Figure 21 - uploaded by Simon Jennings
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1 The generalized scaling of the total biomass of individuals in a marine food web sorted into logarithmic size bins (e.g., 1 g-10 g, 10 g-100 g), illustrating the biomass " size spectrum. " Body mass spans many orders of magnitude from primary producers to top predators and trophic level increases with body mass owing to size-based predation. The scaling exponent is approximately − 0.1, so the total biomass of smaller organisms tends to be slightly higher than the biomass of larger ones; but smaller organisms have relatively faster turnover times so their production is much higher. The ineffi cient transfer of energy from prey to predators means that production falls by 80-90% at each step in the food chain. Owing to their considerable scope for growth, the same species are found in several size-classes and feed at several trophic levels. Drawings and photographs of organisms courtesy of R. Beckett, S. R. Jennings, and J. H. Nichols.
Source publication
This chapter presents size-based analyses of aquatic food webs, where body size rather than species identity is the principle descriptor of an individual's role in the food web, provides insights into food web structure and function that complement, and extends those from species-based analyses. Focus is given to body size because it underpins pred...
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Citations
... Size distribution analysis describes the rate at which abundance and/or biomass of pelagic organisms changes with increasing body size and is determined by the efficiency of energy transfer from prey to predator and the relationship between body sizes (Trebilco et al., 2013;Blanchard et al., 2017;Hatton et al., 2021). The "height" of the size spectrum (i.e., intercept) reflects the productivity of the ecosystem (Jennings, 2012). In typical marine environments, the log-transformed slope is not affected by primary production levels and is theoretically considered to be around −1 for datasets using abundance and zero for datasets using biomass (Trebilco et al., 2013). ...
... In typical marine environments, the log-transformed slope is not affected by primary production levels and is theoretically considered to be around −1 for datasets using abundance and zero for datasets using biomass (Trebilco et al., 2013). The slope has a higher likelihood of being skewed in coastal ecosystems with strong grazing pressures and benthic-pelagic coupling, where pelagic food webs may be altered by the benthos (Jennings, 2012). Long-term bay-scale plankton data in shellfish aquaculture sites are essential to understand how bivalve aquaculture potentially impacts fisheries resources and how these interactions may vary under future climate conditions. ...
... Our data provide slopes ranging from −3.5 to −2.9 where the x-axis represents body size expressed as length, a unidimensional measurement. These results, when expressed as a three-dimensional measure of size such as volume or weight, would range approximately −1.13 to −0.93, which are comparable to those typically observed (near −1;Jennings, 2012;Anderson, 2019;Gonzalez-Garcıá et al., 2023). Jennings (2012) suggested that size distribution slopes do not encompass all the complex interactions within marine food webs and are most consistent in the open ocean where pelagic ecosystems are least impacted by benthic processes. ...
Introduction
Bivalve aquaculture has direct and indirect effects on plankton communities, which are highly sensitive to short-term (seasonal, interannual) and long-term climate changes, although how these dynamics alter aquaculture ecosystem interactions is poorly understood.
Methods
We investigate seasonal patterns in plankton abundance and community structure spanning several size fractions from 0.2 µm up to 5 mm, in a deep aquaculture embayment in northeast Newfoundland, Canada.
Results
Using flow cytometry and FlowCam imaging, we observed a clear seasonal relationship between fraction sizes driven by water column stratification (freshwater input, nutrient availability, light availability, water temperature). Plankton abundance decreased proportionally with increasing size fraction, aligning with size spectra theory. Within the bay, greater mesozooplankton abundance, and a greater relative abundance of copepods, was observed closest to the aquaculture lease. No significant spatial effect was observed for phytoplankton composition.
Discussion
While the months of August to October showed statistically similar plankton composition and size distribution slopes (i.e., food chain efficiency) and could be used for interannual variability comparisons of plankton composition, sampling for longer periods could capture long-term phenological shifts in plankton abundance and composition. Conclusions provide guidance on optimal sampling to monitor and assess aquaculture pathways of effects.
