Niche partitioning in a guild of invasive mammalian predators

Predators compete aggressively for resources, establishing trophic hierarchies that influence ecosystem structure. Competitive interactions are particularly important in invaded ecosystems where introduced predators can suppress native prey species. We investigated whether niche partitioning exists within a guild of invasive mammalian predators and determined the consequences for native species. Over 4405 camera-trap days, we assessed interactions among three invasive predators: two apex predators (feral cats Felis catus and ferrets Mustela furo) and a mesopredator (stoats Mustela erminea), in relation to their primary prey (lagomorphs, rodents and birds) and habitat use. Further, we tested for mesopredator release by selectively removing cats and ferrets in a pulse perturbation experiment. We found compelling evidence of niche partitioning; spatiotemporal activity of apex predators maximized access to abundant invasive prey, with ferrets targeting lagomorphs and cats targeting rodents. Mesopredators adjusted their behavior to reduce the risk of interference competition, thereby restricting access to abundant prey but increasing predation pressure on diurnal native birds. Stoats were only recorded at the treatment site after both larger predators were removed, becoming the most frequently detected predator at 6 months post-perturbation. We suggest there is spatial and resource partitioning within the invasive predator guild, but that this is incomplete, and avoidance is achieved by temporal partitioning within overlapping areas. Niche partitioning among invasive predators facilitates coexistence, but simultaneously intensifies predation pressure on vulnerable native species.

Leveraging Motivations, Personality, and Sensory Cues for Vertebrate Pest Management

Managing vertebrate pests is a global conservation challenge given their undesirable socio-ecological impacts. Pest management often focuses on the 'average' individual, neglecting individual-level behavioural variation ('personalities') and differences in life histories. These differences affect pest impacts and modify attraction to, or avoidance of, sensory cues. Strategies targeting the average individual may fail to mitigate damage by 'rogues' (individuals causing disproportionate impact) or to target 'recalcitrants' (individuals avoiding standard control measures). Effective management leverages animal behaviours that relate primarily to four core motivations: feeding, fleeing, fighting, and fornication. Management success could be greatly increased by identifying and exploiting individual variation in motivations. We provide explicit suggestions for cue-based tools to manipulate these four motivators, thereby improving pest management outcomes.

Zooming in on mechanistic predator-prey ecology: Integrating camera traps with experimental methods to reveal the drivers of ecological interactions

Camera trap technology has galvanized the study of predator-prey ecology in wild animal communities by expanding the scale and diversity of predator-prey interactions that can be analysed. While observational data from systematic camera arrays have informed inferences on the spatiotemporal outcomes of predator-prey interactions, the capacity for observational studies to identify mechanistic drivers of species interactions is limited. Experimental study designs that utilize camera traps uniquely allow for testing hypothesized mechanisms that drive predator and prey behaviour, incorporating environmental realism not possible in the laboratory while benefiting from the distinct capacity of camera traps to generate large datasets from multiple species with minimal observer interference. However, such pairings of camera traps with experimental methods remain underutilized. We review recent advances in the experimental application of camera traps to investigate fundamental mechanisms underlying predator-prey ecology and present a conceptual guide for designing experimental camera trap studies. Only 9% of camera trap studies on predator-prey ecology in our review use experimental methods, but the application of experimental approaches is increasing. To illustrate the utility of camera trap-based experiments using a case study, we propose a study design that integrates observational and experimental techniques to test a perennial question in predator-prey ecology: how prey balance foraging and safety, as formalized by the risk allocation hypothesis. We discuss applications of camera trap-based experiments to evaluate the diversity of anthropogenic influences on wildlife communities globally. Finally, we review challenges to conducting experimental camera trap studies. Experimental camera trap studies have already begun to play an important role in understanding the predator-prey ecology of free-living animals, and such methods will become increasingly critical to quantifying drivers of community interactions in a rapidly changing world. We recommend increased application of experimental methods in the study of predator and prey responses to humans, synanthropic and invasive species, and other anthropogenic disturbances.

Exploiting interspecific olfactory communication to monitor predators

Olfaction is the primary sense of many mammals and subordinate predators use this sense to detect dominant species, thereby reducing the risk of an encounter and facilitating coexistence. Chemical signals can act as repellents or attractants and may therefore have applications for wildlife management. We devised a field experiment to investigate whether dominant predator (ferret Mustela furo) body odor would alter the behavior of three common mesopredators: stoats (Mustela erminea), hedgehogs (Erinaceus europaeus), and ship rats (Rattus rattus). We predicted that apex predator odor would lead to increased detections, and our results support this hypothesis as predator kairomones (interspecific olfactory messages that benefit the receiver) provoked "eavesdropping" behavior by mesopredators. Stoats exhibited the most pronounced responses, with kairomones significantly increasing the number of observations and the time spent at a site, so that their occupancy estimates changed from rare to widespread. Behavioral responses to predator odors can therefore be exploited for conservation and this avenue of research has not yet been extensively explored. A long-life lure derived from apex predator kairomones could have practical value, especially when there are plentiful resources that reduce the efficiency of food-based lures. Our results have application for pest management in New Zealand and the technique of using kairomones to monitor predators could have applications for conservation efforts worldwide.

