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Articles 61 - 72 of 72
Full-Text Articles in Life Sciences
The Consequences Of Changing The Top Predator In A Food Web: A Comparative Experimental Approach, Mark A. Mcpeek
The Consequences Of Changing The Top Predator In A Food Web: A Comparative Experimental Approach, Mark A. Mcpeek
Dartmouth Scholarship
Changing the top predator in a food web often results in dramatic changes in species composition at lower trophic levels; many species are extirpated and replaced by new species in the presence of the new top predator. These shifts in species composition also often result in substantial alterations in the strengths of species interactions. However, some species appear to be little affected by these changes that cause species turnover at other positions in the food web. An example of such a difference in species responses is apparent in the distributions of coenagrionid damselflies (Odonata: Zygoptera) among permanent water bodies with …
Thermodynamic Constraints On Nitrogen Transformations And Other Biogeochemical Processes At Soil-Stream Interfaces, Lars O. Hedin, Joseph C. Von Fischer, Nathaniel E. Ostrom, Brian P. Kennedy, Michael G. Brown, G. Philip Robertson
Thermodynamic Constraints On Nitrogen Transformations And Other Biogeochemical Processes At Soil-Stream Interfaces, Lars O. Hedin, Joseph C. Von Fischer, Nathaniel E. Ostrom, Brian P. Kennedy, Michael G. Brown, G. Philip Robertson
Dartmouth Scholarship
There is much interest in biogeochemical processes that occur at the interface between soils and streams since, at the scale of landscapes, these habitats may function as control points for fluxes of nitrogen (N) and other nutrients from terrestrial to aquatic ecosystems. Here we examine whether a thermodynamic perspective can enhance our mechanistic and predictive understanding of the biogeochemical function of soil-stream interfaces, by considering how microbial communities interact with variations in supplies of electron donors and acceptors. Over a two-year period we analyzed >1400 individual samples of subsurface waters from networks of sample wells in riparian wetlands along Smith …
Site-Dependent Regulation Of Population Size: A New Synthesis, Nicholas L. Rodenhouse, Thomas W. Sherry, Richard T. Holmes
Site-Dependent Regulation Of Population Size: A New Synthesis, Nicholas L. Rodenhouse, Thomas W. Sherry, Richard T. Holmes
Dartmouth Scholarship
The nature and extent of population regulation remains a principal unanswered question for many types of organisms, despite extensive research. In this paper, we provide a new synthesis of theoretical and empirical evidence that elucidates and extends a mechanism of population regulation for species whose individuals preemptively use sites that differ in suitability. The sites may be territories, refuges from predation, oviposition sites, etc. The mechanism, which we call site dependence, is not an alternative to density dependence; rather, site dependence is one of several mechanisms that potentially generate the negative feedback required for regulation. Site dependence has two major …
Trade-Offs, Food Web Structure, And The Coexistence Of Habitat Specialists And Generalists, Mark A. Mcpeek
Trade-Offs, Food Web Structure, And The Coexistence Of Habitat Specialists And Generalists, Mark A. Mcpeek
Dartmouth Scholarship
Species differ greatly in the breadth of their environmental distributions. Within the same collection of habitats, some species occur in many habitats, while others are only able to exist in one of a few. Trade-offs in the abilities of species to perform in various ecological interactions are important both to facilitating species coexistence within a habitat and to limiting the distributions of species among habitats. In this article I use a food web model to explore how in the same collection of habitats some species may be limited by trade-offs to occupying only one habitat, while other species may face …
Linking Local Species Interactions To Rates Of Speciation In Communities, Mark A. Mcpeek
Linking Local Species Interactions To Rates Of Speciation In Communities, Mark A. Mcpeek
Dartmouth Scholarship
Regional species diversity limits the diversity of local communities by defining the pool of species that are available to colonize sites. Biogeographical processes that influence speciation and extinction rates determine the size and composition of this regional species pool. Community ecologists are beginning to recognize the importance of these biogeographical processes in influencing diversity patterns among local communities, but the potential for local interactions to influence biogeographical processes, especially speciation, has been little considered. In this paper I discuss one mechanism by which variation in the strengths of local interactions can influence the potential for population differentiation and thus for …
Foraging Behavior Of American Redstarts In Breeding And Wintering Habitats: Implications For Relative Food Availability, Irby J. Lovette, Richard T. Holmes
Foraging Behavior Of American Redstarts In Breeding And Wintering Habitats: Implications For Relative Food Availability, Irby J. Lovette, Richard T. Holmes
Dartmouth Scholarship
We investigated food availability for a long-distance migrant species, the American Redstart (Setophaga ruticilla), in both its summer breeding habitat in New Hampshire and in its winter habitat in Jamaica. We used four components of foraging behavior (prey attack rate, foraging speed, time spent foraging, and foraging maneuver use) as indicators of the relative availability of prey in the two seasons. Redstarts attacked prey at a significantly greater rate in summer than in winter, indicating that foraging birds encountered prey more frequently in summer. The winter prey-encounter rate was low even though redstarts moved almost twice as fast …
