Influence of some abiotic and biotic factors, especially water content and patch size, on the composition of the species community in sheep lumps at an old pasture area with an interruption in grazing through the dry summer months

Diploma Thesis of the Institute of Biology I (Zoology),
Albert-Ludwigs-University Freiburg i. Brg., Germany







Summary:
From April to November 1990, sheep excrements were gathered once a month on 2 directly neighbouring pastures, located at the Schönberg near Freiburg (SW-Germany). These pastures were grazed by sheep since 18 years.
For each portion of excrement the following data were registered: Excrement class (the bigger compact "lumps" or small "pellets", which are mostly deposited in whole groups or individually), surface structure (damp, leathery or dry) and origin (pasture A or B).
In the laboratory, water capacity and dry weight were determined for each portion of excrement. Beetles were extracted by flotation, preserved and determined.

22 species of Scarabaeidae and 14 species of Hydrophilidae could be found.
In an equal quantity of manure significantly more beetles could be found on pasture B as compared to pasture A. However, in the months of September and October more beetles were found on pasture A. Due to differences of the relief and the exposition, in these months the local climate of the pasture A was more favorable than on pasture B. An analysis of the distribution of individual species showed specialists for both pastures. This differentiation could not be solely explained by a different ecology of the dominant species.

The genus Apodius showed a pronounced phenological segregation of dominant species, whereas Onthophagus and the species of the family Hydrophilidae did not show a clear temporal niching.

Sheep lumps were settled much more densely, than pellets. No individual species deviated from this trend.

Almost all species showed a clear preference for damp or leathery and therefore young excrements. Sphaeridium scarabaeoides clearly preferred damp and therfore very young excrements. In contrast to this Aphodius fimetarius and within certain limits also Cryptopleurum minutum showed some preference for dry and therefore older excrements.
Excrements with a water content below 75% were settled only sparsely. No species preferred clearly these more dry faeces.

Excrements above 20g dry weight were settled much more densely than expected following the relative abundance of this class. Bigger beetle species like Aphodius rufipes, Aphodius fimetarius, Aphodius luridus as well as Sphaeridium scarabaeoides showed a clear trend to the bigger faeces (above 40g dry weight).

With regard to the colonisation of excrements by coprophagous beetles, "favorable" faeces are therefore relatively young, damp and big.

75.5% of all collected excrements displayed less than 5 individuals; 45.1% remained without any colonization. In spring, 79.8% of all beetles were found within only 15.9% of the collected faeces. In the fall, 30.6% of all beetles gathered in only 2.3% of the excrement samples. Individual species showed the same a striking concentration in some few faeces. Onthophagus ovatus was found in 33 individuals in a single excrement (25.2% of all collected beetles of this species in April). 31.4% of all individuals of Aphodius rufipes concentrated in the month of September in only a a single excrement. In April 21, specimen of Sphaeridium scarabaeoides were found within one sheep lump (65.6%). Finally, in May, 735 speciemen of the only approx. 3mm small Cercyon haemorrhoidalis colonised a single faeces (31.9%).
In individual, especially attractive faeces not only individual species gathered but also a substantial part of the whole species community of a sample month could be found (between 35.7-68% of the species community), in most cases in respectively high numbers of specimen.
This strikingly clumped distribution of specimen and species could hardly be explained by the assumption of only a few especially more nutritious and more save habitats. It appears more plausible to assume, that this strategy coheres with a strategy to increase encounters for mating.

Weighments and measurements of the microclimate of sheep excrements under outdoor conditions allowed to correlate the course of the desiccation and rehumidification of faeces with some climate elements. Air temperature, illumination, humidity, precipitation quantity and wind force proved to be the most effective. It is especially remarkable, that water losses between two measurements could make up to almost 70%, but rehumidification could reach up to 100%. Pellets and lumps behave very differently. Due to their extreme conduct pellets prove to be uncertain and dangerous biotops.
 
 
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