The role of water abundance, thermoregulation, perceived predation risk and interference competition in water access by African herbivores

In African savannas, surface water can become limiting and an understanding of how animals address the trade-offs between different constraints to access this resource is needed. Here, we describe water access by ten African herbivore species in Hwange National Park, Zimbabwe, and we explore four possible determinants of the observed behaviours: water abundance, thermoregulation, perceived predation risk and interference competition. On average, herbivores were observed to drink in 80% of visits to a waterhole. The probability of drinking was higher in 2003 (474 mm) than in 2004 (770 mm), and at the end of the dry season than at its beginning. For larger species, this probability may also be related to risks of interference competition with elephants or other herbivores. For smaller species, this probability may also be related to the perceived risk of predation. We also investigate the time spent accessing water to drink. The influence of herd size and the presence of young on the time spent accessing water for most species suggests that perceived predation risk plays a role. Thermoregulation also affects this time: during the hottest periods, herbivores spend less time in open areas, unless when wind is strong, probably owing to evapotranspired heat loss.     

Diet of Pacific sleeper shark, a potential Steller sea lion predator, in the north-east Pacific Ocean

Pacific sleeper sharks Somniosus pacificus were captured near Steller sea lion Eumetopias jubatus rookeries during the period when Steller sea lion pups are most vulnerable to Pacific sleeper shark predation (first water entrance and weaning). Analysis of stomach contents revealed that teleosts were the dominant prey in August and cephalopods were the dominant prey in May ( n = 198). Marine mammals were found in 15% of stomachs regardless of season, but no Steller sea lion tissues were detected. Molecular genetic analysis identified grey whale Eschrichtius robustus and harbour seal Phoca vitulina remains in some Pacific sleeper shark stomachs. Most mammals were cetacean and at least 70% of the cetaceans were probably scavenged. Although Pacific sleeper shark and Steller sea lion ranges overlapped, so predation could potentially occur, the diet study suggested that predation on Steller sea lions is unlikely, at least when pups first enter the water or during weaning. Harbour seals were infrequent prey and may have been consumed alive. Pacific sleeper sharks consume fast-swimming prey like Pacific salmon Oncorhynchus sp., most likely live animals rather than scavenged animals. Pacific sleeper sharks appeared to be opportunistic consumers of the available prey and carrion, feeding both on the bottom and in the water column, and their diet shifted to teleosts and cetacean carrion as the fish grew larger.     

Complex tactics in a dynamic large herbivore–carnivore spatiotemporal game

The spatiotemporal game between predators and prey is a fundamental process governing their distribution dynamics. Players may adopt different tactics as the associated costs and benefits change through time. Yet few studies have investigated the potentially simultaneous and dynamic nature of movement tactics used by both players. It is particularly unclear to what extent perceived predation risk mediates the fine‐scale distribution of large and dangerous prey, which are mostly driven by bottom–up, resource‐related processes. We built habitat use and movement models based on 10 years of monitoring GPS‐collared grey wolves Canis lupus and plains bison Bison bison bison in Prince Albert National Park, Canada, to investigate the predator–large prey game in a multi‐prey system. Bison did not underuse patches of high‐quality vegetation at any time during the seasonal cycle even though wolves were selectively patrolling these areas. Rather, in at least one season, bison engaged in complex tactics comprised of proactive responses to the long‐term distribution (risky places) and reactive responses to the immediate proximity (risky times) of their opponent. In summer–autumn, bison reduced the time spent in food‐rich patches as both the long‐term use and the immediate proximity of wolves increased. By demonstrating that wolf distribution triggers patch abandonment by bison, we provide a key element in support of the shell game hypothesis – where prey move constantly to avoid predators attempting to anticipate their location. In winter, a season of relatively high energetic stress, bison no longer abandoned food‐rich patches as predation risk increased, while no bison responses to wolves were observed in spring–summer. Our work demonstrates the highly dynamic and complex nature of the predator–large prey spatiotemporal game, a key trait‐mediated mechanism by which trophic interactions structure ecological communities.     

