Quickscan Contraceptie Hoefdieren
Lammertsma, D.R. ; Jansman, H.A.H. - \ 2016
Wageningen : Alterra, Wageningen-UR (Alterra-notitie ) - 18
dierenwelzijn - wilde dieren - grote grazers - hoefdieren - huisvesting, dieren - diergezondheid - dierethiek - animal welfare - wild animals - large herbivores - ungulates - animal housing - animal health - animal ethics
Establishing the link between habitat-selection and animal population dynamics
Matthiopoulos, J. ; Fieberg, J. ; Aarts, G.M. ; Beyer, H.L. ; Morales, J.M. ; Haydon, D.T. - \ 2015
Ecological Monographs 85 (2015)3. - ISSN 0012-9615 - p. 413 - 436.
species distribution models - point process models - resource selection - functional-responses - growth rate - large herbivores - climate-change - niche breadth - fitness - ecology
Although classical ecological theory (e.g., on ideal free consumers) recognizes the potential effect of population density on the spatial distribution of animals, empirical species distribution models assume that species–habitat relationships remain unchanged across a range of population sizes. Conversely, even though ecological models and experiments have demonstrated the importance of spatial heterogeneity for the rate of population change, we still have no practical method for making the connection between the makeup of real environments, the expected distribution and fitness of their occupants, and the long-term implications of fitness for population growth. Here, we synthesize several conceptual advances into a mathematical framework using a measure of fitness to link habitat availability/selection to (density-dependent) population growth in mobile animal species. A key feature of this approach is that it distinguishes between apparent habitat suitability and the true, underlying contribution of a habitat to fitness, allowing the statistical coefficients of both to be estimated from multiple observation instances of the species in different environments and stages of numerical growth. Hence, it leverages data from both historical population time series and snapshots of species distribution to predict population performance under environmental change. We propose this framework as a foundation for building more realistic connections between a population's use of space and its subsequent dynamics (and hence a contribution to the ongoing efforts to estimate a species' critical habitat and fundamental niche). We therefore detail its associated definitions and simplifying assumptions, because they point to the framework's future extensions. We show how the model can be fit to data on species distributions and population dynamics, using standard statistical methods, and we illustrate its application with an individual-based simulation. When contrasted with nonspatial population models, our approach is better at fitting and predicting population growth rates and carrying capacities. Our approach can be generalized to include a diverse range of biological considerations. We discuss these possible extensions and applications to real data.
Deriving animal behaviour from high-frequency GPS: tracking cows in open and forested habitat
Weerd, N. de; Langevelde, F. van; Oeveren, H. van; Nolet, B.A. ; Kölzsch, A. ; Prins, H.H.T. ; Boer, W.F. de - \ 2015
PLoS ONE 10 (2015)6. - ISSN 1932-6203 - 17 p.
collar performance - large herbivores - telemetry data - movement - cattle - ecology - states - technology - selection - position
The increasing spatiotemporal accuracy of Global Navigation Satellite Systems (GNSS) tracking systems opens the possibility to infer animal behaviour from tracking data.We studied the relationship between high-frequency GNSS data and behaviour, aimed at developing an easily interpretable classification method to infer behaviour from location data. Behavioural observations were carried out during tracking of cows (Bos Taurus) fitted with high-frequency GPS (Global Positioning System) receivers. Data were obtained in an open field and forested area, and movement metrics were calculated for 1 min, 12 s and 2 s intervals. We observed four behaviour types (Foraging, Lying, Standing and Walking). We subsequently used Classification and Regression Trees to classify the simultaneously obtained GPS data as these behaviour types, based on distances and turning angles between fixes. GPS data with a 1 min interval from the open field was classified correctly for more than 70% of the samples. Data from the 12 s and 2 s interval could not be classified successfully, emphasizing that the interval should be long enough for the behaviour to be defined by its characteristic movement metrics. Data obtained in the forested area were classified with a lower accuracy (57%) than the data from the open field, due to a larger positional error of GPS locations and differences in behavioural performance influenced by the habitat type. This demonstrates the importance of understanding the relationship between behaviour and movement metrics, derived from GNSS fixes at different frequencies and in different habitats, in order to successfully infer behaviour. When spatially accurate location data can be obtained, behaviour can be inferred from high-frequency GNSS fixes by calculating simple movement metrics and using easily interpretable decision trees. This allows for the combined study of animal behaviour and habitat use based on location data, and might make it possible to detect deviations in behaviour at the individual level.
