Eaton RL. 1974. Ecology. In The Cheetah - The biology, ecology, and behavior of an endangered species.Van Nostrand Reinhold Company. New York. Pp 41-87.

The sex ratio among adults in the two observed areas Nairobi National Park and Amboslie Game Reserve was about 2:1, in the litters 1:1.
In Nairobi National Park, impala, Grant's gazelle, kongoni and waterbuck occur most frequently in the cheetah's diet. 12 of 30 aged kills were adults, 18 juveniles. Details on group size while hunting and of the herd size of the hunted species, prey selection, the cheetah's energy budget and the interaction of cheetahs with other species are presented.

Eaton_1974_The_cheetah_3_Ecology.pdf

Eaton RL. 1974. Predatory and Killing Behavior. In The Cheetah - The biology, ecology, and behavior of an endangered species.Van Nostrand Reinhold Company. New York. Pp. 129-145.

Detailed description of hunting and killing behavior. Cheetahs seldom crouches like most cats. It walks along slowly, looking for game. The "crouch" aspect of predatory behavior in the cheetah is modified to a state of alertness that requires holding the head high and remaining motionless enough to maintain visual contact with the prey. The cheetah knocks over the fleeing prey. The ontogeny of killing behavior was observed with a litter of four cubs and the mother.

Eaton_1974_The_cheetah_7_Predation.pdf

Farhadinia_&_Hemami_2010_Prey_selection_by_cheetah_in_Iran.pdf

Frame GW, Herbison Frame L. 1976. Population study of cheetahs and wild dogs.  Serengeti Research Institute Annual Report 1974-5. pp. 129-138. Serengeti Research Institute, Tanzania.

Cheetahs (Acinomyx jubatus) and African wild dogs (Lycaon pictus) are being studied in the Serengeti National Park and adjacent areas. The purpose of the research is to determine the size and trend of their populations, and to describe the extent of their movements and their ecological requirements. The ultimate objective is to formulate management recommendations for preserving cheetahs and wild dogs within the artificial confines of the park's boundaries. The cheetah population within the Serengeti ecosystem is probably in excess of 250. The high recruitment of young cheetahs into the population indicates either an expanding population or a stable population with high adult mortality. Individual cheetahs are identified by means of a photographic recognition file, which is based on the unique spot pattern on the face of every cheetah. Movements are being studied with respect to season and the availability of prey, water and cover. The maximum known migration distance for adult male and female cheetahs is 40 km. for each. The minimum dry season density of cheetahs around Seronera is about one cheetah per 3 km2.

Frame_&_Herbison_Frame_1976_Population_study_of_cheetahs_and_wild_dogs.pdf

Frame GW. 1976. Cheetah Biology and behaviour.
In Annual Report 1974-75 of the Serengeti Research Insitute, Arusha, Tanzania. Pp. 74-87.

The status of cheetah in the Serengeti ecosystem is considered good, with an estimated population of at least 500. The secrecy of most cheetahs accounts for the apparent scarcity. In the dry season cheetahs concentrate along the woodland edge, and around Seronera, where the density becomes one cheetah per 3 km2. - the highest known density of wild cheetahs anywhere in Africa. Optimum habitat is lightly wooded or bushed grassland. Cover is very important for hunting, protection, and shade. Cheetahs prey on whatever is abundant, small, and easily caught; at Seronera this is mainly Thomson's gazelle. Various aspects of behaviour are being studied; these are grouping, spacing, courtship, and development of cub play. Aspects of tourist viewing and management are discussed.

Frame_1976_Cheetah_biology_and_behaviour.pdf

Ghosh_2009_Evaluating_cheetah_reintroduction_into_Kuno_wildlife_sanctuary.pdf

Hayward MW, Hofmeyr M, O'Brien JO, Kerley GIH. 2006. Prey preferences of the cheetah (Acinonyx jubatus) (Felidae:Carnivora): morphological limitations or the need to capture rapidly consumable prey before kleptoparasites arrive? J. Zool., Lond. 270, 615-627.

