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Biotic Environment (biotic + environment)
Selected AbstractsTrophic role of Atlantic cod in the ecosystemFISH AND FISHERIES, Issue 1 2009Jason S. Link Abstract As the world's oceans continue to undergo drastic changes, understanding the role of key species therein will become increasingly important. To explore the role of Atlantic cod (Gadus morhua Gadidae) in the ecosystem, we reviewed biological interactions between cod and its prey, predators and competitors within six ecosystems taken from a broad geographic range: three are cod-capelin (Mallotus villosus Osmeridae) systems towards cod's northern Atlantic limit (Barents Sea, Iceland and Newfoundland,Labrador), two are more diverse systems towards the southern end of the range (North Sea and Georges Bank,Gulf of Maine), and one is a species-poor system with an unusual physical and biotic environment (Baltic Sea). We attempt a synthesis of the role of cod in these six ecosystems and speculate on how it might change in response to a variety of influences, particularly climate change, in a fashion that may apply to a wide range of species. We find cod prey, predators and competitors functionally similar in all six ecosystems. Conversely, we estimate different magnitudes for the role of cod in an ecosystem, with consequently different effects on cod, their prey and predator populations. Fishing has generally diminished the ecological role of cod. What remains unclear is how additional climate variability will alter cod stocks, and thus its role in the ecosystem. [source] Intraspecific seed trait variations and competition: passive or adaptive response?FUNCTIONAL ECOLOGY, Issue 3 2009Cyrille Violle Summary 1The phenotype of offspring depends on the abiotic and biotic environment in which the parents developed. However, the direct effects of competition experienced by parent plants on single-seed traits are poorly documented despite their impact on plant fitness. 2We hypothesize that single-seed traits can differentially respond to the resource deficiencies of parent plants due to competition: seed quality may decrease as seed number does, magnifying the negative effects of competition for offspring (,passive response' hypothesis), or increase and then enhance offspring fitness to offset the reduction in offspring number (,adaptive response' hypothesis). Here we tested these hypotheses for four single-seed traits. We assessed the sensibility of their responses to changes in competition intensity due to species with different competitive effects and to contrasting soil nitrogen conditions. 3In a common-garden experiment, four single-seed traits related to fitness , seed mass, seed nitrogen concentration (SNC), germinability and the timing of germination , were measured on a phytometer species transplanted in 14 different neighbours grown in monoculture with and without soil nitrogen limitation. 4Under nitrogen-limiting conditions, the responses of SNC and of the timing of germination were passive and mainly related to the effects of neighbours on soil nitrogen availability, as shown by the increase in SNC with N-fixing neighbours. Within-individual seed mass variability decreased with increasing competition intensity, as an adaptive response to counterbalance the reduction in seed production. With nitrogen supplementation, competitors had no detectable effect on single-seed traits despite an overall increase in SNC and germination rate, confirming their nitrogen-dependent passive responses to competition. Germinability did not change among treatments. 5The impact of competition on single-seed traits depends on both phytometer trait identity and resource modulation by neighbours. The passive response of seed chemical composition to competitors may magnify the competitive effects on offspring. By contrast, the adaptive response of seed size variability may offset these competitive effects. As a consequence, experiments looking at the fitness consequences of competition should not only consider the effects on fitness parameters of a target plant but also on the offspring. [source] Unravelling the effects of temperature, latitude and local environment on the reproduction of forest herbsGLOBAL ECOLOGY, Issue 6 2009P. De Frenne ABSTRACT Aim, To investigate the effect of temperature, latitude and local environment on the reproductive traits of widespread perennial forest herbs to better understand the potential impacts of rising temperatures on their population dynamics and colonization capacities. Location, Six regions along a latitudinal gradient from France to Sweden. Methods, Within each region, we collected data from three to five populations of up to six species. For each species, several variables were recorded in each region (temperature, latitude) and population (local abiotic and biotic environmental variables), and seed production and germination were estimated. Resource investment in reproduction (RIR) was quantified as seed number × seed mass, while germinable seed output (GSO) was expressed as seed number × germination percentage. We performed linear regression and mixed effect models to investigate the effects of temperature (growing