Do Arctic breeding geese track or overtake a green wave during spring migration?
Si, Y. ; Xin, Q. ; Boer, W.F. de; Gong, P. ; Ydenberg, R.C. ; Prins, H.H.T. - \ 2015
Scientific Reports 5 (2015). - ISSN 2045-2322
goose branta-leucopsis - russian barnacle geese - anser-brachyrhynchus - time-series - brent geese - large herbivores - forage quality - bird migration - decision - bernicla
Geese breeding in the Arctic have to do so in a short time-window while having sufficient body reserves. Hence, arrival time and body condition upon arrival largely influence breeding success. The green wave hypothesis posits that geese track a successively delayed spring flush of plant development on the way to their breeding sites. The green wave has been interpreted as representing either the onset of spring or the peak in nutrient biomass. However, geese tend to adopt a partial capital breeding strategy and might overtake the green wave to accomplish a timely arrival on the breeding site. To test the green wave hypothesis, we link the satellite-derived onset of spring and peak in nutrient biomass with the stopover schedule of individual Barnacle Geese. We find that geese track neither the onset of spring nor the peak in nutrient biomass. Rather, they arrive at the southernmost stopover site around the peak in nutrient biomass, and gradually overtake the green wave to match their arrival at the breeding site with the local onset of spring, thereby ensuring gosling benefit from the peak in nutrient biomass. Our approach for estimating plant development stages is critical in testing the migration strategies of migratory herbivores.
Modeling elephant-mediated cascading effects of water point closure
Hilbers, J.P. ; Langevelde, F. van; Prins, H.H.T. ; Grant, C.C. ; Peel, M. ; Coughenour, M.B. ; Knegt, H.J. de; Slotow, R. ; Smit, I. ; Kiker, G.A. ; Boer, W.F. de - \ 2015
Ecological Applications 25 (2015)2. - ISSN 1051-0761 - p. 402 - 415.
kruger-national-park - african savanna - south-africa - distribution patterns - wildlife management - sexual segregation - large herbivores - habitat use - landscape - systems
Wildlife management to reduce the impact of wildlife on their habitat can be done in several ways, among which removing animals (by either culling or translocation) is most often used. There are however alternative ways to control wildlife densities, such as opening or closing water points. The effects of these alternatives are poorly studied. In this paper, we focus on manipulating large herbivores through the closure of water points (WPs). Removal of artificial WPs has been suggested to change the distribution of African elephants, which occur in high densities in national parks in Southern Africa and are thought to have a destructive effect on the vegetation. Here, we modeled the long-term effects of different scenarios of WP closure on the spatial distribution of elephants, and consequential effects on the vegetation and other herbivores in Kruger National Park, South Africa. Using a dynamic ecosystem model, SAVANNA, scenarios were evaluated that varied in (1) availability of artificial WPs, (2) levels of natural water, and (3) elephant densities. Our modeling results showed that elephants can indirectly negatively affect the distributions of mesomixed feeders, mesobrowsers and some mesograzers under wet conditions. The closure of artificial WPs hardly had any effect during these natural wet conditions. Only under dry conditions the spatial distribution of both elephant bulls and cows changed when the availability of artificial water was severely reduced in the model. These changes in spatial distribution triggered changes in the spatial availability of woody biomass over the simulation period of 80 years and this led to changes in the rest of the herbivore community, resulting in increased densities of all herbivores, except for giraffe and steenbok, in areas close to rivers. The spatial distributions of elephant bulls and cows showed to be less affected by the closure of WPs than most of the other herbivore species. Our study contributes to ecologically informed decisions in wildlife management. The results from this modeling exercise imply that long-term effects of this intervention strategy should always be investigated at an ecosystem scale.
