Individual variation in life-history timing: synchronous presence, asynchronous events and phenological compensation in a wild mammal.

Many animals and plants have species-typical annual cycles, but individuals vary in their timing of life-history events. Individual variation in fur replacement (moult) timing is poorly understood in mammals due to the challenge of repeated observations and longitudinal sampling. We examined factors that influence variation in moult duration and timing among elephant seals (Mirounga angustirostris). We quantified the onset and progression of fur loss in 1178 individuals. We found that an exceptionally rapid visible moult (7 days, the shortest of any mammals or birds), and a wide range of moult start dates (spanning 6-10× the event duration) facilitated high asynchrony across individuals (only 20% of individuals in the population moulting at the same time). Some of the variation was due to reproductive state, as reproductively mature females that skipped a breeding season moulted a week earlier than reproductive females. Moreover, individual variation in timing and duration within age-sex categories far outweighed (76-80%) variation among age-sex categories. Individuals arriving at the end of the moult season spent 50% less time on the beach, which allowed them to catch up in their annual cycles and reduce population-level variance during breeding. These findings underscore the importance of individual variation in annual cycles.

Quantifying dispersal between two colonies of northern elephant seals across 17 birth cohorts.

Dispersal drives extinction-recolonization dynamics of metapopulations and is necessary for endangered species to recolonize former ranges. Yet few studies quantify dispersal and even fewer examine consistency of dispersal over many years. The northern elephant seal (Mirounga angustirostris) provides an example of the importance of dispersal. It quickly recolonized its full range after near extirpation by 19th century hunting, and though dispersal was observed it was not quantified. Here we enumerate lifetime dispersal events among females marked as pups at two colonies during 1994-2010, then correct for detection biases to estimate bidirectional dispersal rates. An average of 16% of females born at the Piedras Blancas colony dispersed northward 200 km to breed at Año Nuevo, while 8.0% of those born at Año Nuevo dispersed southward to Piedras Blancas. The northward rate fluctuated considerably but was higher than southward in 15 of 17 cohorts. The population at Piedras Blancas expanded 15-fold during the study, while Año Nuevo's declined slightly, but the expectation that seals would emigrate away from high density colonies was not supported. During the 1990s, dispersal was higher away from the small colony toward the large. Moreover, cohorts born later at Piedras Blancas, when the colony had grown, dispersed no more than early cohorts. Consistently high natal dispersal in northern elephant seals means the population must be considered a single large unit in terms of response to environmental change. High dispersal was fortuitous to the past recovery of the species, and continued dispersal means elephant seals will likely expand their range further.

Assessment of the Impact of an Endpoint Committee in the Ocular Hypertension Treatment Study.

PURPOSE: To assess the impact of a masked Endpoint Committee on estimates of the incidence of primary open-angle glaucoma (POAG) treatment efficacy and statistical power of the Ocular Hypertension Treatment Study-Phase 1, 1994-2002 (OHTS-1). DESIGN: Retrospective interrater reliability analysis of endpoint attribution by the Endpoint Committee. METHODS: After study closeout, we recalculated estimates of endpoint incidence, treatment efficacy, and statistical power using all-cause endpoints and POAG endpoints. To avoid bias, only the first endpoint per participant is included in this report. RESULTS: The Endpoint Committee reviewed 267 first endpoints from 1636 participants. The Endpoint Committee attributed 58% (155 of 267) of the endpoints to POAG. The incidence of all-cause endpoints vs POAG endpoints was 19.5% and 13.2%, respectively, in the observation group and 13.1% and 5.8%, respectively, in the medication group. Treatment effect for all-cause endpoints was a 33% reduction in risk (relative risk = 0.67, 95% confidence interval [CI] of 0.54-0.84) and a 56% reduction in risk for POAG endpoints (relative risk = 0.44, 95% CI of 0.31-0.61). Post hoc statistical power for detecting treatment effect was 0.94 for all-cause endpoints and 0.99 for POAG endpoints. CONCLUSION: Endpoint Committee adjudication of endpoints improved POAG incidence estimates, increased statistical power, and increased calculated treatment effect by 23%. An Endpoint Committee should be considered in therapeutic trials when common ocular and systemic comorbidities, other than the target condition, could compromise study results.

A Bioenergetics Approach to Understanding the Population Consequences of Disturbance: Elephant Seals as a Model System.

Using long-term empirical data, we developed a complete population consequences of acoustic disturbance (PCAD) model and application for northern elephant seals. We assumed that the animals would not successfully forage while in a 100-km-diameter disturbance region within their foraging and transit paths. The decrease in lipid gain due to exposure was then translated to changes in birth rate and pup survival. Given their large foraging range, elephant seals were resilient to such a disturbance, showing no population-level effects. However, similar track analysis showed that given their more coastal nature, California sea lions were within a 25-km-diameter region of disturbance more often.