The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
Peter Leimgruber - One of the best experts on this subject based on the ideXlab platform.
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on the brink of extinction habitat selection of Addax and dorcas gazelle across the tin toumma desert niger
Diversity and Distributions, 2017Co-Authors: Jared A Stabach, Tim Wacher, Thomas Rabeil, Vincent Turmine, Thomas D Mueller, Peter LeimgruberAbstract:Aim To assess the distribution and occurrence of Addax (Addax nasomaculatus), the most critically endangered ungulate species globally, and dorcas gazelle (Gazelle dorcas), for which the ecology in the southern Sahara is virtually unknown. Location Tin Toumma desert, Niger Methods Integrating field surveys, collected over a 7-year period (2008–2014), with remote sensing-derived measures of vegetation productivity (NDVI) and surface roughness, we fit models in a generalized linear regression framework to predict and evaluate the occurrence of Addax and dorcas gazelle. Results Addax declined significantly over the course of the study, strongly affecting the outcomes of our regression models. Other factors, namely surface roughness and the occurrence of the perennial grass Stipagrostis acutiflora, were important in predicting Addax occurrence. Dorcas gazelle, inhabiting areas further to the south of our study area, were more positively associated with increases in vegetation productivity than Addax. Both species were observed to have a strong negative response to human disturbance. Predictive models, relying only on remotely sensed derived variables, provided insight into areas of habitat suitability and highlighted niche partitioning across the Sahelo-Saharan biome. Main conclusions Our results provide improved insight into the factors contributing to the occurrence of this critically endangered (Addax) and vulnerable (dorcas gazelle) species and may help guide future field surveys across the region to locate small and geographically isolated populations. Developing statistically based ecological habitat models provide a first-step towards improved management and policy development for the long-term conservation of these species and complement field surveys conducted across the region to monitor species that are increasingly being pushed to extinction.
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On the brink of extinction—Habitat selection of Addax and dorcas gazelle across the Tin Toumma desert, Niger
Diversity and Distributions, 2017Co-Authors: Jared A Stabach, Tim Wacher, Thomas Rabeil, Vincent Turmine, Thomas D Mueller, Peter LeimgruberAbstract:Aim To assess the distribution and occurrence of Addax (Addax nasomaculatus), the most critically endangered ungulate species globally, and dorcas gazelle (Gazelle dorcas), for which the ecology in the southern Sahara is virtually unknown. Location Tin Toumma desert, Niger Methods Integrating field surveys, collected over a 7-year period (2008–2014), with remote sensing-derived measures of vegetation productivity (NDVI) and surface roughness, we fit models in a generalized linear regression framework to predict and evaluate the occurrence of Addax and dorcas gazelle. Results Addax declined significantly over the course of the study, strongly affecting the outcomes of our regression models. Other factors, namely surface roughness and the occurrence of the perennial grass Stipagrostis acutiflora, were important in predicting Addax occurrence. Dorcas gazelle, inhabiting areas further to the south of our study area, were more positively associated with increases in vegetation productivity than Addax. Both species were observed to have a strong negative response to human disturbance. Predictive models, relying only on remotely sensed derived variables, provided insight into areas of habitat suitability and highlighted niche partitioning across the Sahelo-Saharan biome. Main conclusions Our results provide improved insight into the factors contributing to the occurrence of this critically endangered (Addax) and vulnerable (dorcas gazelle) species and may help guide future field surveys across the region to locate small and geographically isolated populations. Developing statistically based ecological habitat models provide a first-step towards improved management and policy development for the long-term conservation of these species and complement field surveys conducted across the region to monitor species that are increasingly being pushed to extinction.
Tim Wacher - One of the best experts on this subject based on the ideXlab platform.
