Migration patterns of Thomson's gazelles and cheetahs on the Serengeti Plains

Monthly changes in abundance of Thomson's gazelles at 142 locations on the Serengeti Plains are presented over a 3½ year period. Numbers of gazelles on the eastern plains were strongly correlated with rainfall, whereas numbers in the central and western plains appeared to be related to other variables. Movements of female cheetahs and non-resident male cheetahs corresponded closely to the movements of Thomson's gazelles but those of resident male cheetahs remained relatively independent of the gazelle migration.     

HUNTING BEHAVIOUR OF THE CHEETAH IN THE SERENGETI NATIONAL PARK, TANZANIA

Eighty-nine per cent, of 136 cheetah kills in the Serengeti National Park consisted of Thomson's gazelles, the most abundant and readily available species in the size category (60 kg or less) preferred by the cheetah. Fifty-four per cent, of the Thomson's gazelle kills were subadult; among the adults all age classes were represented. One female cheetah captured 24 Thomson's gazelles in 26 days, a killing rate of 10 kg/day. The actual food intake of this female was about 4 kg/day. The hunting success of cheetah pursuing large subadult and adult Thomson's gazelles was about 50 per cent. The hunting methods–including the various means of approaching prey–are described as are the typical ways of killing and feeding. Twelve per cent, of the cheetah kills were appropriated by lions and hyaenas.     

Ecological characteristics of territories of male cheetahs (Acinonyx jubatus)

Ecological characteristics of nine male cheetahs territories in the Serengeti National Park are described. Territories were centred on areas that provided cover but did not have particularly high rainfall or prey abundance. Resident male cheetahs did not occupy their territories continuously. Some territories were vacated in the dry season, others in the wet season, but in both cases this occurred when numbers of Thomson's gazelles (females' main prey) and female cheetahs seen there were low. Although changes in territory ownership appeared to be related to demographic rather than ecological factors, territories that remained vacant seemed to contain rather little prey. Over two years, evidence suggested that territories occupied by males of larger group size contained greater numbers of Thomson's gazelles.     

Mother Cottonmouths (Agkistrodon piscivorus) Alter Their Antipredator Behavior in the Presence of Neonates

Neonate‐directed care is rare in non‐avian reptiles, but female pitvipers attend their young for a period of time after birth. One of the primary functions of parental care is the protection of offspring from predators, and parents of diverse taxa are able to modulate their antipredator behavior in the presence of offspring. To test the hypothesis that the antipredator behavior of post‐parturient pitvipers is altered during neonate attendance, we conducted behavioral trials on female cottonmouths (Agkistrodon piscivorus) in which we measured female response to a simulated predator encounter. Cottonmouths were divided into three treatment groups: (1) post‐parturient, attending neonates; (2) post‐parturient, not attending neonates; and (3) non‐reproductive. All females were subjected to a second trial approximately 3 wk later, when females in Group 1 were no longer attending neonates. When mothers were attending offspring, they were more hesitant to engage the predator and exhibited more warning than aggressive behaviors once they did, relative to non‐attending and non‐reproductive females. When these same mothers were no longer attending offspring, they significantly increased their antipredator behavior by engaging the predator quickly and displaying more aggressive than warning behaviors. This change in behavior was not observed in post‐parturient females who did not have neonates present during either trial, nor was it observed in non‐reproductive females, indicating that the presence of neonates directly affected the antipredator behavior of attending females. We discuss hypotheses concerning the possible adaptive value of reduced antipredator behavior in female pitvipers attending neonates.     

The impacts of burning on Thomson's gazelles', Gazella thomsonii,vigilance in Serengeti National Park,Tanzania

Alterations to habitats that increase the distance at which prey can detect predators can decrease the risk of predation. In grasslands, burning may have this effect for mammalian herbivores by decreasing vegetation height, potentially making burned areas safer habitats. However, few studies have tested the impacts of burning on the perceived predation risk of herbivores. Vigilance can be used as a measure of habitat safety and therefore should be lower in burned areas than unburned areas. We tested the impacts of prescribed burning on vigilance by Thomson's gazelles in Serengeti National Park, Tanzania. Both individual vigilance, proportion of time an individual spends looking, and group vigilance, proportion of a group looking, of Thomson's gazelles was observed in burned and unburned areas before and after presenting a model cheetah to each group. Surprisingly, both individual and group vigilance was the same in both habitats pre‐ and post‐cheetah addition and removal. This is despite the fact that both vegetation height and biomass were lower in burned areas than unburned areas. Thus, it does not appear that Thomson's gazelles perceive burned areas to be safer habitats than unburned areas.     

