Savannah Ecosystems Research Articles

Quantification of dynamic soil–vegetation feedbacks following an isotopically labelled precipitation pulse

Abstract. The presence of vegetation alters hydrological cycles of ecosystems. Complex plant–soil interactions govern the fate of precipitation input and water transitions through ecosystem compartments. Disentangling these interactions is a major challenge in the field of ecohydrology and a pivotal foundation for understanding the carbon cycle of semi-arid ecosystems. Stable water isotopes can be used in this context as tracer to quantify water movement through soil–vegetation–atmosphere interfaces. The aim of this study is to disentangle vegetation effects on soil water infiltration and distribution as well as dynamics of soil evaporation and grassland water use in a Mediterranean cork oak woodland during dry conditions. An irrigation experiment using δ18O labelled water was carried out in order to quantify distinct effects of tree and herbaceous vegetation on the infiltration and distribution of event water in the soil profile. Dynamic responses of soil and herbaceous vegetation fluxes to precipitation regarding event water use, water uptake depth plasticity, and contribution to ecosystem soil evaporation and transpiration were quantified. Total water loss to the atmosphere from bare soil was as high as from vegetated soil, utilizing large amounts of unproductive evaporation for transpiration, but infiltration rates decreased. No adjustments of main root water uptake depth to changes in water availability could be observed during the experiment. This forces understorey plants to compete with adjacent trees for water in deeper soil layers at the onset of summer. Thus, understorey plants are subjected to chronic water deficits faster, leading to premature senescence at the onset of drought. Despite this water competition, the presence of cork oak trees fosters infiltration and reduces evapotranspirative water losses from the understorey and the soil, both due to altered microclimatic conditions under crown shading. This study highlights complex soil–plant–atmosphere and inter-species interactions controlling rain pulse transitions through a typical Mediterranean savannah ecosystem, disentangled by the use of stable water isotopes.

Freshwater fishes of northern Australia

Northern Australia is biologically diverse and of national and global conservation signicance. Its ancient landscape contains the world's largest area of savannah ecosystem in good ecological condition and its rivers are largely free-flowing. Agriculture, previously confined largely to open range-land grazing, is set to expand in extent and to focus much more on irrigated cropping and horticulture. Demands on the water resources of the region are thus, inevitably increasing. Reliable information is required to guide and inform development and help plan for a sustainable future for the region which includes healthy rivers that contain diverse fish assemblages. Based on a range of information sources, including the outcomes of recent and extensive new field surveys, this study maps the distribution of the 111 freshwater fishes (excluding elasmobranches) and 42 estuarine vagrants recorded from freshwater habitats of the region. We classify the habitat use and migratory biology of each species. This study provides a comprehensive assessment of the diversity and distribution of fishes of the region within a standardised nomenclatural framework. In addition, we summarise the outcomes of recent phylogeographic and phylogenetic research using molecular technologies to identify where issues of taxonomy may need further scrutiny. The study provides an informed basis for further research on the spatial arrangement of biodiversity and its relationship to environmental factors (e.g. hydrology), conservation planning and phylogentic variation within individual taxa.

Forecasting ecosystem responses to climate change across Africa's Albertine Rift

Climate change is likely to shift the distributions of ecosystems worldwide. Most assessments of climate change are primarily species-focused and do not directly estimate how entire ecosystems may change. Using an ecosystem-based modelling approach, we provide a region-wide climate change vulnerability assessment of the seven major ecosystems across Africa's Albertine Rift. The Albertine Rift is a global biodiversity hotspot, containing more endemic vertebrates than anywhere else in Africa. We used Maxent to estimate each ecosystem's extent using current climate data, then we projected the potential distribution of each ecosystem for 2050 and 2070. We found that suitable conditions for most ecosystems are predicted to contract rapidly in extent and shift upwards in altitude. High-altitude ecosystems and the endemic species they support are at immediate risk, owing to rapid predicted shrinkage in their suitable extent. Only the Combretum-grasslands savannah ecosystem is predicted to expand, with suitable conditions increasing by 32% in area by 2050. The extent and structure of boundary zones between the Rift's ecosystems may change significantly through time, due to the contractions and shifts of the environmental conditions for existing ecosystem distributions. By 2070, 44% of the region could be climatically unsuitable for the current ecosystems. Conservation planning across the Rift will need to account for these ecosystem shifts and rapidly changing boundary zones to ensure the long-term persistence of the many endemic species. Beyond the Albertine Rift, this ecosystem-based modelling technique can be adapted to any terrestrial region, providing critical information for conservation vulnerability assessments.

