Asynchronous food-web pathways could buffer the response of Serengeti predators to El Niño southern oscillation

Understanding how entire ecosystems maintain stability in the face of climatic and human disturbance is one of the most fundamental challenges in ecology. Theory suggests that a crucial factor determining the degree of ecosystem stability is simply the degree of synchrony with which different species in ecological food webs respond to environmental stochasticity. Ecosystems in which all food-web pathways are affected similarly by external disturbance should amplify variability in top carnivore abundance over time due to population interactions, whereas ecosystems in which a large fraction of pathways are nonresponsive or even inversely responsive to external disturbance will have more constant levels of abundance at upper trophic levels. To test the mechanism underlying this hypothesis, we used over half a century of demographic data for multiple species in the Serengeti (Tanzania) ecosystem to measure the degree of synchrony to variation imposed by an external environmental driver, the El Niño Southern Oscillation (ENSO). ENSO effects were mediated largely via changes in dry-season vs. wet-season rainfall and consequent changes in vegetation availability, propagating via bottom-up effects to higher levels of the Serengeti food web to influence herbivores, predators and parasites. Some species in the Serengeti food web responded to the influence of ENSO in opposite ways, whereas other species were insensitive to variation in ENSO. Although far from conclusive, our results suggest that a diffuse mixture of herbivore responses could help buffer top carnivores, such as Serengeti lions, from variability in climate. Future global climate changes that favor some pathways over others, however, could alter the effectiveness of such processes in the future

Avifauna in Relation to Habitat Disturbance in Wildlife Management Areas of the Ruvuma Miombo Ecosystem, Southern Tanzania

Understanding of relative distribution of avifauna provides insights for the conservation and management of wildlife in the community managed areas. This study examined relative diversity, abundance, and distribution of avifauna in selected habitat types across five Wildlife Management Areas of the Ruvuma landscape in miombo vegetation, southern Tanzania. Five habitat types were surveyed during the study: farmland, swamps, riverine forest, dense and open woodland. Transect lines, mist-netting, and point count methods were used to document 156 species of birds in the study sites. Descriptive statistics and Kruskal-Wallis tests were used to compare species richness and diversity across habitat types. We found differences in avifaunal species distribution in the study area whereby farmland had the highest abundance of avifauna species and lowest in the riverine forest. These results suggest that variations of avifauna species abundance, diversity, and distribution could be attributed by human activities across habitat types; due to the reason that habitats with less human encroachment had good species diversity and richness. Therefore, to improve avitourism and avoid local extinction of species, we urge for prompt action to mitigate species loss by creating awareness in the adjacent community through conservation education on the importance of protecting such biodiversity resources

Range expansion of the globally Vulnerable Karamoja apalis Apalis karamojae in the Serengeti ecosystem