The condition and age of Thomson's gazelles killed by cheetahs and wild dogs

The condition and age of Thomson's gazelles ( Gazella thomsoni ) killed by two species of predators were compared. The wild dog, a coursing predator, was predicted to take a greater proportion of young, old and sick animals than the cheetah, a stalker. As measured by the marrow fat content of limb bones, wild dogs captured more Thomson's gazelles in poor condition than cheetahs. This appeared to be a consequence of their preference for male gazelles, which were in worse condition than females. Cheetahs did not capture fewer young and old gazelles than wild dogs.     

Modified netting technique for capturing gazelles in Serengeti,Ngorongoro and Loliondo,Tanzania

During serological surveillance of peste des petits ruminants (PPR) disease, it required capture of randomly selected herds of gazelles as part of a study to determine the epidemiological role of these species in the circulation of peste des petits ruminants virus (PPRV). The study targeted capturing 135 Grant's gazelles (Gazella granti) from the Serengeti ecosystem, Tanzania. A modified netting technique was used aiming at providing safe, efficient and cost‐effective method for capture of gazelles. Locally available materials were used, and wildlife professionals guided the process of manufacturing supporting frame for the nets. Twenty (20) black metal pipes, 20 metal bars, four nets and three vehicles were used in the procedure. A total of 136 Grant's gazelles and nine Thomson's gazelles were captured in three missions. The Grant's gazelles were captured as per sample size calculated in all locations: Loliondo (n = 25), Serengeti National Park (n = 44) and Ngorongoro Conservation Area (NCA) (n = 67) using less time and minimum cost than estimated. Injuries of three fawns (2%) inadvertently captured with the groups of adults and sub‐adult animals were recorded. Comparing with 2014 and other studies, modified netting technique showed high animal and operator safety levels with minimal injuries. With this technique, it was possible to capture even flighty animals that behave nervously because of hunting and other human activities, including Thomson's gazelles, a species previously found to be difficult to capture by netting.     

Orientation and navigation relative to water flow, prey, conspecifics, and predators by the nudibranch mollusc Tritonia diomedea

Progress in understanding sensory and locomotory systems in Tritonia diomedea has created the potential for the neuroethological study of animal navigation in this species. Our goal is to describe the navigational behaviors to guide further work on how the nervous system integrates information from multiple senses to produce oriented locomotion. Observation of T. diomedea in its habitat has suggested that it uses water flow to navigate relative to prey, predators, and conspecifics. We test these hypotheses in the field by comparing slug orientation in time-lapse videos to flow direction in circumstances with and without prey, predators, or conspecifics upstream. T. diomedea oriented upstream both while crawling and after turning. This trend was strongest before feeding or mating; after feeding or mating, the slugs did not orient significantly to flow. Slugs turned downstream away from an upstream predator but did not react in control situations without an upstream predator. These data support the hypothesis that T. diomedea uses a combination of odors (or some other cue transported downstream) and water flow to navigate relative to prey, predators, and conspecifics. Understanding the context-dependent choice between upstream and downstream crawling in T. diomedea provides an opportunity for further work on the sensory integration underlying navigation behavior.     

Variation in the neonate size of Daphnia pulex: the effects of predator exposure and clonal origin

Daphnia pulex clones originating from twelve small pond habitats were exposed to chemical cues from a size-selective predator, larvae of the phantom midge Chaoborus. Exposure delayed the onset of reproduction and increased the size at first reproduction. On the other hand, the neonates produced by these larger mothers were slightly smaller than the neonates produced by the smaller control mothers. In cladocerans, neonate size is usually positively correlated to the size of the mother. Thus exposure to Chaoborus kairomone apparently had direct effects on neonate size counterbalancing the maternal effects. Daphnia clones collected from Chaoborus-free and Chaoborus-rich environments exhibited different responses. In first adult instar, the clones from Chaoborus inhabited environments increased their offspring size under Chaoborus exposure whereas clones from Chaoborus-free environments did not. This may reflect clonal adaptation to the predation prehistory of their original habitat since larger neonates more quickly reach a size protected from the predator.     

