Demography and parental investment in orange-crowned warblers: testing life history theory

2012 Fall.Includes bibliographical references.Understanding the diversification of life history strategies is a major goal of evolutionary ecology. Research on avian life history strategies has historically focused on explaining variation in clutch size, and most studies have tested whether this variation can be explained by variation in a single ecological factor, such as food availability or mortality risk. However, relatively few studies have evaluated whether the causes of variation within populations are distinct from or similar to the causes of variation between populations. In my dissertation, I compare the life history strategies of orange-crowned warbler (Oreothlypis celata) populations and study the causes of variation in clutch sizes, incubation behavior, nestling provisioning rates, nestling growth rates, and breeding phenology. I tested alternative hypotheses for the ecological causes of divergent life histories, and assessed the consequences of these different reproductive strategies for parents and offspring. My results indicate that no single ecological factor can explain life history variation either within or between populations. Instead, life history and behavioral traits differ in their sensitivities to different ecological factors, and while differences between nearby populations can reflect plastic responses to ecological variation, populations that are more geographically and evolutionarily distant can differ in both their responses to ecological variation and in the consequences of variation in parental behavior for offspring growth and development

Human-associated species dominate passerine communities across the United States

Aim: Human development and agriculture can have transformative and homogenizing effects on natural systems, shifting the composition of ecological communities towards non-native and native species that tolerate or thrive under human-dominated conditions. These impacts cannot be fully captured by summarizing species presence, as they include dramatic changes to patterns of species abundance. However, how human land use patterns and species invasions intersect to shape patterns of abundance and dominance within ecological communities is poorly understood even in well-known taxa. Location: Conterminous United States. Time period: 2010–2012. Major taxa studied: Passeriformes. Methods: We analyse continental-scale monitoring data to study the proportional abundance of non-native and native synanthropic species within passerine bird communities. Synanthropic species are those that benefit from an association with humans. We estimate how the amount and configuration of human development and agriculture relate to the degree to which human-associated species dominate passerine communities across the continent. Results: Human-associated species comprised the majority of detected passerine individuals across two-thirds of bird surveys. Non-native and synanthropic species responded differently to land cover and reached highest relative abundance in different portions of the continent. The proportional abundance of synanthropic birds increased rapidly with development, but was not related to the configuration of land cover. The proportion of non-native individuals was higher when intensively-used land cover was more aggregated. Main conclusions: Even low amounts of intensively-used lands were associated with a dramatic reshaping of passerine communities, with consequences for patterns of relative abundance across the continent

Regional models do not outperform continental models for invasive species

Aim: Species distribution models can guide invasive species prevention and management by characterizing invasion risk across space. However, extrapolation and transferability issues pose challenges for developing useful models for invasive species. Previous work has emphasized the importance of including all available occurrences in model estimation, but managers attuned to local processes may be skeptical of models based on a broad spatial extent if they suspect the captured responses reflect those of other regions where data are more numerous. We asked whether species distribution models for invasive plants performed better when developed at national versus regional extents. Location: Continental United States. Methods: We developed ensembles of species distribution models trained nationally, on sagebrush habitat, or on sagebrush habitat within three ecoregions (Great Basin, eastern sagebrush, and Great Plains) for nine invasive plants of interest for early detection and rapid response at local or regional scales. We compared the performance of national versus regional models using spatially independent withheld test data from each of the three ecoregions. Results: We found that models trained using a national spatial extent tended to perform better than regionally trained models. Regional models did not outperform national ones even when considerable occurrence data were available for model estimation within the focal region. Information was often unavailable to fit informative regional models precisely in those areas of greatest interest for early detection and rapid response. Main conclusions: Habitat suitability models for invasive plant species trained at a continental extent can reduce extrapolation while maximizing information on species’ responses to environmental variation. Standard modeling methods can capture spatially varying limiting factors, while regional or hierarchical models may only be advantageous when populations differ in their responses to environmental conditions, a condition expected to be relatively rare at the expanding boundaries of invasive species’ distributions

Data from: The relationship between female brooding and male nestling provisioning: does climate underlie geographic variation in sex roles?

Comparative studies of populations occupying different environments can provide insights into the ecological conditions affecting differences in parental strategies, including the relative contributions of males and females. Male and female parental strategies reflect the interplay between ecological conditions, the contributions of the social mate, and the needs of offspring. Climate is expected to underlie geographic variation in incubation and brooding behavior, and can thereby affect both the absolute and relative contributions of each sex to other aspects of parental care such as offspring provisioning. However, geographic variation in brooding behavior has received much less attention than variation in incubation attentiveness or provisioning rates. We compared parental behavior during the nestling period in populations of orange-crowned warblers (Oreothlypis celata) near the northern (64°N) and southern (33°N) boundaries of the breeding range. In Alaska, we found that males were responsible for the majority of food delivery whereas the sexes contributed equally to provisioning in California. Higher male provisioning in Alaska appeared to facilitate a higher proportion of time females spent brooding the nestlings. Surprisingly, differences in brooding between populations could not be explained by variation in ambient temperature, which was similar between populations during the nestling period. While these results represent a single population contrast, they suggest additional hypotheses for the ecological correlates and evolutionary drivers of geographic variation in brooding behavior, and the factors that shape the contributions of each sex

Sofaer_etal_OCWA_AdultSurvival

Files with input and results from analysis of orange-crowned warbler adult survival in Program MARK

Data from: Offspring growth and mobility in response to variation in parental care: a comparison between populations

Life history theory emphasizes the importance of trade-offs in how time and energy are allocated to the competing demands of growth, fecundity, and survival. However, avian studies have historically emphasized the importance of resource acquisition over resource allocation to explain geographic variation in fecundity, parental care, and offspring development. We compared the brood sizes and nestling mass and feather growth trajectories between orange-crowned warblers (Oreothlypis celata) breeding in Alaska versus California, and used 24-hour video recordings to study the relationship between parental care and growth rates. Per-offspring provisioning rates were highest in the smallest broods, and food delivery was positively correlated with nestling growth over the 24-hour period only in Alaska. Females in Alaska spend more time brooding, and juveniles there showed faster feather growth and earlier mobility compared with those in California. We also found differences in the energetic and nutritional content of insect larvae that could potentially facilitate the observed differences in nestling growth relative to food provisioning. Our results point to the potential importance of food quality and parental provisioning of warmth, in addition to food, for explaining avian growth patterns. We highlight the need to quantify multiple dimensions of parental care and of offspring growth and development, and to better understand the relationships between feather growth, nestling period length, and fledgling mobility

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