Species richness and succession of aquatic beetles in some kettle‐hole ponds in northern Sweden

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Abstract
Ten closely‐located kettle‐hole ponds in northern Sweden were ordered along a vegetational, successional gradient from the present‐day representation of the six vegetational units distinguished. Different rates of vegetational development caused by differences in depths of basins have made possible the long‐term existence of early successional stages. A fact that has offered the possibility of studying most of the vegetational succession of these habitats.The number of water beetle species inhabiting each pond were correlated to successional stage and area of pond. Mean species numbers decreased from 34 to 14 per pond with increasing maturity of the vegetational succession. This decrease in species richness of water beetles is caused by a decrease in number of habitats or vegetational units present. The increased floral conformity is mainly due to a more stable water‐level caused by lower rates of bottom seepage from the accumulation of organic deposits. Besides the extended zonation of littoral vegetation, a high water‐amplitude is also connected with recurrent nutrient pulses caused by the faster detritus composition during drought periods. Thus the changing water‐levels contribute to a high water beetle diversity through the maintenance of both a high habitat complexity and a high production.A positive correlation between pond size and number of water beetle species were only found if the fen ponds were excluded. From this it is concluded that the area effect is here a good predictor of species richness only within ponds of a similar successional stage.