The Adaptive Significance of Avian Mobbing

A distinction is made between fitness-enhancing aspects of a trait and selective force(s) that result in its optimization. Any functional explanation conceived to account for the occurrence of mobbing behaviour must explain both the benefits for the initiator and for the birds joining it. Nine teleonomic hypotheses are proposed that permit predictions about the behaviour of the prey and/or the predator in terms of mobbing or its subsequent effects on the behaviour of both parties. Predictions of different hypotheses refer to different aspects of mobbing when prey and predator are considered concurrently. Only two hypotheses lead to contrasting predictions, i. e. to “strong inference tests”. The weakness of the teleonomic method is that it does not enable us to determine when the list of possible functions of a behaviour is exhausted.     

Prey preferences of the cheetah (Acinonyx jubatus) (Felidae: Carnivora): morphological limitations or the need to capture rapidly consumable prey before kleptoparasites arrive?

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.     

Dynamic Risk Assessment: Prey Rapidly Adjust Flight Initiation Distance to Changes in Predator Approach Speed

The pre‐eminent model of flight initiation distance assumes that the function relating predation risk to distance between predator and prey is constant. However, the risk–distance function can change dramatically during approaches by predators. Changes in predator behavior during approach and in availability of benefits (e.g. food or potential mates) may alter risks and/or costs during encounters. Thus, prey should be able to respond appropriately to changes in cues to risk, such as predator approach speed. Under the assumption that prey assess risk in real time, it was predicted that flight initiation distance (distance between predator and prey when escape begins) decreases when approach speed increases and increases when approach speed decreases during an encounter. Effects of single, abrupt changes from slower to faster approach or the reverse were studied in a lizard, Anolis lineatopus. Flight initiation distances were determined solely by final approach speed, being nearly identical for: (1) continuously fast approaches and approaches initially at the slower and finally at the faster speed and (2) for continuously slower approaches and approaches initially at faster and finally at slower speed. Escape should be adjusted to match changes in risk and cost caused by changes in predator behavior, ability to escape, and costs of escape as attacks unfold. A recent model by Broom and Ruxton [Behavioural Ecology (2004) vol. 16, pp. 534—540] predicts that cryptic prey should stay motionless until detected, then flee immediately. Our results suggest that current escape models can be applied to prey escape strategies when cues to risk change, by assuming that prey base decisions on the current relationship between risk and distance. Empirical studies are needed to test predictions concerning continuous risk assessment.     

Effect of Risk on Aspects of Escape Behavior by a Lizard, Holbrookia propinqua, in Relation to Optimal Escape Theory

Prey must balance gains from activities such as foraging and social behavior with predation risk. Optimal escape theory has been successful in predicting escape behavior of prey under a range of risk and cost factors. The optimal approach distance, the distance from the predator at which prey should begin to flee, occurs when risk equals cost. Optimal escape theory predicts that for a fixed cost, the approach distance increases as risk increases. It makes no predictions about approach distance for prey in refuges that provide only partial protection or about escape variables other than approach distance, such as the likelihood of stopping before entering refuge and escape speed. By experimentally simulating a predator approaching keeled earless lizards, Holbrookia propinqua, the predictions of optimal escape theory for two risk factors, predator approach speed and directness of approach were tested. In addition, predictions that the likelihood of fleeing into refuge without stopping and the speed of escape runs increase with risk, in this case predator approach speed, and that lizards in incompletely protective refuges permit closer approach than lizards not in refuges were also tested. Approach distance increased with predator approach speed and directness of approach, confirming predictions of optimal escape theory. Lizards were more likely to enter refuge and ran faster when approached rapidly, verifying that predation risk affects escape decisions by the lizards for escape variables not included in optimal escape theory. They allowed closer approach when in incompletely protective refuges than when in the open, confirming the prediction that risk affects escape decisions while in refuge. Optimal escape theory has been highly successful, but testing it has led to relative neglect of important aspects of escape other than approach distance.     