Population and Habitat Objectives for Avian Conservation in California’s Central Valley Grassland–Oak Savannah Ecosystems

In California’s Central Valley, grassland and oak savannah ecosystems provide multiple economic and social benefits, ecosystem services, and vital bird habitat. There is a growing interest in protecting, restoring, and managing these ecosystems, and the Central Valley Joint Venture (CVJV) provides leadership in the formulation of conservation goals and objectives. We defined a long-term goal of protecting, restoring, and managing Central Valley grassland and oak savannah ecosystems so that they are capable of supporting genetically robust, self-sustaining, and resilient wildlife populations. To measure progress toward this goal, we selected a suite of 12 landbird focal species that primarily breed in grasslands and oak savannahs as indicators of the state of these ecosystems on the Central Valley floor (primary focus area) and in the Central Valley’s surrounding foothills (secondary focus area). Using data on current densities and habitat extent, we estimated that at least three of the focal species populations in the primary focus area and at least two of the focal species populations in the secondary focus area are currently small (<10,000 individuals) and may be vulnerable to extirpation. Furthermore, at least two species appear to have steeply declining population trends. We defined long-term (100-year) population objectives for each focal species that we expect to meet the goal of genetically robust, self-sustaining, and resilient populations. We then estimated corresponding short-term (10-year) habitat objectives of 4,183 ha of additional grassland and 3,433 ha of additional oak savannah that will be required to make progress toward the long-term objectives. We expect that habitat restoration and enhancement efforts aimed at reaching these long-term conservation objectives will result in improvements to the function of Central Valley grassland and oak savannah ecosystems.

Evaluation of eddy covariance latent heat fluxes with independent lysimeter and sapflow estimates in a Mediterranean savannah ecosystem

We evaluated the underlying causes of differences between latent heat (LE) fluxes measured with two enclosed-path eddy covariance systems (EC) at two measurement levels and independent estimates in an open oak-tree grass savannah over almost one year. Estimates of LE of the well-stablished underlying grass by replicated weighable tension-controlled lysimiters (LELys) provided a robust baseline against which to compare EC LE measured at 1.6m above ground (LE_1.6). Similarly and at the ecosystem level, LE up-scaled using independent measurements (LEupscaled=sap flow+lysimeter) was benchmarked with 3 EC-derived LE estimates: 1) LE measured by a EC tower at 15m above ground (LE_15), 2) LE_15 adjusted to close the energy balance by using the Bowen ratio method (LEBowen=(Rn −G)/(1+β)), and 3) LE derived from the energy budget residual (LEresidual=Rn −G−H_15). The sensitivity of EC LE to the correction method applied (i.e. corrections for low-pass filtering effects on water vapor fluctuations and the so-called angle-of-attack correction) and its impact on the energy balance closure (EBC) were also evaluated.Comparison of EC LE between 1.6m- and 15m-heights showed that grass dominated annual evaporative loss from 69 to 87% depending upon the spectral correction method applied. Results revealed substantial underestimation of LE_1.6 (up to 35%) compared to LELys, which mostly occurred during the growing season. However those differences were remarkably lower when likening LE_15 versus LEupscaled (14%) suggesting that the dampening of the water vapor fluctuations due to low-pass filtering effects is more pronounced near the surface. Interestingly, a diagnostic evaluation of the errors with a random forest model showed that differences followed quite structured patterns and were associated with certain atmospheric conditions: turbulent mixing deficiencies and or stable atmospheric stratification. In addition, the model showed that differences increased with increasing relative humidity (RH) and soil moisture. Our results revealed that the degree of EBC is highly sensitive to the flux correction method applied, in particular when correcting for flow distortion effects. Typically, turbulent fluxes fell below the measured available energy (slope 0.92) but the slope switched abruptly when the angle-of-attack correction was applied (slope 1.07). Consistent with the EBC, independent LE estimates matched well with LEBowen and the EBC gap decreased when LEupscaled was used (slope 0.96). The use of independent estimates of LE together with machine learning methods are proposed as a powerful means to diagnose the complexity behind LE errors and give insights into the energy imbalance problem. In addition to inherent randomness of EC LE data, accounting for uncertainties associated with the appropriateness of the correction method applied is highly recommended.