Short-term effect of nutrient availability and rainfall distribution on biomass production and leaf nutrient content of savanna tree species
Barbosa, E.R. ; Tomlinson, K.W. ; Carvalheiro, L.G. ; Kirkman, K. ; Bie, S. de; Prins, H.H.T. ; Langevelde, F. van - \ 2014
PLoS ONE 9 (2014)3. - ISSN 1932-6203 - 9 p.
semiarid savannas - mineral-nutrition - african savannas - large herbivores - nitrogen - plants - carbon - fire - phosphorus - responses
Changes in land use may lead to increased soil nutrient levels in many ecosystems (e.g. due to intensification of agricultural fertilizer use). Plant species differ widely in their response to differences in soil nutrients, and for savannas it is uncertain how this nutrient enrichment will affect plant community dynamics. We set up a large controlled short-term experiment in a semi-arid savanna to test how water supply (even water supply vs. natural rainfall) and nutrient availability (no fertilisation vs. fertilisation) affects seedlings’ above-ground biomass production and leaf-nutrient concentrations (N, P and K) of broadleafed and fine-leafed tree species. Contrary to expectations, neither changes in water supply nor changes in soil nutrient level affected biomass production of the studied species. By contrast, leaf-nutrient concentration did change significantly. Under regular water supply, soil nutrient addition increased the leaf phosphorus concentration of both fine-leafed and broad-leafed species. However, under uneven water supply, leaf nitrogen and phosphorus concentration declined with soil nutrient supply, this effect being more accentuated in broad-leafed species. Leaf potassium concentration of broad-leafed species was lower when growing under constant water supply, especially when no NPK fertilizer was applied. We found that changes in environmental factors can affect leaf quality, indicating a potential interactive effect between land-use changes and environmental changes on savanna vegetation: under more uneven rainfall patterns within the growing season, leaf quality of tree seedlings for a number of species can change as a response to changes in nutrient levels, even if overall plant biomass does not change. Such changes might affect herbivore pressure on trees and thus savanna plant community dynamics. Although longer term experiments would be essential to test such potential effects of eutrophication via changes in leaf nutrient concentration, our findings provide important insights that can help guide management plans that aim to preserve savanna biodiversity.
Uit de wetenschap : hoe tel je wilde hoefdieren?
Groot Bruinderink, G.W.T.A. ; Dekker, J. ; Cornelissen, P. - \ 2013
Vakblad Natuur Bos Landschap 10 (2013)3. - ISSN 1572-7610 - p. 14 - 16.
wildbeheer - grote grazers - herbivoren - natuurgebieden - monitoring - populatiedichtheid - zuidelijk flevoland - wildlife management - large herbivores - herbivores - natural areas - monitoring - population density - zuidelijk flevoland
Tellen van wilde hoefdieren wordt steeds belangrijker, onder andere vanwege eventuele beperking van de wildstand. Maar hoe moeten herbivoren geteld worden om een goed beeld te krijgen van de aantallen? Begrippen als precisie (herhaling van tellingen), nauwkeurigheid (geschatte waarneming t.o.v. werkelijkheid) en betrouwbaarheid (systematische fouten)
|Kleine bosmieren versus grote grazers
Mabelis, A.A. ; Houwelingen, V. van - \ 2012
Holland's Duinen 2012 (2012)60. - ISSN 1389-7373 - p. 35 - 41.
