The Role of Body Size in Complex Food Webs: A Cold Case - Advances in Ecological Research - page 195

Table 2 List of the results of the pairwise relationships between species body mass
and trophic position across the different dominant consumer types

r 2 Predatory type p-Value

Carnivorous benthic predator 0.4948 0.0527

Carnivorous benthic suspension feeder - -

Carnivorous pelagic predator 0.4587 0.0056

Carnivorous land-based predator 0.4912 0.0453

Detritivorous/herbivorous grazer

Herbivorous/detritivorous benthic suspension feeder 0.0377 0.6933

Omnivorous benthic predator 0.3142 -

Omnivorous benthic predator/scavenger 0.1226 0.2947

Omnivorous benthopelagic predator - -

Omnivorous land-based predator/scavenger 0.1542 0.8458

Omnivorous pelagic predator 0.0664 0.7705

(Correlation coefficient: r 2 ; Significant probability: p). Values are displayed for predatory groups
with numbers larger than 1.

grazers and benthic suspension feeders, the relationship was not significant
( Figure 4 , Table 2 ).
The correlations between body size, generality or vulnerability of the
Weddell Sea species revealed that the medium-sized species had the highest
numbers of predators and prey ( Figure 5 A and B). An exception here in
terms of the vulnerability were the high values for phytodetritus, the various
diatoms and POM, which are important basal food sources within the
Weddell Sea food web.

C. Extinction Scenarios and Robustness of the Weddell
Sea Food Web

When species were systematically removed from the food web in our simula-
tions, potential secondary extinctions varied among the different types of
removal sequences we applied ( Figure 6 ). Several clear trends emerged: we
found that, of the six trait-based sequences, removing species in order of
decreasing vulnerability lead to the fastest collapse of the web ( Figure 6 ).
Removing species in order of decreasing generality or increasing mass also
caused many secondary extinctions, with the order based on generality
collapsing sooner: in both these cases, no secondary extinctions occurred
until approximately 75 species were removed ( Figure 6 ). The last three trait-
based extinction orders all had a robustness of one and caused no cascades
( Figure 6 ). Random removals normally resulted in high robustness and were