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.
Rainfall and temperature affect tree species distributions in Ghana
Amissah, L. ; Mohren, G.M.J. ; Bongers, F. ; Hawthorne, W.D. ; Poorter, L. - \ 2014
Journal of Tropical Ecology 30 (2014)5. - ISSN 0266-4674 - p. 435 - 446.
tropical forest trees - response curves - environmental gradients - distribution patterns - logistic-regression - continuum theory - soil nutrients - amazon forest - drought - growth
We evaluated the relative importance of annual rainfall, temperature and their seasonality to tree species distribution in Ghana. We used species presence/absence data from 2505 1-ha plots systematically distributed over Ghana's forests. Logistic regression was used to determine species responses to four climatic variables generated from the Worldclim database. The distribution of 95% of 20 species was significantly associated with annual rainfall, 60% with rainfall seasonality, 45% with isothermality and 40% with temperature seasonality. Annual rainfall explained on average most of the variation (17%, range = 0.5–52%) in species distribution, followed by rainfall seasonality 5% (range = 0.5–27%), isothermality 4% (range = 0.8–24%) and temperature seasonality 1% (range = 0.4–4.5%). Our results suggest that, out of the climatic variables investigated, rainfall is the main factor determining tree species distribution in Ghana; temperature also influences the distribution of a number of species, although it explains much less of the variation. The reduction in annual rainfall that prevailing climate-change scenarios predict for the region will result in a shift in the distribution of most species, whereas the predicted increase in temperature variation is likely to have little effect.
Sapling performance along resource gradients drives tree species distributions within and across tropical forests
Sterck, F.J. ; Markesteijn, L. ; Toledo, M. ; Schieving, F. ; Poorter, L. - \ 2014
Ecology 95 (2014)9. - ISSN 0012-9658 - p. 2514 - 2525.
dry forest - shade-tolerance - functional traits - distribution patterns - light requirements - global convergence - community ecology - xylem cavitation - woody-plants - life-history
Niche differentiation is a major hypothesized determinant of species distributions, but its practical importance is heavily debated and its underlying mechanisms are poorly understood. Trait-based approaches have been used to infer niche differentiation and predict species distributions. For understanding underlying mechanisms, individual traits should be scaled up to whole-plant performance, which has rarely been done. We measured seven key traits that are important for carbon and water balance for 37 tropical tree species. We used a process-based plant physiological model to simulate the carbon budget of saplings along gradients of light and water availability, and quantified the performance of the species in terms of their light compensation points (a proxy for shade tolerance), water compensation points (proxy for drought tolerance), and maximum carbon gain rates (proxy for potential growth rate). We linked species performances to their observed distributions (the realized niches) at two spatial scales in Bolivian lowland forests: along a canopy openness gradient at local scale (~1 km2) and along a rainfall gradient (1100–2200 mm/yr) at regional (~1000 km) scale. We show that the water compensation point was the best predictor of species distributions along water and light resource gradients within and across tropical forests. A sensitivity analysis suggests that the stomatal regulation of minimum leaf water potentials, rather than stem hydraulic traits (sapwood area and specific conductivity), contributed to the species differences in the water compensation point of saplings. The light compensation point and maximum carbon gain, both driven by leaf area index and leaf nitrogen concentration, also contributed to differential species distributions at the local scale, but not or only marginally at the regional scale. Trait-and-physiology-based simulations of whole-plant performance thus help to evaluate the possible roles of individual traits in physiological processes underlying species performance along environmental gradients. The development of such whole-plant concepts will improve our ability to understand responses of plant communities to shifts in resource availability and stress under global change.
Forage patch use by grazing herbivores in a South African grazing ecosystem
Venter, J.A. ; Nabe-Nielsen, J. ; Prins, H.H.T. ; Slotow, R. - \ 2014
Acta Theriologica 59 (2014)3. - ISSN 0001-7051 - p. 457 - 466.