duingebieden - fauna - formicidae - begrazing - nadelige gevolgen - grote grazers - spreiding - zuid-holland - duneland - grazing - adverse effects - large herbivores - spread
Hollands duinen bezitten geschikt leefgebied voor bosmieren, vooral op plaatsen waar een eikenberkenbos tot ontwikkeling is gekomen, zoals in de vallei Bierlap in de duinen bij Den Haag. In dit bos hebben veel studenten tijdens de jaarlijkse cursus ecologie onderzoek verricht naar de relatie tussen bosmieren en andere soorten die in het duin leven. Daartoe werden soms dagen achtereen mieren geteld die naar en van een mierennest liepen, al of niet met een prooi in hun kaken. De laatste tien jaar is echter het aantal bosmieren teruggelopen. Getracht is de vraag te beantwoorden of dit een gevolg kan zijn van introductie van grote grazers (koeien en paarden) in het duingebied
Stikstofoverschot door bijvoeren van grazers
Wamelink, G.W.W. ; Klimkowska, A. ; Dobben, H.F. van; Slim, P.A. ; Til, M. van - \ 2012
Vakblad Natuur Bos Landschap 9 (2012)7. - ISSN 1572-7610 - p. 14 - 17.
duingebieden - grote grazers - depositie - emissie - stikstof - habitats - begrazingsbeheer - bijvoeding - noord-holland - duneland - large herbivores - deposition - emission - nitrogen - habitats - grazing management - supplementary feeding - noord-holland
In de Amsterdamse Waterleidingduinen wordt verruiging bestreden door het inscharen van runderen. Het bijvoeren van het vee in de winter zorgt voor een extra input van stikstof boven op de aanwezige atmosferische depositie. Het bijvoeren kan daardoor leiden tot een (verdere) overschrijding van de kritische depositie voor enkele gevoelige habitattypen zoals de grijze duinen.
Ecologische effecten van het ontwormingsmiddel ivermectine
Lahr, J. ; Kats, R.J.M. van; Hout, A. van der; Lammertsma, D.R. ; Werf, D.C. van der; Zweers, A.J. ; Siepel, A. - \ 2011
Vakblad Natuur Bos Landschap 8 (2011)10. - ISSN 1572-7610 - p. 28 - 31.
paarden - excreten - veterinaire producten - wormen - ziektebestrijding - bodembiologie - grote grazers - natuurgebieden - ecosystemen - horses - excreta - veterinary products - helminths - disease control - soil biology - large herbivores - natural areas - ecosystems
Het is inmiddels een bekend feit dat ontwormingsmiddelen die aan vee worden gegeven, giftig kunnen zijn voor de mestfauna, de insecten die zich met mest voeden en er hun eieren in leggen. Het verdwijnen van bepaalde soorten mestfauna kan er in bepaalde gevallen toe leiden dat de afbraak van mest in het veld vertraagd wordt, zo blijkt uit buitenlandse studies. Enquêtes wezen eerder uit dat ontwormingsmiddelen in veel Nederlandse natuurgebieden worden toegediend aan grote grazers. Komen dit soort ecologische effecten dus ook in onze natuurgebieden voor? Dit is de afgelopen jaren door Alterra onderzocht in opdracht van het ministerie van EL&I.
Soil nutrient status determines how elephant utilize trees and shape environments
Pretorius, Y. ; Boer, W.F. de; Waal, C. van der; Knegt, H.J. de; Grant, R.C. ; Knox, N. ; Kohi, E. ; Mwakiwa, E. ; Page, B.R. ; Peel, M.J.S. ; Skidmore, A.K. ; Slotow, R. ; Wieren, S.E. van; Prins, H.H.T. - \ 2011
Journal of Animal Ecology 80 (2011)4. - ISSN 0021-8790 - p. 875 - 883.
