Ulrika Alm Bergvall

Associational effects of plant defences in relation to within- and between-patch food choice by a mammalian herbivore: neighbour contrast susceptibility and defence.

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.

PLANT SECONDARY COMPOUNDS AND THE FREQUENCY OF FOOD TYPES AFFECT FOOD CHOICE BY MAMMALIAN HERBIVORES

We have investigated food choice in individual fallow deer (Dama dama) encountering different relative frequencies of food types in the form of bowls containing pellets with either high or low conc ...

The effect of spatial scale on plant associational defences against mammalian herbivores

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 1 high-tannin branch, and the other bad, with 1 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 branches were spread out, the deer showed a clear preference for low-tannin branches in 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.

A test of simultaneous and successive negative contrast in fallow deer foraging behaviour

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.

Short- and long-term repeatability of docility in the roe deer: sex and age matter

Behavioural consistency is a key assumption when evaluating how between-individual differences in behaviour influence life history tactics. Hence, understanding how and why variation in behavioural repeatability occurs is crucial. While analyses of behavioural repeatability are common, few studies of wild populations have investigated variation in repeatability in relation to individual status (e.g. sex, age, condition) and over different timescales. Here, we aimed to fill this gap by assessing within-population variation in the repeatability of docility, as assessed by the individuals response to human handling, in a free-ranging population of European roe deer, Capreolus capreolus. Docility was an equally repeatable behaviour at both short- and long-term timescales, suggesting that this behavioural trait is stable across time. Repeatability did not differ markedly between age and sex categories but tended to be higher in juvenile males than in juvenile females. Finally, contrary to expectation, individual variation in the repeatability of docility was not correlated with individual body mass. Further studies are required to assess the life history consequences of the individual variation in docility we report here.

Habitat use, bed-site selection and mortality rate in neonate fallow deer Dama dama

An understanding of mortality patterns, and especially the variation in juvenile mortality, is an important component in vertebrate population dynamics. Our study investigates, for the first time, neonate mortality and two levels of spatial behaviour, in a free-ranging fallow deer Dama dama population in southwestern Sweden. In the summers of 2008 and 2009, 36 fawns were marked with radio-collars. Neonate mortality calculated by the Kaplan-Meier method was 23.6%. Mortality caused by predation was low, since only one of eight non-surviving fawns died from predation, probably by red fox Vulpes vulpes. The spatial behaviour of the neonates was examined by habitat selection at home-range level, which in fact is a selection made by the mother, and at bed-site level within that habitat. Compositional analysis revealed a significant preference for arable land, pasture and coniferous forest between 5-15 m high, compared to young forest. Selected bed sites showed significantly lower visibility and higher amount of canopy cover than random sites. Surprisingly, we did not find any relationship between canopy cover and visibility in selected bed sites while it showed a significant and negative relationship at random bed sites. We interpret this finding as while high canopy cover and low visibility covary at the habitat level, fawns seem to select these two bed-site variables independently, perhaps for thermoregulatory reasons. Since there are few predators in our study area and predation pressure is low, this behaviour is not connected to actual survival rates in this area, but would rather be in support of the hypothesis of ‘pleiotropy’ as thermoregulatory reasons for bed-site selection in neonate fawns might be the most important contemporary selection force in the absence of large predators.

Food Selection by Herbivores and Neighbourhood Effects in the Evolution of Plant Defences

A number of studies have reported how neighbouring plants may influence herbivory on palatable or unpalatable plants. Such neighbourhood effects can have important evolutionary consequences as they may either promote the evolutionary stability of plant defences or, alternatively, select against the fixation of plant defences and instead promote a stable polymorphism of palatable and unpalatable plants. These consequences depend on whether the difference in herbivore damage between unpalatable and palatable plants is smaller or, alternatively, greater when the neighbours are unpalatable instead of palatable. Such relations can arise when the neighbourhood effects are non-parallel among palatable and unpalatable plants. We outline two basic situations of non-parallel neighbourhood effects and illustrate how they can come about. A detailed dissection of these interactions reveals that there are several qualitatively distinct mechanisms that promote either evolutionary stability of plant defences or alternatively polymorphism. Our classification of mechanisms can be used to clarify and explain observations obtained in the field of plant—herbivore interactions and predator—prey interactions, both at the population and the community level.

Development of feeding selectivity and consistency in food choice over 5 years in fallow deer

In order to better understand the development and maintenance of feeding selectivity, several feeding experiments were performed with fallow deer (Dama dama L.). In experiments performed when the fawns were between ten and 27 days old, it was found that all fawns showed preferences for sucrose but aversions towards tannic acid and ascorbic acid. However, differences in selectivity towards tannic acid were present already before the fawns became functional ruminants and these individual differences lasted 5 years. Moreover, individuals that ingested overall less tannic acid, searched more thoroughly between food sources. When the foraging behaviour was compared with age (11-41 days old and 65-97 days old), it was found that the time a fawn spent eating, increased with age, and the time spent on exploration, smelling and tasting plants decreased with age. Furthermore, the fawns increased their intake of grass and herbs, while the intake of soil and dead plant material decreased with age.

The influence of spatiotemporal conditions and personality on survival in reintroductions–evolutionary implications

Personality exists in non-human animals and can impact fitness. There is, however, a shortage of empirical studies in certain areas within the field, and fundamental evolutionary theory on personality remains largely untested. For example, little is known on how variation in personality is maintained over evolutionary time. Theory suggests that fluctuating selection pressures due to spatiotemporal variation in conditions, e.g. food availability, is a possible mechanism and a few studies have shown that the success of different personality types varies with spatiotemporal conditions. However, it remains unknown whether different mechanisms can maintain personality within a species. Here we use a reintroduction programme for the critically endangered European mink (Mustela lutreola) to test whether multiple personality trait domains (boldness, exploration and sociability) affected survival in two different years and islands. This was done through pre-release personality tests and post-release radio-tracking monitoring. Survival was positively correlated with boldness, whereas the relationship with exploration was either negative or positive depending on year/island. The results show a complex relationship between personality and survival and suggest that exploration can be maintained over evolutionary time via spatiotemporal variation in conditions. However, in contrast to exploration, boldness did not vary spatiotemporally and sociability had no impact on survival. This indicates that different personality trait domains might be maintained by different mechanisms. To date, personality has been studied primarily within behavioural sciences, but through empirical findings we highlight the importance of personality also in ecology and conservation biology.

Two shades of boldness : novel object and anti-predator behavior reflect different personality dimensions in domestic rabbits

It is increasingly common to quantify and describe behavioral variation in domestic and wild animals in terms of “personality”. Correlating behavioral traits are referred to as personality “dimensions” or “factors” and different dimensions have been reported in different species. “Boldness” is a well-described personality dimension in several species, although some issues remain unclear. Previous models of boldness include both novelty and risk taking, but recent studies indicate that these types of behaviors may reflect separate personality dimensions. In this study, we developed a behavioral test battery for domestic rabbits, and recorded behaviors of 61 individuals in four different situations (novel object, novel arena, social, and predator interactions). We used domestic rabbits as a model because behavioral variation in rabbits has rarely been quantified in terms of personality dimensions, although rabbit behavior is described. We also wanted to investigate behavioral variation in a Swedish rabbit breed of conservation concern — the Gotland rabbit. Factor analysis of the behavioral test measures suggested three personality dimensions: “exploration”, “boldness”, and “anxiety”. Novel object scores clustered in the exploration and boldness factors, whereas scores associated with predator interactions were explained by “anxiety”, indicating that novel object and anti-predator behavior reflect different personality dimensions in rabbits.