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VIEWPOINT Fiddling in biodiversity hotspots while deserts burn? Collapse of the Sahara's megafauna
2020Co-Authors: Sarah M. Durant, Paul De Ornellas, Tim Wacher, C Ransom, Mohanad Abdelgadir, Rosie Woodroffe, John Newby, Bashir, Jonathan E. M. Baillie, M. BeddiafAbstract:Biodiversity hotspots understandably attract considerable conservation attention. However, deserts are rarely viewed as conservation priority areas, due to their relatively low productivity, yet these systems are home to unique species, adapted to harsh and highly variable environments. While global attention has been focused on hotspots, the world’s largest tropical desert, the Sahara, has suffered a catastrophic decline in megafauna. Of 14 large vertebrates that have historically occurred in the region, four are now extinct in the wild, including the iconic scimitar-horned oryx (Oryx dammah). The majority has disappeared from more than 90% of their Saharan range, including Addax (Addax nasomaculatus), dama gazelle (Nanger dama) and Saharan cheetah (Acinonyx jubatus hecki) – all now on the brink of extinction. Greater conservation support and scientific attention for the region might have helped to avert these catastrophic declines. The Sahara serves as an example of a wider historical neglect of deserts and the human communities who depend on them. The scientific community can make an important contribution to conservation in deserts by establishing baseline information on biodiversity and developing new approaches to sustainable management of desert species and ecosystems. Such approaches must accommodate mobility of both people and wildlife so that they can use resources most efficiently in the face of low and unpredictable rainfall. This is needed to enable governments to deliver on their commitments to halt further degradation of deserts and to improve their status for both biodiversity conservation and human well-being. Only by so-doing will deserts be able to support resilient ecosystems and communities that are best able to adapt to climate change.
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on the brink of extinction habitat selection of Addax and dorcas gazelle across the tin toumma desert niger
Diversity and Distributions, 2017Co-Authors: Jared A Stabach, Tim Wacher, Thomas Rabeil, Vincent Turmine, Thomas D Mueller, Peter LeimgruberAbstract:Aim To assess the distribution and occurrence of Addax (Addax nasomaculatus), the most critically endangered ungulate species globally, and dorcas gazelle (Gazelle dorcas), for which the ecology in the southern Sahara is virtually unknown. Location Tin Toumma desert, Niger Methods Integrating field surveys, collected over a 7-year period (2008–2014), with remote sensing-derived measures of vegetation productivity (NDVI) and surface roughness, we fit models in a generalized linear regression framework to predict and evaluate the occurrence of Addax and dorcas gazelle. Results Addax declined significantly over the course of the study, strongly affecting the outcomes of our regression models. Other factors, namely surface roughness and the occurrence of the perennial grass Stipagrostis acutiflora, were important in predicting Addax occurrence. Dorcas gazelle, inhabiting areas further to the south of our study area, were more positively associated with increases in vegetation productivity than Addax. Both species were observed to have a strong negative response to human disturbance. Predictive models, relying only on remotely sensed derived variables, provided insight into areas of habitat suitability and highlighted niche partitioning across the Sahelo-Saharan biome. Main conclusions Our results provide improved insight into the factors contributing to the occurrence of this critically endangered (Addax) and vulnerable (dorcas gazelle) species and may help guide future field surveys across the region to locate small and geographically isolated populations. Developing statistically based ecological habitat models provide a first-step towards improved management and policy development for the long-term conservation of these species and complement field surveys conducted across the region to monitor species that are increasingly being pushed to extinction.
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On the brink of extinction—Habitat selection of Addax and dorcas gazelle across the Tin Toumma desert, Niger
Diversity and Distributions, 2017Co-Authors: Jared A Stabach, Tim Wacher, Thomas Rabeil, Vincent Turmine, Thomas D Mueller, Peter LeimgruberAbstract:Aim To assess the distribution and occurrence of Addax (Addax nasomaculatus), the most critically endangered ungulate species globally, and dorcas gazelle (Gazelle dorcas), for which the ecology in the southern Sahara is virtually unknown. Location Tin Toumma desert, Niger Methods Integrating field surveys, collected over a 7-year period (2008–2014), with remote sensing-derived measures of vegetation productivity (NDVI) and surface roughness, we fit models in a generalized linear regression framework to predict and evaluate the occurrence of Addax and dorcas gazelle. Results Addax declined significantly over the course of the study, strongly affecting the outcomes of our regression models. Other factors, namely surface roughness and the occurrence of the perennial grass Stipagrostis acutiflora, were important in predicting Addax occurrence. Dorcas gazelle, inhabiting areas further to the south of our study area, were more positively associated with increases in vegetation productivity than Addax. Both species were observed to have a strong negative response to human disturbance. Predictive models, relying only on remotely sensed derived variables, provided insight into areas of habitat suitability and highlighted niche partitioning across the Sahelo-Saharan biome. Main conclusions Our results provide improved insight into the factors contributing to the occurrence of this critically endangered (Addax) and vulnerable (dorcas gazelle) species and may help guide future field surveys across the region to locate small and geographically isolated populations. Developing statistically based ecological habitat models provide a first-step towards improved management and policy development for the long-term conservation of these species and complement field surveys conducted across the region to monitor species that are increasingly being pushed to extinction.