degree hours), latitude and local abiotic and biotic environment on RIR and GSO. Results, Temperature and latitude explained most of the variation in RIR and GSO for early flowering species with a northerly distribution range edge (Anemone nemorosa, Paris quadrifolia and Oxalis acetosella). Reproduction of the more southerly distributed species (Brachypodium sylvaticum, Circaea lutetiana and Primula elatior), in contrast, was independent of temperature/latitude. In the late summer species, B. sylvaticum and C. lutetiana, variation in RIR and GSO was best explained by local environmental variables, while none of the investigated variables appeared to be related to reproduction in P. elatior. Main conclusions, We showed that reproduction of only two early flowering, northerly distributed species was related to temperature. This suggests that the potential reproductive response of forest herbs to climate warming partly depends on their phenology and distribution, but also that the response is to some extent species dependent. These findings should be taken into account when predictions about future shifts in distribution range are made. [source] An experimental test for effects of the maternal environment on delayed germinationJOURNAL OF ECOLOGY, Issue 5 2010Katja Tielbörger Summary 1.,Recent models on bet-hedging germination in annual plants assume a negative relationship between the proportion of offspring that germinate and the quality of the maternal environment. An increase in the proportion of seeds remaining dormant in the next year, when produced in seasons with high reproduction may result from selection that avoids overcrowding in the following year. 2.,We present the first empirical test of this prediction by utilizing a field experiment in Israel which manipulated the entire maternal environment. We subjected semi-arid and Mediterranean annual plant communities to different rainfall treatments: control, reduced and increased rainfall. We then related maternal environment quality to offspring germination fractions for three focal species in two consecutive seasons. 3.,There was a negative relationship between the quality of the maternal environment and offspring germination fraction in four out of twelve cases. The negative relationship was stronger for the least competitive species and in the environment with high competition intensity, supporting the role of competition for the observed pattern. 4.,Our results suggest that competition with all neighbours is more likely to explain the pattern than sib competition. 5.,Synthesis. Our findings provide the first experimental evidence of a highly reliable cue (productivity of maternal environment) that allows for plants to respond to their future biotic environment. There is an urgent need for testing predictions of theoretical models in natural populations and for incorporating the role of density dependence in studies of bet-hedging germination. [source] Mechanisms of exclusion of native coastal marsh plants by an invasive grassJOURNAL OF ECOLOGY, Issue 2 2006TODD E. MINCHINTON Summary 1Determining the mechanisms by which invasive species exclude natives is critical for conserving and restoring native populations in impacted habitats. In recent decades the grass Phragmites australis has been aggressively invading coastal marshes of North America, with monocultures often replacing diverse assemblages of plants. 2Our objective was to quantify how P. australis modifies the abiotic (soil and light conditions) and biotic (litter and shoots) environment and to determine the mechanisms by which it excludes two common forbs, the annual chenopod Atriplex patula var. hastata and the perennial aster Solidago sempervirens, from the highest tidal elevations of a brackish marsh in southern New England, USA. 3In a 3-year field experiment we added seeds of both forb species to stands of P. australis, where we manipulated shoots and litter in an orthogonal design, and to uninvaded marsh areas dominated by the rush Juncus gerardi, where we manipulated the shoots of the marsh vegetation. In general, seedling establishment and the number of plants surviving until the end of the growing season were substantially greater in areas not invaded by P. australis, and both shoots and litter limited the abundance of forbs within stands. 4Forbs surviving within stands of P. australis grew larger and produced more seeds than those in uninvaded areas, indicating that changes to the soil resulting from invasion do not preclude the survival of established forbs. This was confirmed by a glasshouse study where the performance of forbs in soil collected from within stands of P. australis was better than in soil from areas dominated by J. gerardi. 5Similar to many invasive grasses in terrestrial communities, P. australis excludes native forbs through competition, modifying the biotic environment of the marsh at both the ground (litter) and above-ground (shoots) levels. Our results suggest that successful invaders, such as P. australis, are likely to be the ones that can engineer habitats in multiple ways and limit populations of native species across several critical stages of their life history. [source] | ||||||||||