Beyond the here and now : herbivore ecology in a spatial-temporal context

Ecological phenomena at a certain location often not only depend on the current characteristics of that location itself, but also on characteristics of the landscape surrounding the site or influences from the past. In other words, in order to be able to understand ecological processes here and now, we often need information that is beyond here and now. This thesis investigates the role of such spatial-temporal context on the relationships between species and their environment. The focus is on large mammalian herbivores, an in particular the factors determining the movement and distribution of African elephants (Loxodonta africana) in Kruger National Park (KNP), South Africa. This thesis covers four main themes. First, it is shown that spatial-temporal variation in the biotic and abiotic environment creates predictable seasonal and daily cyclic patterns in the distribution of elephants in KNP. Then, herbivores are shown not only to respond to environmental heterogeneity: they also can create distinct spatial patterning in savanna vegetation when foraging initiates a positive plant-herbivore feedback and when the foraging process is spatially explicit. This leads to specific sites being revisited often, and therefore the patterns of site revisitation by elephants in KNP are studied, mainly in relation to surface water availability and vegetation characteristics. Lastly, this thesis focuses on the scale-dependent response of organisms to environmental heterogeneity, showing the consequences of a mismatch in the scale of analysis on statistical inference, and then focusing on finding the appropriate spatial scales to analyse and predict the spatial distribution of elephants in KNP. Together, the chapters presented in this thesis highlight the importance of explicitly considering the scale and context dependency of species-environment relationships, and demonstrate methods to take issues of spatial-temporal scale and context into account. These methods have the potential to increase our understanding of ecological phenomena and therefore may lead to better management of natural resources. <br/

Tamoxifen use and potential effects on liver parenchyma:A long-term prospective transient elastographic evaluation

Tamoxifen is a commonly prescribed drug in both early and metastatic breast cancer. Prospective studies in Asian populations demonstrated that tamoxifen‐related liver steatosis occurred in more than 30% of the patients within 2 years after start of treatment. No well‐designed prospective studies on potential tamoxifen‐related liver steatosis have been conducted in Caucasian patients so far. Therefore, our prospective study aimed to assess the incidence of tamoxifen‐related liver steatosis for a period of 2 years in a population of Caucasian breast cancer patients treated with tamoxifen. Patients with an indication for adjuvant treatment with tamoxifen were included in this study. Data were collected at 3 months (T1) and at 2 years (T2) after start of tamoxifen treatment (follow‐up period of 21 months). For the quantification of liver steatosis, patients underwent liver stiffness measurement by transient elastography with simultaneous controlled attenuation parameter (CAP) determination using the FibroScan. A total of 95 Caucasian breast cancer patients were included in this evaluation. Liver steatosis was observed in 46 of 95 (48%) and 48 of 95 (51%) of the patients at T1 and T2, respectively. No clinically relevant increase in liver steatosis was observed during the treatment period of 2 years with tamoxifen (median CAP = 243 ± 49 dB/m (T1) and 253 ± 55 dB/m (T2), respectively; p = 0.038). Conclusion: In this prospective longitudinal study in Caucasian breast cancer patients, no clinically relevant alterations in liver steatosis in terms of CAP values and liver/lipid parameters were observed after 2 years of tamoxifen treatment. This study therefore demonstrates an absence of tamoxifen‐related adverse events such as steatosis and (early) development of fibrosis or cirrhosis during a treatment period of at least 2 years

Seasonal diet changes in elephant and impala in mopane woodland

Elephant and impala as intermediate feeders, having a mixed diet of grass and browse, respond to seasonal fluctuations of forage quality by changing their diet composition. We tested the hypotheses that (1) the decrease in forage quality is accompanied by a change in diet from more monocots in the wet season to more dicots in the dry season and that that change is more pronounced and faster in impala than in elephant; (2) mopane (Colophospermum mopane), the most abundant dicot species, is the most important species in the elephant diet in mopane woodland, whereas impala feed relatively less on mopane due to the high condensed tannin concentration; and (3) impala on nutrient-rich soils have a diet consisting of more grass and change later to diet of more browse than impala on nutrient-poor soils. The phosphorus content and in vitro digestibility of monocots decreased and the NDF content increased significantly towards the end of the wet season, whereas in dicots no significant trend could be detected. We argue that this decreasing monocot quality caused elephant and impala to consume more dicots in the dry season. Elephant changed their diet gradually over a 16-week period from 70% to 25% monocots, whereas impala changed diets rapidly (2-4 weeks) from 95% to 70% monocots. For both elephants and impala, there was a positive correlation between percentage of monocots and dicots in the diet and the in vitro digestibility of these forage items. Mopane was the most important dicot species in the elephant diet and its contribution to the diet increased significantly in the dry season, whereas impala selected other dicot species. On nutrient-rich gabbroic soils, impala ate significantly more monocots than impala from nutrient-poor granitic soils, which was related to the higher in vitro digestibility of the monocots on gabbroic soil. Digestibility of food items appears to be an important determinant of diet change from the wet to the dry season in impala and elephants