This study was funded by the Rufford Maurice Laing Foundation, the Canadian Natural Sciences and Engineering Research Council and Frankfurt Zoological Society.The underlying causes of change in geographic range size are less well understood in African birds than in north temperate species. Here, we examine factors associated with range expansion in the Karamoja apalis (Apalis karamojae), a globally Vulnerable warbler confined to north-east Uganda, north-central Tanzania and southern Kenya. In Tanzania, it was originally known only from the Wembere Steppe, but since 1993 (and possibly as early as 1983) has extended its range into the Serengeti ecosystem, c. 140 km to the north, reaching southern Kenya by 2004. Changes in the warbler's range within the Serengeti have broadly reflected a cyclical change in the density of its main habitat, Acacia drepanolobium woodland, which was low in the 1970s, high during the 1980s and 1990s, and declined in the early 2000s. Karamoja apalis records in the Serengeti showed a 5 year time lag behind A. drepanolobium density, which was in turn negatively correlated with the area of grassland burnt 10 years earlier. Previous studies in the Serengeti have also linked Acacia regeneration to changes in grazing pressure, as increasing wildebeest (Connochaetes taurinus) numbers have reduced the volume of combustible material present, and hence the frequency of damaging 'hot burns'. We conclude that this globally threatened warbler appears to have benefited from changes in ungulate populations in the Serengeti, which have influenced burning intensity and hence tree regeneration. The warbler's range now appears to be declining, however, following a recent reduction in the density and annual survival of A. drepanolobium in the northern Serengeti.Resume Les causes sous-jacentes du changement de la taille d'une distribution geographique sont moins bien connues pour les oiseaux africains que pour les especes du nord tempere. Nous examinons ici des facteurs lies a l'expansion de l'aire de repartition de l'apalis de Karamoja Apalis karamojae, un sylviide classe comme Vulnerable au niveau mondial, confine au NE de l'Ouganda, au centre-nord de la Tanzanie et au sud du Kenya. En Tanzanie, on ne le connaissait a l'origine que dans la steppe de Wembere mais depuis 1993, et peut-etre meme des 1983, il a etendu son aire de repartition dans l'ecosysteme du Serengeti, environ 140 km plus au nord, et atteint le sud du Kenya en 2004. Les changements de l'aire de repartition de ce sylviide dans le Serengeti refletent largement un changement cyclique de la densite de son habitat principal, la foret d'Acacia drepanolobium, qui etait faible dans les annees 1970, forte pendant les annees 1980 et 1990, et qui a diminue au debut des annees 2000. Les rapports sur l'apalis de Karamoja au Serengeti montrent un retard de cinq ans par rapport a l'evolution de la densite d'A. drepanolobium, elle-meme etant negativement liee a la zone de prairie brulee 10 ans plus tot. Des etudes anterieures faites au Serengeti lient aussi la regeneration des acacias aux changements de la pression du paturage, etant donne que le nombre croissant de gnous, Connochaetes taurinus, a reduit le volume des matieres combustibles restantes et donc la frequence des feux trop chauds qui causent beaucoup de degats. Nous concluons que cet oiseau menace au niveau mondial semble avoir beneficie des changements des populations d'ongules au Serengeti, qui ont influence l'intensite des feux et donc la regeneration des arbres. L'aire de repartition de ce sylviide semble pourtant en train de se reduire suite a une recente reduction de la densite et de la survie annuelle d'A. drepanolobium dans le nord du Serengeti.PostprintPeer reviewe

Range expansion of the globally Vulnerable Karamoja apalis Apalis karamojae in the Serengeti ecosystem

The underlying causes of change in geographic range size are less well understood in African birds than in north temperate species. Here, we examine factors associated with range expansion in the Karamoja apalis (Apalis karamojae), a globally Vulnerable warbler confined to north-east Uganda, north-central Tanzania and southern Kenya. In Tanzania, it was originally known only from the Wembere Steppe, but since 1993 (and possibly as early as 1983) has extended its range into the Serengeti ecosystem, c. 140 km to the north, reaching southern Kenya by 2004. Changes in the warbler's range within the Serengeti have broadly reflected a cyclical change in the density of its main habitat, Acacia drepanolobium woodland, which was low in the 1970s, high during the 1980s and 1990s, and declined in the early 2000s. Karamoja apalis records in the Serengeti showed a 5 year time lag behind A. drepanolobium density, which was in turn negatively correlated with the area of grassland burnt 10 years earlier. Previous studies in the Serengeti have also linked Acacia regeneration to changes in grazing pressure, as increasing wildebeest (Connochaetes taurinus) numbers have reduced the volume of combustible material present, and hence the frequency of damaging 'hot burns'. We conclude that this globally threatened warbler appears to have benefited from changes in ungulate populations in the Serengeti, which have influenced burning intensity and hence tree regeneration. The warbler's range now appears to be declining, however, following a recent reduction in the density and annual survival of A. drepanolobium in the northern Serengeti.ResumeLes causes sous-jacentes du changement de la taille d'une distribution geographique sont moins bien connues pour les oiseaux africains que pour les especes du nord tempere. Nous examinons ici des facteurs lies a l'expansion de l'aire de repartition de l'apalis de Karamoja Apalis karamojae, un sylviide classe comme Vulnerable au niveau mondial, confine au NE de l'Ouganda, au centre-nord de la Tanzanie et au sud du Kenya. En Tanzanie, on ne le connaissait a l'origine que dans la steppe de Wembere mais depuis 1993, et peut-etre meme des 1983, il a etendu son aire de repartition dans l'ecosysteme du Serengeti, environ 140 km plus au nord, et atteint le sud du Kenya en 2004. Les changements de l'aire de repartition de ce sylviide dans le Serengeti refletent largement un changement cyclique de la densite de son habitat principal, la foret d'Acacia drepanolobium, qui etait faible dans les annees 1970, forte pendant les annees 1980 et 1990, et qui a diminue au debut des annees 2000. Les rapports sur l'apalis de Karamoja au Serengeti montrent un retard de cinq ans par rapport a l'evolution de la densite d'A. drepanolobium, elle-meme etant negativement liee a la zone de prairie brulee 10 ans plus tot. Des etudes anterieures faites au Serengeti lient aussi la regeneration des acacias aux changements de la pression du paturage, etant donne que le nombre croissant de gnous, Connochaetes taurinus, a reduit le volume des matieres combustibles restantes et donc la frequence des feux trop chauds qui causent beaucoup de degats. Nous concluons que cet oiseau menace au niveau mondial semble avoir beneficie des changements des populations d'ongules au Serengeti, qui ont influence l'intensite des feux et donc la regeneration des arbres. L'aire de repartition de ce sylviide semble pourtant en train de se reduire suite a une recente reduction de la densite et de la survie annuelle d'A. drepanolobium dans le nord du Serengeti.</p

