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I examined the effect of competitor density on foraging success in staging semipalmated sandpipers (Calidris pusilla) foraging on a burrowing amphipod (Corophium volutator) in each of two study years. Little is known about the effect of competitor density when predation attempts disturb prey, causing a temporary decrease in food availability. Controlling for Corophium density and other potentially...
The main ecological factors that are hypothesized to explain the striking variation in the size of social groups among large herbivores are habitat structure, predation, and forage abundance and distribution; however, their relative roles in wild populations are not well understood. I combined analyses of ecological correlates of spatial variation in group size with analyses of individual behaviour...
The ability to understand and predict the success of invasive plant species in their new ranges is increased when there is a sympatric native congener available for comparison. Celastrus orbiculatus (oriental bittersweet) is a liana introduced into the United States in the mid-1800s from East Asia as an ornamental plant. Its native congener, Celastrus scandens (American bittersweet), ranges from the...
Few previous studies have assessed the role of herbivores and the third trophic level in the evolution of local adaptation in plants. The overall objectives of this study were to determine (1) whether local adaptation is present in the ant-defended plant, Chamaecrista fasciculata, and (2) the contribution of ant-plant-herbivore interactions and soil source to such adaptation. We used three C. fasciculata...
Animals in social aggregations often spend more time foraging than solitary conspecifics. This may be a product of the relative safety afforded by aggregations: group members can devote more time to foraging and less time to antipredator behaviors than solitary animals (the “risk reduction” effect). All else being equal, risk reduction should result in higher food intake for grouped animals. However,...
Most theoretical and empirical studies of productivity–species richness relationships fail to consider linkages among trophic levels. We quantified productivity–richness relationships in detritus-based, water-filled tree-hole communities for two trophic levels: invertebrate consumers and the protozoans on which they feed. By analogy to theory for biomass partitioning among trophic levels, we predicted...
Previous studies have found that root carbon inputs to the soil can stimulate the mineralization of existing soil carbon (C) pools. It is still uncertain, however, whether this “primed” C is derived from elevated rates of soil organic matter (SOM) decomposition, greater C release from microbial pools, or both. The goal of this research was to determine how the activities of the microbial exoenzymes...
The stable isotope composition of spines produced serially from the apex of columnar cacti has the potential to be used as a record of changes in climate and physiology. To investigate this potential, we measured the δ18O, δ13C and F14C values of spines from a long-lived columnar cactus, saguaro (Carnegiea gigantea). To determine plant age, we collected spines at 11 different heights along one rib...
The importance of litter in regulating ecosystem processes has long been recognised, with a growing appreciation of the differential contribution of various functional plant groups. Despite the ubiquity of mistletoes in terrestrial ecosystems and their prominence in ecological studies, they are one group that have been overlooked in litter research. This study evaluated the litter contribution from...
In socially living animals, individuals interact through complex networks of contact that may influence the spread of disease. Whereas traditional epidemiological models typically assume no social structure, network theory suggests that an individual’s location in the network determines its risk of infection. Empirical, especially experimental, studies of disease spread on networks are lacking, however,...
The effects of global N enrichment on soil processes in grassland ecosystems have received relatively little study. We assessed microbial community response to experimental increases in N availability by measuring extracellular enzyme activity (EEA) in soils from three grasslands with contrasting edaphic and climatic characteristics: a semiarid grassland at the Sevilleta National Wildlife Refuge,...
Few studies of plant–pollinator interactions in fragmented landscapes evaluate the consequences of floral visitor variation on multiple stages of plant reproduction. Given that fragmentation potentially has positive or negative effects on different organisms, and that self-incompatible plant species depend on pollinators for sexual reproduction, differences in floral visitor assemblages may affect...
Parasites influence host life-history traits and therefore might crucially shape host populations in natural systems. In a series of laboratory experiments, we studied the impact of an oomycete brood parasite on its Daphnia (waterflea) host. We asked whether Daphnia dump the infected brood and subsequently are able to reproduce again as was occasionally observed in a preliminary study. No viable offspring...
In a given period of time, herbivores often eat less as dietary plant secondary metabolite (PSM) concentrations increase. This reduction in total food intake is interpreted as a need for the herbivore to regulate PSM ingestion in order to avoid toxication. However, regulation of PSM ingestion involves more than the reduction of total intake; it involves an alteration of meal patterns, through a reduction...
In grassland systems across the globe, ecologists have been attempting to understand the complex role of fire, grazing and rainfall in creating habitat heterogeneity and the consequences of anthropogenic control of these factors on ecosystem integrity and functioning. Using a South African grassland ecosystem as a model, we investigated the impact of fire and grazing pressure on small mammal communities...
A general feature of the demography of large ungulates is that many demographic traits are dependent on female body mass at early ages. Thus, identifying the factors affecting body mass variation can give important mechanistic understanding of demographic processes. Here we relate individual variation in autumn and winter body mass of moose calves living at low density on an island in northern Norway...
To predict the impacts of climate change on animal populations, we need long-term data sets on the effects of annual climatic variation on the demographic traits (growth, survival, reproductive output) that determine population viability. One frequent complication is that fecundity also depends upon maternal body size, a trait that often spans a wide range within a single population. During an eight-year...
Stable isotope signatures of primary producers display high inter- and intraspecific variation. This is assigned to species-specific differences in isotope fractionation and variable abiotic conditions, e.g., temperature, and nutrient and light availability. As consumers reflect the isotopic signature of their food source, such variations have direct impacts on the ecological interpretation of stable...
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