Community structure and dynamics
We consider a resident consumer-resource system
and examine five scenarios that differ in
the trophic position of the invader, including another basal resource,
another consumer, a top predator, an intraguild predator feeding on both
resident species, or an intraguild prey feeding on the (shared) resident
resource while being consumed by the resident consumer (Fig. 1a-e). This
corresponds to apparent competition (hereafter AC), exploitative
competition (EC), tri-trophic chain (TC) and intraguild predation (IGP)
(Tables S1–S3).
We simulate the dynamics of each module for each combination of
temperature between 0°C and 40°C (step size 0.1°C) and nutrient levels
(IK ) available to the basal resource species the
between 0.1 g.m-2 and 20 g.m-2 (step
size 0.1 g.m-2), yielding 80,200 combinations of
temperature and nutrient levels as in Binzer et al. (2012) and Sentis et
al. (2017). We also vary the body masses of species in each module,
constraining consumers to be at least as large as their resources, which
is true for most predator-prey pairs (McCauley et al. 2018). For
simplicity, we set the body mass of the basal resource species to 1 mg
and express the other masses in relative values (Fig. 1a-e).
We denote the body mass ratio between competing resourcesRINV:RRES (AC module) and the
consumer:resource ratio C:R (TC and IGP modules) as α , the
mass ratio between competing consumersCINV:CRES (EC and IGP modules) or
between predators and intermediate consumers P:C (TC and IGP
modules) as β , and the mass ratio between resident resource and
consumer CRES:RRES (AC and EC
modules) and between the top predator and resident basal resource
(P:R ; TC and IGP modules) as γ = αβ. Furthermore,
we quantify the asymmetry in size ratios between adjacent trophic levels
with a ratio parameter δ = β /α (Table S4). We
consider module-specific sets of mass ratios to reflect the different
trophic positions of the invader: 4 or 15 consumer-resource body mass
ratios for the resident system, and 16 or 25 combinations of species
mass ratios (i.e., at least all pairwise combinations of α andβ = 1, 2, 5 and 10, Text S1) in each module (Tables S5–S7). All
numerical simulations were run in the packages ‘deSolve’ and ‘rootSolve’
in the R software (Soetaert & Herman 2009; Soetaert et al. 2010).