Energetic role of the mycoloop
In the investigated mycoloop food web, there are two alternative energy
pathways: one from edible phytoplankton directly to zooplankton and the
other from inedible phytoplankton\(\ \)via parasitic fungi to
zooplankton (mycoloop). A comparison between three sets of assumptions:
(M1) linear food uptake rates for all species with zooplankton without
prey preference (\(p_{Z}\) = 0.5), (M2) saturating food uptake rates for
phytoplankton and zooplankton without prey preference, and (M2+) in
addition to M2, zooplankton with adaptive prey preference (Fig. 2),
shows that predictions on the dominance of energy flow between both
pathways is independent of the zooplankton feeding strategy. A strong
dominance of energy flow along the direct phytoplankton pathway is
predicted at low nutrient availabilities. An increasing importance of
energy flow along the mycoloop is predicted with nutrient enrichment
(Fig. 2e,f). This reflects the increase in fungi biomass and the
decrease in edible phytoplankton biomass along the nutrient gradient
(Fig. 2a,b,c). For the adaptive preference case, the increasing
importance of the mycoloop along the nutrient gradient is much more
pronounced, with almost exclusive preference of zooplankton for edible
phytoplankton in Regime I to an equal importance of energy flow between
both energy pathways in Regime II (Fig. 2d,e,f). Energy flow along the
mycoloop would even dominate for nutrient enrichment levels beyond the
investigated values (see Appendix S4).
Comparing the shift in the distribution of energy flow between both
pathways along the nutrient gradient, reveals significant differences
between scenarios M1, M2 and M2+ (Fig. 2e,f). At low nutrient
availability, predictions on net energy gain of zooplankton from fungi
are highest under the assumption of linear food uptake terms (Fig. 2e).
However, at high nutrients, under the assumption of saturating food
uptake terms, zooplankton is predicted to gain up to 50-55% of its
energy from fungi, while net energy gain stays well below 40% for the
linear case (Fig. 2e). The difference in predictions is even more
pronounced for the transfer efficiency along the mycoloop, which reaches
30% under the assumption of saturating functional responses while it
remains below 5% under the assumption of linear food uptake rates (Fig.
2f). At lower nutrient availabilities, transfer efficiency is highest
under the assumption of saturating food uptake rates and fixed
preference (pZ = 0.5), however, the adaptive preference case reaches
similarly high values under high nutrient availabilities (Regime II)
(Fig. 2f).