Scott F. Pearson

Bio: Scott F. Pearson is an academic researcher from University of Florida. The author has contributed to research in topics: Population & Plover. The author has an hindex of 18, co-authored 65 publications receiving 1444 citations. Previous affiliations of Scott F. Pearson include University of Washington & Washington Department of Natural Resources.

Effects of elemental composition on the incorporation of dietary nitrogen and carbon isotopic signatures in an omnivorous songbird

Abstract: The use of stable isotopes to infer diet requires quantifying the relationship between diet and tissues and, in particular, knowing of how quickly isotopes turnover in different tissues and how isotopic concentrations of different food components change (discriminate) when incorporated into consumer tissues. We used feeding trials with wild-caught yellow-rumped warblers (Den- droica coronata) to determine d 15 N and d 13 C turnover rates for blood, d 15 N and d 13 C diet-tissue discrimination factors, and diet-tissue relationships for blood and feath- ers. After 3 weeks on a common diet, 36 warblers were assigned to one of four diets differing in the relative proportion of fruit and insects. Plasma half-life estimates ranged from 0.4 to 0.7 days for d 13 C and from 0.5 to 1.7 days for d 15 N. Half-life did not differ among diets. Whole blood half-life for d 13 C ranged from 3.9 to 6.1 days. Yellow-rumped warbler tissues were enriched relative to diet by 1.7-3.6% for nitrogen isotopes and by �1.2 to 4.3% for carbon isotopes, depending on tissue and diet. Consistent with previous studies, feathers were the most enriched and whole blood and plasma were the least enriched or, in the case of carbon, slightly depleted relative to diet. In general, tissues were more enriched relative to diet for birds on diets with high percentages of insects. For all tissues, carbon and nitrogen isotope discrimination factors increased with carbon and nitrogen concentrations of diets. The isotopic signature of plasma increased linearly with the sum of the isotopic signature of the diet and the discrimination factor. Because the isotopic signature of tissues depends on both elemental concentration and isotopic signature of the diet, attempts to reconstruct diet from stable isotope signatures require use of mixing models that incorporate elemental concen- tration.

Asymmetries in male aggression across an avian hybrid zone

Abstract: Recent studies suggest that competitive asymmetries are causing the hybrid zones between hermit and Townsend’s warblers to move, such that Townsend’s warblers are replacing hermit warblers. Here we examine the contribution of male aggression to this competitive asymmetry by measuring aggressive responses to mounts. We presented male mounts of the two parental species to Townsend’s and hermit warblers outside the zone and to hybrids within the zone. Outside the zone, Townsend’s males are more aggressive to both conspecific and heterospecific mounts than are hermit males. This asymmetry should move the zone in the direction inferred from previous studies. Hybrids fall between parentals in their aggressiveness, which should accelerate the movement of the zone. Remarkably, we found no relationship between phenotype and aggression in individual males at a locality within the hybrid zone. The forces of selection and dispersal that maintain narrow hybrid zones should generate such a correlation if aggressive differences between the parental species are genetically controlled. We resolve this conflict by proposing a behavioral model of competitive sorting within localities. If birds are sorted across the hybrid zone according to competitive abilities, and competitive interactions within neighborhoods are more or less complete, then the correlation between phenotype and aggression within any given neighborhood will be eliminated. We tested this model by examining the relationship between phenotype and aggression across the zone. Warblers in hybrid neighborhoods on the Townsend’s side of the zone are more aggressive than warblers in hybrid neighborhoods on the hermit side, indicating that competitive sorting is occurring.

Breeding bird response to riparian buffer width in managed pacific northwest douglas-fir forests

Abstract: We examined the relative importance of riparian vs upland habitats to breeding birds by comparing species abundance, richness, and similarity of bird communities in managed Douglas-fir forests in western Washington State, USA We also examined whether forested buffer strips along second- and third-order streams effectively maintain the pre-logging riparian breeding bird community by comparing species abundance, richness, and turnover among three treatments: (1) unharvested controls; (2) sites that were clear-cut, leaving a narrow (∼14 m) forested buffer on both sides of the stream; and (3) sites that were clear-cut, leaving a wide (∼31 m) forested buffer along both sides of the stream Deciduous trees, berry-producing shrubs, and other deciduous shrubs less common in adjacent upland forest characterized streamside zones Despite different vegetation features, riparian and upland habitats did not differ in any measures of bird species richness and composition No species or species group was more abundant