Confusion Effect in a Reptilian and a Primate Predator

The confusion effect is claimed to be one benefit of group living with respect to predator avoidance: it is more difficult for predators to capture prey that is surrounded by other conspecifics than to capture an isolated individual. So far, the predictions of the confusion effect have been tested mainly in aquatic predators. As the confusion effect is seen to be a general problem for predators, terrestrial predators of two different vertebrate classes were used to test it. The prey (mealworms and black beetles, Tenebrio molitor ) was harmless and had no chance of predator avoidance. Thus, confounding effects of group defence and enhanced vigilance were controlled. Both leopard geckos ( Eublepharis macularius ) and common marmosets ( Callithrix jacchus ) took longer to catch one out of several prey compared to one single prey. Leopard geckos showed more fixations (changing of head position) when confronted with 20 mealworms than when confronted with only one mealworm, thus showing indications of being 'confused'.     

Landscape scale, heterogeneity, and the viability of Serengeti grazers

Species persistence can be threatened by substantial temporal variation in food resources over time. On the other hand, spatial heterogeneity in resources at the landscape scale might allow mobile consumers to compensate for temporal variability in resource availability at the local scale. We evaluated this hypothesis, using an extensive data set on foraging, grass growth, and movement by Thomson's gazelles living on the Serengeti Plains. Here we show that modelled populations of Thomson's gazelles can only persist under Serengeti conditions in the face of observed levels of rainfall stochasticity by making adaptive movements to take advantage of ephemeral spatial distributions of food resources. More importantly, our models suggest that Thomson's gazelles in Serengeti require unrestricted access to relatively large areas of grassland (> 1600 km²) to guarantee long‐term persistence, particularly when there is positive spatial autocorrelation in resource abundance, as is the case in Serengeti. If this proves to be true for other species and/or other systems, then understanding of complex behavioural responses to spatially and temporally heterogeneous food supplies may be essential to successful conservation of grazing herbivores.     

Effects of risk assessment, predator behavior, and habitat on escape behavior in Columbian black-tailed deer

The relationship between preflight risk assessment by prey andthe escape behaviors they perform while fleeing from predatorsis relatively unexplored. To examine this relationship, a humanobserver approached groups of Columbian black-tailed deer (Odocoileushemionus columbianus), varying his behavior to simulate moreor less threatening behavior. We measured the focal deer's angleof escape, distance moved during flight, duration of trottingand stotting behavior, and change in elevation during flight.Analyses revealed positive relationships between the distancemoved during flight and the distance at which they fled. Whenflight was initiated when the approacher was close, deer fledrelatively shorter distances and took flight paths at more acuteangles, a property that would force a real predator to changedirection suddenly. Our results indicate that deer do not compensatefor allowing the observer to approach more closely by fleeinggreater distances. Rather, distance moved and flight initiationdistance are linked by level of reactivity and habituation:more reactive or less habituated deer both flee at a greaterdistance and move away to a greater distance during flight.More threatening behavior by the approacher led to longer durationsof rapid flight behavior (e.g., trotting and stotting), anddeer tended to flee uphill and into taller vegetation, usingthese landscape features as refuge from danger. Finally, weprovide the first evidence for Pitcher's untested "antiambush"hypothesis for the function of stotting and discuss its significance.In general, both preflight predator behavior and habitat featuresinfluence both duration and direction of escape.     

Reversible frequency-dependent predation of a puffer, Takifugu niphobles (Pisces: Tetraodontidae), related to spatial distribution of colour-polymorphic prey

The puffer Takifugu niphobles is a top predator of hard-shelled prey such as molluscs; its predatory tactics may affect the evolution of prey coloration. Two hypotheses concerning its foraging were tested: (1) T. niphobles shows frequency dependence in foraging colour-polymorphic prey, and (2) such dependence reverses in response to changes in prey distribution. Captive fish were provided with 70 artificial prey, coloured either dark brown or pale brown, at four frequencies (1 : 4, 2 : 3, 3 : 2, 4 : 1) and in two distribution patterns (uniform and aggregated). When prey were uniformly distributed, frequency and feeding rate significantly influenced colour preference: the common morph was consumed more. When prey were aggregated, frequency significantly affected preference only when the feeding rate was low, in which case the rare morph was consumed more. Thus both hypotheses were supported. The impact of T. niphobles 's frequency-dependent predation and its reversal on the colour evolution of prey species, especially molluscs, is discussed.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 81 , 197–202.     

