A comparison of the relative contributions of temporal and spatial variation in the density of drifting invertebrates in a Dorset (U.K.) chalk stream

1. Invertebrate drift is commonly investigated in streams, with the majority of studies focussed on temporal (typically diel) variation. In comparison, few studies have investigated spatial variation in drift and there is little consensus among them. We tested the hypothesis that spatial variation in invertebrate drift is as important as temporal variation. 2. The density of drifting invertebrates in a chalk stream was sampled using an array of nets arranged to determine vertical, lateral and longitudinal variation. Samples were collected at dawn, during the day, at dusk and by night, on four separate monthly occasions. Insecta and Crustacea were analysed separately to identify the effect of differing life history strategies. The density of drifting debris was also recorded, to act as a null model. 3. Time of day and vertical position together explained the majority of the variance in invertebrate drift (79% for Insecta and 97% for Crustacea), with drift densities higher at dusk and night, and nearer the stream bed. Independently, time of day (38%, Insecta; 52%, Crustacea) and vertical position (41%, Insecta; 45%, Crustacea) explained a similar amount of the observed variance. Month explained some of the variance in insect drift (9%) but none for Crustacea. 4. Variation in the density of drifting debris showed little in common with invertebrate drift. There was little variation associated with time of day and only 27% of the observed variation in debris could be explained by the factors investigated here, with month explaining the largest proportion (20%). We suggest the difference in drifting debris and invertebrates provides further evidence for a strong behavioural component in invertebrate drift. 5. Spatial variation in invertebrate drift can be of the same order of magnitude as the much‐described diel temporal variation. The extent of this spatial variation poses problems when attempting to quantify invertebrate drift and we recommend that spatial replication should be incorporated into drift studies.     

Evaluating the influence of land use,drought and reach isolation on the occurrence of freshwater mussel species in the lower Flint River Basin,Georgia (U.S.A.)

1. North American freshwater mussels have been subjected to multiple stressors in recent decades that have contributed to declines in the status and distribution of many species. However, considerable uncertainty exists regarding the relative influence of these factors on observed population declines. 2. We used an occupancy modelling approach to quantify relationships between mussel species occurrence and various site‐ and catchment‐level factors, including land cover, stream size, the occurrence of drought and reach isolation due to impoundment for 21 mussel species native to the lower Flint River Basin, Georgia, U.S.A. 3. Our modelling approach accounted for potential biases associated with both incomplete detection and misidentification of species, which are frequently not accommodated as sources of bias in freshwater mussel studies. 4. Modelling results suggested that mussel species were, on average, four times less likely to be present following severe drought, but the negative effects of drought declined rapidly with increasing stream size. Similarly, mussel species were 15 times less likely to occupy small streams that were isolated from mainstem tributaries by impoundments. 5. This study provides insight into the effects of natural and anthropogenic factors on freshwater mussel species. Our findings add to a growing body of literature aimed at improving understanding of the predominant factors influencing freshwater mussel populations and fostering the development of more informed and effective conservation strategies.     

Nutrition, aspects of land use and environment in medieval times in southern Germany: plant macro-remain analysis from latrines (late 11th–13th century a.d.) at the town of Überlingen, Lake Constance

From high medieval courtyards at überlingen, Lake Constance (Bodensee), 17 archaeobotanical samples from seven latrines (11th–13th century) were analysed for plant macrofossils. They contained small amounts of cultivated plants and many well preserved seeds and fruits of wild plants. The most numerous cereal finds were of Triticum spelta followed by Secale cereale. Recorded oil plants were Papaver somniferum and Linum usitatissimum. Cultivated and gathered fruits such as various Prunus species, Pyrus communis and Malus domestica, Rubus sp. and Fragaria vesca were eaten by the people of überlingen. Only one seed of Ficus carica was found which may have been imported; no other imported plants could be recognised. Agrostemma githago and Vaccaria hispanica were prevalent weeds. The presence of the latter probably indicates the cultivation of cereals on the steeper slopes above überlingen. It is shown that in central Europe, V. hispanica became a troublesome weed only around the 12th/13th century A.D. Grassland species—mainly from more or less wet locations—and ruderal plants of nitrogen-rich soils were well represented in the samples and characterize the surrounding area. Electronic Supplementary Material Supplementary material is available in the online version of this article at