What is it about?
Andrew Hull and Jim Hollinshead have been monitoring ponds in Cheshire (northwest England) for almost 20 years. A set of 51 ponds were surveyed in 1995/6 and again in 2005, meaning that we can test whether or not over this 10-year period there was any change in the conservation value of the ponds. Pond surveys recorded all plant and macroinvertebrate (i.e. invertebrates larger than about 1mm, which was the size of the mesh of the net) species in the ponds and we compared (i) the diversity, and (ii) the conservation value of the ponds between the two surveys. Plants showed similar levels of diversity in both surveys, so highly-diverse ponds in the first survey remained that way in the second. However, invertebrate diversity was not correlated between surveys, meaning that species rich ponds in the first survey did not necessarily remain that way. For both groups there was not correlation between conservation value (calculated based on the rarity of the species in the community) in survey 1 compared to survey 2.
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Why is it important?
Ponds are highly variable ecosystems and that is one of the reasons that they support such a wide range of species on a landscape scale. However, it seems that this variability may make it difficult to conserve them adequately, since their conservation value changes over time. This finding supports the conservation of pond clusters, rather than individual sites, which are more likely to contain a stable group of species.
Perspectives
When an area is designated as a site for conservation or special scientific interest that is usually because one or more species of interest have been found or the community as a whole is unique or exceptional. However, the implicit assumption in this approach is that if you come back tomorrow then those species or that community will still be present. If the habitat is dynamic, with frequent population-level extinctions and colonisations, then it may be that this assumption does not hold. Pond ecosystems represent one case where the habitats are small and relatively easily affected by external variables and which may, as a result, vary in their conservation value over time.
Dr Christopher Hassall
University of Leeds
Read the Original
This page is a summary of: Temporal dynamics of aquatic communities and implications for pond conservation, Biodiversity and Conservation, January 2012, Springer Science + Business Media,
DOI: 10.1007/s10531-011-0223-9.
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