A CLIMATIC PATTERN BETWEEN LATITUDES 40o AND 70o N. AND ITS PROBABLE INFLUENCE ON BIOLOGICAL DISTRIBUTIONS

Abstract

SUMMARY Temperature, rainfall and day‐length probably all help to determine limits of plant distributions, but the distributions cannot generally be explained by simple values of any of these quantities alone. There is in most latitudes a negative correlation between annual temperature range and log. winter rainfall and this and other correlations make it difficult to distinguish the effects of the several factors in the delimitation of plant areas. Approximately within the 40o‐70o N. latitude band a strongly marked climatic pattern of increasing annual temperature range inland from the coasts is matched by a pattern of reducing winter temperatures in the same directions. The centre of this pattern, in Eurasia, is in eastern Siberia. This pattern is reflected in many plant areas. Following ideas expressed severally by Vahl, Iversen and Jeffree for plotting plant distribution in terms of temperatures of coldest and warmest months (or of January and July) on Cartesian co‐ordinates it is shown that the areas obtained may be closely related to the above main climatic pattern. Very similar areas may be obtained from values of latitude (which governs day‐length) and log. winter rainfall. Several of these climatic areas have been compared with biological distributions and maps are presented. Some of these can be arranged in progressive series which correspond rather closely with some series of equiformal progressive areas of plant distributions given Hultén.

Temperature and the Biogeographical Distributions of Species

“…4, A)are of approximately the same areas as the horizontal ellipses published byJeffree (1960). Each such basic ellipse (cf.Fig.…”

“…It is fully recognized that climatic variables other than temperature, notable among which is winter rainfall (Jeffree 1960), also play a significant part in determining the distribution of species. It is fully recognized that climatic variables other than temperature, notable among which is winter rainfall (Jeffree 1960), also play a significant part in determining the distribution of species.…”

“…Craddock (1956) showed that the annual Temperature and course of temperature, approximately a sine curve, species could be described by two-term harmonic equations, distributions from which the mean temperature for any day of the year can be calculated. There is a strong precedent for the use of seasonal values of temperatures, among other variables, to explain the mapped boundaries of vegetation types (K6ppen 1900, 1918Thornthwaite 1931Thornthwaite , 1933, and of species (Vahl 1911;Iversen 1944;Jeffree 1960). The observation that the geographical limits of species distributions appear to coincide with a summer or a winter isotherm, and the interpretation that the coincidence might be causal, are frequently encountered in the literature.…”

“…A notable example is given by Iversen (1944), who interpreted the -0.5 0C isotherm of the coldest month as representing the northern limit for hlex aquifolium; and comparable results have been obtained by others (Conolly 1970;Conolly & Dahl 1970;Nobel 1983;Grace 1987;Woodward 1987; see also Hengeveld 1990 and citations therein). Later, the limits of the distribution of many other examples of plant and insect species were defined using fundamentally the same approach (Jeffree 1960). The geographical distributions of species are areas on the world's surface, although species may occupy single continuous or multiple disjunct areas.…”

North Atlantic biota and their history; a symposium held at the University of Iceland, Reykjavík, July 1962, under the auspices of the University of Iceland and the Museum of Natural History. Editors: Askell Löve and Doris Löve. Sponsored by the NATO Advanced Study Institutes Program

“…When an area is studied the average temperature is often used as an indicator to the rigor of its climate, but the annual average is a poor figure so long as the amplitude of the temperature variations is not given. (Jeffre, 1960). Even the average air temperature of the summer months may not give a full answer to the tolerance of a given species.…”