predation risk - heterogeneous pastures - antipredator response - distribution patterns - behavioral-responses - habitat selection - seed dispersal - burned patches - wolf predation - elk
Understanding how different herbivores make forage patch use choices explains how they maintain an adequate nutritional status, which is important for effective conservation management of grazing ecosystems. Using telemetry data, we investigated nonruminant zebra (Equus burchelli) and ruminant red hartebeest (Alcelaphus buselaphus subspecies camaa), use of burnt patches in a landscape mosaic of nutrient-poor, old grassland interspersed with young, recently burnt, nutrient-rich grass patches. The Mkambati Nature Reserve landscape on the east coast of South Africa provided large grazers with a challenge in finding and using appropriate patches in which to forage to meet their nutritional requirements. In Mkambati, grassland fires, mostly ignited by poachers, induce regrowth of young nutrient-rich grass, which subsequently attract grazers. We tested if the study animals foraged more in burnt patches than in the unburned grassland and whether burnt patch use was related to the distance to the previously visited burnt patch, burnt patch size, burnt patch age, and distance to areas with high poaching risk using MANOVA. In general, zebra moved faster than red hartebeest, and both species moved faster in unburnt grassland than in burnt patches. Red hartebeest and zebra patch selection were influenced by interpatch distance, patch age, patch size, and poaching risk. A limited set of intrinsic traits, i.e., body mass, digestion strategy, and muzzle width, yielded different patch use rules for the two species. Large ungulates patch use behaviour varied among species and across conditions and was influenced by anthropogenic impacts such as poaching and changed fire regimes. This could potentially affect biodiversity negatively and needs to be factored into management of conservation areas.
Reconstructing grazer assemblages for protected area restoration
Venter, J.A. ; Prins, H.H.T. ; Slotow, R. - \ 2014
PLoS ONE 9 (2014)3. - ISSN 1932-6203 - 10 p.
south-african savanna - middle stone-age - conservation management - distribution patterns - foraging behavior - landscape-scale - herbivore - fire - heterogeneity - biodiversity
Protected area management agencies often struggle to reliably reconstruct grazer assemblages due to a lack of historical distribution data for their regions. Wrong predictions of grazing assemblages could potentially affect biodiversity negatively. The objective of the study was to determine how well grazing herbivores have become established since introduction to the Mkambati Nature Reserve, South Africa, how this was influenced by facilitation and competition, and how indigenous grazer assemblages can best be predicted for effective ecological restoration. Population trends of several grazing species were investigated in in order to determine how well they have become established since introduction. Five different conceivable grazing assemblages reflecting a range of approaches that are commonly encountered during conservation planning and management decision making were assessed. Species packing was used to predict whether facilitation, competition or co-existence were more likely to occur, and the species packing of the different assemblages were assessed using ANCOVA. Reconstructing a species assemblage using biogeographic and biological information provides the opportunity for a grazer assemblage that allows for facilitatory effects, which in turn leads to an ecosystem that is able to maintain its grazer assemblage structure. The strength of this approach lies in the ability to overcome the problem of depauperate grazer assemblages, resulting from a lack of historical data, by using biogeographical and biological processes, to assist in more effectively reconstructing grazer assemblages. Adaptive management of grazer assemblage restoration through reintroduction, using this approach would further mitigate management risks.
The impact of large herbivores on woodland–grassland dynamics in fragmented landscapes: The role of spatial configuration and disturbance
Schippers, P. ; Teeffelen, A.J.A. van; Verboom-Vasiljev, J. ; Vos, C.C. ; Kramer, K. ; Wallis de Vries, M.F. - \ 2014
Ecological Complexity 17 (2014). - ISSN 1476-945X - p. 20 - 31.
north temperate forests - red deer - population-dynamics - metapopulation dynamics - habitat fragmentation - distribution patterns - grazing systems - management - regeneration - resilience
The vegetation structure of natural ecosystems is usually considered independent of their size and their location in the landscape. In this study, we examine the effect of size, spatial configuration and disturbances on the dynamic interactions of large herbivores and vegetation in a patchy environment using a metapopulation model. Simulations indicate that small, isolated or unfenced patches have low herbivore numbers and high tree cover whereas large, well-connected or fenced patches support high herbivore densities and are covered by grassland. Recovery of both herbivore numbers and forest cover in response to disturbance is slow (>100 years). These long recovery times are partly attributable to negative feedbacks between herbivore numbers and tree cover. When the population of large herbivores is disturbed, forest is able to expand, subsequently inhibiting herbivore population recovery. Likewise, forest disturbance allows herbivore population expansion, which inhibits forest recovery. Additionally, infrequent and limited disturbances like hunting and forest removal also affect the vegetation cover in patches of nature. Thus, our work indicates that the location and size of patches, together with disturbances, largely determine the structure of the vegetation in fragmented landscapes
Vegetation factors influencing density and distribution of wild large herbivores in a southern African savannah
Gandiwa, E. - \ 2014
African Journal of Ecology 52 (2014)3. - ISSN 0141-6707 - p. 274 - 283.
