Did extreme food intake rates permit sauropod gigantism? Insights from feeding trials and muzzle morphometrics.
Zusammenfassung der Projektergebnisse
Food consumption is a central behaviour of free ranging animals. The longer animals spent time for food intake the less time they have for social activities or predator avoidance. Food intake itself is influenced by several factors like feeding behaviour, food abundance and food quality. The rate of food intake is a behavioural factor and one important point for the understanding of how free ranging animals feed on forage. The timescale for food intake rate measurements differs between long term (days), short term (hours).and initial feed intake rate (minutes) studies. For goats, cattle, deer and horses studies estimated food intake rate and related variables like bite rate and bite size. For birds most studies are on geese but also swans and ostriches were investigated. With respect to differences of food intake rates and bite sizes between species (within the mammal or bird group) or groups (mammals vs. birds) only little or nothing is known. Because body mass (BM) is often an important' influencing factor in herbivore nutrition several studies elaborated the influence of BM on bite size, bite rale and food intake rate. For mammalian herbivores one study showed that the exponent for bite size was B M 0.71 and that intake rate scaled with BM072. Comparable exponents were found for birds (bite size: B M 0.72 intake rate: BM 0.71). The present study aimed to estimate the influence of BM and chewing vs. non-chewing on bite size, bite rate and food intake rate in mammals and birds. Therefore the animals were fed with fresh grass using microswards to ensure that the animals had to crop their food naturally and that bite rate, bite size and intake rate could be measured easily. Because the number of species investigated in this study was small for meaningful statistical analysis literature data was included into considerations. The exponents of bite size with increasing BM for mammals (B M 0.64) and birds ( B M 0.82) were similar to the exponent of increasing basal metabolic rates of larger animals ( ~BM 0.75). Regarding the scaling of the energy requirements of mammals the exponent for bite size of mammals in this study (own data + literature data) of B M 0.76 was as high as expected. That the bite rale in birds increases nearly linearly with BM shows that there is no restriction in mastication for the birds as for the mammals. Accordingly bite sizes in mammals and birds increase as the metabolic rate do, hence the animal has no resiriciions to energetic reasons regarding the bite rate. For the maximum feed intake rate comparable exponents to the bite size were estimated (mammals: BM*0.65, birds: B M 0.79). In the literature exponents from BM 0.71- BM 0.76 for the bite size of mammals were found. The exponent of 0.64 found in this study is lower but including the standard error into consideration the range of exponents found in the literature is covered also in this study. For birds there is no literature data available. The exponent of 0.65 for the allometric scaling of MFIR for mammals (literature + own data) was much lower than for bite sizes but regarding the standard error, an exponent of 0.75 was included. Hence mammals are able to compensate the increasing metabolic requirements with their increasing MFIR. For the MFIR allometry of birds an exponent of 0.79 was found in this study. Both datasets for bite sizes and MFIR showed significant lower values for the birds than for mammals. They had similar slopes as mammals but the intercept of the allometric regression was lower which was also found in other studies. Despite the birds do not chew they have smaller bite sizes and lower intake rates. It was shown that there is no advantage of non-chewing when feeding on high pastures because of comparable handling times in mammals and birds and that birds have to feed longer and more selective than comparable sized mammals to ingest enough energy per day.
