Cascading predator control interacts with productivity to determine the trophic level of biomass accumulation in a benthic food web

Abstract

Large-scale exploitation of higher trophic levels by humans, together with global-scale nutrient enrichment, highlights the need to explore interactions between predator loss and resource availability. The hypothesis of exploitation ecosystems suggests that topdown and bottom-up control alternate between trophic levels, resulting in a positive relationship between primary production and the abundance of every second trophic level. Specifically, in food webs with three effective trophic levels, primary producers and predators should increase with primary production, while in food webs with two trophic levels, only herbivores should increase. We provided short-term experimental support for these model predictions in a natural benthic community with three effective trophic levels, where the number of algal recruits, but not the biomass of gastropod grazers, increased with algal production. In contrast, when the food web was reduced to two trophic levels by removing larger predators, the number of algal recruits was unchanged while gastropod grazer biomass increased with algal production. Predator removal only affected the consumer-controlled early life-stages of algae, indicating that both the number of trophic levels and the life-stage development of the producer trophic level determine the propagation of trophic cascades in benthic systems. Our results support the hypothesis that predators interact with resource availability to determine food-web structure.

A cross-scale trophic cascade from large predatory fish to algae in coastal ecosystems

“…Global drivers of variation in trophic cascade strength include temperature, precipitation [7,8], diversity and degree of omnivory [8,9]. At smaller scales, strong contextdependence of top-down and bottom-up control is known to depend on factors such as seasonality [10], nutrient loads [11], consumer behavioural responses [12], habitat complexity [13] and functional traits of both predators [14,15] and prey [16].…”

Metagenomic mining of glycoside hydrolases from the hindgut bacterial symbionts of a termite (Trinervitermes trinervoides) and the characterization of a multimodular β‐1,4‐xylanase (GH11)

“…In addition, intracellular xylanases generally degrade mostly oligosaccharides of low polymerization degree compared to those produced in the periplasmic space [51,52]. As a result of the structural complexity and poor solubilization, the complete enzymatic hydrolysis of branched xylan requires the action of a combination of various classes of xylanases rather than a single kind of enzyme [53].…”

The rise of the three-spined stickleback – eco-evolutionary consequences of a mesopredator release

“…Eriksson et al 2009, Sieben et al 2011b, Eriksson et al 2012, Östman et al 2016. Models of trophic dynamics suggest that predator effects on lower trophic levels interact with resource availability, such that the abundance of every second trophic level increases with primary production (Fretwell 1977, Oksanen et al 1981, Nisbet et al 1997, Oksanen and Oksanen 2000, Eriksson et al 2012). In a system with four trophic levels the predator community accumulates biomass.…”