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Illius, A. W., & Gordon, I. J. (1987). The Allometry of Food Intake in Grazing Ruminants. T. J. Anim. Ecol., 56(3), 989–999.
Abstract: A simulation model of grazing mechanics in ruminants shows that, due to the allometric relations of bite size and metabolic requirements to body size, small animals are able to subsist on shorter swards than large animals. (2) The density of nutrients in the grazed horizon of the modelled swards markedly affected the ability of animals of a given body size to satisfy their energy requirements. (3) By extension, the allometric relationships would be expected to apply in selective grazing and browsing species in their choice of food items of different size and nutrient content. (4) The results support the argument that sexual segregation and habitat choice of dimorphic species is an effect of scramble competition for limited resources, the males thus being excluded from mutually preferred swards. (5) The model provides an explanation for two interspecific phenomena amongst grazers: grazing succession and grazing facilitation.
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Mills, M. G. L., & Shenk, M. G. L. (1992). Predator--Prey Relationships: The Impact of Lion Predation on Wildebeest and Zebra Populations. T. J. Anim. Ecol., 61(3), 693–702.
Abstract: 1. The role of lion Panthera leo predation in the dynamics of blue wildebeest Connochaetes taurinus and zebra Equus burchelli populations was investigated through simulation models. The data used in the models were from intensive observations over 4 years in the south-east of the Kruger National Park. 2. Population estimates of wildebeest and zebra were made from aerial surveys, sex and age ratios from ground counts. Lion numbers were determined from observations of marked and radio-collared animals. Predation was studied by following lions for continuous periods of up to 336 h. 3. Two models were constructed. Model 1 ascertained the number of killing lions (adult females) that could be supported by each prey population while remaining stable. A single model was constructed for the sedentary wildebeest population. A summer and winter model was constructed for the semi-migratory zebra population. The sensitivity of the parameters in the model was tested by changing their value by 10%. In model 2, the kill age structure for each species was changed to determine the number of killing lions the altered prey selection parameters could support. 4. There was no difference in the vulnerability of either species to predation. Zebra foals (<1 year) were killed more frequently than expected. No selection for sex or by season could be found for either species. 5. Model 1 predicted that the wildebeest population stabilizes with 7.7 killing lions, close to the number in the study area. The winter zebra population stabilizes with 6.8 killing lions and the summer zebra population with 19.4. Manipulation of kill rate followed by adult fecundity rate had the greatest effect on population size of both species. In model 2, wildebeest predation was made selective towards calves and zebra predation was made non-selective for sex and age. With these parameters the wildebeest population stabilizes with 10.7 killing lions and the zebra population with 5.4 in winter and 15.1 in summer. 6. The models suggest that lion predation affected wildebeest more severely than zebra during the study. This was through the way in which lions selected their prey, and because of the sedentary behaviour of the wildebeest, as opposed to the semi-migratory behaviour of the zebra.
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R. A. J. Taylor. (1981). The Behavioural Basis of Redistribution I. The Delta -Model Concept. T. J. Anim. Ecol., 50(2), 573–586.
Abstract: (1) A conceptual model is developed in which spatial behaviour is density-dependent. The behaviour is classified as congregatory or migratory according to whether it results in movement towards or away from population concentrations. (2) Spatial behaviour is shown to result from both individual and population interactions. (3) The stability properties of the model are explored and it is shown how, under particular conditions, populations obeying the model have a population density regulating mechanism. (4) The similarity between the model and the potential energy curve of physics is noted, but it is emphasized that this is a behavioural not a physical model.
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Murray, M. G., & Brown, D. (1993). Niche Separation of Grazing Ungulates in the Serengeti: An Experimental Test. T. J. Anim. Ecol., 62(2), 380–389.
Abstract: 1. The niche separation of three species of alcelaphine antelope (wildebeest, topi and hartebeest) with similar body size was compared by measuring bite weight, bite rate, intake rate and selectivity of tame animals in plots containing grass at different growth stages. 2. On growing swards, hartebeest had a smaller bite weight and lower intake rate, and were also less selective of green leaf, than either topi or wildebeest. On senescent swards, hartebeest were more selective of leaf than the other two species. 3. Wildebeest had a faster bite rate than either topi or hartebeest on swards with low biomass and high protein content of green leaf (green flush). Bite weight and intake rate of wildebeest and topi were similar despite the difference in breadth of their incisor rows. 4. Topi were significantly more selective of green leaf than the other two species and were the only species to maintain a rapid bite rate on swards with high green leaf biomass. 5. The feeding experiments did not reveal significant cross-overs between species in the rate of food intake on different grass types, but each species was most proficient either in leaf selection or bite rate when feeding on grass swards in a particular growth stage. We suggest that growth stage is a primary determinant of niche separation. 6. In Serengeti, grazing ungulates which migrate are specialists of the earlier growth stages of grass which tend to be transient, while those that are residential specialize on late growth stages which are more enduring. The mobility of species, and the spatial and temporal dynamics of pastures containing different growth stages of grass, contribute to niche separation.
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Schmidt, R., Amrhein, V., Kunc, H. P., & Naguib, M. (2007). The day after: effects of vocal interactions on territory defence in nightingales. T. J. Anim. Ecol., 76(1), 168–173.
Abstract: 1. Models on territory acquisition and tenure predict that territorial animals benefit by adjusting territorial defence behaviour to previous challenges they had experienced within the socially complex environment of communication networks. 2. Here, we addressed such issues of social cognition by investigating persisting effects of vocal contests on territory defence behaviour in nightingales Luscinia megarhynchos (Brehm). 3. Using interactive playback during nocturnal song of subjects, a rival was simulated to countersing either aggressively (by song overlapping) or moderately (by song alternating) from outside the subjects' territory. Thereby, the time-specific singing strategy provided an experimentally controlled source of information on the motivation of an unfamiliar rival. 4. Expecting that nightingales integrate information with time, the same rival was simulated to return as a moderately singing intruder on the following morning. 5. The results show that the vigour with which male nightingales responded to the simulated intrusion of an opponent during the day depended on the nature of the nocturnal vocal interaction experienced several hours before. 6. Males that had received the song overlapping playback the preceding night approached the simulated intruder more quickly and closer and sang more songs near the loudspeaker than did males that had received a song alternating playback. 7. This adjustment of territory defence strategies depending on information from prior signalling experience suggests that integrating information with time plays an important part in territory defence by affecting a male's decision making in a communication network.
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