Search results for "allometry"
showing 10 items of 49 documents
A modified niche model for generating food webs with stage-structured consumers : The stabilizing effects of life-history stages on complex food webs
2021
1. Almost all organisms grow in size during their lifetime and switch diets, trophic positions, and interacting partners as they grow. Such ontogenetic development introduces life-history stages and flows of biomass between the stages through growth and reproduction. However, current research on complex food webs rarely considers life-history stages. The few previously proposed methods do not take full advantage of the existing food web structural models that can produce realistic food web topologies. 2. We extended the niche model by Williams & Martinez (2000) to generate food webs that included trophic species with a life-history stage structure. Our method aggregated trophic species …
Comparison of adult liver flukes from highland and lowland populations of Bolivian and Spanish sheep.
2000
A morphological study of adult liver flukes and eggs from sheep in a human fascioliasis endemic zone in the Northern Bolivian Altiplano showed that they belong to the species Fasciola hepatica. An exhaustive morphometric comparison with a F. hepatica population from Spanish sheep was made using image analysis and an allometric model: (y2m - y2)]#x002F;y2 = c[(y1m - y1)/y1]b, where y1 = body surface or body length, y2 = one of the measurements analysed, y1m, y2m = maximum values towards which y1 and y2 respectively tend, and c, b = constants. Only slight allometric differences in worms were observed despite the geographic distance between both Spanish and Bolivian sheep populations and the v…
Relationships between host species and morphometric patterns in Fasciola hepatica adults and eggs from the northern Bolivian Altiplano hyperendemic r…
2001
The highest prevalences and intensities of human fasciolosis by Fasciola hepatica are found in the northern Bolivian Altiplano, where sheep and cattle are the main reservoir host species and pigs and donkeys the secondary ones. Morphometric comparisons of many linear measurements, areas and ratios of F. hepatica adults (from sheep, cattle and pigs) and eggs (from sheep, cattle, pigs and donkeys) in natural liver fluke populations of the Bolivian Altiplano, as well as of F. hepatica adults and eggs experimentally obtained in Wistar rats infected with Altiplanic sheep, cattle and pig isolates, were made using computer image analysis and an allometric model. Although morphometric values of adu…
Invited Review - Fight on Plankton! or, Phytoplankton Shape and Size as Adaptive Tools to Get Ahead in the Struggle for Life
2011
Abstract A renewed interest in investigating the relationships existing between body size and environmental variables is pervading ecological studies. Phytoplankton has a long tradition as model system in studies of community ecology and several research concepts were developed using these organisms. In this paper we try to review the relevance of analyzing the morphological features of phytoplankton in ecology. Starting with a brief account of allometric relationships existing in phytoplankton, we i) examine the physical context in which phytoplankton grow, and ii) highlight the role of their size in nutrient uptake, and that of their shape in light harvesting. Moreover, the way in which t…
SEXUALLY SELECTED TRAITS EVOLVE POSITIVE ALLOMETRY WHEN SOME MATINGS OCCUR IRRESPECTIVE OF THE TRAIT
2014
Positive allometry of secondary sexual traits (whereby larger individuals have disproportionally larger traits than smaller individuals) has been called one of the most pervasive and poorly understood regularities in the study of animal form and function. Its widespread occurrence is in contrast with theoretical predictions that it should evolve only under rather special circumstances. Using a combination of mathematical modeling and simulations, here we show that positive allometry is predicted to evolve under much broader conditions than previously recognized. This result hinges on the assumption that mating success is not necessarily zero for males with the lowest trait values: for examp…
Biometric analysis of Brachionus plicatilis ecotypes from Spanish lagoons
1983
Univariate comparisons and several multivariate statistical analyses have been performed to study the morphometric variability of B. plicatilis. Both laboratory clones kept under constant conditions and natural populations from different Spanish lagoons and different times of the year have been compared. The results show that not only size, but also allometric coefficients are influenced by environmental factors. However, an important genetic component in the variation of shape and size has been visualized. A clear North-South ordination of the populations of the different lagoons and an important dispersion between their summer populations as well as great differences due to seasonal varia…
smatr 3 - an R package for estimation and inference about allometric lines
2011
Summary 1. The Standardised Major Axis Tests and Routines (SMATR) software provides tools for estimation and inference about allometric lines, currently widely used in ecology and evolution. 2. This paper describes some significant improvements to the functionality of the package, now available on R in smatr version 3. 3. New inclusions in the package include sma and ma functions that accept formula input and perform the key inference tasks; multiple comparisons; graphical methods for visualising data and checking (S)MA assumptions; robust (S)MA estimation and inference tools.
Phenotypic analysis of adults and eggs of Fasciola hepatica by computer image analysis system
2005
AbstractKnowledge of the morphological phenotypes of the liver fluke Fasciola hepatica (Trematoda: Digenea) is analysed. The influence of parasite age on its dimensions, the adult fluke growth model, variation in a biometric variable versus time, and variation in a biometric variable versus another biometric variable (allometric model) are revised. The most useful allometric model appears to be (y2m]#x2212;y2)/y2=c [(y1m−y1)/y1]b, where y1=body area or body length, y2=one of the measurements analysed, y1m, y2m=maximum values towards which y1 and y2, respectively, tend, and c, b=constants. A method based on material standardization, the measurement proposal and allometric analysis is detaile…
Inbreeding depression in intraspecific metabolic scaling
2013
Metabolic scaling (i.e., the relationship between the size and metabolic rate of organisms) has been suggested to explain a large variety of biological patterns from individual growth to species diversity. However, considerable disagreement remains regarding the underlying causes of metabolic scaling patterns, and what these patterns are. As in all biology, understanding metabolic scaling will require understanding its evolution by natural selection. We searched for evidence of natural selection on metabolic scaling indirectly by manipulating the genetic quality of male and female Drosophila montana flies with induced mutations and inbreeding, building on the notion that mutations and inbre…
Evolutionary morphology in shape and size of haptoral anchors in 14 Ligophorus spp. (Monogenea: Dactylogyridae).
2017
The search for phylogenetic signal in morphological traits using geometric morphometrics represents a powerful approach to estimate the relative weights of convergence and shared evolutionary history in shaping organismal form. We assessed phylogenetic signal in the form of ventral and dorsal haptoral anchors of 14 species of Ligophorus occurring on grey mullets (Osteichthyes: Mugilidae) from the Mediterranean, the Black Sea and the Sea of Azov. The phylogenetic relationships among these species were mapped onto the morphospaces of shape and size of dorsal and ventral anchors and two different tests were applied to establish whether the spatial positions in the morphospace were dictated by …