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(A) Specialist predators only feed on a single prey type and will deplete it down (arrows) to a fixed giving-up density (GUD; horizontal line). (B) By contrast, generalist predators feed on multiple prey types, in the present case two. Both prey types will be depleted down to a combination of GUDs (diagonal line), depending on the initial prey densities (open circles, which are equivalent to those in panel A). Depletion trajectories are straight whenever searching efficiencies are similar on both prey types. Gray lines are drawn to guide the eye. Note that in generalist predation, higher initial prey densities in one prey type will lead to lower GUDs in the other prey type—a short-term form of apparent competition (Holt and Kotler 1987).
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Effects of predation may cascade down the food web. By alleviating interspecific competition among prey, predators may promote biodiversity, but the precise mechanisms of how predators alter competition have remained elusive. Here we report on a predator-exclosure experiment carried out in a tropical intertidal ecosystem, providing evidence for a t...
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Context 1
... plotting so-called ''depletion trajectories'' enables exploring the diet strategy applied by the predator (Brown and Mitchell 1989;Fig. 1). In a simple one-predator-two-prey system, a specialist predator will only feed on a single prey (type 1) and deplete its densities towards a critical, so-called ''giving-up density'' (GUD; horizontal line in Fig. 1A) (Brown 1988). By contrast, a generalist will feed on both prey species and will give up feeding at a certain combination of both prey densities (diagonal line in Fig. 1B; Holt and Kotler 1987). Intermediate strategies do exist-e.g., predators can switch from being specialist to becoming a generalist (a strategy termed ''the expanding ...
Context 2
... system, a specialist predator will only feed on a single prey (type 1) and deplete its densities towards a critical, so-called ''giving-up density'' (GUD; horizontal line in Fig. 1A) (Brown 1988). By contrast, a generalist will feed on both prey species and will give up feeding at a certain combination of both prey densities (diagonal line in Fig. 1B; Holt and Kotler 1987). Intermediate strategies do exist-e.g., predators can switch from being specialist to becoming a generalist (a strategy termed ''the expanding specialist'' by Heller [1980])-but they are not considered here. Both prey types will be depleted down to a combination of GUDs (diagonal line), depending on the initial ...
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... 2). Considering the specialist predator and the prey that it specializes on, GUD will be constant and independent of IPD above a certain IPD ( Fig. 2A), whereas GUD and IPD will be similar in the prey type that it ignores (Fig. 2B). Hence, there will be no relation between the GUD on prey type 1 and the GUD on prey type 2 ( Fig. 2C; comparable to Fig. 1A). By contrast, in the generalist predator there will be much variation in the GUD on prey type 1 (Fig. 2D) as well as on type 2 (Fig. 2E), variation that is unrelated to a prey type's IPD. GUDs on prey type 1 will relate negatively to the GUDs on prey 2 ( Fig. 2F; comparable to Fig. ...
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... concentrations of the pore water were lower in the exclosures than in the controls, but only so in the deepest layer of 8-12 cm. Here, concentrations were reduced by 70% ( Fig. 5; N ¼ 21 pairs). A linear mixed- effect model with random intercepts showed the following depth-dependent estimates for log 10 -trans- formed H 2 S excl /H 2 S cont ratios: 0-4 cm, 0.01 (t ¼ 0.04, P ¼ 0.97); 4-8 cm, 0.14 (t ¼ 0.58, P ¼ 0.57); 8-12 cm, À0.51 (t ¼ À2.11, P , 0.05). It is the deepest layer that had the highest natural sulfide ...
Citations
... In ecological studies, predator species are typically classified as either specialists or generalists based on their dietary habits. Specialists (monophagic) focus on a single prey type, while generalists (polyphagic) consume a variety of prey species [57,58]. Contrary to expectations, none of the predator species employed in this study exhibited exclusive predation on Anopheles mosquito larvae. ...
Background: Understanding the trophic interactions of Anopheles gambiae mosquito larvae in aquatic environments is essential for malaria prevention efforts such as in gene drive application. In this study, metagenomics method was employed to explore the feeding behavior and ecological associations of An. gambiae larvae within their aquatic ecosystems.
