Scanning electron microscope observations of Amoeba proteus during phagocytosis.

Phagocytosing Amoeba proteus at different stages of forming foodcups have been observed by scanning electron microscopy. A nonphagocytosing ameba is characterized by dorsal and lateral ridges running longitudinally over the posterior half of the cell and its attachment to the substrate over small areas. When stimulated by prey organisms, the ameba loses polarity and ridges, and adheres to the substrate more firmly over a wider area of contact. Then it forms broad pseudopods to surround its prey and this results in the formation of foodcups. The surface of all ameba is covered with small projections, and membranous blebs are often seen on the surface of phagocytosing organisms.     

Spatial Distribution,Food and Activity of Gomphus pulchellus SELYS 1840 (Insecta; Odonata; Gomphidae) from a Still Water Habitat

Distribution patterns of Gomphus pulchellus larvae in different sediments with different density of prey organisms were studied in the field in a small gravel pit lake in the south of Germany. Larval burrowing behaviour at different temperatures as well as food preference, consumption rates and activity were studied in laboratory experiments. In the study lake G. pulchellus larvae lived exclusively in places where macrophytes were present and in fine sediments (mean grain size <3 mm) with detritus cover. There was a significant positive correlation between larval density and density of food organisms suggesting that abundance of food is one of the determinants of larval distribution. In late autumn larvae migrated to deeper places probably to survive the winter. Low temperatures simulated in laboratory experiments did not induce larvae to burrow deeper. Larvae were always found in a sediment depth of 0.59–0.74 cm. Experiments with mixed prey showed that G. pulchellus larvae preferred tubificid worms and chironomid larvae over gammarids and ephemerid larvae. However, chironomid larvae which stayed in their tubes had a higher survival rate than those outside of tubes. Single-prey experiments showed that G. pulchellus larvae can prey not only on benthic species but also on Daphnia from the open water. Functional-response experiments showed that one G. pulchellus larva consumes a maximum of 2 to 3 tubificid worms or chironomid larvae per day, which corresponds to a maximum biomass (freshweight) of 5 to 30 mg per day. Video recordings of activity showed that G. pulchellus larvae cover long distances of up to 52 m per night on the substrate surface and that activity on the substrate surface started after midnight and ceased before sunrise. Consumption of Zooplankton prey and high activity above the substrate is interpreted as an adaptation of G. pulchellus larvae to the life in still water habitats.     

The feeding behaviour of New Zealand Dolomedes species (Araneae: Pisauridae)

Abstract

The prey spectrum and predatory behaviour of Dolomedes sp. (‘D. III’), D. aquaticus, and D. minor are described from a series of field and laboratory investigations, the former made around Nelson and on Banks Peninsula, Canterbury, during summer months. All species are large, robust spiders that capture prey by directly seizing it in their mouthparts, not using silk at any stage of predation. Adult aquatic insects are their main prey, but these are available only irregularly during their activity period (night-time), and the spiders are opportunistic in their feeding habits. They will eat virtually any available small animal, and at least the largest species, D. III, is able to capture and ingest small fishes. Dead as well as live organisms are taken. Furthermore, the spiders are capable of feeding infrequently; when feeding on small prey organisms they may capture several sequentially, to increase the size of the meal. Live prey is caught while it is in flight, or on the ground, or at the water surface (rarely submerged), and is detected primarily by touch and airborne sound; vision is unnecessary for normal predation. Prey is captured very rapidly, even though this may initially involve a dash of up to 40 cm across the water surface to locate the organism. Stages in the behaviour of an active spider, from waiting for prey to grooming after ingestion, are described.     

Temporal variations in the diet of pearly razorfish Xyrichtys novacula (Osteichthyes: Labridae)

The diet of pearly razorfish Xyrichtys novacula, caught monthly along the shores of the Island of Lampedusa, appeared to be mainly composed of crustaceans, followed by colonial ascidians, molluscs and polychaetes. Among prey, sand dwellers and phanerogam‐associated species were recorded. In winter months, the diet was characterized by a small number of prey items, dominated by colonial ascidians, while in spring and summer a wider prey array was recorded. Dietary indices show that X. novacula do not strictly exploit benthic prey but also pelagic organisms, such as copepods. This feeding behaviour reached its peak in March and October, when the abundance of primary consumers was at its highest after phytoplankton blooms. Furthermore, X. novacula caught prey organisms according to their availability and seasonal patterns during their life cycles, irrespective of fish size.     

