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- Alm Bergvall, Ulrika, 1970-
(författare)
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Food choice in fallow deer – experimental studies of selectivity
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, I experimentally investigate feeding selectivity in fallow deer (Dama dama), with respect to plant secondary compounds, especially tannins, which can decrease the quality of foods. I found that fallow deer avoided foods with higher amounts of tannic acid and Quebracho tannin, even though the deer ate some high-tannin food. The food choice was strongly dependent on the context in which the food was presented, so that the food choice in relation to tannin content was relative rather than absolute. When high-tannin food occurred at low frequency, the deer ate proportionally less from this type of food, at least when the difference in tannin content between the two foods was large. A basic implication is that an unpalatable plant type could benefit from its unpalatability, especially when occurring at low frequency. In experiments with two patches, the finding of a stronger within- than between-patch selectivity was mirrored in associational effects. First, low-tannin, palatable food was more eaten when occurring in a high-tannin patch, which corresponds to neighbour contrast susceptibility. Second, high-tannin, unpalatable food in a less defended patch was less eaten, which corresponds to neighbour contrast defence. A proximate cause of the associational effects can be the presence of a simultaneous negative contrast, which was experimentally demonstrated in an additional study. Individual differences in selectivity were present early in life and were consistent over five years, and selectivity was correlated with foraging exploratory behaviour. The results from this thesis suggest that fallow deer are selective in their food choice with respect to tannins from the beginning, and that the frequency of occurrence of different foods, but also the distance between foods and the complexity of presentation, influence the food choice. It is also suggested that a foraging behavioural syndrome is present in mammalian herbivores.
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| 3. |
- Aronsson, Marianne, 1978-
(författare)
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Colour patterns in warning displays
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In aposematism a prey species use bright colours, often combined with a black contrasting pattern, to signal unprofitability as prey to potential predators. Although there are several different hypotheses about the presence of these internally contrasting patterns, there is little experimental evidence of any beneficial effects. In this thesis I have used bird predators and artificial prey signals to investigate if the contrasting internal patterns in warning displays may have evolved to increase signal efficacy, especially regarding the speed of avoidance learning. In paper I the relative importance of colour and pattern in avoidance learning was studied. The conclusion was that birds primarily attend to colour, not pattern, when learning the discrimination, which was further supported by the results in paper II-IV, all suggesting a secondary role of patterns. In paper II I show that predators may to some degree use patterns for discrimination, if they convey important information about prey quality. The predators showed a hierarchical way of learning warning colour components, where colour is learned to a higher degree than pattern. In paper III I investigate if internal contrasting patterns promote avoidance learning by increasing conspicuousness as prey-to-background contrast does. The study did not support this idea, as the presence of internal black patterns did not improve avoidance learning on a colour matching background. In paper IV, however, I show that the presence of many internal colour boundaries resulted in faster avoidance learning on a multi-coloured background, and predator generalization favoured more internal boundaries, while there was no effect of pattern regularity. From these studies I conclude that internal pattern contrasts may function to increase the efficacy of the warning colour, its salience, and as a means for aposematic prey to be discriminated from harmful mimics. However, the major finding is the importance of colour over pattern.
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| 4. |
- Balogh, Alexandra C.V., et al.
(författare)
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Feature theory and the two-step hypothesis of Müllerian mimicry evolution
- 2010
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Ingår i: Evolution. - : Wiley. - 0014-3820 .- 1558-5646. ; 64:3, s. 810-822
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Tidskriftsartikel (refereegranskat)abstract
- The two-step hypothesis of Müllerian mimicry evolution states that mimicry starts with a major mutational leap between adaptive peaks, followed by gradual fine-tuning. The hypothesis was suggested to solve the problem of apostatic selection producing a valley between adaptive peaks, and appears reasonable for a one-dimensional phenotype. Extending the hypothesis to the realistic scenario of multidimensional phenotypes controlled by multiple genetic loci can be problematic, because it is unlikely that major mutational leaps occur simultaneously in several traits. Here we consider the implications of predator psychology on the evolutionary process. According to feature theory, single prey traits may be used by predators as features to classify prey into discrete categories. A mutational leap in such a trait could initiate mimicry evolution. We conducted individual-based evolutionary simulations in which virtual predators both categorize prey according to features and generalize over total appearances. We found that an initial mutational leap towards feature similarity in one dimension facilitates mimicry evolution of multidimensional traits. We suggest that feature-based predator categorization together with predator generalization over total appearances solves the problem of applying the two-step hypothesis to complex phenotypes, and provides a basis for a theory of the evolution of mimicry rings.