As a charismatic carnivore that is vulnerable to extinction, many studies have been conducted on predation by the cheetah Acinonyx jubatus. Cheetah are generally considered to capture medium-sized prey; however, which species are actually preferred and why has yet to be addressed. We used data from 21 published and two unpublished studies from six countries throughout the distribution of the cheetah to determine which prey species were preferred and which were avoided using Jacobs' index. The mean Jacobs' index value for each prey species was used as the dependent variable in multiple regression, with prey abundance and prey body mass as predictive variables. Cheetah prefer to kill and actually kill the most available prey present at a site within a body mass range of 23-56 kg with a peak (mode) at 36 kg. Blesbok, impala, Thomson's and Grant's gazelles, and springbok are significantly preferred, whereas prey outside this range are generally avoided. The morphological adaptations of the cheetah appear to have evolved to capture medium-sized prey that can be subdued with minimal risk of injury. Coincidentally, these species can be consumed rapidly before kleptoparasites arrive. These results are discussed through the premise of optimality theory whereby decisions made by the predator maximize the net energetic benefits of foraging. Information is also presented that allows conservation managers to determine which prey species should be in adequate numbers at cheetah reintroduction sites to support a cheetah population. Conversely, these results will illustrate which potential prey species of local conservation concern should be monitored for impact from cheetahs as several species are likely to be preyed upon more frequently than others.

Hayward_et_al_2006_Prey_preferences_of_the_cheetah.pdf

Hayward MW, Adendorff J, O'Brien J, Sholto-Douglas A, Bissett C, Moolman LC, Bean P, Fogarty A, Howarth D, Slater R, Kerley GIH. 2007. Practical Considerations for the Reintroduction of Large, Terrestrial, Mammalian Predators Based on Reintroductions to South Africa`s Eastern Cape Province. The Open Conservation Biology Journal 1:1-11.

Hayward_et_al_2007_Assessment_of_large_carnivore_reintroduction_to_the_Eastern_Cape.pdf

Hayward_et_al_2007_Carrying_capacity_of_large_African_predators.pdf

Recently, conservation estate in South Africa's Eastern Cape Province has increased 10-fold resulting in large predators being increasingly reintroduced to restore ecological integrity and maximize tourism. We describe the reintroductions of large carnivores (>10 kg) that have occurred in the Eastern Cape and use various criteria to assess their success. Lion Panthera leo reintroduction has been highly successful with a population of 56 currently extant in the region and problems of overpopulation arising. The African wild dog Lycaon pictus population has increased to 24 from a founder population of 11. Preliminary results for spotted hyaenas Crocuta crocuta  also indicate success. Wild populations of leopards Panthera pardus exist on several reserves and have been supplemented by translocated individuals, although deaths of known individuals have occurred and no estimate of reproduction is available. Cheetah Acinonyx jubatus  reintroduction has also been less successful with 36 individuals reintroduced and 23 cubs being born but only 41 individuals surviving in 2005. Criteria for assessing the success of reintroductions of species that naturally occur in low densities, such as top predators, generally have limited value. Carrying capacity for large predators is unknown and continued monitoring and intensive management will be necessary in enclosed, and possibly all, conservation areas in the Eastern Cape to ensure conservation success.

Hayward_et_al_2007_Practical_considerations_for_the_reintroduction_of_large_predators.pdf

Houser_et_al_2009_Home_range_of_cheetah_in_Botswana.pdf

Houser_et_al_2009_Spoor_density_as_measure_of_true_density.pdf

Johnson_et_al_2010_Modelling_cheetah_relocation_success_in_Southern_Africa.pdf

Jule KR, Leaver LA and Lea SEG. 2008. The effects of captive experience in reintroduction survival in carnivores: a review and analysis. Biol. Conserv. 141, 355-363.

This review focuses on the success and survivorship of captive-born versus wild-caught carnivores used in reintroductions. Previous reviews have suggested that reintroduction projects using captive-born animals are less likely to be successful than projects translocating wild-caught animals. The purpose of this paper is to examine this statistically and investigate how captivity may affect the survival of reintroduced carnivores. We examined results published in previous reviews, and found evidence to support that reintroduction projects using wild-caught animals are significantly more likely to succeed than projects using captive-born animals. We further compiled our own review of 45 case studies in carnivore reintroduction projects (in 17 species across 5 families) to investigate survival rates rather than overall project 'success'. We found that (1) wild-caught carnivores are significantly more likely to survive than captive-born carnivores in reintroductions; (2) that humans were the direct cause of death in over 50% of all fatalities and (3) that reintroduced captive-born carnivores are particularly susceptible to starvation, unsuccessful predator/competitor avoidance and disease.