A STUDY OF PHAGOCYTOSIS IN THE AMEBA CHAOS CHAOS

The process of phagocytosis was investigated by observing the interactions between the ameba Chaos chaos and its prey (Paramecium aurelia), by studying food cup formation in the living cell, and by studying the fine structure of the newly formed cup using electron microscopy of serial sections. The cytoplasm surrounding the food cup was found to contain structures not seen elsewhere in the ameba. The results are discussed in relation to the mechanisms which operate during food cup formation.     

Torsional Movements in the Ameba,Chaos carolinensis,Suggest a Helical Cytoskeletal Organization*†

SYNOPSIS. Centrifugation for 30–40 seconds at 8,000 g has been used to render monopodial specimens of the large free-living ameba. Chaos carolinensis. These monopodial amebae exhibit obvious torsional movements in the tail. In many cases the posterior ectoplasm assumes the form of a screw with helical ridges forming in place of the more common straight dorsal fins. This finding prompted a re-examination of normal polypodial C. carolinensis, and a majority of these were found also to exhibit torsional movement in the tail and in retracting pseudopodia. These movements suggest that the cytoskeleton of Chaos may have a helical component in its organization.     

Riparian ground beetles (Coeloptera, Carabidae) preying on aquatic invertebrates: a feeding strategy in alpine floodplains

The food and feeding habits of riparian ground beetles were studied in four alpine floodplains (Bavaria, Germany): a 5th-order stream (the Isar) and three 3rd-order streams. The riparian fauna along the streams mainly consists of predaceous species. Riparian ground beetle densities were much higher along the Isar than along the small streams. Aquatic invertebrates composed 89% of the potential prey for carnivorous terrestrial insects along the Isar. Besides aquatic organisms washed ashore, stoneflies emerging on land are of considerable importance as potential prey for terrestrial predators. In contrast, only 34% of the potential prey organisms collected along the small streams were of aquatic origin. Food abundance was 9 times higher in the shore region of the Isar compared to the small streams. Surface drift in the Isar, a potentially important food source for riparian organisms, was about 10⁶ organisms and exuviae per meter stream width in 24 h. The drift density in the Isar was 59 times higher than that in a small stream. Terrestrial organisms provided only 3% of the drifting particles in the Isar, but 50% in the small stream. Gut content analysis reveals, that riparian ground beetles in the Isar floodplain mainly feed on aquatic organisms washed ashore or emerging on land. While small Bembidion species prefer chironomids (larvae and adults) the larger species Nebria picicornis feeds on emerging stoneflies, terrestrial riparian organisms and aquatic organisms accumulating along the shoreline. The prey of riparian ground beetles in the floodplain of the three small streams mainly consists of terrestrial species some of which may have been washed ashore. Received: 2 September 1996 / Accepted: 26 February 1997     

Feeding on the edge: foraging White Ibis target inter‐habitat prey fluxes

Avian population dynamics are influenced by the availability of spatiotemporally variable prey resources, but the conditions producing abundant and accessible prey are not always clear. In the Florida Everglades, wading birds nest in the dry season when receding water levels concentrate prey and facilitate improved foraging efficiency. White Ibis (Eudocimus albus) feed extensively on crayfish in sloughs, and previous studies have demonstrated that crayfish move downgradient from higher elevation, heavily vegetated ridge habitats into adjacent less‐vegetated sloughs when ridges are almost dry. Most White Ibis foraging is thought to occur in sloughs with relatively shallow water (< 19 cm), but crayfish move and their densities peak when water in sloughs is deeper (~ 21–32 cm). We conducted an observational study of White Ibis foraging in drying wetlands to determine if White Ibis restricted their foraging to shallow water or if they foraged in relatively deep water when crayfish were migrating. In a series of large drying wetlands, we used time‐lapse imagery to quantify White Ibis foraging activity over 61 d from February to April 2017 and we also quantified crayfish biomass density in sloughs. Crayfish biomass density peaked when ridges were almost dry. Most White Ibis foraging occurred over 2–3 d when ridges were almost dry and water in sloughs averaged ≥ 29 cm deep. White Ibis selected slough edges for foraging, suggesting that they were capturing crayfish migrating between habitats. Our results point to a new mechanism of prey exploitation driven by inter‐habitat prey flux when ridge habitat dries. Although the results of previous studies suggest that White Ibis will not forage on fish in deeper water (> 25 cm), we found that White Ibis will forage on crayfish in water at those depths. Maintenance of habitat elevational differences and hydro‐patterns that promote crayfish production will be necessary to promote this predator–prey interaction in the ridge‐slough landscape of the Everglades.     

