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The dynamics of mutualistic interactions involving more than a single pair of species depend on the relative costs and benefits of interaction among alternative partners. The neotropical myrmecophytes Cordia nodosa and Duroia hirsuta associate with several species of obligately symbiotic ants. I compared the ant partners of Cordia and Duroia with respect to two benefits known to be important in ant-myrmecophyte...
Although increases in sedimentation have been proposed to interfere with benthic communities in many coastal areas worldwide, few experimental studies have investigated the effect of sedimentation on community composition and assessed species-specific responses. In a field experiment on a rocky shore on the Swedish east coast (northern Baltic Proper) we confirmed the hypotheses that ambient sedimentation...
Seed and seedling predation may differentially affect competitively superior tree species to increase the relative recruitment success of poor competitors and contribute to the coexistence of tree species. We examined the effect of seed and seedling predation on the seedling recruitment of three tree species, Acer rubrum (red maple), Liriodendron tulipifera (yellow poplar), and Quercus rubra (northern...
Herbivore dynamics and community structure are influenced both by plant quality and the actions of natural enemies. A factorial experiment manipulating both higher and lower trophic levels was designed to explore the determinants of colony growth of the aphid Aphis jacobaeae, a specialist herbivore on ragwort Senecio jacobaea. Potential plant quality was manipulated by regular addition of NPK-fertiliser...
Questions about individual variation in “quality” and fitness are of great interest to evolutionary and population ecologists. Such variation can be investigated using either a random effects approach or an approach that relies on identifying observable traits that are themselves correlated with fitness components. We used the latter approach with data from 1,925 individual females of three species...
Most studies of climate-driven changes in avian breeding phenology have focused on temperate passerines, yet the consequences of such environmental change may be more deleterious for other avian taxa, such as arctic and sub-arctic waders (Charadrii). We therefore examine large-scale climatic correlates of the breeding phenology of one such species (golden plover Pluvialis apricaria), and the timing...
This paper reports the findings of a short-term natural invasibility field study in constructed Mediterranean herbaceous communities of varying diversities, under a fire treatment. Three components of invasibility, i.e. species richness, density and biomass of invaders, have been monitored in burnt and unburnt experimental plots with resident diversity ranging from monocultures to 18-species mixtures...
In this study, the non-additivity of effects of herbivores and pollinator on fitness of the plant Erysimum mediohispanicum (Cruciferae) has been experimentally tested. The abundance and diversity of the pollinator assemblage of plants excluded from and exposed to mammalian herbivores, and the combined effect of pollinators and herbivores on plant reproduction were determined over a period of 2 years...
Species with restricted gene flow often show trait-shifts from one type of environment to another. In those rock-dwelling marine gastropods that lack larval dispersal, size generally decreases in wave-exposed habitats reducing risk of dislodgement, while increases in less exposed habitats to resist crab-crushing. In Littorina fabalis, however, snails of moderately exposed shores are generally much...
It is by now well established that plants use various strategies to defend themselves against herbivores. Besides conventional weapons such as spines and stinging hairs and sophisticated chemical defenses, plants can also involve the enemies of the herbivores in their defense. It has been suggested that plants could even use entomopathogens as part of their defense strategies. In this paper, we show...
While elaborate carotenoid-based traits in adult birds may have evolved as honest signals of individual quality in the context of sexual selection or other social interactions, the function of carotenoid-based colours in juveniles is less well understood. We investigated the hypothesis that carotenoid-based nestling colouration has evolved in response to parental preference of intensely coloured offspring...
Inter-specific competition, facilitation and predation influence herbivore assemblages, but no study has experimentally explored the interactions between large ungulates and small rodents. In a fully replicated, landscape scale experiment, we manipulated densities of domestic sheep in mountain pastures in Norway. We then determined population growth and densities of rodents by live trapping in each...
The geographic range of many temperate plant species is constrained by climate, but it remains little known how climate affects population performance at low-latitude range margins. This study investigated the reproduction of the Eurasian tree Frangula alnus in relict populations near its southwestern range limit in southern Spain. The aim was to identify the principal stages and causes of ovule loss...
We studied competition between the obligate biotroph Puccinia triticina (designated here as Puccinia) and the facultative saprophyte Pyrenophora tritici-repentis (designated here as Pyrenophora) in older and younger leaves in a set of three host genotypes selected to be resistant to Puccinia only, Pyrenophora only, or neither. Age-related resistance is important for both of these pathogens. The facultative...
Stable isotopes are being increasingly used in wildlife forensics as means of determining the origin and movement of animals. The heavy isotope content of precipitated water and snow (δDp, δ18Op) varies widely and systematically across the globe, providing a label that is incorporated through diet into animal tissue. As a result, these isotopes are potentially ideal tracers of geographic origin. The...
Nutrients, in addition to water, limit desert primary productivity, but nutrient limitations to fecundity and seed quality in desert ecosystems have received little attention. Reduced seed production and quality may affect recruitment, population, and community processes. At the Mono Basin, CA, USA where the alkaline, sandy soil has very low availability of N, P, and most other nutrients, seed production,...
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