Informing aerial total counts with demographic models: population growth of Serengeti elephants not explained purely by demography

Conservation management is strongly shaped by the interpretation of population trends. In the Serengeti ecosystem, Tanzania, aerial total counts indicate a striking increase in elephant abundance compared to all previous censuses. We developed a simple age-structured population model to guide interpretation of this reported increase, focusing on three possible causes: (1) in situ population growth, (2) immigration from Kenya, and (3) differences in counting methodologies over time. No single cause, nor the combination of two causes, adequately explained the observed population growth. Under the assumptions of maximum in situ growth and detection bias of 12.7% in previous censuses, conservative estimates of immigration from Kenya were between 250 and 1,450 individuals. Our results highlight the value of considering demography when drawing conclusions about the causes of population trends. The issues we illustrate apply to other species that have undergone dramatic changes in abundance, as well as many elephant populations

Age structure as an indicator of poaching pressure: insights from rapid assessments of elephant populations across space and time

Detecting and monitoring illegal harvesting pressure on wild populations is challenging due to the cryptic nature of poaching activities. Although change in population age structure has been suggested as an indicator of harvesting pressure, few studies have tested its validity when based on short-term field surveys. Using data from rapid demographic assessment surveys carried out in 2009 at six sites in Tanzania, we examined whether African elephant populations experiencing contrasting levels of poaching pressure showed significant differences in their age structure, operational sex ratio (i.e. adult males to adult females), dependent individual to adult female ratio at the group level, and proportion of tuskless individuals. We also compared similar metrics between the population sampled in Ruaha National Park in 2009 and again in 2015 following a suspected increase in poaching. Elephant populations experiencing medium and high levels of poaching in 2009 were characterised by fewer calves and old individuals, a reduced number of adult males relative to adult females, and a lower ratio of calves to adult females within groups. We also found a higher proportion of tuskless individuals in poached populations (>6%). Changes in age structure in the Ruaha population between 2009 and 15 were similar to those observed across sites in 2009. Our findings are consistent with previous work documenting how the loss of older individuals – targeted for their larger tusks – decreases recruitment and survival of elephant calves. Illegal killing for ivory is a huge threat to the survival of African elephants. In this context, the present study contributes towards validating the use of age structure as an indicator of poaching pressure in elephant populations, but also in other wildlife populations where illegal offtake is targeted at specific age classes

Stabilizing effects of group formation by Serengeti herbivores on predator-prey dynamics

Predator-prey theory often assumes that potential prey individuals are solitary and evenly distributed in space. This assumption is violated in social, mobile prey, such as many ungulates. Here we use data from 80 monthly field censuses to estimate the parameters for a power relationship between herd density and population density for eight species of large herbivores commonly found in the diet of Serengeti lions, confirming a power relationship proposed from a preliminary Serengeti dataset. Here we extend our analysis of that model to demonstrate how parameters of the power function relate to average herd size and density-dependent changes in herd size and evaluate how interspecific variation in these parameters shapes the group-dependent functional response by Serengeti lions for eight prey species. We apply the different prey-specific functional response models in a Rosenzweig-MacArthur framework to compare their impact on the stability of predator–prey dynamics. Model outcomes suggest that group formation plays a strong role in stabilizing lion–herbivore interactions in Serengeti by forcing lions to search over a larger area before each prey encounter. As a consequence of grouping by their prey, our model also suggests that Serengeti lions are forced to broaden their diets to include multiple species of prey in order to persist, potentially explaining the generalist foraging by lions routinely recorded across multiple ecosystems

Conservation and economic benefits of a road around the Serengeti

No abstract available

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

Nyttjande av platstjänster baserat på operativsystem : En studie om användningen av platstjänster hos Android & iOS användare

Dagens svenskar känner sig allt mer övervakade på internet då vi använder våra smartmobiler i större utsträckning med platstjänster från olika appar. Majoriteten av svenskar äger en smartmobil och med ökad mobilanvändning har det uppstått fler platstjänster som mobilanvändare kan ta del av, och med det flera risker för individens personliga integritet. Det här arbetet utgörs av en kvantitativ studie med syftet att undersöka användningen av platstjänster hos Android och iOS användare, samt vilka faktorer som påverkar användningen av platstjänster bland Android och iOS användare. Faktorer från en teoretisk modell om användares uppfattning kring platstjänster kommer att granskas och analyseras för att besvara studiens forskningsfrågor. Undersökningen bestod av en webbenkät, och den insamlade datan analyserades utifrån det teoretiska ramverket E-commerce Acceptance model (EAM), samt modellens medföljande hypoteser. I studien modifierades EAM genom att utesluta frågor från faktorn Avsikt att använda (Intention to use) och använde bara frågor från faktorerna Faktisk användning, Upplevd nytta, upplevd användbarhet, Upplevd risk och Förtroende. Det resultat som den här studien har påvisat är att den större delen av den undersökta populationen använder iOS och minoriteten använder Android. Efter en statistisk analys fann författarna att det finns en skillnad mellan operativsystemens faktorers påverkan på användandet av platstjänster, utifrån EAM. Det gick inte att dra några slutsatser om vad som påverkar iOS-användare att använda platstjänster. Dock kunde analysen påvisa att båda faktorerna Förtroende och Upplevd användbarhet har ett statistiskt signifikant samband med faktorn Faktisk användning hos Android-användare

Serengeti wildebeest population dynamics : regulation, limitation and implications for harvesting

Principal challenges in managing large mammals include methods for estimating abundance, understanding the interaction between environmental conditions, density, and reproductive success and survival, and estimation and regulation of harvest. Here I present the population dynamics of the Serengeti wildebeest (Connochaetes taurinus) as a case study in exploiting large mammals. The Serengeti wildebeest population increased six fold between 1960-1977 from 0.25 to 1.4 million; thereafter it remained constant at 1.3 million. Previous studies have suggested that density dependent mortality regulates the population through food shortage during the dry season. However, little was learned about which stage(s) in the life cycle were involved in the regulation process, or of the extent of human-induced mortality. I present recent demographic data on wildebeest reproduction, recruitment, and adult mortality. I combine my results with those of previous studies to construct a life table, and use key-factor analysis to investigate the influence of density dependence, predation and food limitation on the wildebeest population dynamics. I use poaching data to estimate illegal harvesting, which has been presumed to be extensive. I develop a population dynamics model to test for the consistency of the estimated demographic components. Life table analysis suggests that the Serengeti wildebeest population is regulated through density dependent adult mortality. Fertility loss acted in a density dependent fashion but was weak. Available evidence supports the food limitation hypothesis through dry season calf and adult mortality. Dry season calf mortality was the "key factor" stage causing population fluctuations. While neonatal mortality appeared to contribute the greatest to annual reduction, its pattern was not well understood. Limitation by predators and human offtake appeared to play a minor role. Synthesis of available data suggests that the Serengeti wildebeest population has reached its environmental carrying capacity under the present rainfall regime. Changes in rainfall greatly influence population size, and the reproductive surplus available for harvesting is almost directly related to the amount of rainfall in the dry season of the year. Population dynamics models indicate that in wet years additional animals could be taken in a controlled harvesting program, but elimination of the illegal harvest is essential.Science, Faculty ofZoology, Department ofGraduat