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

Mammalian 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.     

Anthropogenic modifications to fire regimes in the wider Serengeti‐Mara ecosystem

Fire is a key driver in savannah systems and widely used as a land management tool. Intensifying human land uses are leading to rapid changes in the fire regimes, with consequences for ecosystem functioning and composition. We undertake a novel analysis describing spatial patterns in the fire regime of the Serengeti‐Mara ecosystem, document multidecadal temporal changes and investigate the factors underlying these patterns. We used MODIS active fire and burned area products from 2001 to 2014 to identify individual fires; summarizing four characteristics for each detected fire: size, ignition date, time since last fire and radiative power. Using satellite imagery, we estimated the rate of change in the density of livestock bomas as a proxy for livestock density. We used these metrics to model drivers of variation in the four fire characteristics, as well as total number of fires and total area burned. Fires in the Serengeti‐Mara show high spatial variability—with number of fires and ignition date mirroring mean annual precipitation. The short‐term effect of rainfall decreases fire size and intensity but cumulative rainfall over several years leads to increased standing grass biomass and fuel loads, and, therefore, in larger and hotter fires. Our study reveals dramatic changes over time, with a reduction in total number of fires and total area burned, to the point where some areas now experience virtually no fire. We suggest that increasing livestock numbers are driving this decline, presumably by inhibiting fire spread. These temporal patterns are part of a global decline in total area burned, especially in savannahs, and we caution that ecosystem functioning may have been compromised. Land managers and policy formulators need to factor in rapid fire regime modifications to achieve management objectives and maintain the ecological function of savannah ecosystems.     

An isotopic technique to mark mid-sized vertebrates non-invasively

Understanding the basis of habitat choice having important implications for explaining the distribution of organisms, as well as helping to differentiate between habitats of different quality for effective management. In this study, the effects of sex, age and reproductive status on habitat use patterns of cheetahs Acinonyx jubatus in the Serengeti plains were explored using Ecological Niche Factor Analysis (ENFA). Our results showed that gender and territoriality did not affect patterns of habitat use. However, females tended to be more specialized when they were young than when they were older, displaying a more restricted ecological niche. Likewise, older females without cubs were more specialized than the same adult females with young cubs. This result did not hold for younger females. Altogether, the ENFA approach allowed us to (1) use the large amount of incidental sighting data collected over 12 years on cheetah spatial distribution; (2) identify the importance of reproductive status and age on the relationship between animals and their habitat; (3) further demonstrate that ENFA is applicable in a wide range of situations, including for exploring individual variation in niche definition.     

Edaphic,Nutritive, and Species Assemblage Differences between Hotspots and Matrix Vegetation: Two African Case Studies

Areas of locally intense and frequent grazing, or ‘hotspots’, are pervasive features in tropical grasslands and savannas. In some ecosystems, hotspot presence is clearly associated with edaphic factors (e.g., high clay content and elevated soil fertility), such as those that develop in abandoned cattle bomas. Studies in a range of other savanna ecosystems, however, have failed to find intrinsic soil differences between hotspots and the surrounding matrix. Also, it remains unclear to what extent hotspots are associated with specific assemblages of nutrient‐rich plant species, as opposed to being a manifestation of intraspecific variation in nutritive quality. We conducted simultaneous studies in Kruger (South Africa) and Serengeti (Tanzania) National Parks to re‐evaluate the role of edaphic correlates of hotspot occurrence and to test whether intraspecific variation in plant quality occurs across hotspot‐matrix boundaries. We sampled soils and plants in paired hotspot and matrix plots at multiple sites within each ecosystem to test our a priori hypothesis that hotspots would be associated with distinct species assemblages and differences in soil fertility. We found clear hotspot‐matrix differences in foliar N, particularly within species, despite finding no differences in any soil or plant–soil variables, including N mineralization potential and mycorrhizal inoculation levels. We found only weak differences in community composition across the boundary, suggesting that intraspecific variation in foliar N rather than species turnover is mainly responsible for the enhanced nutritive value of hotspot vegetation. We propose that grazer–plant interactions may be stronger drivers of hotspot maintenance in these systems than plant–soil interactions.     

