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Hierarchical Partitioning (hierarchical + partitioning)
Selected AbstractsCarnivore-Livestock Conflicts: Effects of Subsidized Predator Control and Economic Correlates on the Sheep IndustryCONSERVATION BIOLOGY, Issue 3 2006KIM MURRAY BERGER Canis latrans; coyotes; depredación; evaluación de política Abstract:,Despite the importance of carnivores in terrestrial ecosystems, many nations have implemented well-coordinated, state-funded initiatives to remove predators, largely because of conflicts with humans over livestock. Although these control efforts have been successful in terms of the number of carnivores removed, their effects on the viability of the industries they seek to protect are less understood. I assessed the efficacy of long-term efforts by the U.S. government to improve the viability of the sheep industry by reducing predation losses. I used regression analysis and hierarchical partitioning of a 60-year data set to explore associations among changes in sheep numbers and factors such as predator control effort, market prices, and production costs. In addition, I compared trends in the sheep industry in the western United States, where predator control is subsidized and coyotes (Canis latrans) are abundant, with trends in eastern states that lack federally subsidized predator control and that were (1) colonized by coyotes before 1950 or (2) colonized by coyotes between 1950 and 1990. Although control efforts were positively correlated with fluctuations in sheep numbers, production costs and market prices explained most of the model variation, with a combined independent contribution of 77%. Trends in sheep numbers in eastern and western states were highly correlated (r ,0.942) independent of the period during which they were colonized by coyotes, indicating either that control has been ineffective at reducing predation losses or that factors other than predation account for the declines in both regions. These results suggest that government-subsidized predator control has failed to prevent the decline in the sheep industry and alternative support mechanisms need to be developed if the goal is to increase sheep production and not simply to kill carnivores. Resumen:,A pesar de la importancia de carnívoros en los ecosistemas terrestres, muchos países han implementado iniciativas bien coordinadas, financiadas por el gobierno, para remover depredadores, principalmente debido a conflictos entre humanos y ganado. Aunque estos esfuerzos de control han sido exitosos en términos del número de carnívoros removidos, sus efectos sobre la viabilidad de las industrias que se busca proteger son poco comprendidos. Evalué la eficacia de los esfuerzos a largo plazo del gobierno de E.U.A. para mejorar la viabilidad de la industria ovina mediante la reducción de pérdidas por depredación. Utilicé análisis de regresión y partición jerárquica de un conjunto de datos de 60 años para explorar asociaciones entre cambios en el número de ovejas y factores como el esfuerzo de control de depredadores, precios de mercado y costos de producción. Adicionalmente comparé las tendencias en la industria ovina en el oeste de Estados Unidos, donde el control de depredadores está subsidiado y los coyotes (Canis latrans) son abundantes, con las tendencias en los estados orientales que carecen de control subsidiado federalmente y que fueron (1) colonizados por coyotes antes de 1950 o (2) colonizados por coyotes entre 1950 y 1990. Aunque los esfuerzos de control se correlacionaron positivamente con las fluctuaciones en el número de ovejas, los costos de producción y los precios de mercado explicaron la mayor parte de la variación del modelo, con una contribución independiente combinada de 77%. Las tendencias en el número de ovejas en los estados orientales y occidentales estaban muy correlacionadas (r , 0.942) independientemente del período en que fueron colonizados por coyotes, lo que indica que el control ha sido ineficiente en la reducción de depredación o que factores, distintos a la depredación, son responsables de las declinaciones en ambas regiones. Estos resultados sugieren que el control subsidiado por el gobierno ha fallado en prevenir la declinación de la industria ovina y que se necesitan desarrollar mecanismos de soporte alternativos si la meta es incrementar la producción de ovejas y no simplemente matar carnívoros. [source] Catchment urbanisation and increased benthic algal biomass in streams: linking mechanisms to managementFRESHWATER BIOLOGY, Issue 6 2004Sally L. Taylor Summary 1. Urbanisation is an important cause of eutrophication in waters draining urban areas. We determined whether benthic algal biomass in small streams draining urban areas was explained primarily by small-scale factors (benthic light, substratum type and nutrient concentrations) within a stream, or by catchment-scale variables that incorporate the interacting multiple impacts of urbanisation (i.e. variables that describe urban density and the intensity of drainage or septic tank systems). 2. Benthic algal biomass was assessed as chlorophyll a density (chl a) in 16 streams spanning a rural,urban gradient, with both a wide range of urban density and of piped stormwater infrastructure intensity on the eastern fringe of metropolitan Melbourne, Australia. The gradient of urban density among streams was broadly correlated with catchment imperviousness, drainage connection (proportion of impervious areas connected to streams by stormwater pipes), altitude, longitude and median phosphorus concentration. Catchment area, septic tank density, median nitrogen concentration, benthic light (photosynthetically active radiation) and substratum type were not strongly correlated with the urban gradient. 3. Variation in benthic light and substratum type within streams explained a relatively small amount of variation in log chl a (3,11 and 1,13%, respectively) compared with between-site variation (39,54%). 