Habitat shifts in response to predation risk are constrained by competition within a grazing guild

Predators can affect prey not only by killing them, but also by causing them to alter their behavior, including patterns of habitat selection. Prey can reduce the risk of predation by moving to habitats where predators are less likely to detect them, less likely to attack, or less likely to succeed. The interaction of such responses to risk with other ecological processes remains relatively unstudied, but in some cases, changes in habitat use to avoid predation may be constrained by competition: larger, dominant competitors should respond freely to predation risk, but the responses of smaller, subordinate competitors may be constrained by the responses of dominant competitors. For large grazing herbivores, an alternative hypothesis proposes that smaller prey species are vulnerable to more predators, and thus should respond more strongly to predation risk. Here, we tested these two hypotheses with 775 observations of habitat selection by four species of obligate grazers (zebra, wildebeest, puku and oribi) in the immediate presence or absence of four large carnivores (lion, spotted hyena, African wild dog and cheetah) in three ecosystems (Greater Liuwa, Greater Kafue and Luangwa Valley). Patterns of predation within this set were described by observation of 1,105 kills. Our results support the hypothesis that responses to predation risk are strongest for larger, dominant competitors. Even though zebras were killed least often, they showed the strongest shift into cover when carnivores were present. Wildebeest, puku and oribi showed weaker habitat shifts, even though they were more frequently killed. These patterns remained consistent in models that controlled for differences in the hunting mode of the predator (stalking, coursing, or intermediate) and for differences among ecosystems. There was no evidence that smaller species were subject to predation by a broader set of predators. Instead, smaller prey were killed often by smaller predators, and larger prey were killed often by larger predators. Broadly, our results show that responses to predation risk interact with interspecific competition. Accounting for such interactions should help to explain the considerable variation in the strength of responses to predation risk that has been observed

Using dogs to find cats: detection dogs as a survey method for wide-ranging cheetah

Rapid global large carnivore declines make evaluations of remaining populations critical. Yet landscape-scale evaluations of presence, abundance and distribution are difficult, as many species are wide-ranging, occur only at low densities and are elusive. Insufficient information-gathering tools for many large carnivore species compounds these challenges. Specially trained detection dogs have demonstrated effectiveness for carnivore surveys, but are untested on extremely sparse, wide-ranging species, such as cheetah Acinonyx jubatus. In this study, we conducted the first rigorous cheetah survey using detection dogs in a key transboundary area in the remote Liuwa–Mussuma Transfrontier Conservation Area (TFCA) in Western Zambia. We proposed to (1) evaluate the effectiveness of detection dog versus spoor surveys in detecting cheetah presence; (2) extract and analyze DNA from scat samples to estimate minimum population size and genetic effective population size; (3) determine the extent of cheetah occurrence in the unprotected transboundary corridor. Two detection dog teams surveyed 2432 km2 containing 74 randomly located transects in the transfrontier area. Twenty-seven cheetah scats were detected and confirmed by genetic analysis, while no cheetah spoor was detected, clearly demonstrating the superiority of detection dogs in detecting cheetah presence. Combining scat samples with opportunistically collected samples, we estimated 17–19 cheetahs, an effective population size of 8–14 and a density of 5.9–6.6 per 1000 km2. Cheetah utilized key transfrontier areas outside of the national park; however, because utilization appears low, improved connectivity and protection for these areas are critical. Approximately one third of Africa's estimated cheetah resides in protected areas, with 87% in transboundary areas. Our study demonstrates the efficacy of detection dog survey methods in providing information on cheetah across large landscapes. It will have particular value in areas where other survey means may be impossible, such as TFCAs, where size, remoteness and lack of accessibility often make traditional survey methods difficult or cost prohibitive

Risky times and risky places interact to affect prey behaviour.

Both short-term and long-term variation in predation risk can affect the behaviour of prey, thus affecting growth, reproduction, survival and population dynamics. Inferences about the strength of such 'risk effects' in the wild have been limited by a lack of studies that relate antipredator responses to the magnitude of direct predation, measure responses of prey to risk from complete predator guilds, and quantify risk in more than one way. Here, we quantify behavioural responses of a complete ungulate prey guild to long-term and short-term variation in risks from all of the large predators in Liuwa Plain National Park, with known patterns of direct predation. Our analysis allows the first direct test for interaction between responses to long-term and short-term risk in the wild, and reveals that prey vigilance responds strongly to locations with high long-term risk when short-term risk is high, but not when short-term risk is low. This result has broad ramifications for the design and interpretation of field studies of antipredator behaviour, its costs and its consequences for population dynamics

Risky times and risky places interact to affect prey behaviour.