Testing Hypotheses About Evolutionary Change On Single Branches Of A Phylogeny Using Evolutionary Contrasts, Mark A. Mcpeek
Testing Hypotheses About Evolutionary Change On Single Branches Of A Phylogeny Using Evolutionary Contrasts, Mark A. Mcpeek
Dartmouth Scholarship
Interspecific comparisons of phenotypes are used extensively to test hypotheses about the evolutionary forces shaping phenotypic variation, but comparative data analysis is complicated by correlations due to the common ancestry of species. The method of evolutionary contrasts removes such correlations by estimating the amount of character change between pairs of closely related species that has occurred since their most recent common ancestors. The original method allows character change to be estimated only along pairs of branches on a phylogeny, but many hypotheses address change along single branches. In this article the method of evolutionary contrasts is extended to allow character …
Selection Of Foraging And Nesting Sites By Black-Throated Blue Warblers: Their Relative Influence On Habitat Choice, Benjamin B. Steele
Selection Of Foraging And Nesting Sites By Black-Throated Blue Warblers: Their Relative Influence On Habitat Choice, Benjamin B. Steele
Dartmouth Scholarship
To understand why breeding Black-throated Blue Warblers (Dendroica caerulescens) select forests with dense shrubs, I assessed the value of this habitat in supplying opportunities for foraging and nesting. I predicted that these warblers would select shrub foliage for foraging if foraging substrate was important in their selection of habitat and that they would place their nests in areas of dense shrubs if nest-site availability affected habitat choice. To measure foraging and nest-site selection, I compared the proportion of foraging or nests in a particular habitat element to the availability of that element expressed as a proportion of all …
Assessing Population Trends Of New-Hampshire Forest Birds: Local Vs Regional Patterns, Richard T. Holmes, Thomas W. Sherry
Assessing Population Trends Of New-Hampshire Forest Birds: Local Vs Regional Patterns, Richard T. Holmes, Thomas W. Sherry
Dartmouth Scholarship
We examined the changes in abundance between 1969 and 1986 of 19 forest-dwelling, mostly migratory bird species breeding in New Hampshire at 2 different scales: one local (an intensively studied 10-ha plot in unfragmented forest) and the other regional (Breeding Bird Surveys statewide). Twelve of the 19 species exhibited similar trends at both scales. Eight neither increased nor decreased, and 4 (Least Flycatcher, Winter Wren, Wood Thrush, and Swainsoh's Thrush) declined significantly. Others increased, decreased, or re-mained steady at one or the other scale. Overall, more species declined than increased both locally (8 vs. 1) and regionally (5 vs. 1). …
Behavioral Feeding Specialization In Pinaroloxias Inornata, The “Darwin's Finch” Of Cocos Island, Costa Rica, Tracey K. Werner, Thomas W. Sherry
Behavioral Feeding Specialization In Pinaroloxias Inornata, The “Darwin's Finch” Of Cocos Island, Costa Rica, Tracey K. Werner, Thomas W. Sherry
Dartmouth Scholarship
As a population, Cocos Finches exhibit a broad range of feeding behaviors spanning those of several families of birds on the mainland, while individuals feed as specialists year-round. Although this extreme intraspecific variability occurs as predicted in a tropical oceanic island environment, these specializations challenge contemporary ecological theory in that they are not attributable to individual differences in age, sex, gross morphology, or opportunistic exploitation of patchy resources. Instead, they appear to originate and be maintained behaviorally, possibly via observational learning. This phenomenon adds another direction to the evolutionary radiation of the Darwin's Finches and underscores the necessity for detailed …
A Comparative Analysis Of Potential Nitrification And Nitrate Mobility In Forest Ecosystems, Peter M. Vitousek, James R. Gosz, Charles C. Grier, Jerry M. Melillo, William A. Reiners
A Comparative Analysis Of Potential Nitrification And Nitrate Mobility In Forest Ecosystems, Peter M. Vitousek, James R. Gosz, Charles C. Grier, Jerry M. Melillo, William A. Reiners
Dartmouth Scholarship
Mobilization in a wide range of forest ecosystems were investigated through a combination of field and laboratory experiments.Trenched plot experiments were performed in 17 forests, and laboratory incubation studies of potential ammonium and nitrate production were made on soils from 14ofthese sites.
Sunbathing Vermilion-Crowned Flycatchers Repulse Mates, Lawrence Kilham
Sunbathing Vermilion-Crowned Flycatchers Repulse Mates, Lawrence Kilham
Dartmouth Scholarship
Vermilion-crowned Flycatchers (Myiozetetes similis, formerly called Social Flycatchers) remain paired the year around (Skutch 1960). I was watching the members of a pair foraging in close association along the bank of a pond (near Escuintla in the Pacific lowlands of Guatemala) on 29 December 1976, when the two came to a patch of relatively bare earth 1-2 m in extent. This was late in the morning of a hot, sunny day. One of them immediately sprawled belly to the earth, with wings and tail widely spread and head back in the sunbathing posture of a passerine (Hauser 1957). When the …