4. Median chl a was positively correlated with catchment urbanisation, with a large proportion of variance explained jointly (as determined by hierarchical partitioning) by those variables correlated with urban density. Independent of this correlation, the contributions of drainage connection and altitude to the explained variance in chl a were significant. 5. The direct connection of impervious surfaces to streams by stormwater pipes is hypothesised as the main determinant of algal biomass in these streams through its effect on the supply of phosphorus, possibly in interaction with stormwater-related impacts on grazing fauna. Management of benthic algal biomass in streams of urbanised catchments is likely to be most effective through the application of stormwater management approaches that reduce drainage connection. [source] Contrasting response of native and alien plant species richness to environmental energy and human impact along alpine elevation gradientsGLOBAL ECOLOGY, Issue 6 2009Lorenzo Marini ABSTRACT Aim, We tested whether the species,energy and species,human relationships vary between native and both naturalized and casual alien species richness when other environmental variables had been taken into account. Location, Trento Province, a region (c. 6200 km2) on the southern border of the European Alps (Italy), subdivided into 156 contiguous (c. 37.5 km2) cells and ranging in elevation from 66 to 3769 m. Methods, Data were separated into three subsets, representing richness of natives, naturalized aliens and casual aliens and separately related to temperature, human population and various environmental correlates of plant species diversity. We applied ordinary least squares and simultaneous autoregressive regressions to identify potential contrasting responses of the three plant status subsets and hierarchical partitioning to evaluate the relative importance of the predictor variables. Results, Variation in alien plant species richness along the region was almost entirely explained by temperature and human population density. The relationships were positive but strongly curvilinear. Native species richness was less strongly related to either factor but was positively related to the presence of calcareous bedrock. Native species richness had a decelerating positive relationship with temperature (R2= 55%), whereas naturalized and casual aliens had a positive accelerating relationship explaining 86% and 62% of the variation in richness, respectively. Native species richness had a positive decelerating relationship with population density (R2= 42%), whilst both alien subsets had a positive accelerating relationship. Main conclusions, Alien species richness was higher in areas with the most rich and diverse assemblages of native species. Areas at high altitudes are not especially prone to alien invasion due to energy constraints, low propagule pressure and disturbance, even considering a potential increased in temperature. Thus, if we consider future environmental change, we should expect a stronger response of aliens than natives in the currently warm, urbanized, low-altitude areas than in cold, high-altitude areas where human population density is low. [source] Time to establishment success for introduced signal crayfish in Sweden , a statistical evaluation when success is partially knownJOURNAL OF APPLIED ECOLOGY, Issue 5 2010Ullrika Sahlin Summary 1.,The signal crayfish Pacifastacus leniusculus is an invasive species in Sweden, threatening the red-listed nobel crayfish Astacus astacus through spreading the crayfish plague. Time-to-event models can handle censored data on such introduced populations for which the state (successful or not) is only partially known at the last observation, but even though data on introduced populations most often are censored, this type of model is usually not used for likelihood-based inference and predictions of the dynamics of establishing populations. 2.,We specified and fitted a probabilistic time-to-event model to be used to predict the time to successful establishment of signal crayfish populations introduced into Sweden. Important covariates of establishment success were found by the methods of ,model averaging' and ,hierarchical partitioning', considering model uncertainty and multi-colinearity, respectively. 3.,The hazard function that received the highest evidence based on the empirical data showed that the chances of establishment were highest in the time periods immediately following the first introduction. The model predicts establishment success to be <50% within 5 years after first introduction over the current distributional range of signal crayfish in Sweden today. 4.,Among covariates related to temperature, fish species and physical properties of the habitat, the length of the growing season was the most important and consistent covariate of establishment success. We found that establishment success of signal crayfish is expected to increase with the number of days when growth is possible, and decrease with the number of days with extremely high temperatures, which can be seen to approximate conditions of stress. 