Abundance and diversity of rodents at the human–wildlife interface in Western Serengeti, Tanzania

Rodent species abundance and diversity in Western Serengeti are evaluated and discussed in relation to different levels of conservation status [Unprotected Area (UA), Game Reserve (GR) and National Park (NP)] and broad site differences in human livelihood activities. A total of 2170 individuals, spread over 16 rodent species, were caught in a capture‐mark‐recapture study which covered both the dry and wet seasons. The more humid site (Tabora B) in the northern part of Serengeti had the highest diversity of rodents followed by the Mihale site at the western extension. The driest site at Robanda had the lowest overall species diversity. Diversity also varied between the three levels of conservation status whereby the UA had the least diversity while the NP, which enjoyed the highest level of conservation status, had the highest diversity of rodents. Unprotected Area and NP plots at Tabora B showed a rodent species similarity index of 40%; all the other paired plots scored over 50% similarity indices, suggesting that, within a site, species composition did not vary significantly between the three levels of conservation status. The Robanda site had the highest (56%) overall abundance of rodents; Mihale and Tabora B sites had about the same level of rodent abundance (20 and 24% respectively). For the Mihale site, Mastomys natalensis ranked first followed by Arvicanthis niloticus and Tatera robusta, each of which contained 40, 38 and 16%, respectively, of all individuals caught at the site. For the Robanda site, the figures were 66%A. niloticus, 22%M. natalensis and 9%T. robusta; while for the Tabora B site the scores were 37%M. natalensis, 18%T. robusta and 11%Lemniscomys barbarus. The differences in diversity, species composition and population abundance appear to result largely from physiognomic vegetation types, and habitat perturbations caused by livelihood activities in Western Serengeti.     

Vegetation and plant food reconstruction of lowermost Bed II, Olduvai Gorge, using modern analogs

Vegetation and plant foods for hominins of lowermost Bed II, Olduvai Gorge were modeled by examining vegetation in modern habitats in northern Tanzania (Lake Manyara, Ngorongoro, Serengeti) that are analogous to the paleolandscape in terms of climate, land forms, and soil types, as indicated by previous paleoenvironmental studies of Olduvai. Plant species in the modern habitats were identified in a series of sample plots, and those known to be eaten by modern humans, chimpanzees, or baboons were considered potentially edible for early hominins. Within the 50-80 kyr deposition of lowermost Bed II, periods of drier climate were characterized by low lake stands and a broad eastern lacustrine plain containing a mosaic of springs, marsh, woodland, and edaphic grassland. Based on results of this study, plant food diversity in each of those habitats was relatively low, but the mosaic nature of the area meant that hominins could reach several different habitat types within short distances, with access to potential plant foods including marsh plants, grass grains, roots, shrub fruits, edible parts from palms, leafy herbaceous plants, and Acacia pods, flowers, and gum. Based on Manyara analogs, a greater variety of plant foods, such as tree fruits (e.g., Ficus, Trichilia) and the roots and fruits of shrubs (e.g., Cordia, Salvadora) would be expected further east along the rivers in the lacustrine terrace and alluvial fans. Interfluves of the alluvial fans were probably less wooded and offered relatively fewer varieties of plant foods, but there is sparse paleoenvironmental evidence for the character of Olduvai's alluvial fans, making the choice of appropriate modern analogs difficult. In the western side of the basin, based on modern analogs in the Serengeti, riverine habitats provided the greatest variety of edible plant food species (e.g., Acacia, Grewia, Justicia). If the interfluves were grassland, then a large variety of potentially edible grasses and forbs were present seasonally. Periods of wetter climate resulted in a much expanded paleolake and a shrinking of the eastern lacustrine plain mosaic into a narrow zone. The dominant landscape features were then forest-lined rivers in the eastern alluvial fans, and rivers in the western side of the paleo-Olduvai basin were also better watered at these times, supporting denser woody vegetation with large varieties of edible fruits, leaves, and underground parts.     