Rethinking trophic niches: Speed and body mass colimit prey space of mammalian predators

1. Realized trophic niches of predators are often characterized along a one‐dimensional range in predator–prey body mass ratios. This prey range is constrained by an “energy limit” and a “subdue limit” toward small and large prey, respectively. Besides these body mass ratios, maximum speed is an additional key component in most predator–prey interactions.
2. Here, we extend the concept of a one‐dimensional prey range to a two‐dimensional prey space by incorporating a hump‐shaped speed‐body mass relation. This new “speed limit” additionally constrains trophic niches of predators toward fast prey.
3. To test this concept of two‐dimensional prey spaces for different hunting strategies (pursuit, group, and ambush predation), we synthesized data on 63 terrestrial mammalian predator–prey interactions, their body masses, and maximum speeds.
4. We found that pursuit predators hunt smaller and slower prey, whereas group hunters focus on larger but mostly slower prey and ambushers are more flexible. Group hunters and ambushers have evolved different strategies to occupy a similar trophic niche that avoids competition with pursuit predators. Moreover, our concept suggests energetic optima of these hunting strategies along a body mass axis and thereby provides mechanistic explanations for why there are no small group hunters (referred to as “micro‐lions”) or mega‐carnivores (referred to as “mega‐cheetahs”).
5. Our results demonstrate that advancing the concept of prey ranges to prey spaces by adding the new dimension of speed will foster a new and mechanistic understanding of predator trophic niches and improve our predictions of predator–prey interactions, food web structure, and ecosystem functions.

     

An enemy of your enemy is your friend: Impact of predators on aggregation behavior of gammarids

Predation pressure may affect many aspects of prey behavior, including forming groups and changes in social interactions. We studied the aggregation behavior of competing gammarids Dikerogammarus villosus and Pontogammarus robustoides (Amphipoda, Crustacea) to check whether they modify their preferences for conspecifics or heterospecifics in response to predator (the racer goby Babka gymnotrachelus) kairomones in the presence or absence of stone shelters (alternative protection source). Both species exhibited preferences toward shelters occupied by conspecifics over empty shelters and conspecifics apart from shelters, suggesting that their aggregation depends not only on habitat heterogeneity, but also on their social interactions. Moreover, gammarids in the presence of shelters (safer conditions) preferred conspecifics over heterospecifics, but predator kairomones made them form aggregations irrespective of species. In the predator presence, P. robustoides increased its aggregation level only in the sheltered conditions, whereas D. villosus exhibited this response only in the absence of shelters, suggesting that this behavior can protect it against predators. Therefore, we tested the antipredator effectiveness of D. villosus aggregations by exposing them to fish predation. Gobies foraged most effectively on immobile single gammarids compared to moving and aggregated individuals. Fish also avoided aggregated prey, confirming the protective character of aggregations. We have demonstrated that the predator presence increases aggregation level of prey gammarids and affects their social behavior by reducing antagonistic interactions and avoidance between competing species. This is likely to affect their distribution and functioning in the wild, where predator pressure is a standard situation.     

Do anuran larvae respond behaviourally to chemical cues from an invasive crayfish predator? A community-wide study

Antipredator behaviour is an important fitness component in most animals. A co-evolutionary history between predator and prey is important for prey to respond adaptively to predation threats. When non-native predator species invade new areas, native prey may not recognise them or may lack effective antipredator defences. However, responses to novel predators can be facilitated by chemical cues from the predators’ diet. The red swamp crayfish Procambarus clarkii is a widespread invasive predator in the Southwest of the Iberian Peninsula, where it preys upon native anuran tadpoles. In a laboratory experiment we studied behavioural antipredator defences (alterations in activity level and spatial avoidance of predator) of nine anurans in response to P. clarkii chemical cues, and compared them with the defences towards a native predator, the larval dragonfly Aeshna sp. To investigate how chemical cues from consumed conspecifics shape the responses, we raised tadpoles with either a tadpole-fed or starved crayfish, or dragonfly larva, or in the absence of a predator. Five species significantly altered their behaviour in the presence of crayfish, and this was largely mediated by chemical cues from consumed conspecifics. In the presence of dragonflies, most species exhibited behavioural defences and often these did not require the presence of cues from predation events. Responding to cues from consumed conspecifics seems to be a critical factor in facilitating certain behavioural responses to novel exotic predators. This finding can be useful for predicting antipredator responses to invasive predators and help directing conservation efforts to the species at highest risk.