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AbstractSome theories of plant allocation to defence predict that chemical or structural defences against herbivores should be maximised when browsing is most likely to occur. However, plants are constrained by a trade-off between growth and defence such that slow-growing plants usually have higher levels of secondary compounds, such as phenolics and tannins, than faster-growing ones. Thus, it is...
AbstractEnvironmental catastrophes, such as severe drought, can reduce host-plant quality and/or abundance, which in turn decrease levels of herbivore populations. Such changes in herbivore populations affect populations of their natural enemies. As part of a long-term field experiment (19831991), galls of Eurosta solidaginis from 16 fields in central Pennsylvania were systematically collected from...
AbstractThe impact of large ungulate carcasses on grassland dynamics was investigated by monitoring vegetation and soil nutrients in 50-cm circular zones around the center of bison (Bos bison), cattle (B. taurus), and deer (Odocoileus virginianus) carcasses. An ungulate carcass creates an intense localized disturbance that varies with animal size and the season of death. Unlike other natural disturbances,...
AbstractThis study presents model experiments on the effect of the spatial pattern of herbivory on primary producer diversity. Microalgal biofilms (periphyton) were exposed to different mixtures of two benthic herbivores, the isopod Idothea chelipes and the gastropod Littorina littorea. The herbivores are similar in their feeding selectivity but differ strongly in the spatial pattern of grazing. Idothea...
AbstractUnderstanding the evolution of growth rate requires knowledge of the physiology of growth. This study explored the physiological basis of countergradient variation (CnGV) in somatic growth across latitudinal populations of the Atlantic silverside, Menidia menidia. Energetics of northern (Nova Scotia, Canada) and southern (South Carolina, USA) genotypes were compared across resource levels,...
AbstractThis study assessed the effect of nutrient enrichment on organic matter breakdown in an alpine springbrook, using alder leaf packs to which phosphorus and nitrogen were added in the form of slow-release fertilizer briquettes. The breakdown of leaf packs with nutrients added (k=0.0284 day1) was significantly faster than that of unfertilized packs (k=0.0137 day1), resulting in a 30% higher mass...
AbstractMovement is a fundamental feature of vertebrate behavior and can modify processes within populations and communities. Because tropical avian frugivores disperse seeds of many plant species, the temporal and spatial patterning of their movement will influence seed distribution within a habitat. To date, little is known about movement patterns of these birds. Here we consider the movement of...
AbstractThis study examines the relationship between cladoceran species richness and ecosystem functioning. I conducted an experiment in which four cladocerans, Daphnia. magna, D. longispina, D. pulex and Chydorus sphaericus, were cultured in microcosms using different species combinations and levels of species richness. The results demonstrate that even within this closely related group of organisms...
AbstractHair is considered to be a basic mammalian feature that provides protection and insulation, promoting energy conservation and survival. To quantify the functional significance of mammalian pelage, we tested the short-term experimental effects of fur removal in a natural population of the California vole, Microtus californicus, in winter. The daily energy expenditure (DEE) of seven voles was...
AbstractDensity compensation is a community-level phenomenon in which increases in the abundance of some species may offset the population decline, extirpation, or absence of other potentially interacting competitors. In this paper we examine the evidence for density compensation in neotropical primate assemblages using data from 56 hunted and nonhunted, but otherwise undisturbed, forest sites of...
AbstractNitrogen isotope measurements may provide insights into changing interactions among plants, mycorrhizal fungi, and soil processes across environmental gradients. Here, we report changes in 15N signatures due to shifts in species composition and nitrogen (N) dynamics. These changes were assessed by measuring fine root biomass, net N mineralization, and N concentrations and 15N of foliage, fine...
AbstractDespite the common occurrence of ontogenetic niche shifts, their consequences for morphological adaptations have been little studied. To address this question, we studied morphological adaptations related to ontogenetic niche shifts in Eurasian perch (Perca fluviatilis) in eight lakes that varied in density of benthic resources and planktivorous fish biomass. Perch start to feed on pelagic...
AbstractEvidence for interspecific competition between honey bees and wild bees was studied on 15 calcareous grasslands with respect to: (1) foraging radius of honey bees, (2) overlap in resource use, and (3) possible honey bee effects on species richness and abundance of flower-visiting, ground-nesting and trap-nesting wild bees. The grasslands greatly differed in the number of honey bee colonies...
AbstractIndividual hosts constitute a limited resource for parasites, suggesting that density-dependent effects may play a role in within-host growth and parasite regulation. This hypothesis has been tested for several helminth parasites, but not for microparasites. We therefore examined dose-response patterns for the microparasitic bacterium Pasteuria ramosa and the fungus Metschnikowiella biscuspidata...
AbstractMost knowledge of direct and indirect effects of zooplanktivorous fish has come from studies in which a treatment with a zooplanktivore is compared to a fishless control. However, effects of a zooplanktivore may be different in the presence of other fish species because the other fish have direct and indirect effects that may alter the effects of the zooplanktivore in question. To test this...
AbstractTo investigate the potential for and constraints on the evolution of compensatory ability, we performed a greenhouse experiment using Asclepias syriaca in which foliar damage and soil nutrient concentration were manipulated. Under low nutrient conditions, significant genetic variation was detected for allocation patterns and for compensatory ability. Furthermore, resource allocation to storage...
AbstractDecomposition rate constants were measured for boles of 155 large dead trees (10 cm diameter) in central Amazon forests. Mortality data from 21 ha of permanent inventory plots, monitored for 1015 years, were used to select dead trees for sampling. Measured rate constants varied by over 1.5 orders of magnitude (0.0150.67 year1), averaging 0.19 year1 with predicted error of 0.026 year. Wood...
AbstractMany plants employ induced responses against generalist herbivores. Specialist herbivores, however, may employ several mechanisms to overcome the negative effects of induced plant defenses. Here we test how the behavior and development of specialist Manduca sexta larvae are affected by induced responses in their natural host plant Nicotiana attenuata. On a spatial scale relevant to both the...
AbstractThe analysis of long-term floristic changes was conducted on nine west-Mediterranean limestone islands (size range: 295 ha) which have recently undergone a severe demographic explosion in their yellow-legged gull Larus cachinnans colonies. A comparison of past and present plant inventories was used to quantify extinction-colonization events, both from a classical biogeographical perspective...
AbstractThe food webs of rocky infra-littoral ecosystems in the Mediterranean have been little studied. In this investigation stable isotopes and dietary data were compared in an attempt to describe features of the food webs concerned. 13C and 15N were determined for plants, invertebrates and fishes from the Bay of Calvi, Corsica. Dietary data were derived from the literature. 13C of plants ranged...
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