Impacts of Bush Encroachment on Wildlife Species Diversity, Composition, and Habitat Preference in Ol Pejeta Conservancy, Laikipia, Kenya

Savannah ecosystems are currently facing a biome shift that changes grasslands to woody dominated landscapes, attributable to habitat degradation. In Ol Pejeta Conservancy (OPC), Euclea divinorum, an unpalatable and invasive woody species, is expanding to former savannah ecosystems with potential effects on herbivores key resources, wildlife species diversity, composition, and habitat use. We investigated wildlife species diversity, composition, and habitat preference or avoidance by wildlife in the conservancy. Infrared camera traps were deployed at the centroids of 2 km by 2 km, 50 cm above ground surface for 14 days and nights with 9 camera traps in each habitat type. Shannon wiener index revealed that wildlife species diversity was highest in E. divinorum dominated habitats and lowest in open grassland. Hierarchical Cluster Analysis revealed level of similarity in wildlife species composition between E. divinorum and mixed bushland. Jacobs index revealed that E. divinorum and mixed bushland were avoided by all guilds; however E. divinorum was significantly avoided while A. drepanolobium and open grassland were both preferred by all guilds. However, A. drepanolobium dominated habitats were significantly preferred compared to open grasslands. The findings are useful in management of sustainable ecosystems.

Effect of Harvest Time and Nitrogen Doses on Cassava Root Yield and Quality

ABSTRACT Nitrogen is considered the most limiting nutrient for cassava, and N availability can influence the crop cycle, including earlier harvest. The aim of this study was to study the effect of harvest time on the production components of cassava, “Aciolina” cultivar, at different rates of N fertiliser. The experiment was carried out in an area newly incorporated into the productive system in a savannah ecosystem in the northern Amazon. A randomised block experimental design was used in a split [...]

Time Series Monitoring of Bush Encroachment by <i>Euclea divinorum</i> in Ol Pejeta Conservancy Laikipia, Kenya

Bush encroachment refers to the invasion of woody species in Savannah ecosystems driven by either anthropogenic and/or natural factors. This study sought to examine land cover changes and topographic features attributable to patterns of encroachment in Ol Pejeta Conservancy (OPC) where, <i>Euclea divinorum</i> unpalatable woody species has colonised former grasslands and other habitats which provide grazing grounds for herbivore wildlife species. Here, we monitored vegetation cover trends in the period 1987-2016 using five vegetation classes on Landsat images acquired during the dry season. Additionally, slope based NDVI maps and digital elevation models were used to identify topographic influences on vegetation change. Results revealed that <i>E. divinorum</i> increased significantly between 1987 and 2016 (Mann Kendall test for trend analysis tau 1, n=6, p&lt; 0.01). On the other hand, <i>Acacia drepanolobium</i> and <i>Acacia xanthophloea</i> decreased from 49.72% and 5.31% in 1987 to 17.00% and 0.29% in 2016 respectively. Further, areas in low elevation were more colonised by <i>E. divinorum</i>. The colonising <i>E. divinorum</i> is unpalatable hence lacks natural predators whilst, <i>A. drepanolobium</i> and <i>A. Xanthophloea</i> which are alternative herbivory species decreased. Understanding dynamics of woody vegetation in savannah is crucial for management of healthy and sustainable ecosystems.

The complete genome sequence of the African buffalo (Syncerus caffer).