... predators feeding on smaller prey, large pelagic suspension feeders feeding on small suspended particulate organic matter and morphological adaptations of small predators to feed on larger prey (Bode et al., 2007;Jacob, 2005;Jennings, 2005). In particular, in our study, S. beanii was the second largest species sampled (= 55 cm) but had the lowest mean δ 15 N values (= 9.5‰). ...
During ontogeny, the increase in body size forces species to make trade‐offs between their food requirements, the conditions necessary for growth and reproduction as well as the avoidance of predators. Ontogenetic changes are leading species to seek out habitats and food resources that meet their needs. To this end, ontogenetic changes in nocturnal habitat (vertical use of the water column) and in the type of food resources (based on stable isotopes of nitrogen) were investigated in 12 species of deep pelagic fish from the Bay of Biscay in the Northeast Atlantic. Our results revealed the existence of major differences in the ontogenetic strategies employed by deep pelagic fishes. Some species showed ontogenetic changes in both vertical habitat use and food resources (e.g. Jewel lanternfish ( Lampanyctus crocodilus ) and Atlantic soft pout ( Melanostigma atlanticum )). In contrast, other species showed no ontogenetic change (e.g. Koefoed's searsid ( Searsia koefoedi ) and Lancet fish ( Notoscopelus kroyeri )). Some species only changed food resources (e.g. Spotted lanternfish ( Myctophum punctatum ), Spotted barracudina ( Arctozenus risso ) and Stout sawpalate ( Serrivomer beanii )), while others seemed to be influenced more by depth than by trophic features (e.g. Bluntsnout smooth‐head ( Xenodermichthys copei ) and Olfer's Hatchetfish ( Argyropelecus olfersii )). These results suggest that to meet their increasing energy requirements during ontogeny, some species have adopted a strategy of shifting their food resources (larger prey or prey with a higher trophic level), while others seemed to maintain their food resources but are most likely increasing the quantity of prey ingested. As fish species can have different functional roles during their development within ecosystems, characterising ontogenetic changes in mesopelagic fish species is a crucial step to be considered in future research aimed at understanding and modelling the complexity of deep‐pelagic food webs.
... In addition to taxonomic composition and abundance, body size provides critical ecological information in relation to the age-structure, size-abundance [26] metabolism [27], food web structure [28], and trophic transfer efficiencies [29]. Arranz et al. [30] used stream fish size spectra to detect responses to species invasion and eutrophication. ...
The National Ecological Observation Network (NEON) is a thirty-year, open-source, continental-scale ecological observation platform. The objective of the NEON project is to provide data to facilitate the understanding and forecasting of the ecological impacts of anthropogenic change at a continental scale. Fish are sentinel taxa in freshwater systems, and the NEON has been sampling and collecting fish assemblage data at wadable stream sites for six years. One to two NEON wadable stream sites are located in sixteen domains from Alaska to Puerto Rico. The goal of site selection was that sites represent local conditions but with the intention that site data be analyzed at a continental observatory level. Site selection did not include fish assemblage criteria. Without using fish assemblage criteria, anomalies in fish assemblages at the site level may skew the expected spatial patterns of North American stream fish assemblages, thereby hindering change detection in subsequent years. However, if NEON stream sites are representative of the current spatial distributions of North American stream fish assemblages, we could expect to find the most diverse sites in Atlantic drainages and the most depauperate sites in Pacific drainages. Therefore, we calculated the alpha and regional (beta) diversities of wadable stream sites to highlight spatial patterns. As expected, NEON sites followed predictable spatial diversity patterns, which could facilitate future change detection and attribution to changes in environmental drivers, if any.
... It is important to standardise size in trophic position analysis, as bigger fish could result in elevated δ 13 C and δ 15 N values, due to ontogenetic shifts or feeding niche differences among size classes (e.g. Estrada et al. 2006) and also because trophic level correlates with body size (Jennings 2005). ...