Putting floodplain hyperdiversity in a regional context: an assessment of terrestrial–floodplain connectivity in a montane environment

Abstract Aim and location Alluvial flood plains support higher levels of vascular plant species richness than other terrestrial ecosystems. Whereas the spatial and temporal heterogeneity of these ecosystems has been considered the local determinant of high plant richness, regional influences, such as regional species pools have received little attention. In this study we surveyed plant species richness across the entire Nyack catchment (c. 21,000 ha), in Glacier National Park, USA, to determine the relation of upland ecosystem community structure to biodiversity patterns on montane floodplains that are relatively extensive and flood‐scoured ecosystems. Method We surveyed floodplain and other terrestrial ecosystems within the Nyack catchment using 50 × 2 m plots to record species present and visual estimates of percentage cover. Species pools from flood plains and three other terrestrial ecosystems (low elevation forests, sub‐Alpine forests and alpine) were analysed with nested subset analysis, detrended correspondence analysis (DCA), and an index of beta diversity to identify dissimilarity in species composition and richness, and the separate contributions of generalists (species occurring in more than one ecosystem) and specialists to richness in each ecosystem. Analysis of variance and post hoc Tukey–Kramer tests were used to identify where in the Nyack catchment each species was most abundant. Species life form and dispersal strategies were analysed to better understand influences on beta diversity. Results Our data show that in this pristine system, floodplain ecosystems host 202 (63%) of the 320 vascular plants identified within Nyack catchment. Of these species, the nested subset analysis showed that 146 (72%) are found in at least one adjacent upland ecosystem. While the DCA ordination scatter plots show statistically significant separations of ecosystems on the first two axes, values of beta diversity showed that substantial similarity exists between floodplain and all upland species pools. Further, of the 146 floodplain species shared with upland ecosystems, 61% were more frequent in upland ecosystems, whereas 55% were more abundant in uplands than flood plains (Tukey–Kramer P ≤ 0.05). Significant numbers of specialists were found on flood plains (24% of floodplain species), but also within upland ecosystems, where 23% and 40% of low elevation forest and alpine species were found to be specialists, respectively. Whereas 83% of herb generalists were wind dispersed, <70% of specialists were animal dispersed, indicating that similarity in species pools may be driven by wind dispersal. Main conclusions These results suggest a re‐evaluation of the contribution of floodplain ecosystems to regional plant species richness. While flood plains host specialists, other ecosystems had equal or higher levels of regional ‘endemism’. Furthermore, these data suggest that conservation of high levels of biodiversity on floodplain ecosystems may require consideration of upland ecosystems throughout the catchment as the majority of species were relatively rare on flood plains, indicating they may be sink habitats for some species.     

Relaxation of risk-sensitive behaviour of prey following disease-induced decline of an apex predator,the Tasmanian devil

Apex predators structure ecosystems through lethal and non-lethal interactions with prey, and their global decline is causing loss of ecological function. Behavioural changes of prey are some of the most rapid responses to predator decline and may act as an early indicator of cascading effects. The Tasmanian devil (Sarcophilus harrisii), an apex predator, is undergoing progressive and extensive population decline, of more than 90% in long-diseased areas, caused by a novel disease. Time since local disease outbreak correlates with devil population declines and thus predation risk. We used hair traps and giving-up densities (GUDs) in food patches to test whether a major prey species of devils, the arboreal common brushtail possum (Trichosurus vulpecula), is responsive to the changing risk of predation when they forage on the ground. Possums spend more time on the ground, discover food patches faster and forage more to a lower GUD with increasing years since disease outbreak and greater devil population decline. Loss of top–down effects of devils with respect to predation risk was evident at 90% devil population decline, with possum behaviour indistinguishable from a devil-free island. Alternative predators may help to maintain risk-sensitive anti-predator behaviours in possums while devil populations remain low.     

