State-space modelling of the drivers of movement behaviour in sympatric species

Understanding animal movement behaviour is key to furthering our knowledge on intra- and inter-specific competition, group cohesion, energy expenditure, habitat use, the spread of zoonotic diseases or species management. We used a radial basis function surface approximation subject to minimum description length constraint to uncover the state-space dynamical systems from time series data. This approximation allowed us to infer structure from a mathematical model of the movement behaviour of sheep and red deer, and the effect of density, thermal stress and vegetation type. Animal movement was recorded using GPS collars deployed in sheep and deer grazing a large experimental plot in winter and summer. Information on the thermal stress to which animals were exposed was estimated using the power consumption of mechanical heated models and meteorological records of a network of stations in the plot. Thermal stress was higher in deer than in sheep, with less differences between species in summer. Deer travelled more distance than sheep, and both species travelled more in summer than in winter; deer travel distance showed less seasonal differences than sheep. Animal movement was better predicted in deer than in sheep and in winter than in summer; both species showed a swarming behaviour in group cohesion, stronger in deer. At shorter separation distances swarming repulsion was stronger between species than within species. At longer separation distances inter-specific attraction was weaker than intra-specific; there was a positive density-dependent effect on swarming, and stronger in deer than in sheep. There was not clear evidence which species attracted or repelled the other; attraction between deer at long separation distances was stronger when the model accounted for thermal stress, but in general the dynamic movement behaviour was hardly affected by the thermal stress. Vegetation type affected intra-species interactions but had little effect on inter-species interactions. Our modelling approach is useful in interpreting animal interactions, in order to unravel complex cooperative or competitive behaviours, and to the best of our knowledge is the first modelling attempt to make predictions of multi-species animal movement under different habitat mosaics and abiotic environmental conditions

Factors affecting food comminution during chewing in ruminants: a review

A review is presented of the chewing effectiveness of herbivorous mammals dealing with the relationship between food comminution (i.e. reduction of particle size), morphological features of teeth, chewing behaviour (i.e. time spent chewing and chewing rate), and the chemical and physical properties of plant tissues. Chewing is the main food processing mechanism in herbivores, increasing the surface/volume ratio of the food, which is a key factor affecting the efficiency of digestion and, therefore, body condition, reproductive success and life history. Chewing effectiveness (CE) is defined as the reduction of a pre-determined amount and particle size of a given food after a known, but not necessarily determined, number of chews. The two main animal-centred factors influencing CE are tooth effectiveness and chewing behaviour. The most frequently used predictors of tooth effectiveness are molar occlusal surface area, molar occlusal contact area (defined as any surface of the upper and lower teeth in or near contact during occlusion) and the length of the enamel cutting edges of the occlusal surface. There is expected to be a direct positive relationship between the predictors of tooth effectiveness and chewing effectiveness. Chewing behaviour has particular importance to food particle reduction in ruminants, because they spend long periods chewing during both initial ingestion and ruminating. The majority of studies find significant unexplained variance when CE is predicted using tooth features or chewing behaviour parameters. There is also little agreement as to what is the key morphological factor determining tooth effectiveness, or what is the relationship between tooth effectiveness and chewing behaviour. The type, maturity stage and physical presentation of the food also contribute to the final particle size after food has been chewed, because of the involvement of the concentration of chemical components of the cell walls (acid detergent and neutral detergent fibres, lignin) and the architectural structure of the plant tissues in particle breakdown. The relationships between body mass and tooth effectiveness, chewing behaviour and CE are also discussed

The influence of molar occlusal surface area on the voluntary intake, digestion, chewing behaviour and diet selection of red deer (Cervus elaphus)

The loss of tooth effectiveness due to molar wear has been proposed as an important cause of mortality in ungulate populations. Voluntary intakes, digestibility, mean retention times, chewing behaviour (during eating and rumination), and diet selection (physical selection: short vs long particles in hay; and botanical selection: leaf is stem) were compared in two groups of female red deer (Cervus elaphus) which differed in molar occlusal surface area, in order to test the hypothesis that behavioural and physiological mechanisms can be used to maintain assimilation efficiency in the presence of low functional tooth effectiveness.\ud \ud The group with lower values for first lower molar occlusal surface area (OSA) corrected for body weight had lower voluntary food intakes (P = 0.0126). The low OSA group had a greater number of chews per g DM of food ingested (P = 0.0167), a greater time spent chewing (P = 0.0476) but a lower number of chews per min than did those with a high OSA (P = 0.0484). The total number of chews per day was similar for both groups (P = 0.2011). The number of ruminating chews per day was less for the low OSA group (P = 0.0377). The group with low OSA values had a larger average particle size in their faeces (P = 0.0346). No differences were detected between groups in the physical or botanical composition of the diet selected (P = 0.3030, P = 0.3056, respectively) or in total digestibility and mean retention times (P = 0.1357, P = 0.3464, respectively). As a consequence of the lower voluntary intake the low OSA group had a lower digestible dry matter intake (P = 0.0170). This study supports the view that intake modification and the time invested in chewing during eating are the main mechanisms used to compensate for reduced chewing effectiveness associated with changes in tooth morphology, although the compensation is not total

Body size dimorphism and sexual segregation in polygynous ungulates: an experimental test with Soay sheep

