The need for more long-term studies on helminth communities was addressed by examining changes in composition and diversity of the intestinal helminth component and infracommunities in eels of a small isolated river over 12 years. Examination of samples over one summer season indicated that single samples were representative of community richness in that year. In 1985 the community was species poor (1 species only) and with zero diversity, but by 1996 it comprised six species and all parameters at both levels indicated that it was the richest community yet reported from eels. This overall increase in diversity was not regular or uniform from year to year: rather, the general trend could be reversed in any year(s) and variation between years was considerable. The occurrence of many species was erratic and the identity of the dominant species varied between years. The helminth species that colonised the river contributed to helminth species richness and had an impact on community diversity. It is believed that the overall increase in diversity reflects the changing conditions in the habitat and catchment, but the erratic fluctuations in parameters may reflect the size of the river and the absence of any rescue effects. The findings are compared with the few other long-term studies and it is suggested that the extent of the variation over long periods makes it very difficult to use helminths as indicators of other than general environmental changes or to detect short-term changes due to such specific sources as pollution.
1. The Heteroptera, principally mirids, collected in a light-trap run on a field margin at Rothamsted Experimental Station for various periods between 1933 and 2000, have been identified, and the catches analysed to show the extent of change and stability in the community.
2. Trap catch, both in terms of individuals and species, was correlated with maximum daily temperature.
3. α-diversity showed a U-shaped curve over the period. The dip may have been associated with pesticide use, although a lack of days with high maximum temperatures cannot be ruled out.
4. By the late 1990s, α-diversity had again reached a peak (Fisher's = 11), comparable to that in the 1930s.
5. However, the change in the composition of the community over the whole period (β-diversity) was significant, the index of difference being 0.66 on a scale where 0 is no change in composition or relative abundance and 1 no species in common.
6. The value of β-diversity was highest in the water bugs, which disappeared altogether. Categorising the others by host plant type, the greatest change over time was in those associated with perennial herbs. There were decreasing differences in tree-dwellers and grassland species respectively, and the least change was in the community associated with annual plants (arable weeds).
7. Changes in the abundance of Heteroptera since 1933 follow closely those of the macrolepidoptera from the same samples. However changes in diversity show very different patterns, with moth diversity continuing to decline since 1960 in contrast to the increases apparent from the Heteroptera data.
Many aspects in the life-history of aphids are critically dependent on the quality of their host plants and prevailing temperature. Therefore, the fitness of an aphid clone will depend on these parameters and will determine its ecological and ultimately its evolutionary success. Measuring and calculating the fitness of an organism in a natural environment is an important but also a difficult task, as many parameters that code for fitness need special assumptions, e.g. a uniform environment or stable age distribution. In this study, three aspects of environmental variability were considered: (a) the nutritional supply of the host plants (high- and low-quality plants), (b) the changes in host plant quality due to the endogenic life cycle of the host and (c) constant and variable temperature regimes. For each of three successive generations of Cinara pruinosa (Hartig) feeding on Picea abies (L.) Karsten, the change in fitness was determined by calculating the intrinsic rate of increase (rm) and expected total reproductive success (ETRS) when the aphids were reared under greenhouse (constant temperature) or field (variable temperature) conditions. Nutritional supply, plant life cycle and temperature affected the fitness of aphids, with fluctuating temperatures obscuring the effects. As a consequence, differences in fitness values among treatments were most pronounced under the constant temperature regime of a greenhouse and less marked in the field. If plant quality varies but not temperature, the contribution to clonal fitness of early generations is overestimated in comparison to later generations. The limitations and consequences for the interpretation of fit ness values of aphids are discussed.