The effect of digestive capacity on the intake rate of toxic and non-toxic prey inan ecological context
Oudman, T.; Hin, V.; Dekinga, A.; Van Gils, J. (2017). The effect of digestive capacity on the intake rate of toxic and non-toxic prey inan ecological context, in: Oudman, T. Red knot habits : An optimal foraging perspective on intertidal life at Banc d’Arguin, Mauritania. pp. 56-73 |  |
| Authors | | Top | - Oudman, T.
- Hin, V.
- Dekinga, A.
- Van Gils, J.
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| Abstract | Digestive capacity often limits food intake rate in animals. Manyspecies can flexibly adjust digestive organ mass, enabling them toincrease intake rate in times of increased energy requirement and/orscarcity of high-quality prey. However, some prey species are defendedby secondary compounds, thereby forcing a toxin limitation on theforager’s intake rate, a constraint that potentially cannot be alleviatedby enlarging digestive capacity. Hence, physiological flexibility mayhave a differential effect on intake of different prey types, and consequentlyon dietary preferences. We tested this effect in red knots(Calidris canutus canutus), medium-sized migratory shorebirds thatfeed on hard-shelled, usually mollusc, prey. Because they ingest theirprey whole and crush the shell in their gizzard, the intake rate of redknots is generally constrained by digestive capacity. However, one oftheir main prey, the bivalve Loripes lucinalis, imposes a toxin constraintdue to its symbiosis with sulphide-oxidizing bacteria. We manipulatedgizzard sizes of red knots through prolonged exposure to hard-shelledor soft foods. We then measured maximum intake rates of toxic Loripesversus a non-toxic bivalve, Dosinia isocardia. We found that intake ofDosinia exponentially increased with gizzard mass, confirming earlierresults with non-toxic prey, whereas intake of Loripes was independentof gizzard mass. Using linear programming, we show that this leads tomarkedly different expected diet preferences in red knots that try tomaximize energy intake rate with a small versus a large gizzard. Intraandinter-individual variation in digestive capacity is found in manyanimal species. Hence, the here proposed functional link with individualdifferences in foraging decisions may be general. We emphasizethe potential relevance of individual variation in physiology whenstudying trophic interactions. |
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