large herbivores - national-park - habitat selection - african savannas - woody vegetation - patch structure - forage quality - food quality - south-africa - east-africa
Elucidation of the mechanism determining the spatial scale of patch selection by herbivores has been complicated by the way in which resource availability at a specific scale is measured and by vigilance behaviour of the herbivores themselves. To reduce these complications, we studied patch selection by an animal with negligible predation risk, the African elephant. We introduce the concept of nutrient load as the product of patch size, number of patches and local patch nutrient concentration. Nutrient load provides a novel spatially explicit expression of the total available nutrients a herbivore can select from. We hypothesized that elephant would select nutrient-rich patches, based on the nutrient load per 2500m2 down to the individual plant scale, and that this selection will depend on the nitrogen and phosphorous contents of plants. We predicted that elephant would cause more adverse impact to trees of lower value to them in order to reach plant parts with higher nutrient concentrations such as bark and root. However, elephant should maintain nutrient-rich trees by inducing coppicing of trees through re-utilization of leaves. 5.Elephant patch selection was measured in a homogenous tree species stand by manipulating the spatial distribution of soil nutrients in a large field experiment using NPK fertilizer. Elephant were able to select nutrient-rich patches and utilized Colophospermum mopane trees inside these patches more than outside, at scales ranging from 2500 down to 100m2. Although both nitrogen and phosphorus contents of leaves from C. mopane trees were higher in fertilized and selected patches, patch choice correlated most strongly with nitrogen content. As predicted, stripping of leaves occurred more in nutrient-rich patches, while adverse impact such as uprooting of trees occurred more in nutrient-poor areas. Our results emphasize the necessity of including scale-dependent selectivity in foraging studies and how elephant foraging behaviour can be used as indicators of change in the availability of nutrients.
The spatial scaling of habitat selection by African elephants
Knegt, H.J. de; Langevelde, F. van; Skidmore, A.K. ; Delsink, A. ; Slotow, R. ; Henley, S. ; Bucini, G. ; Boer, W.F. de; Coughenour, M.B. ; Grant, C.C. ; Heitkonig, I.M.A. ; Henley, M. ; Knox, N. ; Kohi, E. ; Mwakiwa, E. ; Page, B.R. ; Peel, M. ; Pretorius, Y. ; Wieren, S.E. van; Prins, H.H.T. - \ 2011
Journal of Animal Ecology 80 (2011)1. - ISSN 0021-8790 - p. 270 - 281.
niche factor-analysis - ecological-niche - national-park - large herbivores - landscape - movement - patterns - heterogeneity - distributions - availability
1. Understanding and accurately predicting the spatial patterns of habitat use by organisms is important for ecological research, biodiversity conservation and ecosystem management. However, this understanding is complicated by the effects of spatial scale, because the scale of analysis affects the quantification of species–environment relationships. 2. We therefore assessed the influence of environmental context (i.e. the characteristics of the landscape surrounding a site), varied over a large range of scales (i.e. ambit radii around focal sites), on the analysis and prediction of habitat selection by African elephants in Kruger National Park, South Africa. 3. We focused on the spatial scaling of the elephants’ response to their main resources, forage and water, and found that the quantification of habitat selection strongly depended on the scales at which environmental context was considered. Moreover, the inclusion of environmental context at characteristic scales (i.e. those at which habitat selectivity was maximized) increased the predictive capacity of habitat suitability models. 4. The elephants responded to their environment in a scale-dependent and perhaps hierarchical manner, with forage characteristics driving habitat selection at coarse spatial scales, and surface water at fine spatial scales. 5. Furthermore, the elephants exhibited sexual habitat segregation, mainly in relation to vegetation characteristics. Male elephants preferred areas with high tree cover and low herbaceous biomass, whereas this pattern was reversed for female elephants. 6. We show that the spatial distribution of elephants can be better understood and predicted when scale-dependent species–environment relationships are explicitly considered. This demonstrates the importance of considering the influence of spatial scale on the analysis of spatial patterning in ecological phenomena.
