Feeding appendages of the Euphausiacea (Crustacea)

Publication Type:Journal Article
Year of Publication:1967
Authors:Ashby, KR, Mauchline, J
Journal:Journal of Zoology
Volume:152
Pagination:389-513
Date Published:1967
ISBN Number:1469-7998
Keywords:Apodemus sylvaticus
Abstract:

In a 12-year study on Clethrionomys glareolus, Apodemus sylvaticus, and in less detail, on Microtus agrestis in an area of mixed woodland just south of Durham it has been found that a variety of mark-and-recapture line trapping has provided reliable indices of abundance, making it possible to follow the changes occurring in the populations of the three species. Parameters investigated included distribution, density, sexual condition, sex ratio, mortality, recruitment, growth and variation in pressure on food supplies. The abundance of Clethrionomys has varied cyclically, the periodicity being slightly under four years as previously recorded in the microtine rodents of tundra and grassland habitats. There has been evidence of abnormalities of the generations living during a crash similar to those reported in Microtus agrestis during this phase of a population cycle. Apodemus in contrast has had only a well-defined annual fluctuation in abundance, the rapid decline observed in its population density each spring perhaps being caused by an intensification of territorial behaviour at the beginning of each breeding season. lntraspecific competition also appears to account for male Apodemus, which grow more quickly and to a larger size than females, being more abundant than the latter in most years. After exceptionally favourable seasons, females are as numerous as males, apparently as a result of a temporary reduction of such competition. Microtus, for which the area of study provided a marginal habitat, showed less regular fluctuations in abundance than have been found to occur in this species on moorlands. It is confirmed that Clethrionomys and Apodemus are important in woodland ecosystems as agents transporting, burying and eating tree-seed, and damaging or killing the seedlings. Their influence on regeneration of forest is complex and calls for detailed study. The pressure exerted by these two species on token supplies of seed which were offered, was greatest in winter and least in late summer. Appetite and stockpiling activity were increased relative to rodent abundance, under crowded conditions. The significance of food shortage and of social stimulation respectively as possible causes of these increases are discussed.The Euphausiacea comprises about 85 species and the structure of the feeding appendages of 68 of these species is discussed here. A considerable uniformity is apparent in the appendages throughout the order but generic, and even in some cases, specific differences are evident. It is concluded from the study of the morphology of the appendages and the analyses of stomach contents that the majority of species in the genera Bentheuphwsia, Thysanopoda, Meganyctiphanes, Nyctiphanes, Pseudeuphausia, Euphausia, Tessara-brachion and Thysanoessa are omnivorous; that is, they can feed by filtering material from the water and act as predators of small zooplankton, especially copepods. Species in the genera Nematoscelis, Nematobrachion and Stylocheiron can feed on bottom deposits and also by predation of zooplankton but the amount of filter-feeding which they do may be limited because their mouthparts are not so well adapted for filtering as those of the previous group of genera. It is suggested, from the study of the appendages and several other features of the animals, that the genera Thysanopoda, Meganyctiphanes, and Euphausia are closely related to one another and that a similar relationship exists between the genera Nematoscelis, Nematobrachion and Stylocherion. The genera Nyctiphanes and Pseudeuphausia are probably more closely related to the Thysanopoda group of genera and the genera Tessarabrachion and Thysanoessa to the Nematoscelis group of genera.

URL:http://dx.doi.org/10.1111/j.1469-7998.1967.tb05029.x
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