Adherence to a plant-based, high-fibre dietary pattern is related to regression of non-alcoholic fatty liver disease in an elderly population

Dietary lifestyle intervention is key in treating non-alcoholic fatty liver disease (NAFLD). We aimed to examine the longitudinal relation between well-established dietary patterns as well as population-specific dietary patterns and NAFLD. Participants from two subsequent visits of the Rotterdam Study were included. All underwent serial abdominal ultrasonography (median follow-up: 4.4 years) and filled in a food frequency questionnaire. Secondary causes of steatosis were excluded. Dietary data from 389 items were collapsed into 28 food groups and a posteriori dietary patterns were identified using factor analysis. Additionally, we scored three a priori dietary patterns (Mediterranean Diet Score, Dutch Dietary Guidelines and WHO-score). Logistic mixed regression models were used to examine the relation between dietary patterns and NAFLD. Analyses were adjusted for demographic, lifestyle and metabolic factors. We included 963 participants of whom 343 had NAFLD. Follow-up data was available in 737 participants. Incident NAFLD was 5% and regressed NAFLD was 30%. We identified five a posteriori dietary patterns (cumulative explained variation [R2] = 20%). The patterns were characterised as: vegetable and fish, red meat and alcohol, traditional, salty snacks and sauces, high fat dairy & refined grains pattern. Adherence to the traditional pattern (i.e. high intake of vegetable oils/stanols, margarines/butters, potatoes, whole grains and sweets/desserts) was associated with regression of NAFLD per SD increase in Z-score (0.40, 95% CI 0.15–1.00). Adherence to the three a priori patterns all showed regression of NAFLD, but only the WHO-score showed a distinct association (0.73, 95% CI 0.53–1.00). Hence, in this large elderly population, adherence to a plant-based, high-fibre and low-fat diet was related to regression of NAFLD

Immunosuppressive drug withdrawal late after liver transplantation improves the lipid profile and reduces infections

BACKGROUND: Treatment with immunosuppressive drugs (IS) after transplantation is accompanied by severe side effects. A limited number of studies have investigated the effect of IS withdrawal on IS-related comorbidities after liver transplantation (LTx) and the results are contradictory. PATIENTS AND METHODS: We determined in a retrospective case-control study the clinical effects of complete IS withdrawal in operationally tolerant (TOL) LTx recipients who discontinued IS 10.8 ± 5.1 years after LTx (n = 13) compared with a completely matched control (CTRL) group with a regular IS regimen (n = 22). TOL recipients have been IS and rejection free for 4.0 ± 2.8 years. RESULTS: IS withdrawal in TOL recipients resulted in lower low-density lipoprotein levels (P = 0.027), whereas this was not observed in the CTRL group. Furthermore, persistent infections in individual recipients were resolved successfully by IS withdrawal. TOL recipients also had significantly fewer de novo infections after IS withdrawal (TOL pre vs. post withdrawal P = 0.0247) compared with recipients continued on IS during the same follow-up period (post withdrawal TOL vs. CTRL P = 0.044). Unfortunately, no improvement in kidney function, and lower rates of de novo occurrences of diabetes, hypertension, cardiovascular diseases, and malignancies were observed in the TOL group after IS withdrawal compared with the CTRL group during the same follow-up time period. CONCLUSION: IS withdrawal late after LTx reduces infection rates and low-density lipoprotein levels, but other IS-related side effects persist late after LTx. An accurate tolerance immune profile enabling identification of tolerant LTx recipients eligible for safe IS withdrawal earlier after transplantation is needed to prevent the development of irreversible IS-related side effects