Isolation of the Lembadion-factor,A morphogenetically active signal,that induces Euplotes cells to change from their ovoid form into a larger lateral winged morph

A morphogenetically active substance released by the predatory ciliate Lem-badion bullinum is recognized by ciliates of the genus Euplotes, which are potential prey organisms of Lembadion. The substance (L-factor) induces cells of the genus Euplotes to become less compact, which reduces their likelihood of becoming engulfed. Under the influence of this Lembadion- derived signal, E. octocarinatus develops extended wings and dorsal and ventral ridges and transforms within a few hours from its typical ovoid morph into an enlarged circular morph. This takes place without cell division. We have isolated the L-factor and report that it is a protein with a mass of 31,500 Da. The factor has been purified to chromatographic and electrophoretic homogeneity and was found to be active at concentrations as low as 10^?12 mol/L. © 1992 Wiley-Liss, Inc.     

Mechanisms of selectivity in a nocturnal fish: a lack of active prey choice

Fish that feed on individual zooplankton usually exhibit strong selectivity for large prey. Such selectivity can result from the predator’s active choice of larger prey or from differential encounter rate due to lower detectability of small prey, or both. In diurnal fishes, selectivity is thought to be determined mostly by active choice. In spite of a lack of direct observations, active choice is also considered the prevailing mechanism of prey selectivity in nocturnal fishes. Our objective was to resolve this mechanism in the highly selective, nocturnal zooplanktivorous fish Apogon annularis. Laboratory experiments indicated that the fish’s encounter rate with small prey was lower than that with large prey and that its selectivity became stronger with decreasing light intensity. Feeding efficiency, defined as the ratio between feeding and encounter rates, ranged 41–89% and was positively correlated with prey size. When feeding on a mixture of prey sizes, the fish fed on each size group at a rate similar to that of its feeding on the respective size alone, indicating that selectivity in A. annularis was due to size-dependent encounter rate and differential feeding efficiency. A low visual acuity in A. annularis, as inferred from its inability to detect small prey (<0.9 mm in length), together with the low abundance of large zooplankton in situ, can explain the dominance of differential encounter over active choice in this nocturnal coral-reef fish.     

Degradation of human secretory IgA1 and IgA2 by Entamoeba histolytica surface-associated proteolytic activity

The protozoan Entamoeba histolytica is the etiological agent of amebiasis, an infection with high prevalence worldwide. The host-ameba relationship outcome depends on parasite and host factors, and among these is secretory IgA. These antibodies reduce mucosal colonization by pathogens and neutralize a variety of toxins and enzymes. The functionality of secretory IgA depends on its integrity. Some bacteria produce IgA proteases that cleave mainly the IgA1 subclass; live E. histolytica trophozoites, and other ameba fractions are also able to degrade human IgA. The aim of this study was to determine if serum and secretory IgA, its subclasses and secretory component, are degraded by cysteine proteases, which are present and active on the surface of glutaraldehyde-fixed amebas. It was observed that secretory IgA1, IgA2, free and IgA-bound secretory component were degraded by E. histolytica surface-associated cysteine proteinases. Secretory IgA2, although it was degraded, conserved its ability to agglutinate live amebas better than IgA1. Therefore, while specificity of known ameba cysteine proteases is cathepsin B-like and is different from bacterial IgA proteases, IgA2 was functionally more resistant than IgA1 to ameba surface-associated cysteine protease degradation, similar to the greater resistance of IgA2 to bacterial IgA-specific proteases.     