Jule_et_al_2008_Effect_of_captive_experience_on_reintroduction_success_of_carnivores.pdf

Kelly M. 2001. Serengeti cheetah viability and the lion factor. Cat News 34:28-9.

Serengeti cheetahs are well protected from poaching inside Serengeti National Park, but 70% of cheetah cubs are killed by other predators, mainly lions. Within the National Park it is likely that adult survival will remain high while juvenile survival will fluctuate depending on predation pressure. At low lion density, the cheetah population has a very low risk of extinction. Recently, lions did suffer an extreme population decline on the plains by canine distemper. Currently, however, the lion population is rebounding dramatically. What do you do when one endangered species is killing off another in your very large reserve?

Kelly_2001_Serengeti_Cheetah_Viability_and_Lion_Factor_CatNews_34.pdf

Kelly MJ, Laurenson MK, FitzGibbon CD, Collins DA, Durant SM, Frame GW, Bertram BCR, Caro TM. 1998. Demography of the Serengeti cheetah (Acinonyx jubatus) population: the first 25 years. J Zool , Lond 244:473-88.

Data are presented on the demography and reproductive success of cheetahs (Acinonyx jubatus) living on the Serengeti Plains, Tanzania over a 25-year period. Average age at independence was 17.1 months, females gave birth to their first litter at approximately 2.4 years old, interbirth interval was 20.1 months, and average litter size at independence was 2.1 cubs. Females who survived to independence lived on average 6.2 years while minimum male average longevity was 2.8 years for those born in the study area and 5.3 years for immigrants, with a large proportion of males dispersing out of the Plains population. Females produced on average only 1.7 cubs to independence in their entire lifetime and their average reproductive rates were 0.36 cubs per year or 0.17 litters per year to independence. Variance in lifetime reproductive success in the cheetah is similar to that of other mammals. No significant negative correlations were found between adult cheetah population size and numbers of cubs reaching independence, implying that the Plains population had not reached carrying capacity. Annual numbers of adult female cheetahs only were correlated with rainfall. Adult female cheetah numbers were not correlated with adult female lion numbers on the Plains, however, reproductive rates of cheetahs were negatively correlated with the presence of lions while cheetahs had cubs. Moreover, cheetah reproductive success was lower during the period of high lion abundance (1980±1994) than during the earlier period of relatively few lions (1969±1979).

Kelly_et_al_1998_Long-term_cheetah_demography.pdf

Kruuk H, Turner M. 1967. Comparative notes on predation by lion, leopard, cheetah and wild dog in the Serengeti area, East Africa. Mammalia 31:1-27.

Lions, leopards, cheetahs and wild dogs in the Serengeti area attack different prey size and use different hunting techniques. The diet can change according to the individual (in leopards) or sex (in lions). For lions, the number of hunted prey is a function of their size, however this is not true for hyenas. Thomson's gazelle represents the principal prey attacked by these predators, with the exception of the lion that prefer wildebeests, for that it is responsible of only 1.2% of its natural mortality.

Kruuk_&_Turner_-_Predation_in_the_Serengeti_area.pdf

Labuschagne,W.1981.Aspects of cheetah ecology in the Kalahari Gemsbok National Park. Conference proceeding.

The Kalahari Gemsbok National Park, an area of almost 960'000 hectares, is situated in the north-western corner of the Cape Province. Twenty cheetah groups, comprising 43 individuals, were kept under observations for 115 days. They were followed for more than 1200 kilometres while information on their predator-prey relationship, territoriality and related ecology factors, was collected. It was found that not only did the sizes of prey species differ in relation to the cheetah's group sizes but so did the kill rates and the frequencies at which each group size would kill. During an experiment which lasted 25 days, 11 cheetahs consumed 51.9 per cent of carcasses offered, averaging a daily consumption of 3.8 kilograms per cheetah. On average, cheetahs travelled 12.3 kilometres every 24 hours, drank water once every 82 kilometres, urinated every 4.3 km and defecated 12 every kilometres travelled. The demarcated boundaries by urinating have been found to exceed 300 square metres in Gemsbok Park.