Migration Patterns of Two Endangered Sympatric Species from a Remote Sensing Perspective
Wang, T. ; Skidmore, A.K. ; Zeng, Z. ; Beck, P.S.A. ; Si, Y. ; Song, Y. ; Liu, X. ; Prins, H.H.T. - \ 2010
Photogrammetric Engineering and Remote Sensing 76 (2010)12. - ISSN 0099-1112 - p. 1343 - 1352.
foping-nature-reserve - vegetation dynamics - plant phenology - giant panda - altitudinal movements - large herbivores - forage quality - high-latitudes - golden takin - home-range
Giant pandas (Ailitropoda melanoleuca) and golden takin (Budorcas taxicolor bedfordi) are large mammals that occur together throughout the southern part of the Qin ling Mountains in China. Both species have the habit of altitudinal migration in a mixed forest-bamboo landscape. Although previous studies have reported that the migration patterns of giant pandas and golden takin seem different, little is known about these differences in relation to their food quality and quantity. We used radio-telemetry data from six giant pandas and three golden takin groups to determine whether differences in their migration patterns are related to satellite-derived plant phenology (a surrogate of food quality) and bamboo abundance (a surrogate of food quantity). Our results suggest that the altitudinal migration patterns of both the giant panda and the golden takin follow the phenological development of plants in the study area, and the difference between them seems to be attributable to the difference in the phenology of bamboo and non-bamboo plants, and thus the abundance and quality of food available to these two species.
Enhanced use of beneath-canopy vegetation by grazing ungulates in African savannahs
Treydte, A.C. ; Riginos, C. ; Jeltsch, F. - \ 2010
Journal of Arid Environments 74 (2010)12. - ISSN 0140-1963 - p. 1597 - 1603.
kruger-national-park - large herbivores - forage quality - large trees - habitat use - grass - cattle - productivity - nutrients - tanzania
The cover of large trees in African savannahs is rapidly declining, mainly due to human land-use practices. Trees improve grass nutrient quality and contribute to species and structural diversity of savannah vegetation. However, the response of herbivores to trees as habitat features is unknown. We quantified the habitat use of wild and domestic ungulates in two eastern and southern African savannahs. We assessed grazing intensities and quantified dung depositions beneath and around canopies of different sized trees. Grasses were eaten and dung was deposited twice as frequently beneath large (ca. 5 m in height) and very large trees (7-10 m) than in open grasslands. Small trees (
Allometric scaling of resource acquisition by ruminants in dynamic and heterogeneous environments
Kramer, K. ; Prins, H.H.T. - \ 2010
Ecological Modelling 221 (2010). - ISSN 0304-3800 - p. 2555 - 2564.
functional-response - large herbivores - mammalian herbivores - competitive interactions - population-dynamics - foraging behavior - grazing ruminants - body-size - model - ecology
We present a mechanistic formulation of the intake response of ruminants to vegetation biomass based solely on physiological and morphological parameters that scale allometrically with the animal's body mass. The model is applied to describe herbivore–vegetation interactions in dynamic and heterogeneous landscapes with low quality but abundant “tall grass” and high quality but sparsely available “short grass”, under two conditions: “uncoupled” (such that the effect of food intake on vegetation biomass can be neglected), or “coupled” (such that the vegetation biomass is determined by herbivore feeding). The results show that under uncoupled conditions, the minimum acceptance (proportion of vegetation consumed by the herbivore) at which the herbivore can leave its current patch without reducing its intake rate is when it has depleted the current patch by the energetic cost required to travel to another patch. The maximum acceptance at which the herbivore should leave its patch is when it has depleted the current patch by the cumulative energetic cost of traveling, handling, cropping, and digesting. Under coupled conditions, the optimal acceptance equals half the relative growth rate of the vegetation. Analytical solutions are obtained for equilibrium values for utilization of the vegetation, and for the densities of vegetation and ruminants, expressed in physiological and morphological herbivore parameters.
