Adam T. Ford

Large carnivores make savanna tree communities less thorny

Understanding how predation risk and plant defenses interactively shape plant distributions is a core challenge in ecology. By combining global positioning system telemetry of an abundant antelope (impala) and its main predators (leopards and wild dogs) with a series of manipulative field experiments, we showed that herbivores’ risk-avoidance behavior and plants’ antiherbivore defenses interact to determine tree distributions in an African savanna. Well-defended thorny Acacia trees (A. etbaica) were abundant in low-risk areas where impala aggregated but rare in high-risk areas that impala avoided. In contrast, poorly defended trees (A. brevispica) were more abundant in high- than in low-risk areas. Our results suggest that plants can persist in landscapes characterized by intense herbivory, either by defending themselves or by thriving in risky areas where carnivores hunt. Changes to thorny plant defenses and high predator risk for impala determine density and distribution of savanna trees. A thorny defense keeps grazers at bay Fear and avoidance of predators are known to influence how and where herbivore prey species, such as impala, forage. This in turn has cascading effects on plant morphologies and communities. Plants, however, have their own defenses, and so may not just be hapless victims of the predator-prey “dance.” Ford et al. found that thorny Acacia trees are more common in areas where impala experience a low risk of predation by wild dogs. A related Acacia, without thorns, is most abundant in areas where risk of predation is high, and so the number of hungry impala is low. Science, this issue p. 346

Movement Patterns of Eastern Chipmunks (Tamias striatus) Near Roads

Abstract Previous studies suggest that eastern chipmunks (Tamias striatus) avoid roads, but it is unclear whether vehicle traffic plays a role in this avoidance. The purpose of this study was to determine whether road avoidance in chipmunks increases with traffic. We tracked the movements of 68 chipmunks released near roads with widely varying volumes of traffic. Our results suggest that chipmunks responded to changes in traffic volume only in the preliminary stages of their movement pathways. Apart from this initial response, we found that road avoidance was independent of traffic, with evidence that chipmunks avoided both the roadside verge and the road surface. Because avoidance of roads was independent of traffic, effects of roads on populations of chipmunks may be manifest more as population subdivision than as direct mortality.

Behavioral Responses of Northern Leopard Frogs (Rana pipiens) to Roads and Traffic: Implications for Population Persistence

A key goal in road ecology is to determine which species are most vulnerable to the negative effects of roads on population persistence. Theory suggests that species that avoid roads are less likely to be negatively affected by roads than those that do not avoid roads. The goal of this study was to take a step toward testing this prediction by evaluating the behavioral response to roads and traffic of a species whose populations are known to be negatively affected by roads and traffic, the northern leopard frog (Rana pipiens). We studied the movement patterns of northern leopard frogs during their spring migration from overwintering sites in a river to various breeding ponds that were disconnected from the river by roads. We performed short-distance translocations of migrating frogs, followed them visually, and documented their movement coordinates following each hop, both near the roads and in non-roaded areas. We found that frogs took longer to move near roads with more traffic and that their movement was quickest in areas without roads nearby. Frogs tended to deviate more from a straight-line course when they were released near roads than compared with control areas, but this response was independent of traffic volume. All frogs released near roads attempted to cross the road. On very low traffic roads (10.86 mean vehicles per hour), 94% of frogs crossed the road successfully, whereas at higher traffic roads (58.29 mean vehicles per hour) 72% were successful. Our results suggest that frogs inability to avoid going onto roads and their slow movement combine to make them particularly vulnerable to road mortality, which likely explains the strong negative effects of roads on frog population abundance. Conservation efforts should focus on preventing frogs from accessing the road surface through the use of drift fencing and culverts.

