Spatial impacts and the characterisation of resource use in a heterogeneous landscape.

Highly spatially variable environments pose animals with diet selection decisions that need to account for the patchy nature of their resource. Improved rangeland management would result from being able to predict patterns of animal utilisation of such vegetation. Whilst progress is being made in the comprehension of large scale influences (e.g., location of drinking water, landscape topography), little is known about how these integrate with smaller scales. It is likely that animals view landscapes in differing ways, depending on the scale that processes operate. Identification of the appropriate scale at which a species is affected by the spatial heterogeneity of a resource requires characterisation of the resource spatial structure, independent of our own biases. We tend to view landscapes in terms of vegetation communities, whilst the appropriate unit for animal perception remains unclear. This poster describes a study of foraging behaviour carried out as a method by which to associate animal activity with space use as an independent estimate of spatial heterogeneity

Spatial variation in springtime food resources influences the winter body mass of roe deer fawns. Oecologia 137

Abstract It is well established that the dynamics of mammalian populations vary in time, in relation to density and weather, and often in interaction with phenotypic differences (sex, age and social status). Habitat quality has recently been identified as another significant source of individual variability in vital rates of deer, including roe deer where spatial variations in fawn body mass were found to be only about a tenth of temporal variations. The approach used was to classify the habitat into blocks a priori, and to analyse variation in animal performance among the predefined areas. In a fine-grained approach, here we use data collected over 24 years on 1,235 roe deer fawns captured at known locations and the plant species composition sampled in 2001 at 578 sites in the ChizØ forest to determine the spatial structure at a fine scale of both vegetation and winter body mass of fawns, and then to determine links between the two. Space and time played a nearly equal role in determining fawn body masses of both sexes, each accounting for about 20% of variance and without any interaction between them. The spatial distribution of fawn body mass was perennial over the 24 years considered and predicted values showed a 2 kg range according to location in the reserve, which is much greater than suggested in previous work and is enough to have strong effects on fawn survival. The spatial distribution and the range of predicted body masses were closely similar in males and females. The result of this study is therefore consistent with the view that the life history traits of roe deer are only weakly influenced by sexual selection. The occurrence of three plant species that are known to be important food items in spring/summer roe deer diets, hornbeam (Carpinus betulus), bluebell (Hyacinthoides sp.) and Star of Bethlehem (Ornithogalum sp.) was positively related to winter fawn body mass. The occurrence of species known to be avoided in spring/summer roe deer diets [e.g. butcher's broom (Ruscus aculeatus) and beech (Fagus sylvatica)], was negatively related to fawn body mass. We conclude that the spatial variation in the body mass of fawns in winter in this forest is as important as the temporal variation, and that the distribution of plant species that are actively selected during spring and summer is an important determinant of spatial variation in winter fawn body mass. The availability of these plants is therefore likely to be a key factor in the dynamics of roe deer populations

Rangelands at equilibrium and non-equilibrium recent developments in the debate around rangeland ecology and management

The debate on equilibrium vs non-equilibrium dynamics in pastoral systems emerged in the early 1980s, when economists, ecologists and social scientists began to challenge the widespread claims of overgrazing and degradation in African rangelands and subsequent interventions based on rangeland succession theory and correct stocking rates (for example, Sandford 1982; 1983; Homewood & Rodgers 1987; Ellis & Swift 1988; Abel & Blaikie 1989; Westoby et al. 1989). The debate gained momentum in the early 1990s after two international workshops around emergent new paradigms in rangeland ecology and socio-economics (Woburn I and II), which resulted in the publication of two books, Range Ecology at Disequilibrium edited by Behnke et al. (1993) and Living with Uncertainty edited by Scoones (1994). The ‘new rangeland ecology’ argued that the traditional, equilibrium-based rangeland models did not take into account the considerable spatial heterogeneity and climatic variability of semi-arid rangelands, and that mobility, variable stocking rates and adaptive management were essential for the effective and sustainable utilisation of semi-arid and arid rangelands