Methods: Anopheles gambiae larvae and their co-existing fauna species were collected from December 2022 to June 2023. DNA from dissected midguts of the co-existing fauna was sequenced using Illumina NovaSeq for diet analysis through a shotgun sequencing approach.
Results: The study revealed a complex network of trophic interactions in the freshwater habitat, with significant resource sharing between A. gambiae larvae and other filter-feeding species, including various Diptera and non-Dipteran feeders. Contrary to assumptions, predator species did not exhibit exclusive predation on Anopheles larvae, preferring other fauna instead.
Conclusion: This study has demonstrated complex trophic interactions among Anopheles gambiae larvae and other organisms in freshwater ecosystems. It has offered essential insights for optimizing vector control strategies, such as in gene drive applications. Additionally, the study has provided valuable information on the aquatic fauna of the study area, which can serve as a baseline for developing a macroinvertebrate identification database for freshwater systems in Ghana. A complementary study that further explores the ecological role of An. gambiae larvae in these freshwater habitats is presented in a subsequent publication.
... The study was carried out in January and February 2018 in Parc National du Banc d'Arguin in Mauritania (20°14'N, 16°06'W), where red knots Calidris canutus canutus (Linnaeus, 1758) feed amongst others on Loripes orbiculatus (Poli, 1795) (Oudman 2017;van Gils et al. 2012). Red knots are midsized shorebirds (average weight in winter in Mauritania 124 g, ten Horn et al. unpub. ...
A forager’s energy intake rate is usually constrained by a combination of handling time, encounter rate and digestion rate. On top of that, food intake may be constrained when a forager can only process a maximum amount of certain toxic compounds. The latter constraint is well described for herbivores with a limited tolerance to plant secondary metabolites. In sulfidic marine ecosystems, many animals host chemoautotrophic endosymbionts, which store sulfur compounds as an energy resource, potentially making their hosts toxic to predators. The red knot Calidris canutus canutus is a molluscivore shorebird that winters on the mudflats of Banc d’Arguin, where the most abundant bivalve prey Loripes orbiculatus hosts sulfide-oxidizing bacteria. In this system, we studied the potential effect of sulfur on the red knots’ intake rates, by offering Loripes with various sulfur content to captive birds. To manipulate toxicity, we starved Loripes for 10 days by removing them from their symbiont’s energy source sulfide. As predicted, we found lower sulfur concentrations in starved Loripes. We also included natural variation in sulfur concentrations by offering Loripes collected at two different locations. In both cases lower sulfur levels in Loripes resulted in higher consumption rates in red knots. Over time the red knots increased their intake rates on Loripes, showing their ability to adjust to a higher intake of sulfur.
... For instance, this applies to the feeding behaviour of some deposit feeding bivalves, such as the nuculids N. nitidosa, Nucula sulcata Bronn, 1831 and the solemyoid Solemya togata (Poli, 1791), which are equipped with little siphons and feed ingesting sediment detritus by labial palps (Purchon, 1977;Zardus, 2002). Furthermore, this latter bivalve supplements its food supply through endosymbiotic sulphur bacteria, like other suspension feeders do, such as those belonging to the order Lucinida (Fisher, 1990;van Gils et al., 2012;Taylor et al., 2011). Finally, other noteworthy bivalves are the selective carnivores Cuspidaria spp. ...
Molluscan assemblage of coastal area facing the very polluted Sarno River estuary to offshore (Gulf of Naples, Italy) was studied, focusing on temporal and depth-related distribution of species diversity, quali-quantitative composition and trophic guilds structure. A total of 9 stations, at depths ranging between 7 and 95m, were sampled in triplicate by means of a 0.17 m2 Van Veen grab in four sampling occasions (2 seasons, winter and summer, during 2 years, 2015 and 2016). A total of 1,744 individuals, belonging to 78 species and 3 classes (Bivalvia, Gastropoda and Scaphopoda), was recorded. Bivalves, followed by gastropods, qualitatively and quantitatively dominated the mollusc assemblages and both these taxonomic groups showed the highest values in the shallower stations down to about 25 m depth. In the deeper stations, only the bivalve taxon was dominant, even though exhibiting a much lower species richness and abundance. On the overall, the molluscan species were ascribed to 6 feeding guilds: Suspension and deposit feeders were the dominant trophic groups, occurring at all stations along the bathymetrical gradient, while predators, detritus feeders, ecto-parasites and scavengers were poorly represented and mainly occurred in the shallowest stations. The mollusc composition and distribution pattern along the bathymetrical gradient over time show signs of structural stability that might be mainly due to the continuous supply of organic matter from the river mouth expanding to all area. These results are of primary importance for filling the knowledge gaps on benthic biodiversity over a still poorly known and very fragile coastal area under continuous anthropogenic pressures mainly through the runoff of a very polluted river.
