3.1
4
94
3
78
Link (2002)
Weddell Sea
492 0.07
33.19
2.5
6.7
79.7
13.6
67.27
Jacob (2005)
Data analyzed in
Dunne et al. (2004)
.
B. Functional Consumer Classification of
the Weddell Sea Food Web
Average body mass of Weddell Sea shelf species stretched across 22 orders of
magnitude, from 1.53
10
8
gin
baleen whales. The trophic level calculated via the diet matrix ranged from 1
in the primary producers up to 4.9 in a predatory scavenging seabird.
Detritus and planktonic copepods had the highest vulnerability (220 preda-
tors for detritus and 146 for copepods) whereas the nemertean Parborlasia
corrugatus had no reported predators at all due to its toxic skin (i.e.
Jacob,
2005
). The species with the highest generality was an omnivorous benthic
ophiuroid with 246 prey items. Species with the lowest generality were either
benthic grazers who only preyed on detritus, which was problematic, as
detritus may consist of an unconsolidated mixture of dead material from
many sources.
All mobility levels were represented; sessile or floating species, such as
Porifera, bryozoans, detritus and diatoms; crawlers, such as asteroids, echi-
noids and holothurians; facultative swimmers, such as some amphipods,
crinoids and octopods; and obligate swimmers such as copepods, euphau-
siids, squids, fishes and whales.
The assignment of predatory, feeding type and environmental classifica-
tions (i.e. our 11 groups) resulted in five major combined consumer cate-
gories and/or species trophic roles. The first group included carnivorous
crawling and swimming benthic predators (n
10
14
g in small unicellular algae to 8.58
¼
34), swimming carnivorous
benthopelagic (n
¼
19), swimming pelagic predators (n
¼
35) and swimming
land-based predators (n
17): this group included all those species that only
feed on alive prey of trophic heights higher than one.
The second group encompassed omnivorous crawling benthic predators
¼
¼
¼
(n
24), swimming omnivorous benthopelagic (n
19) and swimming
pelagic predators (n
¼
35): this category included all those species that
