The Survivorship, distribution, growth rates, and natural predation rates on the population of Rana aurora tadpoles in Marion Lake, British Columbia, were studied during the summers of 1969 and 1970. Natural survivorship appeared to have two phases: a rapid decline in numbers during the first 4 weeks after hatching was followed by a less rapid decline, until approximately 5% of the population remained at metamorphosis, after 11—14 weeks. The size attained by tadpoles living at any depth in the lake was strongly correlated with the accumulated degree—days since hatching (r = .93). The regression equation (degree—days vs size) obtained from the data on animals in the lake could accurately predict the growth rate of tadpoles kept in the laboratory at maximum food supply. It was concluded that animals in the lake grew at the maximum rate permitted by the temperature. Alterations of the density of tadpoles and predatory salamanders were performed in enclosures in the lake. The percentage of tadpoles surviving in the enclosures containing no salamanders was twice as high as it was in the natural population. The percentage of tadpoles surviving in the experimental enclosures was independent of density, at least up to 75 tadpoles/m2. Except at the lowest density (5/m2), no significant effects were noted at any density, on the rate of growth or time to metamorphosis. These experimental observations support the notion that food is not limiting to the tadpoles at their normal densities. Most of the mortality of tadpoles observed in the natural population was attributed to predation because: (1) Tadpoles kept in the laboratory on starvation diets survived for many weeks, even though they did not grow. (2) Tadpoles living at densities up to 100 times normal could survive and grow to metamorphosis in the absence of predators. (3) Predation rates observed in the field, and simulated on the basis of laboratory experiments, were sufficient to account for much of the mortality observed in the natural population. Laboratory studies of salamanders preying on tadpoles in multi—prey systems showed that the number of tadpoles eaten was proportional to the density of tadpoles present except at very low density, where fewer tadpoles than expected were eaten. The tadpoles also had a refuge from some predators after they had grown to a certain size. Salamanders were observed to move into areas of high tadpole density, thereby increasing locally the intensity of predation. It was concluded from the laboratory and field observations that mortality of tadpoles is density—dependent. However, the limiting factors for the Rana aurora population are unknown, since the frogs were not studied after they left the lake. The numbers of eggs laid in the 2 years of the study were very similar, but no social mechanisms for controlling the breeding population were observed.

Summary The theoretical maximum rate of increase for the African elephant is calculated at 7%. This figure agrees closely with the rate of increase observed at Addo Elephant Park, the highest rate of increase reported for elephants living under natural conditions. An elephant population increasing at the maximum rate soon reaches a stable age distribution in which 48% of the animals are older than 11 years of age, (the age of first reproduction) and 6.7% are calves (less than one year old). Several papers have reported frequencies of calves in natural populations of up to twice this percentage. Calculations are presented to show that such high calf frequencies are both theoretically impossible on a sustained basis, and internally inconsistent with the population data presented in these papers.

ABSTRACT. The responses of barren-ground caribou to fixed-wing aircraft and to helicopters were observed in the northern Yukon and Alaska. Effects of aircraft altitude, type of aircraft, season and terrain were determined together with the activity and size of group of the caribou. Panic reactions or strong escape reactions were observed in a high percentage of all groups when aircraft flew at altitudes of less than 60 metres. Flying at a minimum aircraft altitude of 150 metres during spring and fall migrations, and 300 metres at other periods, would prevent the caribou reacting in the ways most immediately injurious to them. R h U M k

The Kaminuraik caribou herd apparently declined from about 120 000 animals in 1950 to 63 000 in 1968. Beginning in 1968 documentation of herd trend was based on the estimate of the number of breeding (pregnant and post-partum) females on the calving ground during the birth peak. It appeared as if we understood the basic population processes responsible for the decline when we correctly predicted a drop from 14 800 breeding females in 1977 to 13 000 in 1980. However a three-fold increase, to 41 000 breeding females in 1982, and continued growth thereafter, was unanticipated. Most of that increase must have resulted from an immigration of cows to the herd's traditional calving ground around Kaminuriak Lake, although increased birth rates, and increased survival rates also contributed to herd growth. Immigrant cows probably came from the northeastern mainland of the NW

A strong correlation between the abundance of the blue—green alga Trichodesmium thiebautii and the abundance of the harpacticoid copepod Macrosetella gracilis is reported at 34 stations off the northeastern coast of South America. This field observation supports previous laboratory observations that filaments of Trichodesmium are required as a substratum for the development of M. gracilis.