The effect of different types of sports on resting heart rate variability and autonomic nervous system balance

Heart rate variability (HRV) refers to the beat-to-beat variation in heart rate, largely due to fluctuating influences of the autonomic nervous system. There are indications that active participation in sport can alter the resting HRV and autonomic nervous system balance. The aim of this preliminary study was to determine whether different sports have different effects on autonomic balance, and whether HRV differs when top performers from their respective fields are compared. HRV measured in a control group and three groups of elite South African athletes were compared: endurance athletes, field hockey players and skydivers. Time domain, frequency domain and Poincaré analyses of baseline HRV were used to determine whether a difference exists between the three groups. Results were compared by means of a Kruskal-Wallis one way analysis of variance statistical test. This study indicated statistically significant differences between elite athletes from different sport types and a control group with regard to HRV and resting autonomic regulation of cardiac function. Of the three groups the endurance athletes had the highest HRV, as well as the highest vagal tone. The skydivers recorded the lowest HRV with sympathetic nervous system dominance. The control group and hockey players showed intermediate values between the other two groups for all parameters. Different types of sports influence resting autonomic balance to different extents. The results of this study point towards higher fitness levels, in terms of autonomic control of cardiac function in participants involved in aerobic-demanding sports activities. Lower HRV and increased sympathetic CV influence in the skydiving group may indicate increased dysrhythmogenic risk. Further studies conducted during non-participating periods and also in the later, post- participation years are recommended

When less is more : heterogeneity in grass patch height supports herbivores in counter-intuitive ways

Herbivores are an integral part of the African landscape and have evolved with the vegetation to create the savanna landscape. Managers of these landscapes can benefit from a better understanding of how indigenous herbivores use the landscape to which they are adapted. In this study we observed which patches were frequently utilised, by doing regular monthly road counts, grass height observations and dung counts on selected short grass patches in the Kruger National Park. Smaller-framed impala and blue wildebeest (meso-herbivores) were most regularly seen on these nutritious patches, while from dung deposits it was clear that the even larger-framed buffalo (mega-herbivores) spent time there. This preference can be explained by considering the nutritional needs and food intake of the herbivores. Smaller-framed herbivores seem to be able to satisfy their dietary requirements on the high-quality forage patches, while larger-framed herbivores seem to supplement the quality forage by also spending foraging time on areas of higher grass biomass. From this insight we propose that range management should take herbivore preferences into account and allow herbivores to select and concentrate their foraging on the most nutritious forage. This approach is likely to decrease inputs while allowing animals to maintain or increase production.South African National Parks and the Agricultural Research Council.http://www.tandfonline.com/loi/tarf202020-03-14hj2020Animal and Wildlife Science

When less is more: heterogeneity in grass patch height supports herbivores in counter-intuitive ways

Herbivores are an integral part of the African landscape and have evolved with the vegetation to create the savanna landscape. Managers of these landscapes can benefit from a better understanding of how indigenous herbivores use the landscape to which they are adapted. In this study we observed which patches were frequently utilised, by doing regular monthly road counts, grass height observations and dung counts on selected short grass patches in the Kruger National Park. Smaller-framed impala and blue wildebeest (meso-herbivores) were most regularly seen on these nutritious patches, while from dung deposits it was clear that the even larger-framed buffalo (mega-herbivores) spent time there. This preference can be explained by considering the nutritional needs and food intake of the herbivores. Smaller-framed herbivores seem to be able to satisfy their dietary requirements on the high-quality forage patches, while larger-framed herbivores seem to supplement the quality forage by also spending foraging time on areas of higher grass biomass. From this insight we propose that range management should take herbivore preferences into account and allow herbivores to select and concentrate their foraging on the most nutritious forage. This approach is likely to decrease inputs while allowing animals to maintain or increase production.Keywords: diet selection, grazing management, forage quality, nutritio

Evaluating herbivore management outcomes and associated vegetation impacts

African savannas are characterised by temporal and spatial fluxes that are linked to fluxes in herbivore populations and vegetation structure and composition. We need to be concerned about these fluxes only when management actions cause the system to shift towards a less desired state. Large herbivores are a key attribute of African savannas and are important for tourism and biodiversity. Large protected areas such as the Kruger National Park (KNP) manage for high biodiversity as the desired state, whilst private protected areas, such as those adjacent to the KNP, generally manage for high income. Biodiversity, sustainability and economic indicators are thus required to flag thresholds of potential concern (TPCs) that may result in a particular set of objectives not being achieved. In large conservation areas such as the KNP, vegetation changes that result from herbivore impact, or lack thereof, affect biodiversity and TPCs are used to indicate unacceptable change leading to a possible loss of biodiversity; in private protected areas the loss of large herbivores is seen as an important indicator of economic loss. Therefore, the first-level indicators aim to evaluate the forage available to sustain grazers without deleteriously affecting the vegetation composition, structure and basal cover. Various approaches to monitoring for these indicators were considered and the importance of the selection of sites that are representative of the intensity of herbivore use is emphasised. The most crucial step in the adaptive management process is the feedback of information to inform management decisions and enable learning. Feedback loops tend to be more efficient where the organisation’s vision is focused on, for example, economic gain, than in larger protected areas, such as the KNP, where the vision to conserve biodiversity is broader and more complex. Conservation implications: In rangeland, optimising herbivore numbers to achieve the management objectives without causing unacceptable or irreversible change in the vegetation is challenging. This manuscript explores different avenues to evaluate herbivore impact and the outcomes of management approaches that may affect vegetation