Unpredictable Environmental Changes Research Articles

Non‐interactive fish communities in the coastal streams of North‐western France

1. Spatial patterns of freshwater fish species at regional and local scales were investigated to explore the possible role of interspecific interactions in influencing distribution and abundance within communities occupying coastal streams of North‐Western France. 2. Nine sites from nine streams situated in the same biogeographical region were sampled annually over the 6‐year period from 1990 to 1995. 3. Similar habitats (sites) with richer regional colonization pools exhibited proportionally richer local communities in terms of number of species, total density and total biomass of individuals. Furthermore, no negative relationships were found between density and biomass of each of the most common species and local species richness. 4. Results of dynamic regression models (applied to the above‐mentioned species) suggest an absence of strong competition between all pairs of species. 5. The evidence on lack of density compensation for species‐poor communities and absence of perceptible interspecific competition between species suggest that the communities studied are non‐interactive. 6. Two main explanations can be advanced. First, the local abundance of species in the communities studied could be determined through differential responses to unpredictable environmental changes, rather than through biological interactions. Second, as a result of historical events, the communities studied are reduced in congeneric species which can limit, in turn, the influence of interspecific competition in structuring these communities. 7. These results underline the strong influence of regional processes in shaping local riverine fish communities and minimize the possible influence of species interactions in governing these communities.

Population dynamics of animals in unpredictably-changing tropical environments

We studied population dynamics of a solitary phytophagous beetle,Epilachna viqintioctopunctata and a social stingless bee,Trigona minangkabau, in Sumatra, Indonesia for 5 years from 1981. Population increase ofEpilachna vigintioctopunctata was suppressed in months of normal rainfall (≥300mm) but was released in the 1982–1983 El Nino-Southern. Oscillation when rainfall dropped to 50% of the long-term average. Mechanisms might be direct; rainfall lowered egg hatchability and the time of adult’s residence on host plants. When dry weather continued for more than three generations, theEpilachna vigintioctopunctata population reached a density at which food shortage due to defoliation occurred. Although parasitism of immature stages was high, it was not a population-regulating factor. Thus, there were two types of ecological crunch: competition for food resources at the end of favourable dry periods and high mortality during heavy rainfall periods that usually followed El Nino-Southern Oscillation dry conditions. By an experimental addition of artificial nest sites, colony density ofTrigona minangkabau increased 2.5 times the original density of natural colonies. One-half of artificial nest sites were occupied by arboreal ants and thus competition for nest sites with ants suppressed further increase ofTrigona minangkabau. Intermediate rainfall was favourable forTrigona minangkabau because the rate of colony foundation decreased both during dry El Nino-Southern Oscillation months and months with heavy rain. Colony death was independent from rainfall. Many colonies that survived for 6 months persisted for >2 years and colony density was quite stable.Trigona minangkabau colonies could survive even under unfavourable periods, by hoarding resources in the nest. There was no significant ecological crunch during the study period and colony density almost always tracked the carrying capacity of the habitat, which was basically determined by nest-site abundance. Climatic conditions, especially rainfall, changed with various periodicities, 4–5 years for El Nino-Southern Oscillation, and 2 years for the monsoon and other shorter periods. The contribution of periodicities of 1 and 0.5 years, that were linked to movement of the sun, were weak, indicating that animals could not use seasonal changes of environments,e.g. daylength, to predict environmental changes. We discuss traits adaptive to such unpredictably-changing tropical environments. Separation of predictability of temporal environmental change and synchronous changes among patches improves our understanding. Low oviposition rate and resulting prolonged life-span ofEpilachna vigintioctopunctata, usually associated withK-selected traits of life history, seem to be adaptations for unpredictable environmental changes.

Temperature activation of foot muscle d-(−)-lactate dehydrogenase in the whelk Bullia digitalis

The rate of oxygen consumption of the sandy-beach whelk Bullia digitalis is virtually temperature-independent over the thermal range typical of its environment. This may be a physiological adaptation to sudden and unpredictable environmental temperature changes. Physiological adaptation mechanisms include the development of temperature-sensitive isozymes, often regulated by enzyme-substrate interactions. Examination of kinetics of d-(−)-lactate dehydrogenase (EC 1.1.1.28) in B. digitalis revealed differential temperature sensitivity of the two major isozymes. It is concluded that this mechanism may contribute to the successful adjustment of the whelk's metabolism to its environmental temperature, without impairment of physical activity.

Dissolution of Governments in Scandinavia: A Critical Events Perspective*

For many years, scholars have sought to discover why governments in Western European parliamentary democracies frequently dissolve before the time constitutionally mandated for the holding of elections. Recent research has suggested the potential importance of unpredictable changes in the political environment for bringing about governmental dissolutions. Although not specifically described. the importance of ‘critical events‘ is suggested by both aggregate patterns of dissolutions and anecdotal accounts of particular governments.It is our purpose in this paper to develop further this critical evenrs perspective and evaluate empirically actual governmental histories in light of these developments. Two specific goals are pursued. First, we delineate categories of critical events, thereby grounding the concept of a critical event within existing knowledge of governmental stability. Second, we apply this categorical schema of events to the dissolution of Scandinavian governments during the years 1945–1980. In so doing, we seek not only to assess the adequacy of our conceptualization of events, but also to provide a theoretically and substantively accurate account of the death of modern Scandinavian governments.

On the synthesis of the least sensitive control

Publisher Summary This chapter discusses the synthesis of the least sensitive control. It presents the concept of sensitivity in the synthesis of control policy when the controlled process is subjected to unpredictable environmental changes. It discusses the possible effects of small parameter perturbations, the missing of the desired state of the process and change of the process performance index. In the subsequent considerations these effects are used as a quantitative measure of process performance. By imposing the requirement that the control policy should be chosen so as to minimize the effects of parameter perturbations, a reduced sensitivity can be attained. The compound control that is obtained by combining the sensitivity criterion with some other criteria of optimality is optimal and less sensitive to small parameter variations.