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Ecological Trade-offs (ecological + trade-off)
Selected AbstractsAn ecological cost of plant defence: attractiveness of bitter cucumber plants to natural enemies of herbivoresECOLOGY LETTERS, Issue 3 2002Anurag A. Agrawal Abstract Plants produce defences that act directly on herbivores and indirectly via the attraction of natural enemies of herbivores. We examined the pleiotropic effects of direct chemical defence production on indirect defence employing near-isogenic varieties of cucumber plants (Cucumis sativus) that differ qualitatively in the production of terpenoid cucurbitacins, the most bitter compounds known. In release,recapture experiments conducted in greenhouse common gardens, blind predatory mites were attracted to plants infested by herbivorous mites. Infested sweet plants (lacking cucurbitacins), however, attracted 37% more predatory mites than infested bitter plants (that produce constitutive and inducible cucurbitacins). Analysis of the headspace of plants revealed that production of cucurbitacins was genetically correlated with large increases in the qualitative and quantitative spectrum of volatile compounds produced by plants, including induced production of (E,)-,-ocimene (3E,)-4,8-dimethyl-1,3,7-nonatriene, (E,E)-,-farnesene, and methyl salicylate, all known to be attractants of predators. Nevertheless, plants that produced cucurbitacins were less attractive to predatory mites than plants that lacked cucurbitacins and predators were also half as fecund on these bitter plants. Thus, we provide novel evidence for an ecological trade-off between direct and indirect plant defence. This cost of defence is mediated by the effects of cucurbitacins on predator fecundity and potentially by the production of volatile compounds that may be repellent to predators. [source] Characterizing the pigment composition of a variable warning signal of Parasemia plantaginis larvaeFUNCTIONAL ECOLOGY, Issue 4 2010Carita Lindstedt Summary 1.,Aposematic animals advertise their defences to predators via warning signals that often are bright colours combined with black patterns. Predation is assumed to select for large pattern elements and conspicuousness of warning signals because this enhances avoidance learning of predators. However, conspicuousness of the colour pattern can vary among individuals of aposematic species, suggesting that warning signal expression may be constrained by opposing selection pressures. If effective warning signals are costly to produce, variation in signal expression may be maintained via physiological trade-offs. To understand the costs of signalling that might underlay both physiological and ecological trade-offs, it is crucial to identify the pigments involved in aposematic traits, how they or their precursors are acquired and how their production and/or deposition interact with other physiological processes. 2.,We characterized the pigments responsible for the genetically and phenotypically variable orange-black warning signal of the hairy larvae of an Arctiid moth, Parasemia plantaginis. We tested orange and black coloured hairs for the presence of six candidate pigment types using high-performance liquid chromatography, spectral and solubility analyses. 3.,After excluding the presence of carotenoids, ommochromes, pterins and pheomelanins in orange hairs, our results suggest that tiger moth larvae produce their orange warning signal by depositing both diet-derived flavonoids and trace levels of synthesized eumelanin in their hairs. The nearby black hairs are coloured by eumelanin. 4.,In light of previous studies, we conclude that although a large orange patch increases the 1larvae's antipredator efficacy, variation in the size of orange patches within a population can be driven by scarcity of flavonoids in diet. However, traces of eumelanin found in the orange hairs of the larvae may also play a significant role in the maintenance of the signal pattern on poor quality diets. 5.,The goal of the future studies will be to test the condition dependence of pigment deposition in aposematic colour patterns by directly manipulating relevant nutritional parameters such as dietary flavonoid or nitrogen content (i.e. amino acid content). [source] Ecological aspects of seed desiccation sensitivityJOURNAL OF ECOLOGY, Issue 2 2003John C. Tweddle Summary 1The ability of seeds to survive desiccation is an important functional trait and is an integral part of plant regeneration ecology. Despite this, the topic has received relatively little attention from ecologists. In this study, we examine the relationships between seed desiccation tolerance and two important aspects of plant regeneration ecology: habitat and dormancy. This is done by comparative analysis of a data set of 886 tree and shrub species from 93 families. 2The proportion of species displaying desiccation sensitive seeds declines as the habitat becomes drier, and possibly also cooler, although the latter observation requires cautious interpretation. Desiccation sensitivity is most common in moist, relatively aseasonal vegetation zones, but is infrequent in, though not absent from arid and highly seasonal habitats. 3The highest frequency of desiccation sensitivity occurs in non-pioneer evergreen rain forest trees, although 48% of the species examined have desiccation tolerant seeds. In contrast, all pioneer taxa within the data set have drying tolerant seeds. 4Desiccation sensitivity is more frequent in seeds that are non-dormant on shedding (c. 31%), than dormant (c. 9%). Highest frequencies of drying tolerance occur in seeds with physical or combinational dormancy, at 99% and 100%, respectively. 5Although there is an association between non-dormancy and desiccation sensitivity in both tropical and temperate zones, the relationship does not appear to be causal. 6Working from the hypothesis that seed desiccation sensitivity represents a derived state in extant species, we use the results to investigate and discuss possible ecological trade-offs and associated fitness advantages. These may explain the hypothesized repeated loss of this trait. The frequent association between large seed size and desiccation sensitivity is also considered. [source] JOINTLY-DETERMINED ECOLOGICAL THRESHOLDS AND ECONOMIC TRADE-OFFS IN WILDLIFE DISEASE MANAGEMENTNATURAL RESOURCE MODELING, Issue 4 2007ELI P. FENICHEL ABSTRACT. We investigate wildlife disease management, in a bioeconomic framework, when the wildlife host is valuable and disease transmission is density-dependent. Disease prevalence is reduced in density-dependent models whenever the population is harvested below a host-density threshold a threshold population density below which disease prevalence declines and above which a disease becomes epidemic. In conventional models, the threshold is an exogenous function of disease parameters. We consider this case and find a steady state with positive disease prevalence to be optimal. Next, we consider a case in which disease dynamics are affected by both population controls and changes in human-environmental interactions. The host-density threshold is endogenous in this case. That is, the manager does not simply manage the population relative to the threshold, but rather manages both the population and the threshold. The optimal threshold depends on the economic and ecological trade-offs arising from the jointly-determined system. Accounting for this endogene-ity can lead to reduced disease prevalence rates and higher population levels. Additionally, we show that ecological parameters that may be unimportant in conventional models that do not account for the endogeneity of the host-density threshold are potentially important when host density threshold is recognized as endogenous. [source] | ||||||||||