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Fritz, Julia (2007): Allometrie der Kotpartikelgröße von pflanzenfressenden Säugern, Reptilien und Vögeln. Dissertation, LMU München: Faculty of Veterinary Medicine
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Abstract

Among different factors – such as food characteristics and ingesta retention time -, ingesta particle size (measurable in the faeces) is an important parameter that influences digestion in herbivores. In the literature, there are only four comparative studies on the faecal particle size in herbivores. These studies either concentrate on only a few different species, or are restricted to one taxonomic order. Comparative data on reptiles and birds are totally lacking. Thus the present study represents the first attempt to quantify the faecal particle size across broad range of herbivore species within all three taxonomic classes, and to investigate whether there is an allometric relationship to body mass. Relevant factors influencing ingesta particle size, such as body mass, type of dentition, phylogenetic affiliation and digestive strategy, are discussed in context. In total, more than 1100 faecal samples from herbivorous mammals (205 species), reptiles (12 species) and birds (14 species) are analysed with a standardized wet-sieving procedure using nine sieves ranging from 0,063 mm to 16 mm mesh size. For the description of faecal particle size two different particle dimensions (in mm particle length) are used, the mean particle size (“Mittelwert”: MW) obtained by curve fitting, and the weighted average (WA) obtained by calculation. The following results are obtained: It is confirmed that faecal particle size is a reliable measure for the extent to which food is processed by mastication. However, this only applies to terrestrial forage plants. Faecal particle size increases with increasing body mass in all three classes. For all mammal groups faecal particle size scales positively to body mass to the power of 0.34 (MW) or 0.31 (WA), respectively. Given the literature assumption that tooth size scales isometrically to body mass, these results underline the fact that there is a functional relationship between tooth size and the achieved ingesta particle length. Considering their body mass range, ruminants - and also equids - achieve particularly small faecal particles and therefore are peculiar among the mammals. Species adapted to grazing (Przewalski horse, auerochs) showed comparable faecal particle sizes in the wild and in captivity, whereas species adapted to browsing (tapir, giraffe) had smaller faecal particles in the wild compared to captivity. Reptiles have distinctively higher mean faecal particle sizes than mammals and birds. Ingesta comminution in the gizzard of herbivorous birds is comparable to that achieved by chewing in non-ruminant mammals, as faecal particle size does not differ between these two groups. Before it enters the gizzard, however, bird ingesta have a similar particle size as reptile faeces. With respect to the ongoing paleobiological discussion on the competition of two dinosaur groups – the sauropods and ornithopods – the present study supports the theory that comminution by gizzard is not less effective than comminution by mastication. The differences in the comminution efficiency between and within mammal groups can partly be related to the evolutionary success of certain species.