BackgroundThe African buffalo (Syncerus caffer) is an important role player in the savannah ecosystem. It has become a species of relevance because of its role as a wildlife maintenance host for an array of infectious and zoonotic diseases some of which include corridor disease, foot-and-mouth disease and bovine tuberculosis. To date, no complete genome sequence for S. caffer had been available for study and the genomes of other species such as the domestic cow (Bos taurus) had been used as a proxy for any genetics analysis conducted on this species. Here, the high coverage genome sequence of the African buffalo (S. caffer) is presented.ResultsA total of 19,765 genes were predicted and 19,296 genes could be successfully annotated to S. caffer while 469 genes remained unannotated. Moreover, in order to extend a detailed annotation of S. caffer, gene clusters were constructed using twelve additional mammalian genomes. The S. caffer genome contains 10,988 gene clusters, of which 62 are shared exclusively between B. taurus and S. caffer.ConclusionsThis study provides a unique genomic perspective for the S. caffer, allowing for the identification of novel variants that may play a role in the natural history and physiological adaptations.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-3364-0) contains supplementary material, which is available to authorized users.

How diverse is the lichenized fungal familyTrypetheliaceae(Ascomycota: Dothideomycetes)? A quantitative prediction of global species richness

AbstractA quantitative prediction of global species richness in the lichenized familyTrypetheliaceaeemploying a grid method previously used in similar approaches for the familyGraphidaceaeand the genusCora(Hygrophoraceae) is provided. 421 currently known taxa were used as a base for the calculation and we predict a total of nearly 800 species, corresponding to an increase of almost 100%. Most of the unrecognized taxa are predicted to occur in the Neotropics, which have the highest known species richness. The Palaeotropics are less diverse. In contrast toGraphidaceae, which are mostly confined to rainforests,Trypetheliaceaeshow substantial species richness in dry forest and savannah ecosystems, and future collection efforts should take well-preserved areas representing such ecosystems into consideration.

Mapping vulnerability to multiple hazards in the savannah Ecosystem in Ghana

The interior savannah ecosystem in Ghana is subjected to a number of hazards, including droughts, windstorms, high temperatures and heavy rainfall. The frequency and intensity of these hazards are projected to increase during the twenty-first century as a result of climate variability and change. Vulnerabilities to these hazards vary, both spatially and temporally, due to differences in susceptibilities and adaptive capacities. Many mapping exercises in Ghana have considered the impacts of single hazards on single sectors, particularly agriculture. But the hazards often occur concurrently or alternately and have varying degrees of impacts on different sectors. The impacts also interact. These interactions make mapping of the vulnerabilities of multiple sectors to multiple hazards imperative. This paper presents an analysis of the spatial dimension of vulnerabilities by mapping vulnerability of sectors that support livelihood activities at a single point in time, using the Upper East Region of Ghana as a case study. Data collected to develop the maps were largely quantitative and from secondary sources. Other data drew on fieldwork undertaken in the region from July to September 2013. Quantitative values were assigned to qualitative categorical data as the mapping process is necessarily quantitative. Data were divided into susceptibility and adaptive capacity indicators and mapped in ArcGIS 10.2 using weighted linear sum aggregation. Agriculture was found to be the most vulnerable sector in all districts of the Upper East Region and experienced the greatest shocks from all hazards. Although all districts were vulnerable, the Talensi, Nabdam, Garu-Temapane and Kassena-Nankana West Districts were most vulnerable. Findings highlight the need for more targeted interventions to build adaptive capacity in light of the spatial distributions of vulnerabilities to hazards across sectors.

At home in the postcolony: Ecology, empire and domesticity at the Lamto field station, Ivory Coast.

This article is a history of the field station Lamto, in Ivory Coast, which was created by French ecologists in 1962, after independence. It retraces the origins, the logics and the contradictions of an extraordinarily ambitious scientific project, which aimed at the systematic, holistic, quantitative and multi-disciplinary description of a unit of African nature - the savannah ecosystem. It explores how knowledge-making was articulated with work hierarchies and postcolonial politics, lifestyles, values and affects. It reconstitutes the political ecology of a research station in ecology, following in its residences, laboratories and open-air experiments the co-production of domesticity, nature, science and (post-)colonial situations.

