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The evolution of thermal resistance and acclimation is reviewed at the population level using populations and isofemale lines of Drosophila buzzatii and D. melanogaster originating from different climatic regions. In general, ample genetic variation for thermal resistance was found within and among populations. A rough correlation between the climate of origin and thermal resistance was apparent. Acclimation at a non-lethal temperature led to a significant increase in survival after heat shock, and recurrent acclimation events generally increased survival even further. Acclimation effects lasted over several days, but this effect decreased gradually with time since acclimation. Protein studies showed that the concentration of Hsp70 in adult flies is greatly increased by acclimation and thereafter gradually decreases with time. For populations with relatively high survival at one life stage, survival often was low at other life stages. Furthermore, selection on different life stages showed that a selection response in one life stage did not necessarily result in a correlated response in another. These observations indicate that different mechanisms or genes at least in part are responsible for or are expressed at different developmental stages. Selection for increased resistance was successful despite low heritabilities for the trait. Survival and fertility were compared between acclimated and non-acclimated flies, and a cost of expressing the “heat shock response” was identified in that increased survival after acclimation was accompanied by reduced fertility. The relative costs increased under nutritional stress. Metabolic rate was genetically variable but did not correlate with temperature resistance. The more resistant lines, however, often had shorter developmental time. Inbreeding reduced thermal stress tolerance of adult flies, but it did not reduce tolerance of embryos that possibly are exposed to strong natural selection for thermal stress resistance. In general, inbreeding may reduce stress resistance, and thus multiple stressful events may account for increased inbreeding depression in harsh environments.

Beyond the biotic and abiotic attributes of the habitat, the social behavior and the social experiences of individuals during their infancy are central for the survival of many primate species in the wild. The social organization of groups within primate species can also influence the extent to which a species is endangered by man-made environmental changes. The notable characteristics, for example, of some macaque species, baboons, and vervets are their adaptiveness to human changes of their habitats, whereas this seems much less so in the apes. These differences in adaptive success are considered to be a consequence of the social organization (Hall, 1968).

How do organisms adapt to environmental change? This question is not new, and was the focal point of studies of natural animal populations by Andrewartha and Birch (1954), Levins (1968), Parsons (1983), and Hoffmann and Parsons (1991). For the conservation of rare species, how populations respond to environmental change is an important consideration when estimating the level of care and monitoring that should be expended to guarantee their survival. Few environments are truly constant, either in time or space, and therefore environmental change, at some scale, will affect the majority of animal and plant species (Grime, 1989). Many recent changes to the environment have been induced by humans over a much shorter time frame than normal without human disturbance (Dobson et al., 1989; Holt, 1990; Kareiva et al., 1983). Such changes may cause physiological stress that is expressed by a reduction in growth or performance. Where genetic variation is present for resistance to stress factors, populations may adapt according to the stress experienced. Without this variation, no genetic response is possible, although stress effects will continue to act on the physiology, influence population size, and may cause extinction. Therefore, knowledge of the effects of stress and of genetic variation for stress resistance is necessary for decision-making with respect to choices of reserves designed to protect particular species, choosing the individuals to introduce to a reserve, and estimating long-term performance of populations in environments that may change unpredictably.

"The source of this book is a symposium on 'Populationsbiologische Aspekte des Artenschutzes' held in October 1989 at the Akademie der Wissenschaften und der Literatur in Mainz, FRG"--Pref.

Arten sterben aus und neue entstehen. Arten andern sich in der phanotypischen Zusammensetzung in bestimmten Perioden ihres Daseins, und verbleiben, zumindest in unseren Augen, recht unverandert in anderen Zeitabschnitten.