Abstract
Biodiversity is typically considered as a one-dimensional metric (e.g., species richness), yet the consequences of species loss may be different depending on where extinctions occur in the food web. Here, I used a manipulative field experiment in a temperate subtidal marine system to explore the implications of diversity loss at multiple trophic levels for ecosystem functioning and food web structure. The four manipulated predators included the small painted goby and common prawn, which are also fed on by the larger black goby and shore crab. Antagonistic interactions between the manipulated predators (e.g., intraguild predation, intimidation, interference competition) limited their negative effects on the rest of the food web. Top-down control was so suppressed at the highest level of multitrophic diversity that the resulting food webs were as complex and productive as those containing no manipulated predators. Negative interactions between the predators weakened as multitrophic diversity decreased, however, resulting in stronger consumption of lower trophic levels and a simpler food web with lower rates of two key ecosystem processes: primary production and decomposition. These results show how indirect interactions between predators on multiple trophic levels help to promote the complexity and functioning of natural systems.
Highlights
It is well established that species loss reduces the functioning and stability of natural ecosystems and the services that humans derive from them (Isbell et al 2017)
There was an interactive effect of multitrophic diversity on all the ecosystem functions and food web properties that were studied
Primary production (F4,39 = 8.066; P < 0.0001; Fig. 4a) and decomposition rate (F4,39 = 4.668; P = 0.0036; Fig. 4b) were greatest in the absence of all manipulated predators and when multitrophic diversity was highest, with significantly lower process rates when intermediate predators occurred in the absence of top predators (90% reduction in primary production and 60% reduction in decomposition rate, on average)
Summary
It is well established that species loss reduces the functioning and stability of natural ecosystems and the services that humans derive from them (Isbell et al 2017). While the loss of plant species directly lowers the productivity of an ecosystem (Cardinale et al 2007), predator diversity plays a crucial role in dampening trophic cascades that can lead to either the suppression or release of basal resource biomass (Finke and Denno 2004, Bruno and O’Connor 2005, Frank et al 2006, Haggerty et al 2018). Predators are more susceptible to anthropogenic actions than lower trophic levels (Estes et al 2011) and their effects typically percolate further through food webs than those of bottom-up processes (Borer et al 2006, Scherber et al 2010).
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