Ecologische risico's van doorvergiftiging door cadmium in het Dommeldal : ruimtelijke modellering voor de steenuil en grote grazers met het BERISP-model
Lahr, J. ; Jacobs, T. ; Heidema, A.H. ; Winter, W.P. de; Brink, N.W. van den - \ 2010
Wageningen : Alterra (Alterra-rapport 2019)
bodemverontreiniging - cadmium - overstromingen - strigidae - uilen - voedselketens - ecotoxicologie - beekdalen - bodemecologie - grote grazers - noord-brabant - soil pollution - cadmium - floods - strigidae - owls - food chains - ecotoxicology - brook valleys - soil ecology - large herbivores - noord-brabant
In het overstromingsgebied van de Dommel ten zuiden van Eindhoven is in het verleden vastgesteld dat er een doorvergiftigingsrisico van cadmium via de voedselketen van de steenuil bestaat. Om een indruk te krijgen van deze problematiek op gebiedsniveau is een studie uitgevoerd naar de ruimtelijke risico’s van doorvergiftiging voor steenuilen en groter grazers aan de hand van het model BERISP. De modelberekeningen wijzen uit dat de huidige risico’s voor steenuilen in het gebied (situatie 2003) groot zijn. De risico’s treden vooral op in habitats waar de uilen veel op gecontamineerde wormen foerageren, zowel in het overstromingsgebied als op bouwland en weilanden hierbuiten. Realisatie van het Natuurgebiedsplan (NGP 2006) zal vooral binnen het overstromingsgebied zelf leiden tot een afname van de risico’s doordat men habitats laat ontstaan waar uilen op minder verontreinigde woelmuizen foerageren, met name door verruiging.
Tree cover and biomass increase in a southern African savanna despite growing elephant population
Kalwij, J.M. ; Boer, W.F. de; Mucina, L. ; Prins, H.H.T. ; Skarpe, C. ; Winterbach, C. - \ 2010
Ecological Applications 20 (2010)1. - ISSN 1051-0761 - p. 222 - 233.
kruger-national-park - northern botswana - sexual segregation - large herbivores - watering points - colophospermum-mopane - mammalian herbivores - woody vegetation - fire - woodlands
The growing elephant populations in many parts of southern Africa raise concerns of a detrimental loss of trees, resulting in overall reduction of biodiversity and ecosystem functioning. Elephant distribution and density can be steered through artificial waterpoints (AWPs). However, this leaves resident vegetation no relief during dry seasons. We studied how the introduction of eight AWPs in 1996 affected the spatiotemporal tree-structure dynamics in central Chobe National Park, an unfenced savanna area in northern Botswana with a dry-season elephant density of ~3.34 individuals per square kilometer. We hypothesized that the impact of these AWPs amplified over time and expanded in space, resulting in a decrease in average tree density, tree height, and canopy volume. We measured height and canopy dimensions of all woody plants around eight artificial and two seasonal waterpoints for 172 plots in 1997, 2000, and 2008. Plots, consisting of 50 × 2 m transects for small trees (0.20–3.00 m tall) nested within 50 × 20 m transects for large trees (=3.0 m tall), were located at 100, 500, 1000, 2000, and 5000 m distance classes. A repeated-measures mixed-effect model showed that tree density, cover, and volume had increased over time throughout the area, caused by a combination of an increase of trees in lower size classes and a decrease in larger size classes. Our results indicate that the decrease of large trees can be attributed to a growing elephant population. Decrease or loss of particular tree size classes may have been caused by a loss of browser-preferred species while facilitating the competitiveness of less-preferred species. In spite of 12 years of artificial water supply and an annual elephant population growth of 6%, we found no evidence that the eight AWPs had a negative effect on tree biomass or tree structure. The decreasing large-tree component could be a remainder of a depleted but currently restoring elephant population
Potential of endozoochorous seed dispersal by sheep in calcareous grasslands: correlations with seed traits.
