DOI: 10.5061/dryad.z08kprrdg
title: Individual heterogeneity in fitness in a long‐lived herbivore

description: Heterogeneity in the intrinsic quality and nutritional condition of
 individuals affects reproductive success and consequently fitness. Black
 brant (Branta bernicla nigricans) are long-lived, migratory, specialist
 herbivores. Long migratory pathways and short summer breeding seasons
 constrain the time and energy available for reproduction, thus magnifying
 life-history trade-offs. These constraints, combined with long lifespans
 and trade-offs between current and future reproductive value, provide a
 model system to examine the role of individual heterogeneity in driving
 life-history strategies and individual heterogeneity in fitness. We used
 hierarchical Bayesian models to examine reproductive trade-offs, modeling
 the relationships between within-year measures of reproductive energy
 allocation and among-year demographic rates of individual females breeding
 on the Yukon-Kuskokwim Delta, Alaska using capture-recapture and
 reproductive data from 1988 to 2014. We generally found that annual
 survival tended to be buffered against variation in reproductive
 investment, while breeding probability varied considerably over the range
 of clutch size-laying date combinations. We provide evidence for
 relationships between breeding probability and clutch size, breeding
 probability and nest initiation date, and an interaction between clutch
 size and initiation date. Average lifetime clutch size also had a weak
 positive relationship with apparent survival probability. Our results
 support the use of demographic buffering strategies for black brant. These
 results also indirectly suggest associations among environmental
 conditions during growth, fitness, and energy allocation, highlighting the
 effects of early growth conditions on individual heterogeneity, and
 subsequently, lifetime reproductive investment.
description: We collected data at the Tutakoke River Colony
 (61.25◦N,
 165.61◦W) and related
 brood rearing areas on the Yukon-Kuskokwim Delta near the mouth of the
 Kashunuk River from 1988-2014. May - June, nests were monitored every four
 days throughout nest initiation, and again before and during hatch.
 Observers recorded clutch sizes and initiation dates of nests during this
 time. Incubation time is generally 23-29 days, varying with laying date
 and clutch size. Thus, we back-calculated initiation dates for hatched
 nests using mean incubation period (~26 days). Mid-late July, adult and
 juvenile brant were herded into pens and marked with a unique U.S.
 Geological Survey metal band and an alpha-numerically coded plastic band
 during the adult wing-molt. Resighting occured throughout the breeding
 season (May-late July). We included capture-history data only for marked
 adult females (<i>n </i>= 7<i>,</i>845). We
 included data on mean lifetime clutch sizes for 6<i>,</i>256
 individuals (<i>µ </i>= 3<i>.</i>83;
 SD<i> </i>= 1<i>.</i>129) and mean initiation
 dates for 5<i>,</i>207 individuals (<i>µ </i>=
 146<i>.</i>45 (Julian Day); SD<i> </i>=
 5<i>.</i>6). When clutch size or initiation date was
 unavailable for females included in the capture-history data, we filled
 out the clutch size and/or initiation date dataset row for those
 individuals with NAs.
description: Columns contain data for the years 1988-2014. Rows corresponding
 with the same individuals are the same across all datasets. Initiation
 dates are Julian dates.