gonarezhou-national-park - distribution patterns - ungulate diversity - semiarid savanna - water sources - zimbabwe - heterogeneity - populations - elephant - habitat
Understanding factors influencing large herbivore densities and distribution in terrestrial ecosystems is a fundamental goal of ecology. This study examined environmental factors influencing the density and distribution of wild large herbivores in Gonarezhou National Park, Zimbabwe. Vegetation and surface water were predicted to have a stronger influence than anthropogenic-related disturbances (livestock grazing, fires, settlements and poaching) on the density and distribution of wild large herbivores. Aerial survey data for seven common wild large herbivores conducted in 2007 and 2009 and environmental data were collected. Only grass cover explained a significant proportion of the variation in large herbivore densities and distribution. Moreover, only two species densities significantly differed across the Gonarezhou, namely impala and zebra. In contrast, buffalo, elephant, giraffe, kudu and nyala densities did not differ significantly across the Gonarezhou. Overall, the findings only partly support the study prediction. The study results suggest the need to further investigate the roles of environmental factors at smaller scales in order to tease out their relative strengths in influencing density and distribution of large herbivores.
Distributional congruence of mammalian herbivores in the Trans-Himalayan Mountains
Namgail, T. ; Wieren, S.E. van; Prins, H.H.T. - \ 2013
Current Zoology 59 (2013)1. - ISSN 1674-5507 - p. 116 - 124.
cross-taxon congruence - species richness - environmental gradients - distribution patterns - iberian peninsula - blue sheep - conservation - ladakh - similarity - biogeography
Large-scale distribution and diversity patterns of mammalian herbivores, especially less charismatic species in alpine environments remain little understood. We studied distributional congruence of mammalian herbivores in the Trans-Himalayan region of Ladakh to see if the distributions of less prominent and smaller herbivores can be determined from those of larger and more prominent herbivores like ungulates. Using a similarity index, we assessed shared distributions of species in 20x20 km2 grid-cells in an area of about 80,000 km2. We used the Unweighted Pair-Group Method with Arithmetic Average (UPGMA) to classify mammalian herbivores into groups with similar distributions. We then used the G-test of independence to look for statistical significance of the groups obtained. We identified six groups of mammalian herbivores with distributions more similar than expected at random. The largest group was composed of nine species whereas the other large group comprised six species. Canonical Correspondence Analysis (CCA), used to relate the groups with environmental features, showed that the largest group occurred in higher and flatter areas, while the other large group occurred in lower and steeper areas. Large herbivores like ungulates can be used as surrogate for less prominent small herbivores while identifying areas for latter’s protection in the inaccessible mountainous regions of the Trans-Himalaya
Species in a dynamic world: Consequences of habitat network dynamics on conservation planning
Teeffelen, A.J.A. van; Vos, C.C. ; Opdam, P.F.M. - \ 2012
Biological Conservation 153 (2012). - ISSN 0006-3207 - p. 239 - 253.
habitats - ecologische verstoring - natuurbescherming - biodiversiteit - dynamische systemen - ruimtelijke ordening - landgebruiksplanning - soorten - habitats - ecological disturbance - nature conservation - biodiversity - dynamic systems - physical planning - land use planning - species - colonization-extinction dynamics - structured metapopulation model - climate-change - landscape dynamics - reserve design - patch dynamics - fragmented landscapes - dependent disturbance - distribution patterns - density regulation
Habitat dynamics (habitat turnover due to natural perturbations or human activity) are commonplace, particularly in intensively used landscapes. Conservation planning requires an understanding of how spatio-temporal habitat dynamics and species characteristics interact with and relate to species persistence. We conducted a systematic literature review to determine how spatial and temporal properties of habitat networks can be changed to improve species viability in dynamic landscapes. We searched for both generalities that can be interpreted as spatial planning guidelines and gaps in knowledge that limit the application in spatial planning. Seventy studies matched our inclusion criteria. From these studies, we extracted knowledge regarding the role of four spatial and five temporal network properties (e.g. network area and habitat turnover rate) for species viability. We found that improving spatial network properties often effectively counterbalances the negative effects of habitat dynamics. Furthermore, changes in several temporal properties can alleviate the impact on species viability, for example, by reducing clustering in habitat turnover events. From these findings, we formulated a first set of general qualitative guidelines for planning practices. Moreover, we identified gaps between the available and required knowledge for planning ecological networks in dynamic landscapes, thereby leading to a research priority list containing the following recommendations: (1) provide guidance regarding the effective management of network properties; (2) compare alternate management regimes and their cost-effectiveness; (3) study management regimes for a wide range of species and habitat properties. Given the continuing climate change and economic development, guiding network design—including habitat dynamics—is urgently needed.