... Even a solemyid excavated from the burrow could potentially be a difficult prey due to its flexible shell and very thick periostracum (Beedham and Owen, 1965), which is of highly defensive value (Wright and Francis, 1984;Harper and Skelton, 1993). Chemosymbiotic metabolism and toxicity of sulfide could also act as a deterrent for predators, which should ideally look for other prey than risk sulfide poisoning and related digestive issues (Gijs et al., 2012). ...
The paper reports rare occurrence of deep-water solemyid and lucinid bivalves from Cenozoic sequences of Outer Eastern Carpathians, Ukraine. The studied bivalves occur in the Eocene Pasichna Formation, represented by deep-water marls and pelagic limestones intercalated with thin-bedded calcareous sandstones yielding material re-deposited from shallow water. This find offered a chance to study the unaltered shell breakage pattern of these deep-burrowing solemyid bivalves buried in situ by turbidites. The breakage includes arcuate breaks representing likely syn-vivo damage related to active burrowing of the animal while telescopic breaks are most likely post-mortem distortions produced by the load of the heavy sediment covering sea bottom after a turbiditic event. Taxonomic study indicates that both solemyid and lucinid bivalves from the Eocene of the Pasichna Formation are most similar to deep-water members of their respective clades, known from roughly coeval deposits from the Tethys. The available evidence indicates that bivalves in question lived on the deep-sea muddy bottom, influenced by turbidite deposits, and were buried by them syn-vivo or early post-mortem. This is in contrast to the great majority of molluskan faunas from the Carpathian Paleogene, reworked during transport downbasin from shallow-marine settings by mass gravity flows. The detailed study of the occurrence mode of deep-water bivalves in the Carpathian part of the Tethys during the Paleogene, influenced by frequent build-up of oxygen-depleted waters, offers implications for the evolutionary histories of both groups in question. For both solemyids and lucinids, adaptations to oxygen-depleted environments are primordial, and are carried from the Silurian until today, as supported by the presented fossil and actualistic evidence. This is in contrast to their histories in high-redox potential environments, with solemyids known from cold seeps from the Devonian onwards and lucinid seep record only from the Jurassic.
... Consequently, the combined direct and indirect dredging effects negatively affected the distribution and survival of predators such as a red knots Calidris canutus and oystercatchers Haematopus ostralegus (Verhulst et al., 2004;van Gils et al., 2006;. Apart from such bottom up effects, however, it is likely that the change in predator abundances in turn also cascades down into the system where disruption did not take place, as predation by species such as red knot have been demonstrated to significantly impact prey populations (van Gils et al., 2009;van Gils et al., 2012) Here, we studied the interactive effects of predation and intraspecific competition on an intertidal cockle population at adjacent sites with contrasting habitat characteristics, that are both typical for Wadden Sea condition in the intertidal. One of the sites was located on a sandy intertidal flat, characterized by sediments with large grain sizes and low natural cockle densities. ...
... Each exclosure consisted of 8 PVC-poles (0.5 m long) that were inserted in the sediment to a depth of 0.4 m and aligned in a square of 1 m 2 . A nylon rope connected the tops of the poles thereby acting as a fence ( Fig. 2A) to keep birds out but note that crabs can enter the plot (see method: van Gils et al., 2012). Control plots were marked by two small PVC-poles. ...
... Specifically, the frequency of inundation and stronger tidal current have provided the food (suspended particle) for suspension feeders (bivalves), leading to the increase in their abundance in the deltaic zone. Gills et al. (2012) also found that Dosinia ceylonica as a specialist suspension feeder has a preference mangrove habitat type, such that it uses its short siphons to feed on suspended particles. In contrast, coastal and island zones appeared to mostly favor the deposit feeders (worms and crabs) of different sizes, which often feed on mangrove leaves and detritus. ...