Biodiversity, scenery and infrastructure: Factors driving wildlife tourism in an African savannah national park

Wildlife tourism is an important cultural ecosystem service, benefiting regional economies and biodiversity conservation. Many wildlife tourism destinations remain below their visitor and income capacities. Management strategies are needed that increase visitor satisfaction and a destination's reputation to attract more visitors. Wildlife tourism can be directly linked to biodiversity, but might also be directly and indirectly influenced by other factors, such as landscape features or infrastructure. We investigated the relationships between visitor numbers and biodiversity, along with other factors, in a major wildlife tourism destination using structural equation modeling and additionally assessed visitors' expectations and viewing preferences. We simultaneously recorded large mammal and visitor data along 78 road transects in Kruger National Park (KNP), South Africa, and conducted interviews with visitors. We also collected data on vegetation cover, visibility, landscape features and infrastructure. We found high visitor numbers at transects with high sighting probabilities of large predators, while other factors, e.g. ungulate densities or infrastructure, were only weakly associated with visitor numbers. Consistently, interview results suggested that seeing wildlife was the main reason for visiting the park, and large predators, especially lions and leopards, ranked highest among the visitors' wildlife preferences. Our results demonstrate that wildlife tourists in KNP are primarily attracted to large predators. To meet visitor expectations and to increase visitor numbers, park management should focus on the conservation of natural savannah ecosystems with large predator and prey populations. With such an ecosystem-based management, biodiversity conservation can be successful while securing wildlife tourism and its revenues.

Effects of entomopathogenic fungus Metarhizium anisopliae on non-target ants associated with Odontotermes spp. (Isoptera: Termitidae) termite mounds in Kenya

AbstractTermites are an important component of savannah ecosystems throughout Africa. Despite their importance in the ecosystem, they can be serious pests of structures, houses, rangelands, tropical forestry, and agriculture. For many decades, chemical insecticides have remained popular for termite management worldwide. However, with the growing environmental concerns over pesticides, biological control using entomopathogenic fungi such asMetarhizium anisopliae(Metschnikoff) Sorokin has become an often-considered alternative.Metarhizium anisopliaeis an ubiquitous, naturally occurring pathogen, which has been reported infecting over 200 insect species; therefore, there is concern that use ofM. anisopliaemay affect non-target organisms. The effects ofM. anisopliaeisolate ICIPE 30 were experimentally tested on the ants which associate withOdontotermesspp. termite mounds. Laboratory bioassays were carried out to assess the effects of direct exposure toM. anisopliaeonCrematogaster mimosaeandCamponotusspp. In addition, ant diversity was monitored over 18 months from termite mounds treated withM. anisopliae in situnear the Mpala Research Centre in Laikipia District of central Kenya. Results obtained revealed no effects of direct exposure toM. anisopliaeisolate ICIPE 30 on the mortality ofC. mimosae(F1= 7.29,P= 0.0072) orCamponotusspp. (F1= 13.01,P= 0.0004) in the laboratory. No significant difference in Shannon indices of ant diversity from treated and untreated mounds (F1= 0.016,P= 0.8989) was found. It is evident thatM. anisopliaehas no negative effects on ants that are associated withOdontotermesspp. termites.

Alternative hypotheses for mammalian herbivore preference of burned areas in a savannah ecosystem

AbstractMammalian herbivores prefer burned areas and this attraction has largely been attributed to the increased nutrient content of the postfire green flush and more recently to the avoidance of predators. However, alternative reasons for this attraction could be: (i) to avoid disease carrying and behaviour changing invertebrates; (ii) because burned areas are warmer microclimates; or (iii) to obtain minerals from the ash. This study tests for differences in tick and fly (Diptera) numbers between burned and unburned areas in Serengeti National Park, Tanzania. It also tests for differences in ground and air column temperatures between burned and unburned areas and for differences in the mineral content of ash in burned areas compared to the mineral content of green leaves in unburned areas. We found no difference in the abundance of either type of invertebrate between burned and unburned areas. Only ground temperature was higher in burned areas and this was only during the middle of the day, when increases in temperature would be less important than at night. Ash was higher in Al, Ca, Cu, Mg, Mn and P than nearby green leaves from unburned vegetation. Thus, obtaining minerals from ash is the only alternative reason for attraction to burned areas that maybe supported by this study.