Seasonal variation in soil and plant water potentials in a Bolivian tropical moist and dry forest
Markesteijn, L. ; Iraipi, J. ; Bongers, F. ; Poorter, L. - \ 2010
Journal of Tropical Ecology 26 (2010). - ISSN 0266-4674 - p. 497 - 508.
tree species distributions - lowland rain-forest - silvicultural treatments - distribution patterns - topographic position - habitat associations - xylem cavitation - woody-plants - growth-rates - drought
We determined seasonal variation in soil matric potentials (¿soil) along a topographical gradient and with soil depth in a Bolivian tropical dry (1160 mm y-1 rain) and moist forest (1580 mm y-1). In each forest we analysed the effect of drought on predawn leaf water potentials (¿pd) and drought response (midday leaf water potential at a standardized ¿pd of -0.98 MPa; ¿md) of saplings of three tree species, varying in shade-tolerance and leaf phenology. ¿soil changed during the dry season and most extreme in the dry forest. Crests were drier than slopes and valleys. Dry-forest top soil was drier than deep soil in the dry season, the inverse was found in the wet season. In the moist forest the drought-deciduous species, Sweetia fruticosa, occupied dry sites. In the dry forest the short-lived pioneer, Solanum riparium, occupied wet sites and the shade-tolerant species, Acosmium cardenasii drier sites. Moist-forest species had similar drought response. The dry-forest pioneer showed a larger drought response than the other two species. Heterogeneity in soil water availability and interspecific differences in moisture requirements and drought response suggest great potential for niche differentiation. Species may coexist at different topographical locations, by extracting water from different soil layers and/or by doing so at different moments in time
Biological geography of the European seas: results from the MacroBen database
Arvanitidis, C. ; Somerfield, P.J. ; Rumohr, H. ; Faulwetter, S. ; Craeymeersch, J.A.M. - \ 2009
Marine Ecology Progress Series 382 (2009). - ISSN 0171-8630 - p. 265 - 278.
norwegian continental-shelf - taxonomic distinctness - distribution patterns - biodiversity - community - diversity - ecosystem - benthos - scale - gradient
This study examines whether or not biogeographical and/or managerial divisions across the European seas can be validated using soft-bottom macrobenthic community data. The faunal groups used were: all macrobenthos groups, polychaetes, molluscs, crustaceans, echinoderms, sipunculans and the last 5 groups combined. In order to test the discriminating power of these groups, 3 criteria were used: (1) proximity, which refers to the expected closer faunal resemblance of adjacent areas relative to more distant ones; (2) randomness, which in the present context is a measure of the degree to which the inventories of the various sectors, provinces or regions may in each case be considered as a random sample of the inventory of the next largest province or region in a hierarchy of geographic scales; and (3) differentiation, which provides a measure of the uniqueness of the pattern. Results show that only polychaetes fulfill all 3 criteria and that the only marine biogeographic system supported by the analyses is the one proposed by Longhurst (1998). Energy fluxes and other interactions between the planktonic and benthic domains, acting over evolutionary time scales, can be associated with the multivariate pattern derived from the macrobenthos datasets. Third-stage multidimensional scaling ordination reveals that polychaetes produce a unique pattern when all systems are under consideration. Average island distance from the nearest coast, number of islands and the island surface area were the geographic variables best correlated with the community patterns produced by polychaetes. Biogeographic patterns suggest a vicariance model dominating over the founder-dispersal model except for the semi-closed regional seas, where a model substantially modified from the second option could be supported.