The wet and dry weights of both axenic and monoxenic cultures of the ciliate Tetrahymena were determined directly. These estimates are dependent upon the method of volume determination. Assuming a prolate spheroidal shape for the ciliate, we calculate a mean wet weight of 0.4157±0.0713 pg μm and a mean dry weight of 0.2793±0.0652 pg μm. Using electronic cell sizing, our estimates are 0.7869±0.1659 pg μm and 0.5239±0.1101 pg μm, respectively. Independent of the method of volume determination, we estimate a mean biomass conversion ratio (dry weight/wet weight) of 0.59±0.08.

1976. Growth responses of cohabiting ciliate protozoa to various prey bacteria. Can. J. Zool. 54: 1111-1 114.Four species of cjliate protozoans isolated from a small pond were grown monoxenically on eight species of bacteria. Four of the bacterial species were common "laboratory" specie^, the others were isolated from the same pond as the ciliates. The ciliates showed dimerent growth responses to the wild bacteria. confirming the hypothesiq that they were specialized with respect to the bacterial species on which they couId grow. The laboratory bacteria all permitted good growth of all ciliates. suggesting that the wild bactrna possessed mechanisms to discourage predation. The results are interpreted as supporting the concept that food specialization may he part of a niche partitioning that accounts For the high species richness observed in protozoan communities. TAYLOR, W. D., et J. BERGER. 1976. Growth responses of cohabiting ciliate protozoa to various prey bacteria. Can. J. Zool. 54: 11 11-1 114.Quatre espkces de protozoaires cilih recueillies dans un p t i t etangont i t @ pardtes en cultures rnonoxiniques avec huit espires de bacttries. Quatre des espkces ttactiliennes sont des espkes communes de laboratoire, les autres pmvicnnent du mime itang que les cilies. LES c i l~t s ont une croissance differentielle lorsqu'&levr?s avec les bactiries sauvages: cela confirme I'hyporhtse selon laquelle les ciliks se spkcialisent en Fonction des especes de bactiries sur lesquelles ils peuvent se developper. Les hacteries de laboratoire permettent toute? une crolssance normale des cilics: les bacttries sauvags semblent donc posstder des mtcanismes propres B dCcourager Pa predation. On interprkte les rtsultats dans le sens de I'hypothese qui veut que la spicialisation alimentaire soit un facreur de separation de niches, expl~quant ainsi la pnnde diversite des especes obsewte au sein des communautCs de protozoaires.[Traduit par le journal]

Under starvation conditions, 50% survivorship times displayed no significant relationship with cell size in 2 ciliate species in this study and 5 protozoan species from the literature. Differences in survival ability were attributed to differences in weight-specific respiratory rate and relative motility among these 7 species. At low bacterial levels, 4 ciliate species in this study displayed significant differences in survivorship. High survivorship ofEuplotes patella relative to that ofParamecium caudatum andParaurostyla sp. at low ciliate densities was attributed to the lower individual energy requirements of this smaller species. High survivorship ofStentor coeruleus was interpreted as an effect of its large quantity of reserves and low respiratory rate. The survivorship ofE. patella was reduced at a higher population density. Four ciliate species survived longer at 15‡C than at 22‡C. Q10 values based on 50% survivorship times at these 2 temperatures were much lower than Q10 values based on respiratory rates and growth rates of well-fed ciliates over a similar temperature range.

The trophic role of ciliated protozoans in the functioning of freshwater ecosystems is little known despite the abundance and high reproductive rates of ciliates relative to most aquatic metazoa. By the use of direct and indirect methods, we examined the ability of 9 species of metazoa to prey on Halteria grandinella, a common and abundant planktonic ciliate. Five metazoan species proved capable of capturing the ciliate, despite its 'jumping'escape behaviour. In general, metazoan species described in the literature as 'predaceous' or as filter-feeders on planktonic particles consumed H. grandinella; those described otherwise did not.

Five transects of contiguous samples from the surface of a small pond and one transect from its bottom were collected in order to quantify microspatial heterogeneity in the distribution of ciliated protozoa. Examination of the frequency-abundance relations for these transects suggests that they can be approximated by negative binomial distributions with a commonk of 1.87. Contagiousness or crowding increases with population density.Mean patch size and mean interpatch distance were measured for 4 transects as 1.5 to 2 cm and 3 to 4 cm, respectively. This heterogeneity is suggested to arise from behavioral aggregation about discrete food sources and be very ephemeral.Blocking of adjacent contiguous samples was used to investigate the effect of sample size on the apparent correlation between the numbers of pairs of taxa. In all cases examined, taxa were relatively independent in their distribution at small sample sizes and became more negatively or positively associated as samples were combined. This may reflect that the small scale patches are essentially monospecific.