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- Bergvall, Ulrika A, et al.
(författare)
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A test of simultaneous and successive negative contrast in fallow deer foraging behaviour
- 2007
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Ingår i: Animal Behaviour. - : Elsevier BV. - 0003-3472 .- 1095-8282. ; 74:3, s. 395-402
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Tidskriftsartikel (refereegranskat)abstract
- The study of contrast investigates how rewards influence behaviour when animals are exposed to two or more levels of rewards compared to when they experience only a single level. The appearance of an exaggerated response to a shift in reward is referred to as a contrast effect and is an empirically well-established phenomenon. Although contrast effects could be important in foraging behaviour, no direct experimental tests of contrast effects in foraging by mammalian herbivores exist. During foraging, mammalian herbivores can encounter a range of plants that vary in the amount of nutrients and toxins. They may thus compare food items by taste, which in turn can give rise to contrast effects. In feeding experiments with fallow deer, Dama dama, we investigated the presence of simultaneous negative contrast. We found that the deer consumed less from a bowl of pellets containing 1% tannin when they shifted to it from a bowl with pellets containing only 0.25% tannin than when they shifted from another bowl with pellets containing 1% tannin. We estimated a fourfold difference between treatments in test food consumption at the highest levels of preloading, but none at the lowest levels. We found no support for successive negative contrast in experiments where the deer approached food in a runway, comparing a current reward with the memory of a previous reward. We suggest that simultaneous negative contrast can influence foraging decisions in mammalian herbivores.
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| 2. |
- Bergvall, Ulrika A, et al.
(författare)
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Associational effects of plant defences in relation to within- and between-patch food choice by a mammalian herbivore : neighbour contrast susceptibility and defence
- 2006
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Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 147:2, s. 253-60
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Tidskriftsartikel (refereegranskat)abstract
- A basic idea of plant defences is that a plant should gain protection from its own defence. In addition, there is evidence that defence traits of the neighbouring plants can influence the degree of protection of an individual plant. These associational effects depend in part on the spatial scale of herbivore selectivity. A strong between-patch selectivity together with a weak within-patch selectivity leads to a situation where a palatable plant could avoid being grazed by growing in a patch with unpalatable plants, which is referred to as associational defence. Quite different associational effects will come about if the herbivore instead is unselective between patches and selective within a patch. We studied these effects in a manipulative experiment where we followed the food choice of fallow deer when they encountered two patches of overall different quality. One of the two patches consisted of pellets with low-tannin concentration in seven out of eight buckets and with high concentration in the remaining bucket. The other patch instead had seven high- and one low-tannin bucket. We performed the experiment both with individuals one at a time and with a group of 16-17 deer. We found that the deer were unselective between patches, but selective within a patch, and that the single low-tannin bucket among seven high-tannin buckets was used more than a low-tannin bucket among other low-tannin buckets. This corresponds to a situation where a palatable plant that grows among unpalatable plants is attacked more than if it was growing among its own kind, and for this effect we suggest the term neighbour contrast susceptibility, which is the opposite of associational defence. We also found that the high-tannin bucket in the less defended patch was less used than the high-tannin buckets in the other patch, which corresponds to neighbour contrast defence. The neighbour contrast susceptibility was present both for individual and group foraging, but the strength of the effect was somewhat weaker for groups due to weaker within-patch selectivity.
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| 3. |
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| 4. |
- Bergvall, Ulrika A, et al.
(författare)
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The effect of spatial scale on plant associational defences against mammalian herbivores
- 2008
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Ingår i: Ecoscience. - 1195-6860. ; 15, s. 343-348
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Tidskriftsartikel (refereegranskat)abstract
- Intraspecific variation in plant toxins at different spatial scales can influence foraging decisions by wild herbivores. In order to investigate plant associational defences in relation to spatial scale, we performed an experiment with fallow deer encountering 2 patches of low- and high-tannin hazel branches. One patch was good, consisting of 7 low- and I high-tannin branch, and the other bad, with low- and 7 high-tannin branches. We kept the between-patch spatial scale constant and varied the within-patch spatial scale: the branches in a patch were either spread out or close together in a bundle. When the low-tannin branches were spread out, the deer showed a clear preference for low_tannin branches both patches and consumed similar amounts from low-tannin branches in the good and the bad patch, which means that there was no associational defence. In contrast, when the branches instead were together in a bundle, within-patch selectivity decreased and between-patch selectivity increased, and the low-tannin branches in the bad patch were less eaten than the low-tannin branches in the good patch, which corresponds to associational defence. We conclude that small inter-plant distances can be crucial for the operation of plant associational defences
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