Beyond the here and now : herbivore ecology in a spatial-temporal context

Ecological phenomena at a certain location often not only depend on the current characteristics of that location itself, but also on characteristics of the landscape surrounding the site or influences from the past. In other words, in order to be able to understand ecological processes here and now, we often need information that is beyond here and now. This thesis investigates the role of such spatial-temporal context on the relationships between species and their environment. The focus is on large mammalian herbivores, an in particular the factors determining the movement and distribution of African elephants (Loxodonta africana) in Kruger National Park (KNP), South Africa. This thesis covers four main themes. First, it is shown that spatial-temporal variation in the biotic and abiotic environment creates predictable seasonal and daily cyclic patterns in the distribution of elephants in KNP. Then, herbivores are shown not only to respond to environmental heterogeneity: they also can create distinct spatial patterning in savanna vegetation when foraging initiates a positive plant-herbivore feedback and when the foraging process is spatially explicit. This leads to specific sites being revisited often, and therefore the patterns of site revisitation by elephants in KNP are studied, mainly in relation to surface water availability and vegetation characteristics. Lastly, this thesis focuses on the scale-dependent response of organisms to environmental heterogeneity, showing the consequences of a mismatch in the scale of analysis on statistical inference, and then focusing on finding the appropriate spatial scales to analyse and predict the spatial distribution of elephants in KNP. Together, the chapters presented in this thesis highlight the importance of explicitly considering the scale and context dependency of species-environment relationships, and demonstrate methods to take issues of spatial-temporal scale and context into account. These methods have the potential to increase our understanding of ecological phenomena and therefore may lead to better management of natural resources

Hibernation site requirements of bats in man-made hibernacula in a spatial context

Bat hibernacula selection depends on various spatial and nonspatial variables that differ widely between sites. However, previous studies have focused mainly on nonspatial variables. This research investigated factors that determined the abundance and species richness of hibernating bats in hibernation objects of the New Dutch Waterline, The Netherlands, and determined the relevant scales over which spatial factors operate using regression techniques and ecological-niche factor analyses. The effects of 32 predictor variables on several response variables, i.e., the total bat abundance, species richness, and abundance and presence of bat species, were investigated. Predictor variables were classified as internal variables (e.g., building size, climatic conditions, and human access) or external variables (e.g., ground and vegetation cover and land cover type) that were measured at different spatial scales to study the influence of the spatial context. The internal building variables (mainly the size of hibernacula and the number of hiding possibilities) affected the hibernating bat abundance and species richness. Climatic variables, such as changes in temperature and humidity, were less important. The hibernation site suitability was also influenced by spatial variables at a variety of scales, thereby indicating the importance of scale- dependent species–environment relationships. The absence of human use and public access enhanced hibernation site suitability, but the internal size-related variables had the greatest positive effect on hibernation site suitability. These results demonstrate the importance of considering the different spatial scales of the surrounding landscape to better understand habitat selection, and they offer directives to managers to optimize objects for hibernating bats and to improve management and bat conservation. The analyses have wider applications to other wildlife–habitat studies

Hibernation site requirements of bats in man-made hibernacula in a spatial context

Bat hibernacula selection depends on various spatial and nonspatial variables that differ widely between sites. However, previous studies have focused mainly on nonspatial variables. This research investigated factors that determined the abundance and species richness of hibernating bats in hibernation objects of the New Dutch Waterline, The Netherlands, and determined the relevant scales over which spatial factors operate using regression techniques and ecological-niche factor analyses. The effects of 32 predictor variables on several response variables, i.e., the total bat abundance, species richness, and abundance and presence of bat species, were investigated. Predictor variables were classified as internal variables (e.g., building size, climatic conditions, and human access) or external variables (e.g., ground and vegetation cover and land cover type) that were measured at different spatial scales to study the influence of the spatial context. The internal building variables (mainly the size of hibernacula and the number of hiding possibilities) affected the hibernating bat abundance and species richness. Climatic variables, such as changes in temperature and humidity, were less important. The hibernation site suitability was also influenced by spatial variables at a variety of scales, thereby indicating the importance of scale- dependent species–environment relationships. The absence of human use and public access enhanced hibernation site suitability, but the internal size-related variables had the greatest positive effect on hibernation site suitability. These results demonstrate the importance of considering the different spatial scales of the surrounding landscape to better understand habitat selection, and they offer directives to managers to optimize objects for hibernating bats and to improve management and bat conservation. The analyses have wider applications to other wildlife–habitat studies