Specialized foraging habits of adult female California sea lions Zalophus californianus

Individual foraging specialization occurs when organisms use a small subset of the resources available to a population. This plays an important role in population dynamics since individuals may have different ecological functions within an ecosystem related to habitat use and prey preferences. The foraging habitat fidelity and degree of specialization of California sea lions (Zalophus californianus) were evaluated by analyzing the stable isotopes values of carbon and nitrogen in vibrissae collected from 16 adult females from the reproductive colony on Santa Margarita Island, Magdalena Bay, Mexico, in 2012 and 2013. Based on the degree of individual specialization in δ¹⁵N, 62.5% of the females assessed can be considered specialist consumers focusing on the same prey or different prey from the same trophic level. The degree of individual specialization in δ¹³C indicated that 100% of the individuals showed fidelity to their foraging habitat as some fed in the lagoon, others foraged along the coast, and a third group preferred prey from the pelagic environment during both the breeding and nonbreeding seasons, suggesting diversification of foraging areas. Foraging area fidelity persisted despite the 2°C increase in the sea surface temperature over the course of the study period.     

Food selectivity versus prey availability: a study using the marine fish Pomatoschistus microps

Summary The food selection of the common goby, Pomatoschistus microps Krøyer, was studied in the field and in laboratory experiments on the Swedish west coast. The three most important prey organisms for P. microps in the study area were Corophium volutator, chironomid larvae and Nereis spp. Corophium was consumed more than any other prey, even when it was not the most abundant prey species in the bottom. One reason may be the higher activity of Corophium above the sediment surface, which may increase its visibility and consequently its vulnerability to visual predators. When P. microps was offered Corophium and chironomid larvae with similar exposure in laboratory experiments, it showed no preference for either of the prey items. It always took the closest mobile prey, regardless of species and size.     

Predatory behavior of Cupelopagis vorax (Rotifera; Collothecacea; Atrochidae) on protozoan prey

By rotating on a short, flexible, pedal stalk, Cupelopagis vorax captures prey that traverse the substratum to which this sessile rotifer attaches. Microvideographic analysis (including slow motion and freeze-frame) permitted us to examine some of the details of Cupelopagis foraging behavior. When undisturbed, Cupelopagis usually faces forward in a resting or neutral position (NP) with its unciliated infundibulum (corona) directed parallel to the surface of the substratum. However, vibrations produced by artificial means (fine pins) or small prey (protists) evoke unique behaviors in Cupelopagis. Our analysis of Cupelopagis foraging on two protozoan prey (Paramecium bursaria and a small, unidentified flagellate, SUF) indicates that this predator possesses a 360 ° encounter field (EF) biased towards the NP Size of the EF appears to be a function of both predator and prey size, but it extends at least 650 µm, as measured from the point of attachment of the predator's pedal stalk to the substratum. When a prey comes close to Cupelopagis, this predator can lean toward the organism, stretching forward on its pedal stalk and extending its corona over the prey in a swift motion (< 0.5 s). Probability of capture after attack was a function of prey type (61.6% for P. bursaria and 41.5% for the SUF). Analysis of prey capture by Cupelopagis indicates that this predator has a handling time ranging from a few seconds to several minutes: 24.6 ± 16.8 s for P. bursaria (n= 274) and 34.6 ± 25.4 s for the SUF (n=111). Occasionally Cupelopagis sweeps part of the EF by retracting its corona, turning to the right or left (mean angle subtended 63 ° ± 42 °), unfolding the corona, and slowly returning to the original resting position. This behavior, termed surveillance, occurs in the presence or absence of prey. While not unique in its ability to detect water movements, Cupelopagis is the only rotifer known to exhibit specific behaviors to vibrations produced by potential prey.     

CHRYSOCHROMULINA BREVITURRITA SP. NOV., A NEW FRESHWATER MEMBER OF THE PRYMNESIOPHYCEAE1

Chrysochromulina breviturrita sp. nov. is described as a new haptonema-bearing member of the freshwater Prymnesiophyceae. It is ca. three times larger than the only other known freshwater member of the genus (C. parva Lackey)and possesses a haptonema only ca. 0.2–0.3 as long as the haptonema of C. parva. Two equal flagella (1.5–2 as long as the haptonema), a large contractile vacuole, two parietal plasties, a single pyremid, nucleus, Chrysolaminarin-like droplets and a food vacuole are features readily observed with the light microscope. Dried and shadoweast whole mounts examined with the electron microscope reveal the cell surface covered with two types of small, delicate scales: outer spined scales with a clubshaped terminus and with the spine anchored to a circular to oval base-plate by 2–6 (7) branching arms; and, spineles oval plate scales with concentric lines and radiating ridges on one face and parallel ridges on the other. C. breviturrita has been found in nine lakes in Ontario (Canada). Pereliminary observations suggest that it is an important component of lake plankton and has probably not been delected in previous work, more because of its fragility than because of its scarcity. Living specimens are a prerequisite for initial identification, since cells frequently rupture and haptonemata are often lost when the organisms are killed with the commonly used fixatives.     