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fiddling in biodiversity hotspots while deserts burn collapse of the sahara s megafauna
Diversity and Distributions, 2014Co-Authors: Paul De Ornellas, Tim Wacher, Sultana Bashir, C Ransom, Rosie Woodroffe, Sarah M. Durant, John Newby, Teresa Abaigar, Mohanad AbdelgadirAbstract:Biodiversity hotspots understandably attract considerable conservation attention. However, deserts are rarely viewed as conservation priority areas, due to their relatively low productivity, yet these systems are home to unique species, adapted to harsh and highly variable environments. While global attention has been focused on hotspots, the world's largest tropical desert, the Sahara, has suffered a catastrophic decline in megafauna. Of 14 large vertebrates that have historically occurred in the region, four are now extinct in the wild, including the iconic scimitar-horned oryx (Oryx dammah). The majority has disappeared from more than 90% of their Saharan range, including Addax (Addax nasomaculatus), dama gazelle (Nanger dama) and Saharan cheetah (Acinonyx jubatus hecki) - all now on the brink of extinction. Greater conservation support and scientific attention for the region might have helped to avert these catastrophic declines. The Sahara serves as an example of a wider historical neglect of deserts and the human communities who depend on them. The scientific community can make an important contribution to conservation in deserts by establishing baseline information on biodiversity and developing new approaches to sustainable management of desert species and ecosystems. Such approaches must accommodate mobility of both people and wildlife so that they can use resources most efficiently in the face of low and unpredictable rainfall. This is needed to enable governments to deliver on their commitments to halt further degradation of deserts and to improve their status for both biodiversity conservation and human well-being. Only by so-doing will deserts be able to support resilient ecosystems and communities that are best able to adapt to climate change. © 2013 John Wiley & Sons Ltd.
Thomas D Mueller - One of the best experts on this subject based on the ideXlab platform.
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on the brink of extinction habitat selection of Addax and dorcas gazelle across the tin toumma desert niger
Diversity and Distributions, 2017Co-Authors: Jared A Stabach, Tim Wacher, Thomas Rabeil, Vincent Turmine, Thomas D Mueller, Peter LeimgruberAbstract:Aim To assess the distribution and occurrence of Addax (Addax nasomaculatus), the most critically endangered ungulate species globally, and dorcas gazelle (Gazelle dorcas), for which the ecology in the southern Sahara is virtually unknown. Location Tin Toumma desert, Niger Methods Integrating field surveys, collected over a 7-year period (2008–2014), with remote sensing-derived measures of vegetation productivity (NDVI) and surface roughness, we fit models in a generalized linear regression framework to predict and evaluate the occurrence of Addax and dorcas gazelle. Results Addax declined significantly over the course of the study, strongly affecting the outcomes of our regression models. Other factors, namely surface roughness and the occurrence of the perennial grass Stipagrostis acutiflora, were important in predicting Addax occurrence. Dorcas gazelle, inhabiting areas further to the south of our study area, were more positively associated with increases in vegetation productivity than Addax. Both species were observed to have a strong negative response to human disturbance. Predictive models, relying only on remotely sensed derived variables, provided insight into areas of habitat suitability and highlighted niche partitioning across the Sahelo-Saharan biome. Main conclusions Our results provide improved insight into the factors contributing to the occurrence of this critically endangered (Addax) and vulnerable (dorcas gazelle) species and may help guide future field surveys across the region to locate small and geographically isolated populations. Developing statistically based ecological habitat models provide a first-step towards improved management and policy development for the long-term conservation of these species and complement field surveys conducted across the region to monitor species that are increasingly being pushed to extinction.
