David T. Iles

Terrestrial predation by polar bears: not just a wild goose chase

Behavioral predictions based on optimal foraging models that assume an energy-maximizing strategy have been challenged on both theoretical and empirical grounds. Although polar bears (Ursus maritimus) are specialist predators of seal pups on the Arctic ice pack, the use of terrestrial food sources during the ice-free period has received increased attention in recent years in light of climate predictions. Across a 10-day period of observation, we documented between four and six individual polar bears successfully capture at least nine flightless lesser snow geese (Chen caerulescens caerulescens) and engage in at least eight high-speed pursuits of geese. The observed predatory behaviors of polar bears do not support predictions made by energy-optimizing foraging models and suggest that polar bears may frequently engage in energy inefficient pursuits of terrestrial prey. Further study of the nutritional needs and foraging behaviors of polar bears during the ice-free period is warranted, given that polar bears are predicted to spend more time on land as climate change advances.

Predators, alternative prey and climate influence annual breeding success of a long-lived sea duck

1. Perturbations to ecosystems have the potential to directly and indirectly affect species interactions, with subsequent impacts on population dynamics and the vital rates that regulate them. 2. The few long-term studies of common eider breeding ecology indicate that reproductive success is low in most years, interrupted by occasional boom years. However, no study has explicitly examined the drivers of long-term variation in reproductive success. 3. Here, we use encounter history data collected across 41 years to examine the effects of arctic foxes (a terrestrial nest predator), local abundance and spatial distribution of lesser snow geese (an alternative prey source), and spring climate on common eider nest success. 4. Eider nest success declined over the course of the study, but was also highly variable across years. Our results supported the hypothesis that the long-term decline in eider nest success was caused by apparent competition with lesser snow geese, mediated by shared predators. This effect persisted even following a large-scale exodus of nesting geese from the eider colony. Nest success was also lowest in years of low arctic fox index, presumably driven by prey switching in years of low small mammal availability. However, increased snow goose abundance appeared to buffer this effect through prey swamping. The effect of spring climate depended on the stage of the breeding season; cold and wet and warm and dry conditions in early spring were correlated with decreased nest success, whereas warm and wet conditions in late spring increased eider nest success. 5. These results underscore the significance of both trophic interactions and climate in regulating highly variable vital rates, which likely have important consequences for population dynamics and the conservation of long-lived iteroparous species.

A life-history perspective on the demographic drivers of structured population dynamics in changing environments

Current understanding of life-history evolution and how demographic parameters contribute to population dynamics across species is largely based on assumptions of either constant environments or stationary environmental variation. Meanwhile, species are faced with non-stationary environmental conditions (changing mean, variance, or both) created by climate and landscape change. To close the gap between contemporary reality and demographic theory, we develop a set of transient life table response experiments (LTREs) for decomposing realised population growth rates into contributions from specific vital rates and components of population structure. Using transient LTREs in a theoretical framework, we reveal that established concepts in population biology will require revision because of reliance on approaches that do not address the influence of unstable population structure on population growth and mean fitness. Going forward, transient LTREs will enhance understanding of demography and improve the explanatory power of models used to understand ecological and evolutionary dynamics.

Costs of locomotion in polar bears: when do the costs outweigh the benefits of chasing down terrestrial prey?

Trade-offs between locomotory costs and foraging gains are key to predator–prey interactions. As climate change forces polar bears to spend more time ashore, their prey base and these trade-offs may be altered. We show that polar bears can profitably capture seasonally available land-based prey, such as geese, over a range of pursuit speeds.

Developing a citizen science web portal for manual and automated ecological image detection

Image recognition is challenging in the field of wildlife ecology as samples of a specific species can be rare, making manual detection cumbersome. With over 2,060,000 images taken from motion-sensor trail cameras and unmanned aerial vehicle flights, a touch enabled web interface has been developed to allow citizen scientists and ecologists to categorize positive samples. To minimize categorization errors, the same images are shown to multiple separate users. The observations of each user are then compared using two novel validation strategies: percentage of overlapping area and maximum corner distance. Two novel methods for the extraction of final images from validated results are presented and compared as well: average corner points and area intersection. These methods were evaluated using a set of 142 images with a total of 811 observations of objects generated by citizen scientists that were manually inspected for ground truth. Results show that for this research a maximum corner distance of 10 pixels and the use of area intersection provided the best extracted imagery for future use as training and testing data by computer vision methods.