Bird community responses to changes in vegetation caused by increasing large mammal populations in the Serengeti woodlands

Context: The increase in density of large tree species, Vachellia robusta and V. tortilis, in the Serengeti Ecosystem of Tanzania has resulted in a decline of small tree species Senegalia senegal, V. hockii, Commiphora spp. This change has occurred since the late 1970s, a consequence of an increase in wildebeest following the extirpation of rinderpest, which reduced the dry grass fuel for fires, resulting in low fire frequencies. Change in tree species raises the question of whether there are indirect consequences for the avifauna that depend on the large trees for food and nesting. Aims: To determine how an increase in large mammals could influence diversity and distribution of avifauna communities in the Serengeti ecosystem woodlands. Methods: Data used to estimate changes in density of large and small trees were measured by Point Centre Quarter (PCQ). Bird species were recorded in 19 small-tree sites and 18 large-tree sites in the Serengeti National Park. Richness of bird guilds was calculated in the two habitat complexes (small and large trees), and the ‘rarefaction’ method was used to assess the difference in richness in habitats of the study area. Mean abundance for each species was calculated over the total number of sites for each habitat and compared using the Wilcoxon Rank Sum test to examine how the abundance of avifauna changes with each habitat type. Key results: There was an increase in the density of large trees in some areas in which they have replaced the original small trees. Such changes have resulted in greater richness of hole nesters and bark feeders, and a greater abundance of large-hole nesters and gleaner bird species. Conclusions: Because the increase in tree density was caused by an increase in large mammals, we conclude that this increasing mammal population is indirectly increasing richness and abundance of birds using the trees. Implications: Understanding the influence of large mammal populations on bird distributions has important conservation implications because the Serengeti ecosystem is classified as an important, endemic bird area

Episodic outbreaks of small mammals infl uence predator community dynamics in an east African savanna ecosystem

Little is known about the dynamics of small mammals in tropical savanna: a critical gap in our understanding of Africa's best known ecosystems. Historical evidence suggested small mammals peak in abundance (outbreak) in Serengeti National Park (SNP), as in agricultural systems. We asked 1) what are bottom–up drivers of small mammals and 2) do predators have top–down effects? We documented dynamics of small mammals, birds of prey, and mammalian carnivores in SNP and agricultural areas. We used climatic fluctuations and differences between unmodified and agricultural systems as perturbations to examine trophic processes, key to understanding responses to climate change and increasing human pressures. Data were derived from intermittent measures of abundance collected 1968–1999, combined with systematic sampling 2000–2010 to construct a 42-year time series. Data on abundance of black-shouldered kites (1968–2010), eight other species of rodent-eating birds (1997–2010), and 10 carnivore species (1993–2010) were also collated. Outbreaks occurred every 3–5 years in SNP, with low or zero abundance between peaks. There was a positive relationship between rainfall in the wet season and 1) small mammal abundance and 2) the probability of an outbreak, both of which increased with negative Southern Oscillation Index values. Rodent-eating birds and carnivores peaked 6–12 months after small mammals. In agricultural areas, abundance remained higher than in natural habitats. Abundances of birds of prey and mammalian carnivores were extremely low in these areas and not related to small mammal abundance. Small mammals are an important food resource for higher trophic levels in the Serengeti ecosystem. Changes in climate and land use may alter their future dynamics, with cascading consequences for higher trophic levels, including threatened carnivores. Although outbreaks cause substantial damage to crops in agricultural areas, small mammals also play a vital role in maintaining some of the diversity and complexity found in African savanna ecosystems