Nearest Tree Research Articles

The Spatial Distribution of Two Pine Sawflies and Methods of Sampling for the Study of Population Dynamics

AbstractThe spatial distribution of egg clusters and cocoons of Neodiprion swainei and N. sertifer is described, and methods are developed for estimating the density of different stages on the same numerical basis.Egg-cluster density varies directly with height in the tree, branch length, and tree size, evidently due to the females’ preference for illuminated sites. The overdispersion of egg-cluster counts reflects the heterogeneity of distribution of suitable oviposition sites rather than an inherent aggregative behaviour of parent females. Cocoon density within stands is not strongly related to the distance from the nearest tree, due to the wide dispersal of cocoon-spinning larvae. Some of the overdispersion of cocoon counts is due to differences in cocoon density between sections of a stand. Cocoons of males are more highly aggregated than those of females, and cocoons attacked by predators are more highly aggregated than ones not attacked.The sampling unit selected for each life-history stage is one that permits density estimates of desired precision at minimum cost. In some stands, egg density can be estimated at minimum cost by direct counts per quadrat, in most stands, however, the whole tree is the most economical unit, despite the fact that per-tree density must be converted to absolute density in order to express all stages on a common basis. Sampling error can be reduced by stratification according to tree size. Gradients in cocoon density are seldom steep enough to permit stratification, but the cost of sampling can be minimized by adjusting unit size. Optimal unit size varies inversely with cocoon density and degree of aggregation, and is affected by soil type and the method used to extract cocoons.The role of spatial distribution and sampling programs in studies of population dynamics is discussed.

Societies and Academies

Societies and Academies

Scorpion carrying Flower

ONE evening last February, while sitting in the verandah of my house at Aden, my attention was drawn to an object advancing across the floor, which seemed to be some peculiar leaf insect or phasma. On looking at it closer I saw it to be a scorpion (identified by Mr. Pocock from my description as Parabuthus liosoma), which was holding over its back by one claw a large blossom of Poinciana regia, known in Aden as the white-gold mohur tree. Its tail, curled over its back, further assisted in retaining the flower in position. The nearest tree from which it could have obtained it was at least 30 feet away, and to bring it the scorpion must have carried it over a low stone parapet and up two or three steps, so that intention seems to be proved. What that intention was it is hard to define. Hardly for concealment, for the size of the flower made it more conspicuous; besides, it was night. If it was the lamp-light it wanted to avoid, it is necessary to assume that, finding the light too strong, it went back to get the flower. It could hardly be as food, for scorpions are not known to live on vegetable substances; nor, as far as I know, do they construct nests. I regret that I did not allow the creature to reach its destination, and so ascertain its intention; but, unfortunately, I gave in to my first impulse and crushed it. My wife suggested that perhaps it was going to a wedding, but this explanation is more poetical than scientific.

Sound-producing Ants

REFERRING to Mr. Blanford's letter in NATURE, vol. xxv. p. 32; whilst lying awake early one morning before the servants were stirring, when camped in the Deccan at the present small station of Chota or Chick-Soogoor, on the G.I.P. Railway, during the winter of 1868–69, I beard a sound, as Mr. Blanford suggests, repeated at regular intervals of about a second. It sounded as though the wall of the tent was being struck by a light fringe along one side; but noticing that the air was perfectly still, I listened for some minutes, wondering what it was and trying to fix the locality. I got out of bed cautiously and looked out; the whole of one side of the tent for a height of two feet was covered with white ants so thickly that at the first glance I thought the wall was covered with a grey-reddish mud to this height. I was trying to make out how the sound could be produced, when it stopped suddenly, the ants evidently having become aware of my presence; they then began to clear off the wall rapidly, and in a few moments it had become white again. They had not attacked the cotton wall. On looking at the ground round the tent I found their runs extending from a tamarind tope, the nearest trees of which were about 50 feet away. The runs were built in the usual way of red Deccan soil, there were great numbers of them, varying in width from the thickness of twine to 21/2) inches, often crossing each other diagonally. No doubt the ants had found the tent in the evening, and were prepared to make a morning meal of a portion of it, when I disturbed them on looking out. The impression on my mind at the time was that the whole body of ants struck the tent wall at the same time with their heads, and that it was very extraordinary that they all stopped at once; there were no dropping shots, it was an instantaneous cessation along the whole line. The tent, which was a double one, was at least 30 feet long, and the ants possibly extended round the ends.