... The overall evidence from similar studies suggests that trophic level of predators is density-dependent (Bas et al. 2019). The proposed mechanism behind the increase in trophic level involves a niche shift towards a more selective diet in favour of larger prey as a consequence of intraspecific competition release (Saporiti et al. 2014;Bas et al. 2019), hence a higher trophic level (Jennings 2005). A similar situation could be playing a role in niche partitioning and the increased trophic position of C. taurus, as this species is considered to be overexploited or threatened with overexploitation (ICMBio 2018). ...
... Furthermore, populations of marine predators under fishing pressure would have constrained growth rates, due to direct and indirect effects of predation (Heithaus et al. 2008). Lower population growth rates would indirectly reduce trophic levels, as it correlates with body size (Jennings 2005), which does not seem to be the case for C. taurus in this study. ...
Sharks are essential components of marine communities, and their removal might simplify ecosystems and lead to unpredictable and detrimental effects on the food web. Comparing the isotopic niche of species between archaeological and modern communities can provide information to assess temporal changes in the ecological dynamics of communities. Here, stable isotope analysis was used to compare food web topology metrics between two shark guilds or communities, a late Holocene archaeological community (AC) dating from 700 to 500 years ago and a modern community (MC) trophic web, both from South Brazil. In the same line of comparison, we assess the trophic position of a top predator, Carcharias taurus. Results showed topological temporal differences such as higher trophic redundancy and higher patterns of niche overlap in the AC. Higher trophic redundancy could be expected in late Holocene food webs, as similar studies also observed these findings. In contrast, the MC showed less dense packing of species within the isotopic niche space, thus higher niche partitioning and higher trophic diversity, suggesting changing ecological interaction dynamics. We found that Carcharias taurus has increased its trophic level, possibly due to a release from the intraspecific competition and a dietary shift towards larger prey items. We suggest that anthropic impacts, such as overfishing, may cause these differences in the trophic position of this species. We also advocate that this study method might help future trophic reconstructions using shark teeth, as information about past marine environments is scarce, and could serve as a baseline for future studies.
... It is important to standardize size in trophic position analysis, as bigger sh could result in elevated δ 13 C and δ 15 N values, due to ontogenetic shifts or feeding niche differences among size classes (e.g. Estrada et al. 2006) and also because trophic level correlates with body size (Jennings 2005 ...
... Furthermore, populations of marine predators, under shing pressure would have constrained growth rates, due to direct and indirect effects of predation (Heithaus 2008). Lower population growth rates would indirectly reduce trophic levels, as it correlates with body size (Jennings 2005), which does not seem to be the case for C. taurus in this study. ...
Sharks are essential components of marine food webs, but their removal might simplify ecosystems and food webs. Comparing the isotopic niche of species between archaeological and modern communities can provide information to assess temporal changes in the ecological dynamics of communities. Here, stable isotope analysis was used to compare food web topology metrics between two shark guilds or communities, a late Holocene archaeological community (AC) dating from 724 − 542 years ago and a modern community (MC) trophic web, both from South Brazil. In the same line of comparison, we assess the trophic position of a top predator, Carcharias taurus . Results showed topological temporal differences such as higher trophic redundancy and higher patterns of niche overlap in the AC. Higher trophic redundancy could be expected in late Holocene food webs, as similar studies also observed these findings. In contrast, the MC showed dispersion of species throughout the isotopic space, thus higher niche partitioning and higher trophic diversity, suggesting changing ecological interaction dynamics. We found that Carcharias taurus has increased its trophic level, possibly due to a release from the intraspecific competition and a dietary shift towards larger prey items. We suggest that anthropic impacts, such as overfishing, may cause these differences in the trophic position of this species. We also advocate that this study method might help future trophic reconstructions using shark teeth, as information about past marine environments is scarce, and could serve as a baseline for future studies.
