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barbatula (L.) (n
¼
5) and three-spined stickleback Gasterosteus aculeatus L.
(n
5)), specimens were sacrificed and frozen for subsequent dissection.
Gut contents analysis was carried out for the fish assemblage on each
sampling occasion, whereas invertebrates had much less variable diets and
were therefore only characterised in May and October. Individuals of the
numerically dominant or trophically important invertebrate taxa in the
benthos were taken from the Surber samples, linear dimensions of each
individual measured to the nearest 0.1 mm, dissected and the contents of
the foregut were examined for animal prey, which were identified at 400
¼
magnification by comparison with reference specimens. The taxa chosen for
gut contents analysis encompassed
95% of individuals found in the ben-
thos. Gut contents of predators were identified to species wherever possible
and linear body dimensions were measured. Dry mass of prey items and
invertebrate predators was estimated using of published regression equations
(
Benke et al., 1999; Burgherr and Meyer, 1997; Edwards et al., 2009a,b;
Ganihar, 1997; Gonzalez et al., 2002; Meyer, 1989; Sabo et al., 2002;
Smock, 1980
).
>
B. Aggregation into Different Levels of Resolution and
Groupings
We use the letters A-F to denote the different levels of resolution and
information (grouping method) that were used on each of the seven empirical
food webs. The individual-level data (raw interaction data) are always
denoted by the letter A. The letters B-D correspond to three levels of
taxonomic aggregation. The letters E and F correspond to two levels of
size-based aggregation. All levels of aggregation, grouping method, and the
corresponding letters (A-F) are illustrated in
Figure 1
and explained in the
following sections.
1. Different Levels of Resolution Based on Taxonomic Groupings
Level A: The individual-based raw data, representing the individual feeding
events, form the lowest level of aggregation possible (
Figure 1
A).
Level B: The initial stage of taxonomic aggregation is to group the focal
entity (either predator or prey individuals) by species. This means that there
is now a grouping of either prey or predator. In the schematic example
(
Figure 1
B), the focal entity is always the predator, but for some of the
responses (those responses which examined variation in a focal entity's
predators (set #3, Section
II.C.2
), the focal entity was the prey. Therefore