Comparison of Methods of Monitoring Wildlife Crossing-Structures on Highways

Abstract Wildlife crossing-structures (e.g., underpasses and overpasses) are used to mitigate deleterious effects of highways on wildlife populations. Evaluating performance of mitigation measures depends on monitoring structures for wildlife use. We analyzed efficacy of 2 noninvasive methods commonly used to monitor crossing-structure use by large mammals: tracking and motion-activated cameras. We monitored 15 crossing-structures every other day between 29 June and 24 October 2007 along the Trans-Canada Highway in Alberta, Canada. Our objectives were to determine how species-specific detection rates are biased by the detection method used, to determine factors contributing to crossing-event detection, and to evaluate the most cost-effective approach to monitoring. We detected 3,405 crossing events by tracks and 4,430 crossings events by camera for mammals coyote-sized and larger. Coyotes (Canis latrans) and grizzly bears (Ursus arctos) were significantly more likely to be detected by track-pads, whereas elk (Cervus elaphus) and deer (Odocoileus sp.) were more likely to be detected by cameras. Crossing-event detection was affected by species, track-pad length, and number of animals using the crossing structure. At the levels of animal activity observed in our study our economic analysis indicates that cameras are more cost-effective than track-pads for study durations >1 year. Understanding the benefits and limitations of camera and track-pad methods for monitoring large mammal movement at wildlife crossing-structures will help improve the efficiency of studies designed to evaluate the effectiveness of highway mitigation measures.

Low functional redundancy among mammalian browsers in regulating an encroaching shrub (Solanum campylacanthum) in African savannah

Large herbivorous mammals play an important role in structuring African savannahs and are undergoing widespread population declines and local extinctions, with the largest species being the most vulnerable. The impact of these declines on key ecological processes hinges on the degree of functional redundancy within large-herbivore assemblages, a subject that has received little study. We experimentally quantified the effects of three browser species (elephant, impala and dik-dik) on individual- and population-level attributes of Solanum campylacanthum (Solanum incanum sensu lato), an encroaching woody shrub, using semi-permeable exclosures that selectively removed different-sized herbivores. After nearly 5 years, shrub abundance was lowest where all browser species were present and increased with each successive species deletion. Different browsers ate the same plant species in different ways, thereby exerting distinct suites of direct and indirect effects on plant performance and density. Not all of these effects were negative: elephants and impala also dispersed viable seeds and indirectly reduced seed predation by rodents and insects. We integrated these diffuse positive effects with the direct negative effects of folivory using a simple population model, which reinforced the conclusion that different browsers have complementary net effects on plant populations, and further suggested that under some conditions, these net effects may even differ in direction.

Recovery of African wild dogs suppresses prey but does not trigger a trophic cascade

Increasingly, the restoration of large carnivores is proposed as a means through which to restore community structure and ecosystem function via trophic cascades. After a decades-long absence, African wild dogs (Lycaon pictus) recolonized the Laikipia Plateau in central Kenya, which we hypothesized would trigger a trophic cascade via suppression of their primary prey (dik-dik, Madoqua guentheri) and the subsequent relaxation of browsing pressure on trees. We tested the trophic-cascade hypothesis using (1) a 14-year time series of wild dog abundance; (2) surveys of dik-dik population densities conducted before and after wild dog recovery; and (3) two separate, replicated, herbivore-exclusion experiments initiated before and after wild dog recovery. The dik-dik population declined by 33% following wild dog recovery, which is best explained by wild dog predation. Dik-dik browsing suppressed tree abundance, but the strength of suppression did not differ between before and after wild dog recovery. Despite strong, top-down limitation between adjacent trophic levels (carnivore-herbivore and herbivore-plant), a trophic cascade did not occur, possibly because of a time lag in indirect effects, variation in rainfall, and foraging by herbivores other than dik-dik. Our ability to reject the trophic-cascade hypothesis required two important approaches: (1) temporally replicated herbivore exclusions, separately established before and after wild dog recovery; and (2) evaluating multiple drivers of variation in the abundance of dik-dik and trees. While the restoration of large carnivores is often a conservation priority, our results suggest that indirect effects are mediated by ecological context, and that trophic cascades are not a foregone conclusion of such recoveries.

