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The Distribution, Dispersal and Size of a Population of Nebria brevicollis (F.), with Comparative Studies on Three Other Carabidae

1964; Wiley; Volume: 33; Issue: 2 Linguagem: Inglês

10.2307/2633

1365-2656

P. J. M. Greenslade,

Forest Insect Ecology and Management

The main purpose of the work described in this paper was to investigate the spatial distribution of populations of Carabidae, and the amount of movement by individuals within and between them. The term population is used loosely to include both its usual meanings, that is the sum total of individuals in a given area, and alternatively a group of individuals communicating more among themselves than with other similar groups of the same taxon. In the latter sense population is synonymous with gamodeme in Gilmour & Gregor's (1939) terminology. A secondary purpose of this study was to investigate the probability of different factors limiting numbers in different parts of a population. Elton (1949) pointed out that populations commonly consist of centres of varying density, and Wellington (1957) showed that there may be important seasonal and spatial variation in behaviour and physiology among individuals within a population. Richards (1961) suggested that at the climatically optimal centre of a species' geographical distribution, Nicholsonian controls maintain steady populations with only minor year-to-year fluctuations due to weather, while at the limits of the range, climate may cause more drastic variation. It is possible that Richards's suggestion can be applied also to local populations, Nicholson (1958) stating that at the fringes of a population there may be a gradient of favourability in an environmental factor over which 'density-governing reaction' does not occur. Some information is available on the effect of climate on Carabidae, and this is a factor in which gradients may occur at the edge of population areas. Briggs (1961) and Greenslade (1961), found a correlation between Carabid activity and temperature, while several workers, reviewed by Greenslade (1964b) have observed that Carabid adults, and more especially the larvae, are susceptible to desiccation; in some cases the habitats of species have been related to microclimate factors. Greenslade (1964b) concluded that although open habitats with high temperatures may be the most favourable for Carabidae, many species are excluded from them by low humidities. Tipton (1960) investigated the water and temperature relations of Nebria brevicollis (F.), one of the species studied here. The effect of weather on insect numbers may be simple and direct or delayed, Edwards (1960) for example correlating grasshopper abundance and aspects of climate over the previous three years.