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On the brink of extinction—Habitat selection of Addax and dorcas gazelle across the Tin Toumma desert, Niger
Diversity and Distributions, 2017Co-Authors: Jared A Stabach, Tim Wacher, Thomas Rabeil, Vincent Turmine, Thomas D Mueller, Peter LeimgruberAbstract:Aim To assess the distribution and occurrence of Addax (Addax nasomaculatus), the most critically endangered ungulate species globally, and dorcas gazelle (Gazelle dorcas), for which the ecology in the southern Sahara is virtually unknown. Location Tin Toumma desert, Niger Methods Integrating field surveys, collected over a 7-year period (2008–2014), with remote sensing-derived measures of vegetation productivity (NDVI) and surface roughness, we fit models in a generalized linear regression framework to predict and evaluate the occurrence of Addax and dorcas gazelle. Results Addax declined significantly over the course of the study, strongly affecting the outcomes of our regression models. Other factors, namely surface roughness and the occurrence of the perennial grass Stipagrostis acutiflora, were important in predicting Addax occurrence. Dorcas gazelle, inhabiting areas further to the south of our study area, were more positively associated with increases in vegetation productivity than Addax. Both species were observed to have a strong negative response to human disturbance. Predictive models, relying only on remotely sensed derived variables, provided insight into areas of habitat suitability and highlighted niche partitioning across the Sahelo-Saharan biome. Main conclusions Our results provide improved insight into the factors contributing to the occurrence of this critically endangered (Addax) and vulnerable (dorcas gazelle) species and may help guide future field surveys across the region to locate small and geographically isolated populations. Developing statistically based ecological habitat models provide a first-step towards improved management and policy development for the long-term conservation of these species and complement field surveys conducted across the region to monitor species that are increasingly being pushed to extinction.
Jared A Stabach - One of the best experts on this subject based on the ideXlab platform.
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on the brink of extinction habitat selection of Addax and dorcas gazelle across the tin toumma desert niger
Diversity and Distributions, 2017Co-Authors: Jared A Stabach, Tim Wacher, Thomas Rabeil, Vincent Turmine, Thomas D Mueller, Peter LeimgruberAbstract:Aim To assess the distribution and occurrence of Addax (Addax nasomaculatus), the most critically endangered ungulate species globally, and dorcas gazelle (Gazelle dorcas), for which the ecology in the southern Sahara is virtually unknown. Location Tin Toumma desert, Niger Methods Integrating field surveys, collected over a 7-year period (2008–2014), with remote sensing-derived measures of vegetation productivity (NDVI) and surface roughness, we fit models in a generalized linear regression framework to predict and evaluate the occurrence of Addax and dorcas gazelle. Results Addax declined significantly over the course of the study, strongly affecting the outcomes of our regression models. Other factors, namely surface roughness and the occurrence of the perennial grass Stipagrostis acutiflora, were important in predicting Addax occurrence. Dorcas gazelle, inhabiting areas further to the south of our study area, were more positively associated with increases in vegetation productivity than Addax. Both species were observed to have a strong negative response to human disturbance. Predictive models, relying only on remotely sensed derived variables, provided insight into areas of habitat suitability and highlighted niche partitioning across the Sahelo-Saharan biome. Main conclusions Our results provide improved insight into the factors contributing to the occurrence of this critically endangered (Addax) and vulnerable (dorcas gazelle) species and may help guide future field surveys across the region to locate small and geographically isolated populations. Developing statistically based ecological habitat models provide a first-step towards improved management and policy development for the long-term conservation of these species and complement field surveys conducted across the region to monitor species that are increasingly being pushed to extinction.