A general parameterized mathematical food web model that predicts a stable green world in the terrestrial ecosystem

AbstractTerrestrial ecosystems are generally green with vegetation and only a small part (&lt;10%) of the total plant matter is consumed by herbivores annually, which means herbivore density is consistently low and stable. Nonetheless, the mechanism underlying this pattern has been unclear without suitable food web models for predicting the absolute density of the herbivore biomass in physical units. Here, I present a parameterized mathematical food web model describing three‐trophic‐level systems that can predict the biomass density of herbivores h (kg protein/m3) and carnivores c from factors such as nutritive values of plants (np, kg protein/m3), herbivores (nh), and carnivores (nc), searching efficiency (volume) of carnivores (S, m3·m−3·d−1 = d−1), eating efficiency (speed) of herbivores (eh) and carnivores (ec; m3·m−3·d−1 = d−1), respiratory decreases in biomasses (dh and dc, kg·kg−1·d−1 = d−1), absorption efficiencies αh and αc (ratios), and probabilities of carnivores preying on herbivores or carnivores, Phc and Pcc (ratios). The model predicts a stable equilibrium with low herbivore biomass h sufficient to keep the world green provided the food web consists of the three trophic levels, plants, herbivores, and carnivores; intraguild predation exists but is rarer than interguild predation (Phc &gt; Pcc &gt; 0); plants are less nutritive than animals (np &lt; nh, nc); and carnivore searches huge volume daily while eating speed of herbivore is limited (S _ eh). These conditions are well‐realized in aboveground terrestrial ecosystems where plant‐rich “green worlds” are common, vs. animal‐rich belowground and aquatic ecosystems where some conditions are not realized. The h and c calculated from our model agreed well with those from empirical observations in forest ecosystems, where both h and c are within an order of magnitude of 100 mg (fresh biomass/m2 forest), and in savannah ecosystems. The model predicts that plant nutritive value np, digestibility of plants by herbivores αh, and herbivore eating speed eh are positively correlated with h and the intensity of herbivory, which theoretically explains the outdoor defensive effects of plant anti‐nutritive or quantitative defenses (e.g., tannins, protease inhibitors), and predicts that c and the carnivore/herbivore ratio c/h are positively correlated with the relative growth rate of herbivores Gh. The present model introduced parameterized realities into food web theory that previous models lack.

Differential Persistence of Foot-and-Mouth Disease Virus in African Buffalo Is Related to Virus Virulence.

Foot-and-mouth disease (FMD) virus (FMDV) circulates as multiple serotypes and strains in many regions of endemicity. In particular, the three Southern African Territories (SAT) serotypes are maintained effectively in their wildlife reservoir, the African buffalo, and individuals may harbor multiple SAT serotypes for extended periods in the pharyngeal region. However, the exact site and mechanism for persistence remain unclear. FMD in buffaloes offers a unique opportunity to study FMDV persistence, as transmission from carrier ruminants has convincingly been demonstrated for only this species. Following coinfection of naive African buffaloes with isolates of three SAT serotypes from field buffaloes, palatine tonsil swabs were the sample of choice for recovering infectious FMDV up to 400 days postinfection (dpi). Postmortem examination identified infectious virus for up to 185 dpi and viral genomes for up to 400 dpi in lymphoid tissues of the head and neck, focused mainly in germinal centers. Interestingly, viral persistence in vivo was not homogenous, and the SAT-1 isolate persisted longer than the SAT-2 and SAT-3 isolates. Coinfection and passage of these SAT isolates in goat and buffalo cell lines demonstrated a direct correlation between persistence and cell-killing capacity. These data suggest that FMDV persistence occurs in the germinal centers of lymphoid tissue but that the duration of persistence is related to virus replication and cell-killing capacity. Foot-and-mouth disease virus (FMDV) causes a highly contagious acute vesicular disease in domestic livestock and wildlife species. African buffaloes (Syncerus caffer) are the primary carrier hosts of FMDV in African savannah ecosystems, where the disease is endemic. We have shown that the virus persists for up to 400 days in buffaloes and that there is competition between viruses during mixed infections. There was similar competition in cell culture: viruses that killed cells quickly persisted more efficiently in passaged cell cultures. These results may provide a mechanism for the dominance of particular viruses in an ecosystem.

