Overwinter Survival Of Adults Research Articles

Detecting Resource Limitation in a Large Herbivore Population Is Enhanced With Measures of Nutritional Condition

Resource limitation at the population level is a function of forage quality and its abundance relative to its per capita availability, which in turn, determines nutritional condition of individuals. Effects of resource limitation on population dynamics in ungulates often occur through predictable and sequential changes in vital rates, which can enable assessments of how resource limitation influences population growth. We tested theoretical predictions of bottom-up (i.e., resource limitation) forcing on moose (Alces alces) through the lens of vital rates by quantifying the relative influence of intrinsic measures of nutritional condition and extrinsic measures of remotely sensed environmental data on demographic rates. We measured rates of pregnancy, parturition, juvenile, and adult survival for 82 adult females in a population where predators largely were absent. Life stage simulation analyses (LSAs) indicated that interannual fluctuations in adult survival contributed to most of the variability in λ. We then extended the LSA to estimate vital rates as a function of bottom-up covariates to evaluate their influence on λ. We detected weak signatures of effects from environmental covariates that were remotely sensed and spatially explicit to each seasonal range. Instead, nutritional condition strongly influenced rates of pregnancy, parturition, and overwinter survival of adults, clearly implicating resource limitation on λ. Our findings depart from the classic life-history paradigm of population dynamics in ungulates in that adult survival was highly variable and generated most of the variability in population growth rates. At the surface, lack of variation explained by environmental covariates may suggest weak evidence of resource limitation in the population, when nutritional condition actually underpinned most demographics. We suggest that variability in vital rates and effects of resource limitation may depend on context more than previously appreciated, and density dependence can obfuscate the relationships between remotely sensed data and demographic rates.

Demography of Sooty Fox Sparrows (Passerella unalaschcensis) following a shift from a migratory to resident life history

Identifying causes and consequences of variation in species life history has the potential to improve predictions about how climate and land-use change may affect the demography and distribution of species in future. Sooty Fox Sparrows (Passerella unalaschcensis (J.F. Gmelin, 1789); or commonly grouped within the Fox Sparrow, Passerella iliaca (Merrem, 1786)) were migrants that rarely bred in the Georgia Basin of British Columbia prior to ∼1950 but have since established resident populations. Data on 270 color-banded birds and 54 nests on Mandarte Island, British Columbia, allowed us to estimate demographic vital rates and population growth in one recently established population. Annual fecundity (F), estimated as the product of the number of broods initiated (1.5 ± 0.01; mean ± SD), clutch size (2.82 ± 0.44), and probability of survival to fledging (0.68 ± 0.02), exceeded values reported for migrants, supporting the hypothesis that residents invest more in reproduction, on average, than migrants within species. Estimating juvenile and adult overwinter survival (Sj = 0.32 ± 0.06 and Sa = 0.69 ± 0.05) next allowed us to simulate an expected distribution of population growth rates as λexp = Sa + (Sj × F), given parameter error. Our estimate of λexp (1.61 ± 0.57) implies expeditious population growth, consistent with the species’ recent colonization of the region.

Influence of European Corn Borer (Lepidoptera: Pyralidae) Damage to Potato and Foliage Availability on Overwinter Survival of First-Generation Colorado Potato Beetle Adults (Coleoptera: Chrysomelidae) in North Carolina

Survival of 1st-generation Colorado potato beetle, Leptinotarsa decemlineata (Say), adults following harvest of the Irish potato, Solanum tuberosum L., crop in late June was investigated in eastern North Carolina. First-generation adults that emerge before harvest may have access to postbloom-stage potato plants injured by European com borer, Ostrinia nubilalis (Hubner), whereas beetles that emerge after harvest may have access only to cull tubers. We tested the hypotheses that adult overwinter survival is positively correlated with the period 1st-generation adult beetles had fed on potato foliage and that feeding on com borer-damaged plants affect overwinter survival of 1st-generation adults. Therefore, overwinter survival was examined after beetles were presented a continuous supply of potato tubers as the only source of food or were fed for 3, 7, 11-12, or 17 d on potato plants that were either damaged by the European com borer or undamaged, and then were provided tubers. Feeding on com borer-damaged plants did not affect overwinter survival of 1st-generation potato beetle adults (survival in 1993: damaged, 15% and undamaged, 14%; 1994: damaged, 11% and undamaged, 9%). First-generation adults that had access to potato foliage in late June and early July had a significantly better chance of surviving overwinter and reproducing the following year compared with beetles that had access only to tubers. Overwinter survival of 1st-generation beetles that had only tubers as a host was 0 and 0.5% in 1993 and 1994, respectively.

Population biology of swift (Apus apus) ectoparasites in relation to host reproductive success

Abstract. We censused ectoparasite populations of adult and nestling swifts over the course of the host's breeding season. Nearly all of the birds were infested with chewing lice and two‐thirds of the nests were infested with louse flies. Feather mites were observed but not quantified. Lice and louse flies both showed aggregated distributions among hosts. Louse eggs, hatched lice and adult louse flies had negative binomial distributions, whereas the aggregated distribution of louse fly pupae was not adequately described by negative binomial or Poisson models. Transmission of lice from parents to offspring was documented. A comparison of the age structure of lice on parents and offspring indicated that most transmission was by nymphal lice. Host reproductive success and survival appeared to be independent of the number of lice or louse flies. Neither parasite correlated with the number, body mass, or date of fledging of young birds, nor with the overwinter survival of adults. We caution, however, that experimental manipulations of parasite load are required for a definitive test of the impact of ectoparasites on evolutionary fitness components.