Kuiters, A.T. ; Huiskes, H.P.J. - \ 2010
Applied Vegetation Science 13 (2010)2. - ISSN 1402-2001 - p. 163 - 172.
vascular plants - cattle dung - species richness - large herbivores - establishment - restoration - landscape - impact - communities - migration
Questions: What is the potential of sheep to serve as seed dispersers via ingestion and defecation in calcareous grasslands? Is the presence of viable seeds from dung correlated with specific seed traits? Location: Calcareous grasslands, South Limburg, the Netherlands/Belgium. Methods: Dung samples (n=24) from sheep were collected between September 2006 and November 2007 from five sites with Mesobromion plant communities, and communities of Nardo-Galion saxatilis. Germinability and identity of seeds in the dung samples were ascertained from germination of seedlings under glasshouse conditions. Seed traits of species with viable seeds in dung were compared with those present in the local species pool. Results: Seventy-two plant species from 23 plant families had viable seeds in sheep dung. The plant families encountered most frequently were Gramineae and Compositae. The most abundant and frequently recorded plant species in dung samples was Urtica dioica, accounting for >80% of the total number of seeds. Mean seed density in sheep dung was 0.8 seeds g-1 dry matter. Seeds with low seed mass and a high seed longevity index were over-represented in dung. Viable seeds >2.5 mg were infrequent in the dung samples. Conclusions: We conclude that sheep are potentially important dispersers of plant species in Dutch calcareous grasslands. Although smaller seeds were relatively abundant in sheep dung, it cannot be excluded that this was mainly caused by differences in seed abundance.
Herstel van hellingschraallanden : verslag veldwerkplaats Heuvelland, Gulpen, 30 september 2009
Smits, N.A.C. ; Noordwijk, T. van; Kloet, P. - \ 2009
Gulpen : s.n. - 6
graslanden - hellingen - begrazing - natuurbeheer - natuurgebieden - grote grazers - grasslands - slopes - grazing - nature management - natural areas - large herbivores
Het gaat niet goed met de schaarse reservaten van hellingschraallanden. Al sinds de jaren tachtig wordt geprobeerd om deze unieke ecosystemen te herstellen, maar tot op heden met een tegenvallend resultaat. Onder leiding van het deskundigenteam Heuvelland is van 2004-2008 onderzoek gedaan naar de oorzaken van achteruitgang en de mogelijkheden voor herstel, met de nadruk op de mogelijke beheerstrategieën voor zowel de flora als de fauna. Tijdens deze veldwerkplaats presenteerden twee onderzoekers de resultaten van dit onderzoek en vertelde beheerder Patrick Kloet van Staatsbosbeheer over de pilot gescheperde beweiding.
How resource competition shapes individual life history for nonplastic growth: ungulates in seasonal food environments
Roos, A. de; Galic, N.G. ; Heesterbeek, H. - \ 2009
Ecology 90 (2009)4. - ISSN 0012-9658 - p. 945 - 960.
structured population-models - body-mass - red deer - large herbivores - winter weather - wild reindeer - moose calves - bottom-up - top-down - dynamics
We analyze an age-, size- and sex-structured model to investigate how the interplay between individual-level energy budget dynamics and the feedback of population grazing on resources shapes the individual life history and the dynamics of ungulate populations, living in a predator-free, seasonal resource environment. We formulate a dynamic energy budget model for individual energetics, which accounts for energy requirements for maintenance and growth, and possibly pregnancy and lactation. Growth in structural mass is assumed prescribed. Dynamics of energy reserves are the resultant of energy acquisition through grazing and suckling of milk and the aforementioned energyconsuming processes. The dynamic energy budget model is used as the core for an individualbased population model, which captures general features of ungulate life history and population dynamics, although it is parameterized for a particular system. Model predictions reveal a characteristic dynamic pattern, in which years with low death tolls (,10% of the population dying) alternate with a single year of high death toll (up to 40% of the population dies). In these ‘‘collapse’’ years almost all individuals younger than 2 years die, creating holes in the population age distribution. The die-off of these age classes is shown to be caused by the energy requirements for growth that these individuals face. Individuals between 1 and 2 years of age are more at risk than foals, because they are burdened with the legacy of a poor body condition developed throughout their first winter. The characteristic dynamic pattern is more pronounced at high levels of resource productivity. In contrast, neither a period of snow cover, during which all foraging stops, nor a dependence of fecundity on female body condition change dynamics significantly.