... In jumbo squid (Dosidicus gigas), both δ 13 C and δ 15 N also increase with growth, and its trophic position increases with increasing body size (Ruiz-Cooley et al., 2006). Generally, larger organisms have higher δ 13 C or δ 15 N values (Jennings, 2005). Although it is unclear if there are ontogenetic changes in the feeding habits of diamond squid, prey size may increase with increasing body size. ...
Diamond squid Thysanoteuthis rhombus (Troschel, 1857), which can grow to a dorsal mantle length of ~100 cm in 1 year, is an important fisheries resource in subtropical and temperate waters worldwide. Around Japan, it is an important resource in the East China Sea, Sea of Japan, and western North Pacific Subtropical Gyre, including the Kuroshio area. It is not known if linkages occur between these habitats. To clarify the species distribution, we estimated the habitat of young squid using a generalized additive model based on trawl surveys and analyzed carbon and nitrogen stable isotope ratios (δ13C and δ15N) in tissue samples. Based on trawl observations, young squid were distributed around northeastern Taiwan and the Okinawa Islands in June–July and in the Sea of Japan and the Kuroshio extension areas in August–September. We observed ontogenetic changes in the stable isotope ratios. The δ15N values in large diamond squid (dorsal mantle length > 400 mm) were significantly lower in the Pacific than those in other areas. Considering that the δ15N of forage fish is low in the Pacific and high in the East China Sea and Sea of Japan, large diamond squid in the northwest Pacific presumably have two distinct habitats.
... The OPS is often assumed to follow a linear function of the predator body size (Hansen et al. 1994;Brose et al. 2006;Jennings et al. 2012). This log-log linear scaling relation has been expanded to include other variables originating from mechanistic considerations such as the feeding mode, which discriminates between filter (passive) and raptorial (active) feeding (Caparroy et al. 2000;Kiørboe 2011). ...
Mechanisticapproachestoplanktonfood-websoftenrelyonsize-basedmodels.Thesemodelsdescribe predator–preyrelationshipsbasedonpredator body or cell size. However, size-based representations of trophic relationships fail to encompass the diverse feeding behavior of dinoflagellates, which play an essential role in the food-web due to their abundance and ubiquity. Here, we introduce the specialization factor ( s ) as an effective trait, which aggregates over aspects of morphology, trophic strategy, and feeding behavior and quantifies the degree of specialization towards a specific prey size. We found that specialization to either the upper or lower edge of the prey size spectrum is connected to size independent trophic relations. As a result, dinoflagellates can be divided into three groups with distinct dependencies of optimal prey size on predator size: (1) mixotrophic engulfers specialized on small prey ( s = - 1 ), (2) pallium feeders on large prey ( s=1 s = 1 ), and (3) neutral feeders ( s=0 s = 0 ) encompassing generalist engulfers and tube feeders. Our trait based approach elucidates the evolutionary significance of diverse feeding modes and specialization in dinoflagellates compared to phylogenetically older groups such as ciliates. It furthermore leads to a more accurate representation of trophic relationships of dinoflagellates in models and can provide, more generally, an efficient description of complex and diverse feeding relations in plankton food-webs.
... This is because predators close to satiation select prey to maximize net energy intake, whereas hungry predators close to carrying capacity are less selective and capture prey according to their encounter rates (Schoener 1971;Pulliam 1974;Stephens and Krebs 1986). On the other hand, prey density in aquatic ecosystems decreases with body size (Blanchard et al. 2017), whereas the trophic position of prey is positively correlated with body size (Jennings 2005). From here follows that aquatic carnivores close to carrying capacity rely largely on small, highly abundant prey with a low trophic level. ...
