Search results for "trophic cascade"

Italian marine reserve effectiveness: does enforcement matter?

2008

Marine protected areas (MPAs) have become popular tools worldwide for ecosystem conservation and fishery management. Fish assemblages can benefit from protection provided by MPAs, especially those that include fully no-take reserves. Fish response to protection can thus be used to evaluate the effectiveness of marine reserves. Most target fish are high-level predators and their overfishing may affect entire communities through trophic cascades. In the Mediterranean rocky sublittoral, marine reserves may allow fish predators of sea urchins to recover and thus whole communities to be restored from coralline barrens to macroalgae. Such direct and indirect reserve effects, however, are likely t…

Top consumer abundance influences lake methane efflux

2015

Lakes are important habitats for biogeochemical cycling of carbon. The organization and structure of aquatic communities influences the biogeochemical interactions between lakes and the atmosphere. Understanding how trophic structure regulates ecosystem functions and influences greenhouse gas efflux from lakes is critical to understanding global carbon cycling and climate change. With a whole-lake experiment in which a previously fishless lake was divided into two treatment basins where fish abundance was manipulated, we show how a trophic cascade from fish to microbes affects methane efflux to the atmosphere. Here, fish exert high grazing pressure and remove nearly all zooplankton. This re…

Regulation of decomposer community structure and decomposition processes in herbicide stressed humus soil

1997

Abstract Regulation of soil decomposer community structure and ecosystem processes, such as nutrient cycling, under herbicide stress was studied in a microcosm experiment. For the experiment, coniferous forest soil was defaunated and put into the microcosms. In the microcosms two different food webs including microbes, nematodes, tardigrades and oribatid mites, either with or without predatory mesostigmatid mites, were reconstructed. Half of the microcosms were stressed with a herbicide (active ingredient was terbuthylazine). During the 57 weeks incubation community structure of decomposers and nitrogen mineralisation were studied at five destructive samplings and two water irrigations. Soi…

2002

We carried out enclosure experiments to assess the potential deleterious effects of the alien species common carp (Cyprinus carpio L.), mosquitofish (Gambusia holbrookii Gir.), and pumpkinseed sunfish (Lepomis gibbosus L.) on water quality and food web in a severely degraded floodplain wetland, the Spanish National Park Las Tablas de Daimiel. With addition of either carp or pumpkinseed sunfish, chlorophyll a and turbidity levels, as well as concentrations of total phosphorus and total nitrogen increased. The magnitude of this increase depended on fish species and was severest in the carp treatment. Mosquitofish did not significantly affect water quality. In the treatments with fish, cyclopo…

No evidence of trophic cascades in an experimental microbial-based soil food web

1998

Trophic-dynamic theories predict the biomass and productivity of trophic levels to be partially top-down regulated in food webs, and that the top-down regulation will manifest itself as cascading trophic interactions. We tested the two principal predictions deduced from these theories: trophic cascades of (1) biomass regulation and (2) productivity regulation occur in food webs. We created three food webs with either one, two, or three trophic levels in soil microcosms containing a sterilized mixture of leaf litter and humus. Twenty species of bacteria and fungi formed the first trophic level, a bacterivorous nematode (Caenorhabditis elegans) and a fungivorous nematode (Aphelenchoides sp.) …

Ontogenetic trophic segregation between two threatened smooth-hound sharks in the Central Mediterranean Sea

2020

AbstractElasmobranchs are among the species most threatened by overfishing and a large body of evidence reports their decline around the world. As they are large predators occupying the highest levels of marine food webs, their removal can alter the trophic web dynamic through predatory release effects and trophic cascade. Suitable management of threatened shark species requires a good understanding of their behaviour and feeding ecology. In this study we provide one of the first assessments of the trophic ecology of the “vulnerable” smooth-hounds Mustelus mustelus and M. punctulatus in the Central Mediterranean Sea, based on stomach contents and stable isotope analyses. Ontogenetic diet ch…

Soil animals and ecosystem processes: How much does nutrient cycling explain?

2008

Summary Trophic-dynamic hypotheses have been extensively tested by manipulating the presence of soil animals in experimental laboratory microcosms. Soil animals typically have pronounced effects on microbial populations, nutrient cycling and plant growth. However, because often only the total effect has been reported, the relative importance of feeding interactions versus non-trophic effects remains obscure. Using simple calculations based on mass conservation I argue that the observed faunal effect on microbes and system functioning is often larger than can be explained by trophic dynamics and nutrient cycling. Non-trophic effects may help to explain why microcosm experiments have failed t…

Marine food web perspective to fisheries-induced evolution

2021

Fisheries exploitation can cause genetic changes in heritable traits of targeted stocks. The direction of selective pressure forced by harvest acts typically in reverse to natural selection and selects for explicit life-histories, usually for younger and smaller spawners with deprived spawning potential. While the consequences that such selection might have on the populational dynamics of a single species are well emphasised, we are just beginning to perceive the variety and severity of its propagating effects within the entire marine food webs and ecosystems. Here, we highlight the potential pathways in which fishing-induced evolution, driven by size-selective fishing, might resonate throu…

Trophic cascades in benthic marine ecosystems: lessons for fisheries and protected-area management

2000

An important principle of environmental science is that changes in single components of systems are likely to have consequences elsewhere in the same systems. In the sea, food web data are one of the few foundations for predicting such indirect effects, whether of fishery exploitation or following recovery in marine protected areas (MPAs). We review the available literature on one type of indirect interaction in benthic marine ecosystems, namely trophic cascades, which involve three or more trophic levels connected by predation. Because many indirect effects have been revealed through fishery exploitation, in some cases we include humans as trophic levels. Our purpose is to establish how wi…

Potential for large-bodied zooplankton and dreissenids to alter the productivity and autotrophic structure of lakes

2014

While limnological studies have emphasized the importance of grazers on algal biomass and primary production in pelagic habitats, few studies have examined their potential role in altering total ecosystem primary production and it’s partitioning between pelagic and benthic habitats. We modified an existing ecosystem production model to include biotic feedbacks associated with two groups of large-bodied grazers of phytoplankton (large-bodied zooplankton and dreissenid mussels) and estimated their effects on total ecosystem production (TEP), and the partitioning of TEP between phytoplankton and periphyton (autotrophic structure) across large gradients in lake size and total phosphorus (TP) co…