Factors influencing conservation attitudes of local people in Western Serengeti,Tanzania

Attitudinal studies are increasingly being adopted as tools for evaluating public understanding, acceptance and the impact of conservation interventions. The findings of these studies have been useful in guiding the policy interventions. Many factors affect conservation attitudes positively or negatively. The factors inspiring positive attitudes are likely to enhance the conservation objectives while those inducing negative attitudes may detrimentally undermine these objectives. The magnitude of the resultant effects of each particular factor is determined by the historical, political, ecological, socio-cultural and economic conditions and this may call for different management interventions. In this study we examined how conservation attitudes in western Serengeti are shaped by the following factors: level of conflicts with protected areas; wildlife imposed constraints (inadequate pasture, water, diseases, loss of livestock during migration, theft and depredation); participation in the community based project; and socio-demographic factors (age, education level, wealth, immigration, gender and household size). The results indicated that the level of conflicts, participation in the community based project, inadequate pasture, lack of water, diseases, wealth and education were important in shaping peoples’ attitudes. However, in a stepwise linear regression analysis, 59% of the variation in peoples’ attitudes was explained by three variables i.e., conflict level with protected areas, lack of water and participation in the community based project. In addition to these variables, level of education also contributed in explaining 51% of the variation in people’s attitude regarding the status of the game reserves. Five variables (lack of water, level of education, inadequate pasture, participation in the community based project and diseases) explained 12% of the variation in people’s attitude towards Serengeti National Park. The paper discusses the implications for conservation of these results and recommends some measures to realise effective conservation of wildlife resources.     

Disturbance,species loss and compensation: Wildfire and grazing effects on the avian community and its food supply in the Serengeti Ecosystem,Tanzania

An important question in biodiversity studies is whether disturbances in ecosystems will cause a net loss of species or whether such losses can be compensated by replacement of other species. We use two natural disturbances, fire and grazing, to examine the response of bird and arthropod communities in grasslands of Serengeti, Tanzania. Both burning and grazing by migrant ungulates take place at the end of the rains in June–July. We documented the communities before disturbance, then 1, 4 and 20 weeks after disturbance on three replicate plots and compared them with three undisturbed plots. Birds were recorded by observation, arthropods from pitfall, tray trap and sweepnet samples. We expected that as the grass biomass was reduced by either disturbance, bird communities would change with concomitant change in arthropod food abundance. Alternatively, bird communities would change not with the absolute amount of food but with the greater accessibility of food as the grass structure changed from long to short grass. Results showed first that both bird species richness and abundance increased after both types of disturbance, but burnt sites showed a greater increase than that for grazed sites. Second, there was a change in bird species composition with disturbance. The functionally equivalent athi short‐toed lark (Calandrella athensis) was replaced by the red‐capped lark (Calandrella cinerea). Third, the abundance of most groups of arthropods was lower on disturbed sites than those on undisturbed sites, and the reduction of arthropod numbers was greatest on burnt sites. These results imply that bird abundance did not occur through an increase in arthropod abundance but rather through a change in the grass structure making food more accessible; and the higher predation could have caused the lower arthropod abundance. In addition, some bird species replaced others thus functionally compensating for their loss.     

Relationship between road dust and ungulate density in Serengeti National Park,Tanzania

We measured the responses of ungulate grazers to roads by recording the density of dust on grasses and compared distance sampling of ungulates in Serengeti National Park (SNP), Tanzania. Data were collected on the east and west side of the Ngorongoro–Seronera main gravel road to test if road traffic and dust were important factors determining distribution patterns amongst grazers. Results indicate that dust increased progressively with traffic speed and volume during dry season. More dust was intercepted on the west than on the east side of the road mainly because of wind effects. Dust deposition (measured as density g grass g^?1 dust) was higher on short grasses than on long grasses during the dry and late‐dry seasons than during the wet season, when paired perpendicular distances up to 300 m were compared. Mean number of observed grazer species indicated that most fed further from the west side of the road than from the east perhaps to minimize higher density of dust commonly spread on foliage up to 200 m away from the road. Despite that most grazers avoided road side grass shoulders, supporting the ‘dust aversion hypothesis’, the test predictions from the ‘road disturbance’ and the ‘road attraction’ hypotheses did not support the responsive behaviours of grazers toward roads.