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On the brink of extinction—Habitat selection of Addax and dorcas gazelle across the Tin Toumma desert, Niger
Diversity and Distributions, 2017Co-Authors: Jared A Stabach, Tim Wacher, Thomas Rabeil, Vincent Turmine, Thomas D Mueller, Peter LeimgruberAbstract:Aim To assess the distribution and occurrence of Addax (Addax nasomaculatus), the most critically endangered ungulate species globally, and dorcas gazelle (Gazelle dorcas), for which the ecology in the southern Sahara is virtually unknown. Location Tin Toumma desert, Niger Methods Integrating field surveys, collected over a 7-year period (2008–2014), with remote sensing-derived measures of vegetation productivity (NDVI) and surface roughness, we fit models in a generalized linear regression framework to predict and evaluate the occurrence of Addax and dorcas gazelle. Results Addax declined significantly over the course of the study, strongly affecting the outcomes of our regression models. Other factors, namely surface roughness and the occurrence of the perennial grass Stipagrostis acutiflora, were important in predicting Addax occurrence. Dorcas gazelle, inhabiting areas further to the south of our study area, were more positively associated with increases in vegetation productivity than Addax. Both species were observed to have a strong negative response to human disturbance. Predictive models, relying only on remotely sensed derived variables, provided insight into areas of habitat suitability and highlighted niche partitioning across the Sahelo-Saharan biome. Main conclusions Our results provide improved insight into the factors contributing to the occurrence of this critically endangered (Addax) and vulnerable (dorcas gazelle) species and may help guide future field surveys across the region to locate small and geographically isolated populations. Developing statistically based ecological habitat models provide a first-step towards improved management and policy development for the long-term conservation of these species and complement field surveys conducted across the region to monitor species that are increasingly being pushed to extinction.
Marcus Clauss - One of the best experts on this subject based on the ideXlab platform.
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microanatomy of the digestive tract hooves and some visceral organs of Addax antelope Addax nasomaculatus following a concentrate or forage feeding regime
Anatomia Histologia Embryologia, 2018Co-Authors: S A Tahas, S Hammer, Martin O Jurado, A Arif, Jeanmichel Hatt, Udo Hetzel, B Altenbrunnermartinek, Marcus ClaussAbstract:Subacute ruminal acidosis is a common disease in captive non-domesticated ruminants and is mainly diagnosed by rumen fluid pH and rumen histology. Furthermore, differences in ruminant gastrointestinal histology have been hypothesized to correlate with the browser–grazer continuum. Twelve surplus Addax antelope (Addax nasomaculatus) were divided into two groups, fed either their usual diet, consisting of a concentrate feed with a limited amount of hay, or a diet of unlimited hay only, for 3 months. After culling, descriptive and morphometric histology and pH measurements were compared between groups. Significant variations in cellular subpopulations were noted between groups, with roughage-fed individuals presenting primarily with balloon cells of the Stratum corneum and living layer cell vacuolization, whereas parakeratosis and intermediate-type cells were more frequent in the concentrate-fed group. Lesions typical of subacute ruminal acidosis were significantly more pronounced in concentrate-fed individuals. Ruminal pH measurements did not differ significantly, but were more consistent in forage-fed individuals, indicating a more stable reticuloruminal environment. The results indicate that ruminal histology may be more appropriate in assessing ruminal health compared to a single post-mortem pH measurement. It is proposed that Stratum corneum balloon cells may indicate cell maturation and not, as previously assumed, hyperfunction. Concentrate-fed individuals scored higher on the presence of inflammatory cells on hoof corium histology. The study further emphasizes the adaptability of ruminant digestive tract microanatomy in adult animals even after a short period of time and the positive effects an increased roughage diet may have in populations of captive grazing ruminants.
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gross measurements of the digestive tract and visceral organs of Addax antelope Addax nasomaculatus following a concentrate or forage feeding regime
Anatomia Histologia Embryologia, 2017Co-Authors: S A Tahas, S Hammer, Martin O Jurado, A Arif, Sven Reese, Jeanmichel Hatt, Marcus ClaussAbstract:Differences in macroscopic measurements of the gastrointestinal tract have been hypothesized to correlate with the browser–grazer continuum in the natural diet of ruminants. However, to what extent these characteristics represent species-specific traits, or respond to the actually ingested diet, remains to be investigated. Twelve surplus Addax antelope (Addax nasomaculatus) were divided into two groups and fed, for 3 months, either their usual diet, consisting of a concentrate feed with a limited amount of hay, or a diet of unlimited hay only. After culling, macroscopic measurements were compared between groups. The macroscopic anatomy of the Addax showed many characteristics considered typical for grazing or ‘cattle-type’ ruminants. While both diet groups had mesenteric, pericardial and perirenal adipose tissue, these depots were subjectively more pronounced in concentrate-fed animals. Hay-fed animals had significantly heavier filled forestomach compartments, with corresponding significantly longer linear measurements. Masseter muscles and the surface of first-order omasal leaves were significantly more prominent in hay-fed animals, reflecting possible adaptations to overcome resistance of grass forage and to reabsorb fluid from increased rumination, but differences were not as distinct as reported between ‘cattle-type’ and ‘moose-type’ ruminants. Some measurements such as reticular crests and empty foregut mass remained stable between groups, indicating possibly genetically pre-defined characteristics less prone to change in adult life. The results emphasize the adaptability of ruminant digestive tract anatomy in adult animals even after a short period of time, but also suggest limits to this adaptability that reveals a species-specific anatomy regardless of the diet actually consumed.
