The effects of functional diversity on biomass production, variability, and resilience of ecosystem functions in a tritrophic system

Abstract

Diverse communities can adjust their trait composition to altered environmental conditions, which may strongly influence their dynamics. Previous studies of trait-based models mainly considered only one or two trophic levels, whereas most natural system are at least tritrophic. Therefore, we investigated how the addition of trait variation to each trophic level influences population and community dynamics in a tritrophic model. Examining the phase relationships between species of adjacent trophic levels informs about the strength of top-down or bottom-up control in non-steady-state situations. Phase relationships within a trophic level highlight compensatory dynamical patterns between functionally different species, which are responsible for dampening the community temporal variability. Furthermore, even without trait variation, our tritrophic model always exhibits regions with two alternative states with either weak or strong nutrient exploitation, and correspondingly low or high biomass production at the top level. However, adding trait variation increased the basin of attraction of the high-production state, and decreased the likelihood of a critical transition from the high- to the low-production state with no apparent early warning signals. Hence, our study shows that trait variation enhances resource use efficiency, production, stability, and resilience of entire food webs.

Top predators govern multitrophic diversity effects in tritrophic food webs

“…However, as Δ T is increased further from low to high , the CV of each trophic level increased again. Hence, additional mechanisms governing the dynamics must also have a strong influence of the trophic level CV s. In Ceulemans et al (2019), we observed a similar pattern in the trophic level CV s, which could be explained by the increased relevance of an additional dynamical timescale at high Δ T : the biomasses not only varied rapidly within predator-prey cycles, but also due to slower trait changes. As this slower timescale became more dominant, the CV increased again.…”

“…The importance of considering multitrophic diversity has been emphasized before (Gamfeldt et al, 2005; Filip et al, 2014; Soliveres et al, 2016; Lefcheck et al, 2015; Barnes et al, 2018; Ceulemans et al, 2019). With these complex interactions between functional diversity of different trophic levels clearly exhibited by our model, it is not surprising that studies focusing on a single food web structure or a single parametrization sometimes find incommensurable results.…”

“…In order to capture a high diversity of dynamical outcomes, within a plausible ecological setting, the parameters of the food web were sampled uniformly from certain intervals determined by a standard value from which the boundaries are calculated (Table 1). These standard values are based on Ceulemans et al (2019), and describe an ecologically realistic planktonic system with three trophic levels. In particular, the maximal growth rates (, e/h 0 , & e/η 0 ) were set to correspond to an allometrically scaled food chain with the body mass ratios between adjacent trophic levels of 10 3 , with an allometric scaling exponent of −0.15.…”

“…While it has often been highlighted how important the effects of the third trophic level on ecosystem functions are (Bruno and O’Connor, 2005; Duffy et al, 2007; Daam et al, 2019; Abdala-Roberts et al, 2019; Ehrlich and Gaedke, 2020), relatively few studies have attempted to explicitly take these effects into account. Ceulemans et al (2019) showed that functional diversity increases the biomass production, temporal stability, and biomass transfer efficiency to higher trophic levels of a tritrophic food web, when diversity is increased simultaneously at all three trophic levels. This model analyzed one particular food web structure in detail, which raises the question whether the observed trends are to be expected in general, or whether they are context-dependent as well.…”

Coupled changes in traits and biomasses cascading through a tritrophic plankton food web

“…Tirok and Gaedke (2010) found similar patterns of trait adjustment between phytoplankton and ciliate communities. However, natural food webs usually comprise more than two trophic levels and each of them can interact with the others directly or indirectly (e.g., in a trophic cascade) via changes in biomasses or trait composition (Leibold et al 1997;Schmitz et al 2004;Vadstein et al 2004;Zöllner et al 2009;Ceulemans et al 2019). In such multitrophic systems, indirect effects may emerge, for example between carnivores and primary producers, with underexplored consequences for their biomass and trait dynamics and related ecosystem functions.…”