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| 5. |
- Balogh, Alexandra C.V., et al.
(författare)
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Learning and the mimicry spectrum: from quasi-Bates to super-Müller
- 2008
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Ingår i: Animal Behaviour. - : Elsevier BV. - 0003-3472. ; 76:5, s. 1591-1599
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Tidskriftsartikel (refereegranskat)abstract
- Müllerian mimicry is the mutualistic resemblance between two defended species, while Batesian mimicry is the parasitic resemblance between a palatable species (the mimic) and an unpalatable one (the model). These two kinds of mimicry are traditionally seen as extreme ends of a mimicry spectrum. For the range in between, it has been suggested that mimetic relations between unequally defended species could be parasitic, and this phenomenon has been referred to as quasi-Batesian mimicry. Where a mimetic relation is placed along the mimicry spectrum depends on the assumptions made about predator learning. In this work, we use a variant of the Rescorla-Wagner learning model for virtual predators to analyse the different possible components of the mimicry spectrum. Our model entails that the rate of associative learning is influenced by variation in the stimuli to be learned. Variable stimuli, i.e. unequal defences, can increase the predator learning rate and thus lead to an increased level of mutualism in a mimetic relation. In our analysis, we make use of the concepts of super-Müllerian mimicry, where the benefit of mimicry is even greater than in traditional Müllerian mimicry, and quasi-Müllerian mimicry, where mimicry by a palatable mimic is mutualistic. We suggest that these types of mimicry should be included in the mimicry spectrum along with Müllerian, Batesian and quasi-Batesian mimicry.
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| 6. |
- Balogh, Alexandra C.V. 1975-, et al.
(författare)
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Müllerian mimicry: an examination of Fisher's theory of gradual evolutionary change
- 2005
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Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 272, s. 2269-2275
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Tidskriftsartikel (refereegranskat)abstract
- In 1927, Fisher suggested that Müllerian mimicry evolution could be gradual and driven by predator generalization. A competing possibility is the so-called two-step hypothesis, entailing that Müllerian mimicry evolves through major mutational leaps of a less-protected species towards a better-protected, which sets the stage for coevolutionary fine-tuning of mimicry. At present, this hypothesis seems to be more widely accepted than Fisher’s suggestion. We conducted individual-based simulations of communities with predators and two prey types to assess the possibility of Fisher’s process leading to a common prey appearance. We found that Fisher’s process worked for initially relatively similar appearances. Moreover, by introducing a predator spectrum consisting of several predator types with different ranges of generalization, we found that gradual evolution towards mimicry occurred also for large initial differences in prey appearance. We suggest that Fisher’s process together with a predator spectrum is a realistic alternative to the two-step hypothesis and, furthermore, that it has fewer problems with purifying selection. We also examined factors influencing gradual evolution towards mimicry and found that not only the relative benefits from mimicry but also the mutational schemes of the prey types matter.
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| 7. |
- Balogh, Alexandra, 1975-
(författare)
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Predator psychology and mimicry evolution - a theoretical analysis
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The evolution of Müllerian mimicry depends on many factors, among which predator psychology is the most important one. Predator avoidance learning, generalization and discrimination are primary selective agents during the evolutionary process. This thesis investigates an issue that has been a matter of debate since the 19th century; the question of how a mutant of a potential mimic population can escape the apostatic selection caused by predators that neither recognize it as a member of its own population, nor as being similar to its future model. In paper I, we investigate one of the ideas concerning this issue. Fisher stated that mimicry can evolve gradually by the displacement of an adaptive peak in a fitness landscape. We find this to be a plausible scenario, under certain conditions regarding predator generalization. In paper II, we further investigate the gradual evolutionary process and the implications of different generalization gradients. We find that the gradual process might be even more general than has previously been assumed and that abundant genetic variation in prey populations is an important factor in combination with predator generalization. In paper III, we examine another suggested solution to the problem of apostatic selection, the so-called two-step process, which can be problematic to extend to multiple prey traits. We find that the two-step process works for multidimensional traits provided that predators use feature-based generalization. The selective landscape of mimicry evolution is also shaped by the cost-benefit relationships for models and mimics. In paper IV we explore this matter, by applying the Rescorla-Wagner theory of learning to mimicry. We find that if variation in prey unpalatability gives rise to surprise, the learning rate is increased. This leads to unexpected kinds of mimicry that are more mutualistic than Müllerian mimicry has previously been assumed to be.
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| 8. |
- 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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| 9. |
- 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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