Labuschagnet_1981_Cheetah_ecology_in_the_Kalahari.pdf

In South Africa there are efforts to manage reintroduced subpopulations of the Vulnerable cheetah Acinonyx jubatus in small reserves (10-1,000 km2) as a managed metapopulation. We estimated areas required to support cheetahs given varying prey densities, prey profiles and presence/absence of competing predators. A recent population and habitat viability assessment indicated that 20 subpopulations of 10 cheetahs or 10 subpopulations of 15 cheetahs are required to retain 90% of the heterozygosity of free-ranging cheetahs and to overcome stochastic events in the absence or presence of lions Panthera leo, respectively. We estimate that 203 - SE 42 km2 (range 48-466 km2) is required to support 10 cheetahs in the absence of lions, whereas 703 - SE 311 km2 (166-2,806 km2) is required to support 15 cheetahs given equal numbers of lions, and 2,424 - SE 890 km2 (727-3,739 km2) given equal numbers of leopards Panthera pardus, spotted hyaenas Crocuta crocuta, wild dogs Lycaon pictus and lions. Existing subpopulations of cheetahs generally occur at densities higher than our mean predicted densities but usually within the range of predicted densities. The large area requirements of cheetahs have implications for the development of the managed metapopulation. Sourcing reintroduction sites of the sizes required to support recommended subpopulation sizes will be difficult. Consequently, innovative measures to increase the carrying capacity of reserves for cheetahs and/or to enlarge reserves will be required. Managers may be forced to stock cheetahs close to or beyond the carrying capacity of their reserves. Consequently, careful management of reintroduced subpopulations will be required to prevent declines in prey populations.

Lindsey_et_al_2011_Minimum_prey_and_area_requirements_of_cheetah_South_Africa.pdf

Marker_et_al_2008_Spatial_ecology_of_cheetahs_on_Namibian_farmland.pdf

Marnewick K., Funston PJ and Karanth KU 2008. Evaluating camera trapping as a method for estimating cheetah abundance in ranching areas. South African Journal of Wildlife Research 38(1): 59-65.

In order to accurately assess the status of the cheetah Acinonyx jubatus it is necessary to obtain data on numbers and demographic trends. However, cheetahs are notoriously difficult to survey because they occur at very low population densities and are often shy and elusive. In South Africa the problem is further complicated in areas where land is privately owned, restricting access, with dense bush and cheetahs that are frequently persecuted. Cheetahs are individually identifiable by their unique spot patterns, making them ideal candidates for capture-recapture surveys. Photographs of cheetahs were obtained using four camera traps placed successively at a total of 12 trap locations in areas of known cheetah activity within a 300 km² area in the Thabazimbi district of the Limpopo Province. During 10 trapping periods, five different cheetahs were photographed. These results were used to generate capture histories for each cheetah and the data were analysed using the capture-recapture software package CAPTURE. Closure tests indicated that the population was closed (P = 0.056). The Mh model was used to deal with possible heterogeneous capture probabilities among individual cheetahs. Closure tests did not reject the model assumption of population closure (P = 0.056).The Mh model produced a capture probability of 0.17 with an estimate of 6-14 cheetahs (P = 0.95) and a mean population size of seven cheetahs (S.E. = 1.93). These results are promising and will be improved with employment of more camera traps and sampling a larger area.

Marnewick_et_al_2008_Camera_trapping_as_method_for_estimating_cheetah_abundance.pdf

Mills MGL, Broomhall LS, du Toit JT. 2004. Cheetah Acinonyx jubatus feeding ecology in the Kruger National Park and a comparison across Africa savanna habitats: is the cheetah only a successful hunter on open grassland plains? Wildlife Biology 10(3):177-86.