This study compares the δ15N values and the trophic position of two seabird species throughout the late Holocene in three regions in the southwestern Atlantic Ocean to assess the hypothesis that the decimation of megafauna led to changes in the trophic position of mesopredators. Modern and ancient mollusk shells were also analyzed to account for changes in the isotopic baseline through time. Results revealed that modern Magellanic penguins have higher δ15N values than their ancient conspecifics in the three regions, after controlling for changes in the isotopic baseline. This was also true for modern Imperial shags compared with ancient unidentified cormorants/shags from the two areas where ancient specimens were recovered (southern Patagonia and the Beagle Channel). Such temporal variability might be caused by three non–mutually exclusive processes: decreased availability of pelagic squat lobster resulting from decreasing primary productivity through the late Holocene, increased availability of small fishes resulting from the sequential depletion of other piscivores (South American fur seal and sea lion and Argentine hake) since the late eighteenth century, and modification of the migratory patterns of Magellanic penguins. Although disentangling the relative contribution of all those processes is impossible at this time, the results reported here demonstrate that the ecology of Magellanic penguins and Imperial shags has undergone major changes since the late Holocene.
... Over the last three decades, the size-based analysis of food webs has largely contributed to provide generalizations regarding food web properties [65][66][67][68][69][70][71][72] . Such a conceptual framework assumes that species with a similar body size will have similar diets, and hence that the topology of species within the food webs will be largely determined by body size 72 . ...
... Over the last three decades, the size-based analysis of food webs has largely contributed to provide generalizations regarding food web properties [65][66][67][68][69][70][71][72] . Such a conceptual framework assumes that species with a similar body size will have similar diets, and hence that the topology of species within the food webs will be largely determined by body size 72 . In this way, size-based analysis offers a mechanistic, highly reductionist approach that, when analysing complex food webs, allows to deal with a multitude of species whose body sizes span several orders of magnitude, from grams (e.g. ...
Understanding the trophic niches of marine apex predators is necessary to understand interactions between species and to achieve sustainable, ecosystem-based fisheries management. Here, we review the stable carbon and nitrogen isotope ratios for biting marine mammals inhabiting the Atlantic Ocean to test the hypothesis that the relative position of each species within the isospace is rather invariant and that common and predictable patterns of resource partitioning exists because of constrains imposed by body size and skull morphology. Furthermore, we analyze in detail two species-rich communities to test the hypotheses that marine mammals are gape limited and that trophic position increases with gape size. The isotopic niches of species were highly consistent across regions and the topology of the community within the isospace was well conserved across the Atlantic Ocean. Furthermore, pinnipeds exhibited a much lower diversity of isotopic niches than odontocetes. Results also revealed body size as a poor predictor of the isotopic niche, a modest role of skull morphology in determining it, no evidence of gape limitation and little overlap in the isotopic niche of sympatric species. The overall evidence suggests limited trophic flexibility for most species and low ecological redundancy, which should be considered for ecosystem-based fisheries management.
... Parallel patterns for all species would be expected to result from baseline shifts 40 . However, optimal foraging theory predicts lower trophic levels of species harvested at carrying capacity 58,59 and harvesting can affect trophic dynamics of top predators directly, as has been shown in sea lions 60 and fur seals 61 . The current result on the trophic level of Atlantic cod and haddock support a similar effect. ...
Stable isotope analyses of zooarchaeological material can be used to examine ecological variability in exploited species at centennial to millennial scales. Climate change is a notable driver of marine ecosystem change, although historical fishing is also likely to have impacted past marine systems. Fishing removes the oldest and largest individuals and may thereby result in shorter trophic pathways and reduced niche width of predatory fish species. In the current study we examine the trophic niche of Atlantic cod, haddock and Atlantic wolffish, in the last millennium using δ 13 C and δ 15 N values of bone collagen. We report a lower trophic level of Atlantic cod and haddock but higher level of wolffish in present times, following centuries at consistent and higher trophic levels of Atlantic cod. This results in a concurrent converging trophic niche of the demersal fish. We suggest that the current data set provides a valuable historical baseline facilitating interpretation of current variability in the trophic ecology of northern demersal fish.