Both short-term and long-term variation in predation risk can affect the behaviour of prey, thus affecting growth, reproduction, survival and population dynamics. Inferences about the strength of such 'risk effects' in the wild have been limited by a lack of studies that relate antipredator responses to the magnitude of direct predation, measure responses of prey to risk from complete predator guilds, and quantify risk in more than one way. Here, we quantify behavioural responses of a complete ungulate prey guild to long-term and short-term variation in risks from all of the large predators in Liuwa Plain National Park, with known patterns of direct predation. Our analysis allows the first direct test for interaction between responses to long-term and short-term risk in the wild, and reveals that prey vigilance responds strongly to locations with high long-term risk when short-term risk is high, but not when short-term risk is low. This result has broad ramifications for the design and interpretation of field studies of antipredator behaviour, its costs and its consequences for population dynamics

Response of wildebeest (Connochaetes taurinus) movements to spatial variation in long term risks from a complete predator guild

Many studies have shown that behavioral responses to the risk posed by predators can carry costs for prey by reducing fecundity or survival, with consequent effects on population dynamics. Responses to risk include increased vigilance and reduced foraging, movement to safe habitats, increases or decreases in group size, and changes in patterns of movement. While we know that prey can detect and respond to both long term (LT) and short term (ST) variation in risk, field studies have only recently begun to consider how these responses might differ. Here, we hypothesize that prey movement patterns should respond differently to cues of LT and ST variation in risk. Specifically, cues of elevated LT risk might lead to decreased movement to improve the assessment of ST risk, while elevated ST risk might favor increased movement to reduce the proximity or duration of risks that are already assessed to be acute. We further hypothesize that decreases in movement are likely to be a general response to LT risk, while responses to ST risk are likely to vary in a manner that depends on the type of predator. In Liuwa Plain National Park, we found that wildebeest movements responded to the local intensity of predator use (LT risk), after controlling for other seasonal, diurnal and bottom-up effects. Speed decreased considerably and turning angles increased considerably, combining to markedly decrease linear movements. In contrast, immediate encounters with predators (ST risk) typically provoked fast, linear flight, and this effect was stronger for encounters with coursing predators. The effect of long term risk was to cause wildebeest to move more slowly and less linearly, i.e. to slow down and turn around, as part of a suite of behavioral responses, which also includes increased vigilance, that promote cautious assessment of ST risks when in locations with high levels of LT risk. This result has broad implications of understanding the influence of predation risk on foraging patterns of ungulates as this relationship is much more complex than simple avoidance of areas of ‘high risk’

Response of wildebeest (Connochaetes taurinus) movements to spatial variation in long term risks from a complete predator guild

Many studies have shown that behavioral responses to the risk posed by predators can carry costs for prey by reducing fecundity or survival, with consequent effects on population dynamics. Responses to risk include increased vigilance and reduced foraging, movement to safe habitats, increases or decreases in group size, and changes in patterns of movement. While we know that prey can detect and respond to both long term (LT) and short term (ST) variation in risk, field studies have only recently begun to consider how these responses might differ. Here, we hypothesize that prey movement patterns should respond differently to cues of LT and ST variation in risk. Specifically, cues of elevated LT risk might lead to decreased movement to improve the assessment of ST risk, while elevated ST risk might favor increased movement to reduce the proximity or duration of risks that are already assessed to be acute. We further hypothesize that decreases in movement are likely to be a general response to LT risk, while responses to ST risk are likely to vary in a manner that depends on the type of predator. In Liuwa Plain National Park, we found that wildebeest movements responded to the local intensity of predator use (LT risk), after controlling for other seasonal, diurnal and bottom-up effects. Speed decreased considerably and turning angles increased considerably, combining to markedly decrease linear movements. In contrast, immediate encounters with predators (ST risk) typically provoked fast, linear flight, and this effect was stronger for encounters with coursing predators. The effect of long term risk was to cause wildebeest to move more slowly and less linearly, i.e. to slow down and turn around, as part of a suite of behavioral responses, which also includes increased vigilance, that promote cautious assessment of ST risks when in locations with high levels of LT risk. This result has broad implications of understanding the influence of predation risk on foraging patterns of ungulates as this relationship is much more complex than simple avoidance of areas of ‘high risk’