The basis of food selection in some estuarine fishes. Eels, Anguilla anguilla (L.), whiting, Merlangius merlangus (L.), sprat, Sprattus sprattus (L.) and stickleback, Gasterosteus aculeatus L.

The factors influencing the selection of food by eels, Anguilla anguilla, whiting, Merlanglus merlangius, sprat, Sprattus sprattus, and stickleback, Gasterosteus aculeatus have been investigated by analysing collections made in the Severn Estuary for 1 year. Non–migratory (yellow) eels measuring from 19–5–56–5 cm in length fed mainly on either the decapod Crangon vulgaris or on the mysid Neomysis integer during the warmer months but ceased to feed in the winter. Whiting measuring between 2–5 and 15 cm fed almost exclusively on C. vulgaris, N. integer and the sand goby, Pomatoschistus minutus. Sprats fed chiefly on either the arnphipod Gammarus salinus or N. integer. Sticklebacks seldom contained any food in their stomachs despite the presence of large quantities of suitable prey and the high level of hunting efficiency. Gammarus salinus, although normally abundant in the environment, was usually ingested in disproportionately small quantities by all fishes except sprats reflecting its concealment among floating weeds and a selection against small (less than 1 cm) organisms. Because of the limitations of size and the unusually efficient escape reaction of larger animals, only young representatives of Crangon vulgaris were captured. The isopod Eurydice pulchra was rarely eaten by any of the fishes even though it was common in the environment. Burrowing polychaetes, mainly Nereis diversicolor, were never utilized possibly due to the difficulty involved in removing these organisms from the substrate. Neomysis integer was the most frequently consumed organism. Although the average length of prey ingested by the whitings increased with the size of fish, this was not the case for the other species. The proportion of non–feeding eels and the dry weight of stomach contents of this species depended on the temperature of the water but were not related to the availability of prey and tidal conditions whereas the feeding of whiting could not be related to any environmental parameter.     

Food capture and adhesion by the heliozoonActinophrys sol

Summary The heliozoonActinophrys sol is characterized by needle-like axopodia radiating from the spherical cell body. When helio-zoons capture food organisms, the prey is caught by adhesion to the surface of axopodia where numerous extrusomes are present close to the plasma membrane. To understand the molecular mechanism by which the heliozoons capture prey organisms, crude isolation and characterization of the adhesive substance was carried out. Prey flagellates (Chlorogonium elongatum) adhered and aggregated to remnants of heliozoon cells which had been killed by freezing or treatment at high temperature (80 °C for 10 min). Isolated extrusomes, which were prepared as the supernatant of cells homogenized and centrifuged after freezing and thawing, showed strong adhesion to the prey flagellates which responded to the supernatant by adhering their flagella and cell bodies to each other to form bouquet-like cell clusters. The adhesive substance was further extracted from heat-treatedA. sol. This fraction contained filamentous material similar to the secreted contents of the extrusomes observed during feeding. Its adhesive activity was not inhibited by trypsin treatment.     

Entamoeba histolytica: ADP-ribosylation of secreted glyceraldehyde-3-phosphate dehydrogenase

In addition to its classic glycolytic role, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has been implicated in many activities unrelated to glycolysis, such as membrane fusion, binding to host proteins and signal transduction. GAPDH can be the target of several modifications that allow incorporation to membranes and possible regulation of its activity; among these modifications is mono-ADP-ribosylation. This post-translational modification is important for the regulation of many cellular processes and is the mechanism of action of several bacterial toxins. In a previous study, we observed the extracellular ADP-ribosylation of a 37-kDa ameba protein. We report here that GAPDH and cysteine synthase A are the main ADP-ribosylated proteins in Entamoeba histolytica extracellular medium, GAPDH is secreted from ameba at 37 degrees C in a time-dependent manner, and its enzymatic activity is not inhibited by ADP-ribosylation. Extracellular GAPDH from ameba may play an important role in the survival of this human pathogen or in interaction with host molecules, as occurs in other organisms.     