The literature on cheetah Acinonyx jubatus ecology is dominated by studies on the Serengeti Plains (SNP) in East Africa. Because of this and the cheetah's hunting strategy it is generally considered to be a predator that prefers open grassland plains. However, cheetahs also inhabit a range of bush, scrub and woodland habitats. A field study using direct observations of radio-collared individuals in the woodland savanna habitat of the Kruger National Park (KNP), South Africa, and a literature review of studies across savanna habitats examined cheetah predation, hunting behaviour and habitat use in relation to prey composition, cover availability and kleptoparasitism. The cheetah's main prey is medium-sized herbivores, with a bias towards male prey. The group size and sex of the hunting cheetah may influence the results of prey selection studies as male coalitions tend to take larger prey than females. Cheetahs initiated more hunts and had a higher success rate in the open woodland savanna of the KNP compared to other available habitats with thicker bush, and in other wooded savanna areas they also prefer more open habitat for hunting.

Mills_et_al_2004_Cheetah_feeding_ecology_in_Kruger_NP.pdf

Morsbach D.  The Behaviour, Ecology and Movements of Cheetah on the Farm Areas of SWA/Namibia.  1-30. 1986. 1986.

The document is the progress report of the research project on the behaviour, ecology and movements of the cheetah on farm areas in Namibia for the period between November 1985 to October 1986. Estimation of the number of cheetahs on farmlands, based on basic information on the species' movements and density, is between 2000 and 3000, remarkably less than the number of about 6000 that was estimated through questionnaires and personal communications. From this study it was found that the average loss of cattle due to cheetah predation is three to four calves per farm per year. The few farmers which actually did keep good written records of all calf births and mortalities, had almost always much less losses due to predation by cheetahs. Recommendations include the increase of the cheetah's economic value for farmers, the establishment of reservoir areas that must include a number of farms and where the farmers must agree that a calf loss of 3 to 4 calves a year is acceptable, and an intensive, fulltime study to make an accurate conclusion of the stock losses. Annexes figures of the movements of the studied cheetahs are given, as well as tables indicating their home range area estimations, stock losses on farms, and departmental permit records for the cheetah between 1980 to 1986.

Morsbach_1986_Cheetahs_on_farms_areas_of_Namibia.pdf

Accurate estimates of demographic parameters are key for understanding and predicting population dynamics and for providing insights for effective wildlife management. Up until recently, no suitable methodology has been available to estimate survival probabilities of species with asynchronous reproduction and a high level of individual variation in capture probabilities. The present work develops a capture-mark-recapture model for cheetahs in the Serengeti National Park, Tanzania, which (a) deals with continuous reproduction, (b) takes into account the high level of individual heterogeneity in capture probabilities and (c) is spatially explicit. Results show that (1) our approach, which is an extensive modification of the Cormack-Jolly-Seber model, provides a lower female adult survival estimate and a higher male adolescent survival estimate than previous approaches to estimate cheetah survival in the area, (2) using sighting location alone is not sufficient to capture the individual variation in resighting probabilities for both sexes, and (3) precision in estimated survival probabilities is generally increased. Species which are individually recognizable, wide-ranging and/or where individuals differ substantially in sightability are particularly appropriate to our modelling approach, and our methodology would thus be appropriate for a wide number of species to provide more accurate estimates of survival.

Oliver_et_al_2011_Recapture_probability_and_survival_in_cheetah.pdf

Pettifer HL. 1981. The ecology of the cheetah (Acinonyx jubatus) on the Suikerboard Nature Reserve. Conference proceeding 27 p.

Cheetah were relocated to the Suikerbosrand Nature Reserve between 1975 and 1976. A rapid increase in cheetah numbers with simultaneous declines in certain ungulate species warranted intensive management-oriented research. Social grouping, population dynamics and prey selection of cheetahs are briefly discussed. Home ranges are shown to overlap considerably, although an effective spacing system is in operation. Home range size appears to depend largely upon social dominance and possibly territoriality.