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physical characteristics of rumen contents in four large ruminants of different feeding type the Addax Addax nasomaculatus bison bison bison red deer cervus elaphus and moose alces alces
Comparative Biochemistry and Physiology A-molecular & Integrative Physiology, 2009Co-Authors: Marcus Clauss, S Hammer, Julia Fritz, Dorotheea Bayer, Kaarlo Nygren, Jeanmichela Hatt, Karlheinze Sudekum, Jurgen HummelAbstract:Abstract Based on morphological and physiological observations, it has been suggested that differences exist in the degree that reticuloruminal (RR) contents are stratified between various ruminant species. However, the occurrence of stratification has hardly been measured in non-domestic species. Forestomach contents of free-ranging moose ( n = 22) and red deer (24) shot during regular hunting procedures, and of captive (but 100% forage fed) Addax (6) and bison (10) culled for commercial or management purposes were investigated. There was no difference between the species in the degree by which RR ingesta separated according to size due to buoyancy characteristics in vitro . However, RR fluid of moose was more viscous than that of the other species, and no difference in moisture content was evident between the dorsal and the ventral rumen in moose, in contrast to the other species. Hence, the RR milieu in moose appears less favourable for gas or particle separation due to buoyancy characteristics. These findings are in accord with notable differences in RR papillation between the species. In moose, particle separation is most likely restricted to the reticulum, whereas in the other species, the whole rumen may pre-sort particles in varying degrees; a possible explanation for this pattern is a hypothetically lesser saliva production and fluid throughput in moose. The results suggest that differences in RR physiology may occur across ruminant species. The RR sorting mechanism should be considered a dynamic process that is better measured by its result — the significantly smaller particle size in the distal digestive tract when compared to the RR — than by regional differences in particle size within the RR.
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fluid and particle retention in the digestive tract of the Addax antelope Addax nasomaculatus adaptations of a grazing desert ruminant
Comparative Biochemistry and Physiology A-molecular & Integrative Physiology, 2008Co-Authors: Jurgen Hummel, Patrick Steuer, Karlheinz Sudekum, S Hammer, C Hammer, Jurgen W Streich, Marcus ClaussAbstract:Abstract Retention time of food in the digestive tract is a major aspect describing the digestive physiology of herbivores. Differences in feed retention times have been described for different ruminant feeding types. In this study, a dominantly grazing desert ruminant, the Addax ( Addax nasomaculatus ), was investigated in this respect. Eight animals with a body weight (BW) of 87 ± 5.3 kg on an ad libitum grass hay ( Chloris gayana ) diet were available. Co-EDTA and Cr-mordanted fibers ( 0.75 . The MRT of fluid and particles in the reticulo-rumen (MRT fluid RR and MRT particle RR) were quantified to be 20 ± 5.8 and 42 ± 7.0 h respectively. When compared to literature data, MRT fluid RR was significantly longer than in cattle species, and MRT particle RR was significantly longer than in 11 taxa of all feeding types. The ratio of MRT particle RR/MRT fluid RR (2.3 ± 0.5) was found to be within the range described for grazing ruminants. The long retention times found in the Addax can be interpreted as an adaptation to a diet including a high proportion of slow fermenting grasses, while the long retention time of the fluid phase can be interpreted as a consequence of water saving mechanisms of the desert-adapted Addax with a potentially low water turnover and capacious water storing rumen.
