Selection Of Larger Prey Research Articles

Heterokont Predator Develorapax marinus gen. et sp. nov. - A Model of the Ochrophyte Ancestor.

Heterotrophic lineages of Heterokonta (or stramenopiles), in contrast to a single monophyletic group of autotrophs, Ochrophyta, form several clades that independently branch off the heterokont stem lineage. The nearest neighbors of Ochrophyta in the phylogenetic tree appear to be almost exclusively bacterivorous, whereas the hypothesis of plastid acquisition by the ancestors of the ochrophyte lineage suggests an ability to engulf eukaryotic alga. In line with this hypothesis, the heterotrophic predator at the base of the ochrophyte lineage may be regarded as a model for the ochrophyte ancestor. Here, we present a new genus and species of marine free-living heterotrophic heterokont Develorapax marinus, which falls into an isolated heterokont cluster, along with the marine flagellate Developayella elegans, and is able to engulf eukaryotic cells. Together with environmental sequences D. marinus and D. elegans form a class-level clade Developea nom. nov. represented by species adapted to different environmental conditions and with a wide geographical distribution. The position of Developea among Heterokonta in large-scale phylogenetic tree is discussed. We propose that members of the Developea clade represent a model for transition from bacterivory to a predatory feeding mode by selection for larger prey. Presumably, such transition in the grazing strategy is possible in the presence of bacterial biofilms or aggregates expected in eutrophic environment, and has likely occurred in the ochrophyte ancestor.

Prey selection and functional morphology through ontogeny of Amphiprion clarkii with a congeneric comparison

The relationship between the complexity of the feeding apparatus and prey selection through ontogeny was examined in Amphiprion clarkii larvae. Larvae were reared from 1 to 10 days post-hatch (dph) on a diet of rotifers, wild-caught plankton and newly hatched Artemia sp. nauplii. Results were compared with available data on the relationship between functional morphology and prey selection of Amphiprion frenatus to establish patterns of functional morphology and prey selection between the larvae of two species of coral-reef fishes. Larvae of both species exhibited an increase in selection of larger prey through ontogeny coincident with an increase in the complexity of the feeding apparatus. The first elements to ossify in larvae of both species were the pharyngeal teeth (A. clarkii: 5 dph, near +/-s.d. Standard length, L(S),4. 3 +/- 0. 2 mm; A. frenatus: 5 dph, L(S)5. 0 +/- 0. 4 mm) which, in combination with the development of a more functional feeding apparatus, may have permitted larvae to better process new types and sizes of prey. Prey items, however, were selected differentially between the two fish species, which could not be fully explained by the functional state of the feeding apparatus. While prey selection is influenced by the functional state of the feeding apparatus, all aspects of larval fish biology (morphology, behaviour and physiology) should be considered.

Ontogenetic diet shifts in age-0 striped bass, Morone saxatilis, from the Miramichi River estuary, Gulf of St. Lawrence

Stomach contents of 2928 age-0 striped bass, Morone saxatilis (2.9–153.3 mm total length (TL)), collected from June to November 1992 in the Miramichi River estuary were examined. Seventy-seven percent of the fish stomachs examined contained food organisms and 34 prey taxa were identified. Larval striped bass (< 25 mm TL) fed primarily on immature and adult copepods. The onset of exogenous feeding correlated both spatially and temporally with a peak in the abundance of prey. Chesson's α index indicated progressive selection of larger prey with increasing size of larval striped bass, from small rotifers to larger calanoid copepods to the relatively large calanoid Eurytemora sp. Mysids (Neomysis americand) and sand shrimp (Crangon septemspinosa) were the principal prey of striped bass > 50 mm TL. Contributions by other prey groups (molluscs, polychaetes, amphipods, insects, and larval fish) were minor. Large underyearlings, 64–84 mm TL, in near-fresh water ate proportionally more mysids than fish downriver in more saline waters. Feeding ceased when water temperatures declined below about 3 °C in November.

The influence of prey hardness on Daphnia's selectivity for large prey

The influence of prey hardness on Daphnia's selectivity for large prey

Different ecology in male and female wintering Snowy Owls Nyctea scaandiaca L. in Sweden due to colour and size dimorphism

Wintering Snowy Owls Nyctea scandiaca were studied in southern Sweden during four consecutive winters (November—March, 1989—1993). 85% of the known individuals (9–11 males, 11–12 females) in the provinces of Öland and Skåne were considered properly aged and sexed. They were observed for 92 h during daytime roosting and for an additional 29 h during hunting activity. Males were more often mobbed (p<0.001) during snowfree conditions, more often roosted in forests (p<0.01), left fewer pellets (p>0.05), preferred higher perch sites, and stayed shorter periods in the same area (p<0.01), as compared to females. First to second winter females were mobbed more often during snowcover compared to bare ground conditions (p<0.05), and were mainly selecting medium-sized prey (Oryctolagus, Anas, Perdix.) Two older owls (adult female/sub-adult male) were selecting smaller prey (Microtus, Apodermus, Passerinidae) compared to first second winter females (p<0.001). In conclusion, due to their smaller size and contrasting colouration, males were considered less well adapted to the mainly snowfree conditions in the area, because of a less favourable energy budget due to mobbing, presumed lower hunting success and smaller/less abundant prey. Females, due to their larger size and contrast reducing colouration, were considered better adapted to the same area, due to lower mobbing frequency, presumed higher hunting success and selection of larger prey.

Changes in the foraging pattern of plovers in relation to environmental factors

The effects of environmental conditions on the foraging behaviour of ringed and grey plovers ( Charadrius hiaticula and Pluvialis squatarola) were investigated at Lindisfarne National Nature Reserve, Northumberland. Plovers forage by an apparently visual searching technique, scanning an area while standing still, before running to peck at prey. Plovers appeared to select large prey, in suitable conditions, by not responding to cues of small prey at the start of each waiting period. Within a waiting period, they became progressively more ready to take smaller prey, before eventually giving up and moving to a new waiting site. Giving-up time was adjusted to different conditions, resulting in the selection of larger prey when prey availability was high, notably at high temperatures. The birds tended to concentrate their activity on clumps of high density of available prey, by moving less far after taking large prey than after taking small or no prey. When no prey was taken after a wait, the bird moved on sufficiently far to scan a new area, or further in areas of low-density, highly clumped prey. In addition to feeding by day, plovers also forage at night. Night observations of foraging behaviour and performance are presented, and discussed in relation to visual foraging and the increased activity of some intertidal invertebrates at night. Although plovers apparently use visual searching, for which the prey detection ranges are probably shorter at night, they were able to maintain fairly high pecking rates at night, partly because of higher surface activity levels of prey.