Predicted Impact of Barriers to Migration on the Serengeti Wildebeest Population

The Serengeti wildebeest migration is a rare and spectacular example of a once-common biological phenomenon. A proposed road project threatens to bisect the Serengeti ecosystem and its integrity. The precautionary principle dictates that we consider the possible consequences of a road completely disrupting the migration. We used an existing spatially-explicit simulation model of wildebeest movement and population dynamics to explore how placing a barrier to migration across the proposed route (thus creating two disjoint but mobile subpopulations) might affect the long-term size of the wildebeest population. Our simulation results suggest that a barrier to migration—even without causing habitat loss—could cause the wildebeest population to decline by about a third. The driver of this decline is the effect of habitat fragmentation (even without habitat loss) on the ability of wildebeest to effectively track temporal shifts in high-quality forage resources across the landscape. Given the important role of the wildebeest migration for a number of key ecological processes, these findings have potentially important ramifications for ecosystem biodiversity, structure, and function in the Serengeti

Snout Shape in Extant Ruminants

Copyright: © 2014 Tennant, MacLeod. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. [4.0 license]. The attached file is the published version of the article

Book reviewResource Ecology: Spatial and Temporal Dynamics of ForagingBy Herbert HT Prins and Frank van Langevelde (2008)

2008, Springer, PO Box 17, 3300 AA Dordrecht, The Netherlands306 pages, hardcover or softcoverISBN 978-1-4020-6848-5 (hardcover), 978-1-4020-6849-2 (softcover). Price €119.95 / €59.95African Journal of Range & Forage Science 2010, 27(1): 61–6

The functional significance of the browser-grazer dichotomy in African ruminants

The allometric relationships for the fermentation rate of dry matter, the total energy concentration of volatile fatty acids (VFAs), the energy supplied from VFA production and the mass of the digesta contents within the rumen or caecum and proximal colon (hindgut) were used to test whether the digestive strategies of grazing and browsing African ruminants differ. The wet and dry mass of the contents of the rumen and hindgut were allometrically related to body mass (BM). These relationships did not differ between browsing and grazing ruminants. The fermentation rates in the rumen were strongly allometric and the intercepts of the relationships did not differ between browsers and grazers. The fermentation rates in the hindgut were not allometrically related to BM and did not differ between ruminants with different feeding habits. Likewise, the total energy concentration of the VFAs in the rumen and hindgut showed no allometric scaling and did not differ between browsing and grazing ruminants. The energy supplied by VFA production in both the rumen and hindgut of African ruminants scaled at around 0.8 with BM. Only in the case of the energy supplied by VFAs in the rumen were there significantly different intercepts for browsing and grazing ruminants. The energy supplied by VFA production in the rumen was inadequate to meet the energy requirements for maintenance of browsers and small grazers. The retention time of digesta in the alimentary tract was positively related to BM although there was no difference in the allometric relationships for grazers and browsers. The results of these analyses suggest that, after controlling for the effects of body mass, there is little difference in digestive strategy between African ruminants with different morphological adaptations of the gut

The nutritional ecology of African ruminants: A reinterpretation

1. Two contrasting explanations of niche separation in ruminants emphasize the importance of body mass-related trends in energy requirements and food-processing ability (the diet-quality assumption) and of physiological adaptations to diet type (grass or browse; the diet-type assumption).\ud \ud 2. The quality of the diet consumed in the dry season by 21 species of African ruminants was estimated from observed fermentation rates in the rumens of culled animals using a simulation model of digesta kinetics. The model predicts the effect of food composition (including tannins) on a number of variables on which previous arguments about physiological adaptations have been based: cellulolytic activity, digestion kinetics and volatile fatty acid proportions.\ud \ud 3. The predicted diet quality (potential digestibility) varied from 0.90 in small animals to 0.75 in large ones, and was negatively related to body mass with a shallow allometric exponent(- 0.035 +/- 0.0109).\ud \ud 4. The allometric exponent scaling body mass to predicted energy assimilation rate was 0.852+/-0.0474. The abundance and quality of food available were apparently adequate to allow greater net energy intake, relative to requirements, by large animals than small ones.\ud \ud 5. No difference existed in the predicted potential digestibility or net energy yield from the diet of browsing and grazing species after controlling for body mass. Therefore, although the diets differed in their botanical and chemical composition, the end result had little effect on the nutritional ecology of the animals with different diet types.\ud \ud 6. The model predicted that the level of cellulolytic activity of microbes in the rumen can affect the energy obtained from the diet. Microbial adaptation would cause browsers to suffer a penalty on switching from browse to grass, thereby reinforcing diet choice.\ud \ud 7. The presence of tannins in the diets of browsers was predicted to decrease rumen fermentation rate and increase the digestibility of the diet required to match observed fermentation rates