The community composition of benthic macrofauna and relationships between physiochemical parameters of the water and sediment texture were assessed in Hara Biosphere Reserve, Northern Persian Gulf. The spatial distribution and diversity of macrobenthos were sampled within three distinctive mangrove zones (deltaic, island and coastal) during two sampling seasons between August 2014 and January 2015. A total of nine transects perpendicular to the coastline were selected to cover over the entire study area. The counts of all macrofauna were recorded from each zone and station with three replicate sediment samples. The snails, Cerithidea cingulata and Asseminea sp., were observed throughout three mangrove zones, but their abundance varied among habitats. The bivalve Dosinia ceylonica found to be more abundant in delta, whereas burrowing crabs Ocypode and Uca were dominate in coastal zone. Terebralia palustris and amphipods were recorded frequently in island zone. The nonmetric multidimensional scaling ordinations and a three-way factor PERMANOVA indicated that macro-invertebrate species composition significantly differed among different mangrove zones. The results also showed the seasonal variations. The findings of diversity indices illustrated that deltaic zone had the highest abundance and diversity, while the coastal zone showed the lowest values among the three zones. Taken together, the observations demonstrated that the different hydrological conditions, temperature, salinity and sediment texture were the main factors determining dispersion of benthic faunal assemblages among different mangrove habitats at Hara Biosphere Reserve. There is a need to consider such variables in ecological studies to understand differences of macrofaunal diversities in these complex habitats.
... L. lucinalis derives energy from both filter feeding and through chemosynthetic bacterial symbionts. Predation on D. isocardia may reduce competition for POM and allow L. lucinalis to de-emphasize chemosynthetic pathways of energy production, which may result in higher concentrations of toxic porewater sulfide (Van Gils et al. 2012). As can be seen, top-down control through the manipulation of bottom-up processes can be important in structuring the chemical, nutrient, and physical environment in which seagrasses live, with implications for the persistence of seagrass ecosystems. ...
Seagrass ecosystems were traditionally assumed to be structured by competition as well as by “bottom up forces” such as resource availability and disturbance. However, a wealth of new evidence demonstrates that exertion of “top down control” by animals may be widespread. The strength and direction of top down control is context dependent, however, and varies with properties of organisms, the community, and the physical environment. Consumers can facilitate, consume, or destroy primary producers, aid or inhibit seagrass reproduction, or alter bottom up processes with implications for the properties and persistence of seagrass ecosystems. Studies in Australian ecosystems have been critical in helping to elucidate the role of consumers in seagrass ecosystems. Specifically, work investigating the roles of megaherbivores and apex predators and the pioneering of novel experimental approaches which allow for cage-free manipulations of mesograzers have substantially furthered our understanding of top-down control. At the broadest scale, megagrazers are likely to dominate grazing pathways in Australian tropical and subtropical seagrass ecosystems, while macrograzers and mesograzers do so in temperate seagrass ecosystems. However, while we have learned much about mechanisms through which top-down control can operate and its effects on seagrass ecosystems, predicting which grazing pathways dominate at smaller spatial scales, and net herbivore effects on seagrasses in specific ecosystems remains challenging due to context dependence and the highly complex nature of species interactions. Anthropogenic impacts further complicate these relationships. Australian seagrass habitats possess unusual properties, including relatively intact populations of megafauna, remote and pristine locations, and distinctive oceanographic features which allow these habitats to provide unique insights of top down control in seagrass ecosystems.
... The net (mesh size: 1.2 cm) was placed directly on the seafloor with no space below it and had a height of 25 cm. The fenced control (FC) had a string attached to the poles at about 25 cm height, wrapping around the plots as protection against predation from birds (van Gils et al. 2012). The distribution of the plots was randomized within sites. ...
