This paper challenges two paradigms long held in relation to the ecology of parasites in freshwater systems: (1) autogenic species are poorer colonisers than allogenic ones; and (2) parasites with direct life cycles are more successful colonisers than those with complex life cycles. Using new and existing data for Acanthocephala in freshwater fish from the British Isles, it is suggested that all six species present have been able to colonise and persist successfully, in spite of the supposed limitations of their autogenic life-style. It is proposed that these parasites have overcome these limitations by a variety of means, which apply equally to all species considered. Foremost among these is the utilisation of a migratory fish host as either a preferred or a suitable host in their life cycle, allowing colonisation of new areas and rescue effects in established areas, whilst equally important is the use of a common and widespread crustacean as the intermediate host. In addition, all six species appear to exhibit resource partitioning by host at either or both the larval and adult stages, thus reducing the potential for competition and further facilitating colonisation and survival. This hypothesis is supported by data from previous studies both on acanthocephalans from Europe and North America and on other autogenic parasites. It also provides an explanation for the apparently atypical host utilisation patterns of some acanthocephalan species in areas on the edge of their distributions, notably in Ireland.
Interest in insects as conservation foci and as tools in broader conservation assessment has accelerated markedly in recent years, but the diversity and complexity of insect life demands a more focussed and structured approach to \"biodiversity\" and inventory studies than has commonly occurred. Strategies for insect conservation are reviewed, together with the variety of uses for insects as ecological tools in broader monitoring of environmental quality. Principles fur selecting optimal focal groups are discussed, and the importance of developing standard protocols to sample and interpret insect assemblages emphasised. The global values and relevance of the pioneering lessons in insect conservation developed in Europe are summarised.
This review compares the current state of ichthyofauna in the largest rivers of the northern coast of the Black Sea (Don, Kuban, Dnieper and Dniester rivers) with data published by B e r g (1948–1949). Changes in species composition are characterized by the disappearance or decline in anadromous and semi-anadromous fishes. The total number of native species that are extinct, protected, in declined or become rare has reached from 19 % in the Kuban to 36 % in the Dnieper River basins. Appreciable changes have occurred in the ratios between rheophilous and limnophilous fishes (the latter becoming predominant in many parts of the rivers). Euryhaline and even marine species have invaded most of river basins. And the number of introduced or established alien species varies from 9.7 % in the Dnieper to 16.8 % in the Kuban River basins. These changes, which have yielded quite altered ichthyofauna, must be taken into consideration in conservation endeavours.
Chequered blue butterfly, Scolitantides orion (Lepidoptera: Lycaenidae) has severely declined in many parts of Europe and is currently red-listed in many countries. We studied the population structure and turnover of the species in a lake-island system in a National Park in eastern Finland over a three-year period. The incidence of the chequered blue on the suitable islands (n = 41) and habitat patches (n = 123) was high: an average of 82% of the islands and patches were occupied over the three year period. At the island scale, the annual population turnover rate was 17%, with an extinction and colonization rate of 7% and 10%, respectively. At the patch scale, the annual population turnover was 16%, with 7% extinction and 9% colonization rate. Islands that were occupied over the three year period had a larger area of suitable habitat than islands in which turnover events were observed. At the patch scale, turnover events were observed in small and poorly connected patches. Patchy occurrence of the host plant and observed extinction-colonization dynamics suggest that the chequered blue population confirms a metapopulation structure. Although the local populations are small, the observed high patch occupancy and balanced population turnover indicates that the metapopulation is not in immediate risk of extinction.
We consider a single-species stochastic logistic model with the population's nonlinear diffusion between two patches. We prove the system is stochastically permanent and persistent in mean, and then we obtain sufficient conditions for stationary distribution and extinction. Finally, we illustrate our conclusions through numerical simulation., Li Zu, Daqing Jiang, Donal O'Regan., and Obsahuje bibliografii