Ecological drivers of female lion (Panthera leo) reproduction in the Kruger National Park

The role of social cues in the reproduction of social mammals, particularly carnivores, has been thoroughly studied and documented in literature. However, environmental cues such as resources of water, food, and shelter have been identified to a lesser extent. Pregnant lions (Panthera leo) are notoriously secretive during the final stages of pregnancy and postpartum. Behavioral indicators depicted by movement patterns obtained by remote detection of collared female lions in the Kruger National Park were necessary for the monitoring of birth timing. Over the study period, eight plus a potential three parturition incidences of collared females were recorded. Of the variables measured (step length, range size, duration, prey biomass, and rainfall), range size during the month of parturition was the most indicative movement pattern of a successful birth. By backdating the potential birth month of the litters, date of conception was calculated and our results revealed a correlation between the birthing peaks of preferred prey during the month of conception. Birth timing in conjunction with remote sensing and ecological factors were thus identified behaviors associated with denning.     

Nonconsumptive effects in a multiple predator system reduce the foraging efficiency of a keystone predator

Many studies have demonstrated that the nonconsumptive effect (NCE) of predators on prey traits can alter prey demographics in ways that are just as strong as the consumptive effect (CE) of predators. Less well studied, however, is how the CE and NCE of multiple predator species can interact to influence the combined effect of multiple predators on prey mortality. We examined the extent to which the NCE of one predator altered the CE of another predator on a shared prey and evaluated whether we can better predict the combined impact of multiple predators on prey when accounting for this influence. We conducted a set of experiments with larval dragonflies, adult newts (a known keystone predator), and their tadpole prey. We quantified the CE and NCE of each predator, the extent to which NCEs from one predator alters the CE of the second predator, and the combined effect of both predators on prey mortality. We then compared the combined effect of both predators on prey mortality to four predictive models. Dragonflies caused more tadpoles to hide under leaf litter (a NCE), where newts spend less time foraging, which reduced the foraging success (CE) of newts. Newts altered tadpole behavior but not in a way that altered the foraging success of dragonflies. Our study suggests that we can better predict the combined effect of multiple predators on prey when we incorporate the influence of interactions between the CE and NCE of multiple predators into a predictive model. In our case, the threat of predation to prey by one predator reduced the foraging efficiency of a keystone predator. Consequently, the ability of a predator to fill a keystone role could be compromised by the presence of other predators.     

Detection and avoidance of an entomopathogenic fungus by a generalist insect predator

Abstract.  1. Increasing evidence suggests that insects can assess their environment based on cues related to mortality risks to themselves or their offspring. Limited knowledge is available on such abilities in relation to entomopathogenic fungi, which can cause significant mortality in insect populations. In laboratory bioassays, the ability of the generalist predator Anthocoris nemorum L. (Heteroptera: Anthocoridae) to detect the presence of its natural enemy, the fungal pathogen Beauveria bassiana (Balsamo) Vuillemin (Ascomycota: Hypocreales) was investigated.
2. Behavioural observations were conducted on adults of A. nemorum foraging in choice and non-choice arenas treated with conidia suspensions of B. bassiana or just the carrier (control). The arenas consisted either of nettle leaves or soil. Additionally, behaviours in response to sporulating nettle aphid cadavers compared with uninfected aphids or paper balls were evaluated on nettle leaves. An oviposition experiment was also conducted in choice arenas on conidia-treated and untreated nettle leaves.
3. Males and females detected and avoided contact with leaf surfaces inoculated with B. bassiana . Females that were forced to enter fungus-treated leaf surfaces were very reluctant to do so. When females encountered cadavers sporulating with B. bassiana they rapidly withdrew compared with harmless paper ball dummies. Soil inoculated with B. bassiana did not affect A. nemorum behaviour or residence time compared with control soil. Females inserted significantly more eggs in control leaf areas compared with areas treated with B. bassiana conidia.
4. All results suggest that A. nemorum detects and avoids the pathogen B. bassiana when it forages on host plants with which it is adapted but not on soil surfaces. The adaptive significance of detection of entomopathogenic fungi is discussed.     

