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Size Advantage (size + advantage)
Selected AbstractsCompetitive dynamics in two- and three-component intercropsJOURNAL OF APPLIED ECOLOGY, Issue 3 2007METTE KLINDT ANDERSEN Summary 1Intercropping is receiving increasing attention because it offers potential advantages for resource utilization, decreased inputs and increased sustainability in crop production, but our understanding of the interactions among intercropped species is still very limited. 2We grew pea Pisum sativum, barley Hordeum vulgare and rape Brassica napus as sole crops and intercrops under field conditions using a replacement design. We collected total dry matter data from sequential harvests and fitted the data to a logistic growth model. At each harvest we estimated the relative Competitive Strength (CS) of the three crops by fitting the data to a simple interspecific competition model. 3The pea monocrop produced the largest amount of biomass from the middle to the end of the growth period, but pea was not dominant in intercrops. 4Fitting data to a logistic growth model emphasizes the importance of initial size differences for interactions among intercrops. Barley was the dominant component of the intercrops largely because of its initial size advantage. The competitive effect of barley on its companion crops, measured as CS, increased throughout most of the growing season. 5The performance of each crop species was very different when it grew with a second species rather than in monoculture, but addition of a third crop species had only minor effects on behaviour of the individual crops. 6Synthesis and applications. Including sequential harvests in experiments on intercropping can provide important information about how competitive hierarchies are established and change over time. Our results suggest that increased understanding of the role of asymmetric competition among species and the resulting advantages of early germination and seedling emergence would be valuable in designing intercrops. More focus on understanding the mechanisms that govern interactions between intercropped species is needed for designing optimized intercropping systems. [source] Competition as a selective mechanism for larger offspring size in guppiesOIKOS, Issue 1 2008Farrah Bashey Highly competitive environments are predicted to select for larger offspring. Guppies Poecilia reticulata from low-predation populations have evolved to make fewer, larger offspring than their counterparts from high-predation populations. As predation co-varies with the strength of competition in natural guppy populations, here I present two laboratory experiments that evaluate the role of competition in selecting for larger offspring size. In the first experiment, paired groups of large and small newborns from either a high- or a low-predation population were reared in mesocosms under a high- or a low-competition treatment. While large newborns retained their size advantage over small newborns in both treatments, newborn size increased growth only in the high-competition treatment. Moreover, the increase in growth with size was greater in guppies derived from the low-predation population. In the second experiment, pairs of large and small newborns were reared in a highly competitive environment until reproductive maturity. Small size at birth delayed maturation and the effect of birth size on male age of maturity was greater in the low-predation population. These results support the importance of competition as a selective mechanism in offspring size evolution. [source] Small-scale variation in growing season length affects size structure of scarlet monkeyflowerOIKOS, Issue 1 2004Jennifer L. Williams Growing season length can control plant size over altitudinal and biogeographic scales, but its effect at the scale of meters is largely unexplored. Within the riparian zone of a northern California river, scarlet monkeyflower, Mimulus cardinalis, grows significantly larger at sites high in the channel as compared to sites low in the channel, and even larger where tributaries meet the main stem of the river. We explored the hypothesis that markedly different growing season length controls this size variation. Due to the very gradual retreat of the water level following winter flooding, emergence time is three months longer for plants growing at tributary confluences than for plants growing at low elevations in the channel. Consistent with the growing season length hypothesis, we found no difference in transplant growth between river and tributary confluence sites in an experiment where we equalized growing season length at these locations. Moreover, a second experiment showed that individuals planted earlier in the year gain a distinct size advantage over those planted later, even though growing conditions are less ideal. These results suggest that emergence time may be a key determinant of plant size structure along rivers, an important result considering forecasted variation in water flows with climate change. [source] Growth and survival of Procambarus acutus acutus (Girard, 1852) and P. clarkii (Girard, 1852) in competitive settingsAQUACULTURE RESEARCH, Issue 6 2005Yavuz Mazlum Abstract Third-instar young-of-the-year (YOY) and juvenile Procambarus acutus acutus and P. clarkii stocked in aquaria, rice forage microcosms and a culture pond were evaluated in intraspecific- and interspecific-competitive settings. Procambarus acutus acutus YOY, which were larger than P. clarkii YOY at stocking, grew and survived at significantly greater rates over fall-, winter- and spring-temperature courses in aquaria. Juvenile P. a. acutus starting an aquarium experiment with a mean total length (TL) size advantage survived at a significantly greater rate than P. clarkii juveniles. Growth rate of similar-sized stocked P. a. acutus juvenile was significantly faster than that of P. clarkii juveniles in the same microcosms. Survival of juvenile P. clarkii in the microcosms with P. a. acutus was significantly less than when stocked alone. Estimated survival of 2200 P. a. acutus and 2200 P. clarkii YOY in a culture pond over a 174-day grow-out period was 84% and 57% respectively. Growth rate of these YOY P. a. acutus and P. clarkii was 0.48 and 0.40 mm TL day,1. The body-size advantage at hatching and through the faster growth of P. a. acutus was important in defining competitive interaction with P. clarkii. [source] Male Body Size and Mating Success and Their Relation to Larval Host Plant History in the Moth Rothschildia lebeau in Costa Rican Dry ForestBIOTROPICA, Issue 2 2010Salvatore J. Agosta ABSTRACT The moth Rothschildia lebeau uses three tree species as its primary larval hosts in the tropical dry forest of northwestern Costa Rica. These hosts were shown previously to have different relative effects on caterpillar performance, resulting in an apparent host-related life history trade-off between large adult body size on the one hand but low offspring survival on the other. To further assess the potential ecological and evolutionary importance of this trade-off, an observational field study of the relationship between male body size and mating success was conducted. Across mating trials, larger males had a higher probability of being observed mating. Independent of the effect of size, the amount of wing damage an individual had sustained (a measure of relative age) was negatively correlated with the probability a male was observed mating. Within mating trials, the mated male tended to be larger than the average unmated male, but there was no difference in wing damage. Overall, results of this study were consistent with a positive effect of male body size on mating success, consistent with the idea that larval host plant history and its effects on adult body size matters in terms of adult male fitness. However, all sized males were observed mating over the course of the study, and the size advantage did not appear to be particularly strong. Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp [source] | ||||||||||