Motorist comprehension of the slow-moving vehicle (SMV) emblem

While attaining widespread use and institutional acceptance in its 40 years on the road, crash data indicate that the slow-moving vehicle (SMV) emblem may not be meeting the safety needs of either the motoring public or SMV operators. This article addresses the possibility that the reasons for this include its inconsistent day/night appearance, potential confusion with other roadway symbols, its uncontrolled misuse, and poor driver education. This study is also the first to systematically evaluate the SMV emblem's comprehensibility by the general motoring public. Over 100 male and female drivers from 18 to 84 years of age gave open-ended responses to the presentation of a scale model SMV emblem displayed in its daytime and nighttime appearance. While the older drivers understood the meaning of the emblem better than their younger counterparts, overall emblem comprehension was still under 30%.

Age differences in dynamic contrast thresholds

Contrast thresholds for sinusoidal gratings of 1.5-18 cpd were measured in young (M = 24 years) and older adults (M = 69 years). Thresholds were determined for stationary gratings, and for gratings that traveled along a circular path at 5, 10, and 15 deg/sec. For static gratings, age differences in thresholds were greater for intermediate and higher spatial frequencies. Grating motion increased thresholds for all observers, but older adults exhibited threshold increases at lower target velocities than the young. Age differences in velocity effects were generally greater at intermediate and higher spatial frequencies. Results are discussed in relation to age changes in temporal resolution and smooth pursuit gain.

Age differences in estimating vehicle velocity

Automobile accidents among older adults may be related to difficulties in judging the speed of other vehicles. To examine this possibility, 3 groups of observers in the young adult, middle-aged, and older adult age ranges were asked to estimate the velocity of an isolated automobile traveling at 15-50 mph (24-80 kph). Across all age groups, perceived and actual velocity were related by a power function with an exponent of 1.36. Age was significantly and positively correlated with intercepts, but negatively correlated with exponents; that is, older observers showed less sensitivity to changes in actual velocity. Results bear on the issues of ontogenetic changes in accident involvement and sensitivity to motion.

Age differences in estimating vehicle velocity

Automobile accidents among older adults may be related to difficulties in judging the speed of other vehicles. To examine this possibility, 3 groups of observers in the young adult, middle-aged, and older adult age ranges were asked to estimate the velocity of an isolated automobile traveling at 15-50 mph (24-80 kph). Across all age groups, perceived and actual velocity were related by a power function with an exponent of 1.36. Age was significantly and positively correlated with intercepts, but negatively correlated with exponents; that is, older observers showed less sensitivity to changes in actual velocity. Results bear on the issues of ontogenetic changes in accident involvement and sensitivity to motion.

Bandwidth of the contrast sensitivity function as an index of spatial vision with application to refraction

The contrast sensitivity function (CSF), although containing more information than traditional measures of acuity, has found difficulty gaining clinical acceptance. The hesitancy of clinicians to adopt the CSF stems, in part, from the fact that it is not as readily interpreted as is acuity. In order to facilitate such interpretation, five indices of spatial vision which are derivable from the CSF were examined in a sample of 287 persons aged 5 to 85 years. All indices were found to be both age-sensitive and strongly related to each other, but bandwidth of the CSF was chosen as a practical index for clinical settings. In a second study, acuity and CSF bandwidth were measured under 0 to +/- 1 D optical blur. It was found that the correction providing best acuity also maximized CSF bandwidth, and that bandwidth was more sensitive to optical blur than was acuity. Results support the assertion that CSF bandwidth is a readily interpreted index of spatial vision that can be measured efficiently within the context of clinical refraction.

The effects of target borders on dynamic visual acuity: practical and theoretical implications

The effects of target borders on the ability of observers to resolve moving targets (Landolt Cs) under a range of conditions were examined. Contrary to reported findings with stationary targets, it was predicted that the presence of borders would improve acuity for slow-moving targets because (i) overall stimulus energy is kept relatively constant as target detail varies, and (ii) a low-spatial-frequency component is held constant as target detail varies. In an experiment in which a two-sided border (above and below the target) was used, the predicted beneficial effect of the border at slow speeds was obtained. The results are discussed in terms of practical implications for the assessment of dynamic visual acuity as well as the potential neural mechanisms underlying performance.

Age differences in Vistech near contrast sensitivity

Contrast sensitivity was measured at near using the Vistech 6000 Contrast Test System (VCTS) in 287 persons aged 4 to 87 years. Obtained data compared well with those previously reported for the Vistech charts. Results indicate an age-related loss in sensitivity to intermediate and higher spatial frequencies. This is consistent with the age trends observed using other methods for measuring contrast sensitivity functions (CSFs). However, the Vistech charts yield contrast sensitivity values which are lower than those obtained previously with the Nicolet system. These between-method differences are greatest at lower spatial frequencies, and are attributed to the small number of grating cycles in the Vistech charts. The data are used to develop provisional age norms for the Vistech charts which allow the assessment of an individual's performance relative to their age cohort. Recommendations for use and future development of the Vistech charts are also given.