5.,Synthesis and applications. The results demonstrate lower establishment success of signal crayfish further north in Sweden, which may decrease the incentives of additional illegal introductions that may threaten the red-listed noble crayfish Astacus astacus. We provide a fully probabilistic statistical evaluation that quantifies uncertainty in the duration of the establishment stage that is useful for management decisions of invasive species. The combination of model averaging and hierarchical partitioning provides a comprehensive method to address multi-colinearity common to retrospective data on establishment success of invasive species. [source] Climate and landscape correlates of African lion (Panthera leo) demographyAFRICAN JOURNAL OF ECOLOGY, Issue 1 2010Gastone G. Celesia Abstract Although many studies have documented aspects of lion ecology, they have generally focused on single sites, leaving broader-scaled factors unanalysed. We assessed range-wide effects of eight biotic and 26 abiotic variables on lion distribution and ecology, based on data compiled from published sources on lion population ecology in 27 protected areas in Africa. Lion pride size and composition were independent of lion density; lion density and home range size were inversely related; and lion density was positively related to rainfall, soil nutrients and annual mean temperature, with some interactive effects between rainfall and soil nutrients. Lion demography was associated most strongly with rainfall, temperature and landscape features. Herbivore biomass and lion density were correlated in univariate regression analyses. However, because herbivore biomass was also related to rainfall and temperature, hierarchical partitioning (HP) allowed us to evaluate independent effects of each variable on lion demography revealing that herbivore biomass had negligible independent contributions. HP indicated that climatic parameters explained 62% of overall variance in demographic parameters, whereas landscape features explained only 32%; climatic parameters were fairly balanced between effects of temperature (34%) and rainfall (28%). Prey (herbivore) biomass is important for lion survival, but its effects appear secondary to environmental factors. Résumé Bien que de nombreuses études apportent des informations sur des aspects de l'écologie des lions, elles se sont généralement focalisées sur des sites individuels, laissant de côté les facteurs à plus grande échelle. Nous avons analysé les effets à grande échelle de huit variables biotiques et de 26 variables abiotiques de la distribution et de l'écologie du lion, en nous fondant sur des données compilées à partir de publications portant sur l'écologie de populations de lions dans 27 aires protégées africaines. La taille et la composition des troupes de lions étaient indépendantes de leur densité; la densité et la taille du territoire des lions étaient inversement liées; et la densité des lions était directement liée aux chutes de pluies, aux nutriments du sol et à la moyenne annuelle des températures, certains effets interactifs étant observés entre les chutes de pluies et les nutriments du sol. La démographie des lions était surtout liée aux chutes de pluies, à la température et à certaines caractéristiques du paysage. La biomasse des herbivores et la densité des lions étaient liées dans les analyses de régressions univariées. Cependant, comme la biomasse des herbivores est aussi liée aux chutes de pluies et aux températures, la partition hiérarchique (PH) nous a permis d'évaluer les effets indépendants de chaque variable sur la démographie des lions, ce qui révèle que la biomasse des herbivores, prise indépendamment, représentait une contribution négligeable. La PH indiquait que les paramètres climatiques expliquaient 62% de la variance globale des paramètres démographiques, alors que les caractéristiques du paysage n'en expliquaient que 32%; les paramètres climatiques étaient en assez bon équilibre entre les effets de la température (34%) et ceux des chutes de pluies (28%). La biomasse des proies (herbivores) est importante pour la survie des lions, mais ses effets semblent secondaires par rapport à ceux des facteurs environnementaux. [source] Space,time patterns of co-variation of biodiversity and primary production in phytoplankton guilds of coastal marine environmentsAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 6 2003Maria Rosaria Vadrucci Abstract 1.The relevance of biodiversity to ecosystem processes is a major topic in ecology. Here, we analyse the relationship between biodiversity and productivity of the nano- and micro-phytoplankton guilds in coastal marine ecosystems. 2.The patterns of variation of species richness, diversity and primary productivity (as 14C assimilation) were studied in two marine areas: a eutrophic,mesotrophic area beside the River Po delta (northern Adriatic) and an oligotrophic area around the Salento peninsula (southern Adriatic,Ionian). The study was carried out at 23 sites in the northern area and at 45 sites in the southern area. Sites were arranged on expected spatial and temporal gradients of primary productivity variation, according to distance from the coast, optical depths and seasonal period. 3.167 taxa were identified in the northern area and 153 taxa in the southern area. In both areas, the taxonomic composition of the nano- and micro-phytoplankton guilds exhibited greater temporal than spatial variation. The latter was much higher in the southern area than in the northern area (average dissimilarity between stations being 70.7±0.8% and 44.7±4.2% respectively). 4.Primary productivity varied in space and time on the gradients considered. Phytoplankton species richness and diversity exhibited significant patterns of variation in space and time; overall, these were inversely related to the primary productivity patterns in the northern area, whereas they were directly related in the southern area. 5.The small individual size and the high turnover rate of phytoplankton are likely to underlie the observed relationships, which emphasized a threshold response to nutrient enrichment in agreement with the ,paradox of enrichment'. Under resource enrichment conditions, the high turnover of producers leads to hierarchical partitioning of the available resources with an increasing dominance of a few species. Therefore, the relationship observed here seems likely to be explained by the complementarity hypothesis. Copyright © 2003 John Wiley & Sons, Ltd. [source] | ||||||||||