The Human Immunodeficiency Virus Type 1 Envelope Confers Higher Rates of Replicative Fitness to Perinatally Transmitted Viruses than to Nontransmitted Viruses ▿ †

Selection of a minor viral genotype during perinatal transmission of human Immunodeficiency virus type 1 (HIV-1) has been observed, but there is a lack of information on the correlation of the restrictive transmission with biological properties of the virus, such as replicative fitness. Recombinant viruses expressing the enhanced green fluorescent protein or the Discosoma sp. red fluorescent (DsRed2) protein carrying the V1 to V5 regions of env from seven mother-infant pairs (MIPs) infected by subtype C HIV-1 were constructed, and competition assays were carried out to compare the fitness between the transmitted and nontransmitted viruses. Flow cytometry was used to quantify the frequency of infected cells, and the replicative fitness was determined based on a calculation that takes into account replication of competing viruses in a single infection versus dual infections. Transmitted viruses from five MIPs with the mothers chronically infected showed a restrictive env genotype, and all the recombinant viruses carrying the infants' Env had higher replicative fitness than those carrying the Env from the mothers. This growth fitness is lineage specific and can be observed only within the same MIP. In contrast, in two MIPs where the mothers had undergone recent acute infection, the viral Env sequences were similar between the mothers and infants and showed no further restriction in quasispecies during perinatal transmission. The recombinant viruses carrying the Env from the infants' viruses also showed replication fitness similar to those carrying the mothers' Env proteins. Our results suggest that newly transmitted viruses from chronically infected mothers have been selected to have higher replicative fitness to favor transmission, and this advantage is conferred by the V1 to V5 region of Env of the transmitted viruses. This finding has important implications for vaccine design or development of strategies to prevent HIV-1 transmission

Do protection gradients explain patterns in herbivore densities? An example with ungulates in Zambia's Luangwa Valley

Ungulate populations face declines across the globe, and populations are commonly conserved by using protected areas. However, assessing the effectiveness of protected areas in conserving ungulate populations has remained difficult. Using herd size data from four years of line transect surveys and distance sampling models, we modeled population densities of four important herbivore species across a gradient of protection on the edge of Zambia's South Luangwa National Park (SLNP) while accounting for the role of various ecological and anthropogenic variables. Our goal was to test whether protection was responsible for density dynamics in this protection gradient, and whether a hunting moratorium impacted herbivore densities during the studies. For all four species, we estimated lower densities in partially protected buffer areas adjacent to SLNP (ranging from 4.5-fold to 13.2-fold lower) compared to protected parklands. Density trends through the study period were species-specific, with some species increasing, decreasing, or remaining stable in all or some regions of the protection gradient. Surprisingly, when controlling for other covariates, we found that these observed differences were not always detectably related to the level of protection or year. Our findings highlight the importance of accounting for variables beyond strata of interest in evaluating the effectiveness of a protected area. This study highlights the importance of comprehensively modeling ungulate population density across protection gradients, identifies lands within an important protection gradient for targeted conservation and monitoring, documents prey depletion and expands our understanding on the drivers in a critical buffer area in Zambia

Foraging investment in a long- lived herbivore and vulnerability to coursing and stalking predators

Allocating resources to growth and reproduction requires grazers to invest time in foraging, but foraging promotes dental senescence and constrains expression of proactive antipredator behaviors such as vigilance. We explored the relationship between carnivore prey selection and prey foraging effort using incisors collected from the kills of coursing and stalking carnivores. We predicted that prey investing less effort in foraging would be killed more frequently by coursers, predators that often exploit physical deficiencies. However, such prey could expect delayed dental senescence. We predicted that individuals investing more effort in foraging would be killed more frequently by stalkers, predators that often exploit behavioral vulnerabilities. Further these prey could expect earlier dental senescence. We tested these predictions by comparing variation in age‐corrected tooth wear, a proxy of cumulative foraging effort, in adult (3.4–11.9 years) wildebeest killed by coursing and stalking carnivores. Predator type was a strong predictor of age‐corrected tooth wear within each gender. We found greater foraging effort and earlier expected dental senescence, equivalent to 2.6 additional years of foraging, in female wildebeest killed by stalkers than in females killed by coursers. However, male wildebeest showed the opposite pattern with the equivalent of 2.4 years of additional tooth wear in males killed by coursers as compared to those killed by stalkers. Sex‐specific variation in the effects of foraging effort on vulnerability was unexpected and suggests that behavioral and physical aspects of vulnerability may not be subject to the same selective pressures across genders in multipredator landscapes