Relationship between group dynamics and spatial distribution of African elephants in a semi‐arid environment

Group dynamics related to distribution of African elephants in the semi‐arid environment of Tsavo East National Park, Kenya was studied between 2007 and 2010. I examined the seasonal distribution of lone bulls, bull groups, family units and mixed groups and group size. Lone bulls were widely distributed in the dry season and localized in the wet season, whereas bull groups were localized in both seasons. On average bull group size did not differ with seasons or areas, but larger groups were observed in preferred areas in the dry season. Family units were widely distributed in the dry season and localized in the wet season, whereas mixed groups were localized in both seasons. Although family units and mixed groups tended to be large in all areas in the wet season, large groups were also observed in the dry season. Large family units were widely distributed, whereas large mixed groups were localized. The relationship between group dynamics and distribution was attributed to the combination of social, ecological and poaching factors. This study provided insight into distribution patterns that can be applied to the security of the Tsavo elephant population.     

Inhibition of development of anti-predator morphology in the small cladoceran Bosmina by an insecticide: impact of an anthropogenic chemical on prey–predator interactions

1. The combined effect of the insecticide carbaryl and the predator (Leptodora kindtii) kairomone was assessed on the development of protuberant morphology in the small cladoceran Bosmina fatalis, a feature which evolved originally as a response to the kairomone. The experiment showed that Bosmina changed its morphology in response to the kairomone, but development was inhibited by carbaryl at a sub‐lethal concentration even in the presence of the kairomone. At the same time, reduction of fecundity was observed in animals exposed to carbaryl. 2. A short‐term feeding experiment (B. fatalis versus Leptodora) indicated that such low concentrations of the insecticide had no impact on predation by Leptodora. Thus, it is suggested that the inhibition of development of anti‐predatory defences in Bosmina can increase its vulnerability to predation. 3. Such disturbance of chemical communication by the insecticide reduces the individual survival rate of prey Bosmina in the environment with high predator density. On the other hand, reduction of fecundity may result in decreased population growth rate of animals. 4. The impact of the insecticide on the anti‐predator morphology in Bosmina (inhibition) was opposite to that in Daphnia (enhancement). This suggests that biochemical induction processes in the development of anti‐predatory morphology are evolutionally different between Daphnia and Bosmina.     

An unusual incident of adoption in a wild chimpanzee (Pan troglodytes) population at Gombe National Park

Allomothering and adoption are well documented across primate species. Multiple hypotheses have been proposed to explain the evolution of such behavior according to the costs and benefits to the caregiver, mother, and infant. Permanent adoptions and allomothering have been observed in chimpanzees, but they typically involve the infants' siblings or nulliparous females. Here, I report a unique incident of adoption where an infant was adopted by its grandmother without the death of its mother. I conclude by considering how the adoption may have benefited the grandmother, mother, and infant.     

Population structure and ecology of the African buffalo (Syncerus caffer Sparrman, 1779) in Chebera Churchura National Park,Ethiopia

An investigation of population structure and ecology of the African buffalo (Syncerus caffer Sparrman, 1779) was carried out in the Chebera Churchura National Park, Ethiopia during the wet and dry seasons of 2005–2006. Sample counts of African buffaloes were carried out in an area of 1,215 km². The estimated population of buffalo was 2,617 individuals. Males comprised 35.0%, while females 52.8% of the population. The remaining 12% of the population was young of both sexes and of all ages of unknown sex. It was difficult to categorize the young into male and female in the field, as their primary sexual characteristics were not easily visible. Male to female sex ratio was 1.00 : 1.51. Age structure was dominated by adults, which constituted 72.06% of the total population. Subadults comprised 22.02%, and young accounted for 5.9% of the population. Larger herds of up to 27 individuals were observed during the wet season and smaller herds of eight individuals during the dry season. The mean herd size during wet and dry seasons was 24.81 and 7.77, respectively. The African buffaloes were distributed in four habitat types such as grasslands, woodlands, montane forests and riverine habitat in the study area. They were observed more in the riverine vegetation types during the dry season. Relative abundance of food resources, green vegetation cover and water availability in the area were the major factors governing their distribution in the present study area. They spent a greater proportion of the time in feeding and resting/ruminating activities. On the average, 49.7% of the daytime was spent in feeding, and 38.75% of the day on resting (lying down and standing). Morning and the late afternoon activity peaks were more pronounced during the dry season than the wet season.