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8 - Nutritional ecology of fruit-eating and flower-visiting birds and bats
- Edited by D. J. Chivers, University of Cambridge, P. Langer, Justus-Liebig-Universität Giessen, Germany
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- Book:
- The Digestive System in Mammals
- Published online:
- 18 March 2010
- Print publication:
- 21 July 1994, pp 103-127
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Summary
Volant vertebrates include two extant groups: birds and bats. Both of these taxa are commonly used as model organisms for studies of community and population ecology (Kunz, 1982; Wiens, 1983) and foraging behaviour (Morrison et aL, 1988). Despite this, the nutrition and digestive function of birds and bats are too often considered inscrutable black boxes, or worse, ignored by ecologists and behaviourists (Wheelwright, 1991). There are several reasons why the processes by which these animals digest and absorb nutrients should be of interest to animal ecologists and behaviourists. The design and adaptability of the gut may determine diet diversity and hence niche width (Martinez del Rio et al, 1988). Digestive processes may set limits on metabolizable energy and nutrient intake and thus determine rates of growth and reproduction (Kenward and Sibly, 1977; Karasov et al, 1986). In addition, nutrient assimilation is one of the factors that mediates the interaction of animals with their environment (Martinez del Rio and Restrepo, 1992).
Out of neglect, the contributions of nutrition and digestive physiology to ecology and behaviour have been minor. We know little about how digestion influences feeding choices (Martinez del Rio and Karasov, 1990), constrains meal sizes and frequencies (Carpenter et al, 1991), determines rates of growth and fat accumulation (Konarzewski et al, 1989), or affects interspecies interactions. With the notable exception of several studies on pollinator energetics (summarized in Heinrich, 1975), comparative avian/chiropteran physiologists have also overlooked the potential of their field as a tool to understand interactions among species.
3 - Modelling gut function: an introduction
- Edited by D. J. Chivers, University of Cambridge, P. Langer, Justus-Liebig-Universität Giessen, Germany
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- Book:
- The Digestive System in Mammals
- Published online:
- 18 March 2010
- Print publication:
- 21 July 1994, pp 25-53
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Summary
A cautious man should above all be on his guard against resemblances: they are a very slippery sort of thing.
Plato (in Gordon et al. 1972)Digestive physiologists either focus narrowly, use a reductionist approach and work at the cellular, biochemical and molecular levels, or analyse digestive performance (measured usually as digestive efficiency and retention time of food in the gut) at the whole organism level. Consequently digestive physiology encompasses two more or less exclusive bodies of data: on one hand we have adequate knowledge of the molecular and biochemical characteristics of digestive enzymes and nutrient transport systems (Desnuelle et al., 1986); on the other we have a large catalogue of retention times, assimilation efficiencies and digestive morphologies for a variety of animal tax a fed on an assortment of food types (e.g. Chivers and Hladik, 1980; Warner, 1981; Karasov, 1990). A consequence of the slightly schizophrenic nature of the trade is that we know very little about how the fine details of nutrient digestion and uptake function are integrated to affect whole organism digestive efficiency andrTood intake rates. Until very recently, digestive physiology has lacked a theoretical framework that integrates digestive processes with gut morphology and the chemical properties of food. Because nutrient assimilation is a remarkably complex phenomenon involving a variety of enzymatic and transport pathways that take place in a variety of organs within the gastro- intestinal tract, it is perhaps not surprising that attempts to analyse digestion from an integrated perspective have been few (Sibly, 1981).
Mertens and Ely (1982) and Illius and Gordon (1992), for example, have developed detailed mathematical models that integrate intake, digestion and food characteristics for ungulates.