Geoscience Reference
In-Depth Information
2. Size Structure Dimension Sets #2 and 3: Diet Variation and
Predator variation
a. Predator Mass-Variance of Prey Mass and Prey Mass-Variance of Pred-
ator Mass. This response measured the variance in the body masses of a
predator's prey (incoming links) or prey's predators (outgoing links). Vari-
ance was measured using the logged values of the non-focal entities, to
normalise for the body mass of the focal entity. The relationship examined
took the form aggregated focal log
10
(body mass) versus variance (log
10
(non-
focal body masses)), for which the details are explained below.
For both the diet and predator measures, the resolution comparison used
aggregations B and D. For aggregation B, the focal entities in the diet
measure were the average body mass of all predator individuals of each
species and the non-focal entities were all the prey individuals fed upon by
each predator species. In the predator measure, the focal entities were the
average body mass of all prey individuals of each species and the non-focal
entity was all the predator individuals that fed upon each prey species. For
aggregation D, the focal entities in the diet measure were the species average
body mass of all predator species and the non-focal entity was all the prey
species fed upon by each predator species. In the predator measure, the focal
entities were the species average body mass of all prey species and the non-
focal entity was all the predator species that fed upon each prey species.
The grouping comparisons used aggregations B and E. The aggregations
for B were the same as in the resolution comparisons above. For the calcula-
tion based on aggregation E, the diet measure treated each predator size class
as the focal entities and the non-focal entity associated with each were the
body masses of all prey individuals fed upon by predator individuals in that
size class. In the predator measure, each focal entity was a prey size class and
the associated non-focal entities were all predator individuals feeding upon
prey in that size class.
b. Predator Mass-Range of Prey Mass and Prey Mass-Range of Predator
Mass. The same resolution and grouping comparisons were carried out as
in the prey mass variance and predator mass variance responses, except that
instead of variance of non-focal entities body masses we calculated the range
of non-focal individuals, or species, or size classes. This was done as max
(log
10
(non-focal body mass))
min (log
10
(non-focal body mass)).
c. Species Mass—In-Degree (Generalism) and Out-Degree (Vulnerability).
In-degree is the number of incoming links a node has in a directed graph,
where as out-degree is the number of outgoing links (
Digel et al., 2011
). In the
case of a taxonomic food web, in-degree is the number of prey species a
predator feeds upon, whereas out-degree is the number of predators a species