Sexual segregation in Soay sheep (Ovis aries) was investigated using an experimental approach in order to test the sexual dimorphism-body size hypothesis. Two corollaries of the sexual dimorphism-body size hypothesis were tested: (1) in dimorphic species males, the larger sex, have relatively smaller bite sizes on short swards because of the scaling of incisor arcade with body weight, and (2) they move off earlier to feed on taller but poorer-quality swards when such swards are patchily distributed on a scale which enables the spatial segregation of individuals. Patch choice between sexes was estimated using a matrix of grass patches which differed in both quality and biomass of grass on offer (HQ: high-quality-low-biomass; LQ: low-quality-high-biomass). Sex differences in patch choice and grazing behaviour were tested in short-term preference trials. Incisor breadth showed no significant difference between sexes. On the other hand, muzzle width was dimorphic, with females having a narrower muzzle than males. Bite size was significantly different between the sexes, being smaller in females than in males, although it was not significantly different between sward types. Females had a higher bite rate than males and the bite rate was higher in the HQ award type than the LQ sward type. When the effect elf body mass was removed, no sex differences in muzzle size, bite size or bite rate were found. The intake rate did not differ between the sexes or between sward types. Whilst both sexes preferred the HQ sward type, females spent a significantly longer time feeding on the LQ sward type than did males. The difference detected between the sexes in patch choice was not consistent directly with the sexual dimorphism-body size hypothesis. Alternative explanations based on sex differences in foraging behaviour in relation to body mass sexual dimorphism are discussed to explain the result

Sex differences in feeding behaviour at feeding station scale in Soay sheep (Ovis aries)

Herbivorous ungulates live in a spatially heterogeneous environment making foraging decisions at a range of hierarchical scales, from bite size to landscape. We investigated the factors that control intake rate in Soay sheep (Ovis aries) when discrete items of food were sparsely distributed at the feeding station scale. Within the feeding station we varied the difficulty of accessing food, distance between items of food, difficulty of finding the food and complexity of the feeding station and recorded how intake rate responded in relation to body size, mouth size and the sex of the animal. Our findings demonstrated how increasing difficulty of accessing food, and increasing complexity of the feeding station negatively affected intake rate. The expected mechanistic response that smaller animals or animals with smaller mouth size were better at handling discrete small items of food, was overridden by individual and sexual differences in behaviour. We also considered that intake rate within a feeding station could be maximised by optimising the spatial pattern of offtake, and the results clearly indicated that both sexes tended to show clustered patterns of offtake. Animals of the same sex responded in a similar way to the difficulty in handling food items; males persevered more than females and consequently were less handicaped by having larger mouths. We discussed these results in relation to behavioural and body mass differences between the sexes and animals

Preferences of sheep and goats for straw pellets treated with different food-flavouring agents

In order to assess differences in preferences for flavours between ruminant species, two-choice tests were conducted on sheep (Scottish Blackface, Ovis aries) and goats (feral hybrids, Capra hircus). Feed pellets (nutritionally improved barley straw) were treated with synthetic human food-flavouring agents representing: strawberry (ST), apple (AP), orange (OR), maple (MA), caramel (CA), truffle (TR), garlic (GA) and onion (ON) flavours. Animals were first exposed to each of the flavours and then presented with each, paired with an untreated (control) feed, and the consumption of individual feeds recorded. Preference values (PV) were calculated from the proportion of the total feed consumption derived from the flavour-treated feed. Differences in PV were found between species (P = 0.01) and between flavours (P < 0.005). Although sheep showed stronger preference for flavoured feeds than did goats, both sheep and goats showed a similar pattern of preference across the flavours offered. In general, sheep exhibited significant preference for TR, GA, ON, AP, CA, MA and OR relative to the unflavoured feeds, whereas goats showed significant preference for TR, ON, AP and GA. The findings of this research suggest that it would be of practical use to evaluate feeds flavoured with compounds representing truffle, garlic and onion as intake enhancers in goats and sheep. Only if flavouring agents are successful in enhancing intake could we recommend flavouring as a means of masking undesirable feed flavours, production of a more uniform feed from variable ingredients or in prompting feed consumption

Long-term density-dependent changes in habitat selection in red deer (Cervus elaphus)

Understanding how habitat selection changes with population density is a key concept in population regulation, community composition and managing impacts on biodiversity and ecosystem services. At low density, it is expected that individuals select habitats in terms of their preference, but as population density increases, the availability of resources per individual declines on preferred habitats, leading to competition which forces some individuals to exploit less preferred habitats. Using spatial information of Scottish red deer (Cervus elaphus) winter counts, carried out in 110 areas across Scotland between 1961 and 2004 (a total of 1,206,495 deer observations), we showed how winter habitat niche breadth in red deer has widened with increasing population density. Heather moorland and montane habitats were most and least preferred for deer, respectively. Increasing density favoured the selection of grassland, to the detriment of the selection of heather moorland. The selection of heather and grassland decreased when temperature increased, while the selection of montane and peatland habitats increased. These findings are important for understanding how habitat use, density and population are likely to be affected by weather, and allow us to predict habitat impacts by large mammal herbivory and climate

The origins of sexual dimorphism in body size in ungulates

Jarman (1974) proposed a series of relationships between habitat use, food dispersion, and social behavior and hypothesized a series of evolutionary steps leading to sexual dimorphism in body size through sexual selection in African antelope species. The hypothesis states that sexual size dimorphism evolved in a three-step process. Initially, ancestral monomorphic and monogamous ungulate species occupying closed habitats radiated into open grassland habitats. Polygynous mating systems then rapidly evolved in response to the aggregation of males and females, perhaps in relation to the clumped distribution of food resources in open habitats. Subsequently, size dimorphism evolved ill those species occupying, open habitats, but not in species that remained in closed habitats or retained monogamy. This hypothesis has played all important role in explaining the origins of sexual dimorphism in mammals. However, the temporal sequence of the events that Jarman proposed has never been demonstrated. Here We use it phylogeny of extant ungulate species, along with maximum-likelihood statistical techniques, to provide a test of Jarman's hypothesis