Behavioral asymmetries in a moving hybrid zone

Abstract: Three narrow hybrid zones exist between hermit and Townsend’s warblers in the Pacific Northwest. Character transition curves suggest that these zones are moving and that Townsend’s warblers have a selective advantage over hermit warblers. This study compares year-to-year return rates, male persistence on territories, pairing success, pairing patterns, and territory quality of hermit and Townsend’s warblers and their hybrids in the Washington Cascades hybrid zone. There was no difference in the year-to-year return rate between the parental species. Townsend’s males were more successful in maintaining territories and attracting mates than hermit males. Among mated pairs there were few hermit males compared to females, independently supporting the inferiority of hermit males in competition for territories or female mate choice for Townsend’s-like males. I found no difference in the quality of hermit and Townsend’s territories; however, in poor habitats Townsend’s males were more successful at attracting mates, suggesting female preference for Townsend’s-like males. In high-quality habitats, there was no difference in pairing success between the parental species. The fitness of hybrids relative to parentals affects the width and movement of the zone. Hybrids were intermediate in their ability to maintain territories and to attract mates, which should increase the width of the zone and accelerate its movement. Fewer hybrid males returned to from one year to the next, and among mated pairs there were few hybrid females relative to males, suggesting hybrid inferiority, which should narrow the hybrid zone and slow its movement.

Harbor Seal Diet in Northern Puget Sound: Implications for the Recovery of Depressed Fish Stocks

Abstract: Recovery of severely declining resource stocks often leads to enforced quotas or reduced human access to those resources. Predators, however, do not recognize such restrictions and may be attracted to areas of increased prey abundances where human extraction is being lim- ited. Such targeting by predators may reduce or retard the potential recovery of depressed stocks. In the San Juan Islands, northern Puget Sound, USA, marine reserves were implemented to recover depressed fish populations. We examine the role of harbor seals Phoca vitulina in the San Juan Islands food web. We describe the temporal and spatial variability in their diet, emphasizing species for which reserves were established (rockfish Sebastes spp.) and other important de - pressed stocks, including salmon Oncorhynchus spp. and Pacific herring Clupea pallasii. During winter and spring, seals primarily consumed Pacific herring, Pacific sand lance Ammodytes hexa- pterus, northern anchovy Engraulis mordax, and walleye pollock Theragra chalcogramma. During summer/fall, adult salmonids composed >50% of the diet and were particularly important in odd- numbered calendar years, when pink salmon O. gorbuscha spawn. Rockfish were not a primary prey species at any time of the year, suggesting that the abundance of alternative prey species may reduce predation pressure and provide a critical buffer to rockfish predation. The importance of considering increased visitation by marine predators to areas where potential prey are enhanced through restrictions on human extractions should be considered when modeling the efficacy of quotas and reduced access areas, such as marine reserves.

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

Abstract: The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Determining trophic niche width: a novel approach using stable isotope analysis

Abstract: 1. Although conceptually robust, it has proven difficult to find practical measures of niche width that are simple to obtain, yet provide an adequate descriptor of the ecological position of the population examined. 2. Trophic niche has proven more tractable than other niche dimensions. However, indices used as a proxy for trophic niche width often suffer from the following difficulties. Such indices rarely lie along a single scale making comparisons between populations or species difficult; have difficulty in combining dietary prey diversity and evenness in an ecologically meaningful way; and fail to integrate diet over ecological time-scales thus usually only comprise single snapshots of niche width. 3. We propose an alternative novel method for the comparison of trophic niche width: the use of variance of tissue stable isotope ratios, especially those of nitrogen and carbon. 4. This approach is a potentially powerful method of measuring trophic niche width, particularly if combined with conventional approaches, because: it provides a single measure on a continuous axis that is common to all species; it integrates information on only assimilated prey over time; the integration period changes with choice of tissue sampled; and data production is theoretically fast and testing among populations simple. 5. Empirical studies are now required to test the benefits of using isotopic variance as a measure of niche width, and in doing so help refine this approach.

Isotopic ecology ten years after a call for more laboratory experiments.

Abstract: About 10 years ago, reviews of the use of stable isotopes in animal ecology predicted explosive growth in this field and called for laboratory experiments to provide a mechanistic foundation to this growth. They identified four major areas of inquiry: (1) the dynamics of isotopic incorporation, (2) mixing models, (3) the problem of routing, and (4) trophic discrimination factors. Because these areas remain central to isotopic ecology, we use them as organising foci to review the experimental results that isotopic ecologists have collected in the intervening 10 years since the call for laboratory experiments. We also review the models that have been built to explain and organise experimental results in these areas.

From birds to butterflies: animal movement patterns and stable isotopes

Abstract: Establishing patterns of movement of wild animals is crucial for our understanding of their ecology, life history and behavior, and is a prerequisite for their effective conservation. Advances in the use of stable isotope markers make it possible to track a diversity of animal species in a variety of habitats. This approach is revolutionizing the way in which we make connections between phases of the annual cycle of migratory animals. However, researchers must exercise care in their application of isotopic methods. Here, we review stable isotope patterns in nature and discuss recent tracking applications in a range of taxa. To aid in the interpretation and design of effective and insightful isotope movement studies, we discuss a series of key issues and assumptions. This exciting field will advance rapidly if researchers consider these aspects of study design and interpretation carefully.