Ecological Variables Affecting Predatory Success in <Emphasis Type="BoldItalic">Myxococcus xanthus</Emphasis>

The feeding efficiency of microbial predators depends on both the availability of various prey species and abiotic variables. Myxococcus xanthus is a bacterial predator that searches for microbial prey by gliding motility, and then kills and lyses its prey with secreted compounds. We manipulated three ecological variables to examine their effects on the predatory performance of M. xanthus to better understand its behavior and how it affects prey populations. Experiments were designed to determine how surface solidity (hard vs soft agar), density of prey patches (1 vs 2 cm grids), and type of prey (Gram-positive Micrococcus luteus vs Gram-negative Escherichia coli) affect predatory swarming and prey killing by M. xanthus. The prey were dispersed in patches on a buffered agar surface. M. xanthus swarms attacked a greater proportion of prey patches when patches were densely arranged on a hard-agar surface, compared with either soft-agar surfaces or low-patch-density arrangements. These ecological variables did not significantly influence the rate of killing of individual prey within a patch, although a few surviving prey were more likely to be recovered on soft agar than on hard agar. These results indicate that M. xanthus quickly kills most nearby E. coli or M. luteus regardless of the surface. However, the ability of M. xanthus to search out patches of these prey is affected by surface hardness, the density of prey patches, and the prey species.     

Signal-induced Defensive Phenotypic Changes in Ciliated PProtists: Morphological and Ecological Implications for Predator and Prey1

ABSTRACT. Survival of a potential prey organism depends on the effectiveness of its physical, chemical, behavioral and life history responses to the appearance of a predator. Inducible defenses are flexible responses in which predator (or competitor)-released substances stimulate potential prey organisms to transform into predator-resistant phenotypes. Induced defenses may be highly protective. Benefits however are often balanced by fitness costs such as decreased growth rates or reduced reproductive potential. Here I discuss inducible defenses in ciliates with particular attention to the hypotrich genera: Aspidisca, Euplotes, Onychodromus, Sterkiella, and an undescribed hypotrich genus. I isolated Sterkiella sp. and the undescribed genus from vernal woodland pools on Saint Anselm College campus. Experimental evidence shows that a signal-induced defensive transformation occurs in these ciliates within hours after exposure to a predator cue and results in a significant decrease in susceptibility to predation. Deployment of ciliate antipredator structures such as spines, keels, ridges and other protuberances requires a large investment of cytoskeletal elements, primarily microtubules, and incurs an evolutionary cost in the form of significantly reduced growth rates. Onychodromus quadricornutus exhibits an extraordinary degree of phenotypic plasticity. In response to different environmental conditions individuals within a clone may express one of three general phenotypes: basic, lanceolate, or giant cells. The predacious giant phenotype releases a morphogenetically active signal substance, Onychodromus-factor, that triggers defensive phenotypic transformation in both intraspecific and interspecific prey. Enzyme degradation and ultrafiltration experiments indicate that Onychodromus-factor is a peptide with a molecular weight below 10,000 Da. Conspecifics develop hypertrophied dorsal spines when exposed to Onychodromus-factor. Sterkiella cells develop two defensive dorsal keels and transform to an enlarged ovoid cell in response to Onychodromus-factor as well as inducing signals released by Stylonychia, Urosyla, and Lembadion. Field studies of two vernal pools show that defensive phenotypic transformation in Sterkiella cells coincides with the appearance of Lembadion magnum during vernal pool succession. An undescribed hypotrich genus also expresses its defended phenotype when Lembadion is present in these pools. Aspidisca turrita (Ehrenberg, 1838) Claparede and Lachmann 1858, closely resembles Aspidisca lynceus (Müller, 1773) except for the possession of a dorsal thorn-like structure. Experimental evidence shows that the dorsal thron is a defensive structure induced by signals released by the predacious ciliates Urostyla grandis and Lembadion magnum. Thus, A. turrita and A. lynceus are alternate phenotypes of the same species. I speculate that inducing signals function in predacious ciliates as lectin-like, carbohydrate-binding adhesion proteins during prey recognition and that prey species have evolved specialized cell surface receptors that allow detection of different predator proteins. I consider consequences for both predator and prey.