Planning and prioritization strategies for phased highway mitigation using wildlife-vehicle collision data

Abstract Mitigation measures to reduce wildlife-vehicle collisions (WVCs) on highways are becoming an established practice in many jurisdictions. Most highway mitigation projects occur while roads are being upgraded, enlarged or repaired. Many smaller highways may not be subject to these types of upgrades in the near future but are nonetheless problematic for causing WVCs. Thus, it is important to find cost effective ways to locate and prioritize stretches of highway for mitigation. We present several criteria that can be used to assist in prioritizing the location of wildlife-proof fencing along a 94-km stretch of road in one of Canadas National Parks. We considered temporal consistency of WVC occurrences, conservation value (i.e. reduction in WVC rates), economic benefits (i.e. cost of mitigation vs benefits in WVC reduction), and a combined approach to prioritize management actions. We compared the efficacy of four different lengths of fencing (i.e. phase lengths) at meeting these criteria: 2 km, 5 km, 10 km and 25 km. We used 1,244 WVC records from a long-tem monitoring program (1981-2005) as data to assess mitigation effectiveness. We found that longer fences best address conservation concerns, but all fencing sections, irrespective of length, rarely captured > 50% of WVC locations by species. We found that shorter fences were more economically efficient, but also more variable in performance, than longer fences. Lastly, we found that longer fence lengths tend to produce the best results for the combined metric criteria. Clearly defined management goals will determine the extent to which a phased approach to highway mitigation is viable.

An experimental study on risk effects in a dwarf antelope, Madoqua guentheri

Risk of predation shapes the physiology, behavior, and demography of prey. Among the many studies that have examined effects of risk in ungulates, most have focused on large (> 40kg) and gregarious species. Much less is known about the effect of risk on smaller or territorial ungulates, which is a diverse group of species that can have pronounced effects on plant communities in tropical ecosystems. Using GPS telemetry, we examined spatial responses of Guenthers dik-dik (Madoqua guentheri) to scent marks from a common predator (African wild dogs, Lycaon pictus) or cattle. In response to predator scent marks, dik-diks increased fidelity within territories, avoided scent marks, and decreased use of overstory cover. Similar behaviors occurred in response to cattle scent marks, with the exception that use of overstory cover relative to controls did not change. Total amount (length) of movement did not change in response to either type of scent mark. Thus, an increase in perceived risk of predation changed the pattern and distribution of dik-dik movement but did not change total amount of movement. Our results suggest that territoriality may constrain the options available for prey to avoid predation risk.

Troubling issues at the frontier of animal tracking for conservation and management

Steven J. Cooke, ∗ Vivian M. Nguyen, Steven T. Kessel, Nigel E. Hussey, Nathan Young, and Adam T. Ford Fish Ecology and Conservation Physiology Laboratory, Department of Biology, Carleton University, Ottawa, ON K1S 5B6, Canada Department of Fisheries and Wildlife, Michigan State University, 480 Wilson Road, East Lansing, MI 48824, U.S.A. Department of Biology, University of Windsor, Windsor, ON, N9B 3P4, Canada Department of Sociology and Anthropology, University of Ottawa, Ottawa, ON K1N 6N5, Canada The Irving K. Barber School of Arts and Sciences, Unit 2: Biology, The University of British Columbia, Okanagan campus, Kelowna, BC V1V 1V7, Canada

Context-dependent effects on spatial variation in deer-vehicle collisions

Identifying factors that contribute to the risk of wildlife-vehicle collisions (WVCs) has been a key focus of wildlife managers, transportation safety planners and road ecologists for over three decades. Despite these efforts, few generalities have emerged which can help predict the occurrence of WVCs, heightening the uncertainty under which conservation, wildlife and transportation management decisions are made. Undermining this general understanding is the use of study area boundaries that are incongruent with major biophysical gradients, inconsistent data collection protocols among study areas and species-specific interactions with roads. We tested the extent to which factors predicting the occurrence of deer-vehicle collisions (DVCs) were general among five study areas distributed over a 11,400-km2 region in the Canadian Rocky Mountains. In spite of our system-wide focus on the same genus (i.e., Odocoileus hemionus and O. virginianus), study area delineation along major biophysical gradients, and use ...