Biological diversity is fundamental for the functioning of ecosystems on our planet and thus for the survival of humanity. Today, we are experiencing a global biodiversity crisis that severely disrupts ecosystems worldwide, but surprisingly does not lead to species loss on the local scale. Rather, local species assemblages experience shifts in their composition, such as changes in dominance patterns. The effects of compositional shifts compared to the complete loss of species are less well studied, but first experiments show that negative effects are comparable. Many experiments about the influence of biodiversity on ecosystem functioning are done in highly artificial settings, which makes extrapolating results to real world ecosystems difficult. In my doctoral thesis, I describe the results of biodiversity experiments with increased realism in their set-up. I achieved this by using natural species assemblages or studying species directly in the field, considering multiple spatial and temporal scales, including several measures of biodiversity, and exposing the communities to natural stressors. My results show that increasing realism in experimental ecology changes the response of communities to simulated climate stressors. In addition, I found that initial species composition is crucial for determining community responses to stress and that connectivity between local patches can lead to the maintenance of ecosystem functioning in some communities, but not always, especially in response to regional stressors. I conclude that the move to more realism in experimental ecology is vital for understanding changes in natural community dynamics which enables us to give better recommendations for practical biodiversity conservation.
... The net (mesh size: 1.2 cm) was placed directly on the seafloor with no space below it and had a height of 25 cm. The fenced control (FC) had a string attached to the poles at about 25 cm height, wrapping around the plots as protection against predation from birds ( van Gils et al., 2012). The distribution of the plots was randomized within sites. ...
Intertidal flats are highly productive areas that support large numbers of invertebrates, fish, and birds. Benthic diatoms are essential for the function of tidal flats. They fuel the benthic food web by forming a thin photosynthesizing compartment in the top-layer of the sediment that stretches over the vast sediment flats during low tide. However, the abundance and function of the diatom film is not homogenously distributed. Recently, we have realized the importance of bivalve reefs for structuring intertidal ecosystems; by creating structures on the intertidal flats they provide habitat, reduce hydrodynamic stress and modify the surrounding sediment conditions, which promote the abundance of associated organisms. Accordingly, field studies show that high chlorophyll a concentration in the sediment co-vary with the presence of mussel beds. Here we present conclusive evidence by a manipulative experiment that mussels increase the local biomass of benthic microalgae; and relate this to increasing biomass of microalgae as well as productivity of the biofilm across a nearby mussel bed. Our results show that the ecosystem engineering properties of mussel beds transform them into hot spots for primary production on tidal flats, highlighting the importance of biological control of sedimentary systems.
... All density and depth combinations were offered twice to each bird (although never on the same day). Densities and depths of bivalve prey were well within the range reported for the field (Ahmedou Salem, van der Geest, Piersma, Saoud, & van Gils, 2014; van der Geest, van Gils, van der Meer, Olff, & Piersma, 2011; van Gils et al., 2015; van Gils et al., 2013; Piersma, de Goeij, & Tulp, 1993). Patches were filled with sand (mean medium grain size ± SE (N ¼ 6): 248.0 ± 2.7 mm) collected at the nearby intertidal beach (19 53.026 0 N, 16 17.573 ...
Predators have evolved many different ways to detect hidden prey by using advanced sensory organs. However, in some environmental contexts sensory information may be obscured. The relation between sensory organs, obstruction and searching efficiency remains little explored. In this study we experimentally examined the ways in which a sensory system (‘remote detection’), which enables red knots, Calidris canutus, to detect hard objects buried in wet soft sediments, is obstructed by plants. At an important coastal nonbreeding site of this species, the Banc d'Arguin (Mauritania, West Africa), most of the intertidal foraging area is covered by sea grass. The structurally complex networks of belowground roots and rhizomes and aboveground sea grass may obstruct information on the presence of buried bivalves and thus affect searching efficiency. Under aviary conditions we offered red knots buried bivalves in either bare soft sediments or in sea grass patches and measured prey encounter rates. Red knots detected prey by direct touch in sea grass but remotely in bare sediment. Physical modelling of the pressure field build-up around a probing bill showed that within a layer of sea grass rhizomes, permeability is reduced to the extent that the pressure field no longer reveals the presence of an object. In bare sediment, where searching efficiency is constant, red knot intake rate levelled off with increasing prey density (described by a so-called type II functional response). In the sea grass beds, however, prey density increases with sea grass density and simultaneously decreases searching efficiency, which will at some point lead to a decrease in intake rate when prey densities increase (i.e. a type IV functional response). Clearly, prey detection mechanisms dictate that the combined effects of prey density and habitat complexity should be taken into account when predicting forager distributions and habitat preference.