Pettifer_1981_The_Ecology_of_the_Cheetah_on_the_Suikerbosrand_Nature_Reserve.pdf

An understanding of the factors governing reproductive success has fundamental implications for population demography, conservation, selection and adaptation. Although a consistent positive correlation between lifetime reproductive success and longevity has been reported for many iteroparous organisms, few studies have explored how longevity influences annual individual performance. In this study we show (1) that longevity and lifetime reproductive success are positively but not linearly correlated, (2) that short-lived individuals have higher annual reproductive success, (3) that the generally lower success of the last breeding occasion increased with females 'longevity, and (4) that long-lived females have higher chances of rearing long-lived females. We suggest that experience and the increase in the number of reproductive events with longevity are key processes leading to a strong correlation between (1) lifetime reproductive success and longevity and (2) mother and daughter longevities. Our results demonstrate the importance of long term studies that follow multiple generations in gaining a full understanding of the factors affecting reproductive success.

Pettorelli_&_Durant_2007_Longevity_in_cheetahs.pdf

Pettorelli N, Hilborn A, Broekhuis F, Durant SM. 2008. Exploring habitat use by cheetahs using ecological niche factor analysis. J. Zool., Lond. 277, 141-148.

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.

Pettorelli_et_al_2008_Habitat_use_by_cheetah_using_ENFA.pdf

Sinclair ARE, Mduma S, Brashares JS. 2003. Patterns of predation in a diverse predator-prey system. Nature 425:288-90.

There are many cases where animal populations are affected by predators and resources in terrestrial ecosystems, but the factors that determine when one or the other predominates remain poorly understood. Here we show, using 40 years of data from the highly diverse mammal community of the Serengeti ecosystem, East Africa, that the primary cause of mortality for adults of a particular species is determined by two factors-the species diversity of both the predators and prey and the body size of that prey species relative to other prey and predators. Small ungulates in Serengeti are exposed to more predators, owing to opportunistic predation, than are larger ungulates; they also suffer greater predation rates, and experience strong predation pressure. A threshold occurs at prey body sizes of  ~150 kg, above which ungulate species have few natural predators and exhibit food limitation. Thus, biodiversity allows both predation (top-down) and resource limitation (bottom-up) to act simultaneously to affect herbivore populations. This result may apply generally in systems where there is a diversity of predators and prey.

Sinclair_et_al_2003_Patterns_of_predation.pdf

Stander PE. 1996. Basic ecological parameters and management constraints of lions and cheetahs in Bushmanland and Daudom Game Reserve, Namibia. Report, 8 p.

This report discusses basic ecology, biology and behaviour related to the habits of mainly lions in Namibia with some notes on cheetahs, and where possible compares the results with data from elsewhere in sub-Saharan Africa. The densities of cheetahs are low for both Bushmanland (0.1-0.14/100km2) and Kalahari Gemsbok National Park (0.05-0.07/100km2). Observation on marked cheetahs gives strong suggestions that the species is resident all year round, utilizing enormous home ranges. The cheetah, which normally occur at low densities, are particularly susceptible to fragmentation of continuous habitat and need large "protected" areas that can support the long-term survival of entire large mammal communities.

Stander_1996_Ecology_and_conservation_of_lions_and_cheetahs_in_Namibia.pdf

Accurate assessment of carnivore population status is frequently hindered by insufficient distribution data. For northern South Africa we address this deficit by mapping new records from landscape-scale sign surveys, questionnaire interviews, problem animal records and camera trapping. The black-backed jackal Canis mesomelas and caracal Caracal caracal remain common and widespread. Ranges of the serval Leptailurus serval and brown hyaena Hyaena brunnea were much larger than previous estimates, reducing the risk of simultaneous extirpation across all occupied locations. The proportion of range area occupied was larger for several species, notably the leopard Panthera pardus, cheetah Acinonyx jubatus and serval. We conclude that the serval continues to recover from historical threats and is expanding into new areas. A larger brown hyaena range and less fragmented pattern of occurrence probably confers greater resilience to threats than was suggested by previous data. Reduced extinction risk arising from the increased area occupied by the cheetah and leopard is tempered by probable local range contraction. Our maps provide baseline information for monitoring the distribution of these six species, which is essential in managing ecological issues that have a spatial component such as responses to changing land use. Our results also demonstrate the utility of detection/nondetection surveys in rapid assessment of carnivore populations at large spatial scales.

Thorn_et_al_2011_Distribution_patterns_of_carnivores_in_northern_South_Africa.pdf