Landscape Changes and Fragmentation Analysis in a Guinea Savannah Ecosystem: Case study of Talensi and Nabdam Districts of the Upper East region, Ghana

Landcover change is an observed natural change dynamics at both the local and regional levels. However, its scales are exacerbated by human interaction with its natural environment. The study examines these spatio-temporal changes in landcover and the level to which the change is accompanied by fragmentation of the identifiable cover types in the Talensi and Nabdam districts in Northern Ghana. The research uses digital classification of Landsat satellite imagery for 1999 and 2007 to produce the cover types which results in good accuracy levels of 66.39% and 63.03% respectively. Fragmentation analysis of the landscape was computed using FRAGSTATS® software for categorical maps obtained from the classified landcover maps for the two years. All cover types increased marginally. However, Bare areas decreased by as much as 17.17% and that of water decreased from 3% to 1%. The changing landscape involving conversions within and among various cover types is accompanied by fragmentation in all classes but more pronounced in the Bare class. The Bare class type which has more patches corresponds to the class with increased cover size and rather strangely decreases in the mean path size.

Spatio-temporal analyses of impacts of multiple climatic hazards in a savannah ecosystem of Ghana

Ghana’s savannah ecosystem has been subjected to a number of climatic hazards of varying severity. This paper presents a spatial, time-series analysis of the impacts of multiple hazards on the ecosystem and human livelihoods over the period 1983–2012, using the Upper East Region of Ghana as a case study. Our aim is to understand the nature of hazards (their frequency, magnitude and duration) and how they cumulatively affect humans. Primary data were collected using questionnaires, focus group discussions, in-depth interviews and personal observations. Secondary data were collected from documents and reports. Calculations of the standard precipitation index (SPI) and crop failure index used rainfall data from 4 weather stations (Manga, Binduri, Vea and Navrongo) and crop yield data of 5 major crops (maize, sorghum, millet, rice and groundnuts) respectively. Temperature and windstorms were analysed from the observed weather data. We found that temperatures were consistently high and increasing. From the SPI, drought frequency varied spatially from 9 at Binduri to 13 occurrences at Vea; dry spells occurred at least twice every year and floods occurred about 6times on average, with slight spatial variations, during 1988–2012, a period with consistent data from all stations. Impacts from each hazard varied spatio-temporally. Within the study period, more 70% of years recorded severe crop losses with greater impacts when droughts and floods occur in the same year, especially in low lying areas. The effects of crop losses were higher in districts with no/little irrigation (Talensi, Nabdam, Garu-Tempane, Kassena-Nankana East). Frequency and severity of diseases and sicknesses such as cerebrospinal meningitis, heat rashes, headaches and malaria related to both dry and wet conditions have increased steadily over time. Other impacts recorded with spatio-temporal variations included destruction to housing, displacement, injury and death of people. These impacts also interacted. For example, sicknesses affected labour output; crop losses were blamed for high malnutrition; and reconstruction of properties demanded financial resources largely from sale of agricultural produce. These frequent impacts and their interactions greatly explain the persistent poverty in the area.

Invasive toads shift predator-prey densities in animal communities by removing top predators.

Although invasive species can have substantial impacts on animal communities, cases of invasive species facilitating native species by removing their predators have rarely been demonstrated across vertebrate trophic linkages. The predictable spread of the invasive cane toad (Rhinella marina), however, offered a unique opportunity to quantify cascading effects. In northern Australia, three species of predatory monitor lizards suffered severe population declines due to toad-induced lethal toxic ingestion (yellow-spotted monitor (Varanus panoptes), Mertens' water monitor (V. mertensi), Mitchell's water monitor (V. mitchelli). We, thus, predicted subsequent increases in the abundance and recruitment of prey species due to the reduction of those predators. Toad-induced population-level declines in the water monitor species approached 50% over a five-year period spanning the toad invasion, apparently causing fledging success of the Crimson Finch (Neochmia.phaeton) to increase from 55% to 81%. The consensus of our original and published long-term data is that invasive cane toads are causing predators to lose a foothold on top-down regulation of their prey, triggering shifts in the relative densities of predator and prey in the Australian tropical savannah ecosystem.