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Resource Gradients (resource + gradient)

Distribution by Scientific Domains
Life Sciences90%

Selected Abstracts

Trading off the ability to exploit rich versus poor food quality

ECOLOGY LETTERS, Issue 5 2002
Alan J. Tessier
Abstract Lakes differ in the quality of food for planktonic grazers, but whether grazers adapt to this resource heterogeneity is poorly studied. We test for evidence of specialization to resource environment within a guild of suspension feeding daphniids inhabiting lakes that differ in food web structure. Using bioassays, we demonstrate that food quality for grazers increases from deep to shallow to temporary lakes, which also represents a gradient of increasing predation risk. We compare growth rates and reproductive performance of daphniid taxa specific to each of the three lake types and find they differ greatly in minimum resource requirements, and in sensitivity to the resource gradient. These differences express a trade-off in ability to exploit rich vs. poor resources. Taxa from deep lakes, poor in resources, have low minimal needs, but they do relatively poorly in rich resource environments. We conclude that grazer distribution is consistent with an adaptive match of exploitation ability to resource environments. [source]

Pond canopy cover: a resource gradient for anuran larvae

FRESHWATER BIOLOGY, Issue 3 2006
LUIS SCHIESARI
Summary 1.,The gradient in pond canopy cover strongly influences freshwater species distributions. This study tested the effects of canopy cover on the performance of two species of larval anurans, a canopy cover generalist (Rana sylvatica, the wood frog) and an open-canopy specialist (R. pipiens, the leopard frog), and tested which factors co-varying with canopy cover mediate these effects. 2.,A field transplant experiment demonstrated that canopy cover had negative performance effects on both species. However, leopard frogs, which grow faster than wood frogs in open-canopy ponds, were more strongly affected by closed-canopy pond conditions. 3.,Closed-canopy ponds had lower temperature, dissolved oxygen (DO), and food nutritional quality as indicated by carbon-to-nitrogen ratio (C : N) analysis of field-sampled food types, and of gut contents of transplanted larvae. 4.,Laboratory experiments demonstrated that higher temperature and food quality but not DO substantially increased larval growth. However, only food quality increased growth rates of leopard frogs more than wood frogs. 5.,The strong correlation of growth rates to gut content C : N in the field, and the similarity of growth curves as a function of resource quality in the field and laboratory, strongly suggest that resources are of primary importance in mediating intraspecific, and especially interspecific differences in performance across the canopy cover gradient. [source]

National-scale metacommunity dynamics of carabid beetles in UK farmland

JOURNAL OF ANIMAL ECOLOGY, Issue 2 2008
David R. Brooks
Summary 1Understanding the wide-scale processes controlling communities across multiple sites is a foremost challenge of modern ecology. Here, data from a nation-wide network of field sites are used to describe the metacommunity dynamics of arable carabid beetles. This is done by modelling how communities are structured at a local level, by changes in the environment of the sampled fields and, at a regional level, by fitting spatial parameters describing latitudinal and longitudinal gradients. 2Local and regional processes demonstrated independent and significant capacities for structuring communities. Within the local environment, crop type was found to be the primary determinant of carabid community composition. The regional component included a strong response to a longitudinal gradient, with significant increases in diversity in an east-to-west direction. 3Carabid metacommunities seem to be structured by a combination of species sorting dynamics, operating at two different, but equally important, spatial scales. At a local scale, species are sorted along a resource gradient determined by crop type. At a wider spatial scale species appear to be sorted along a longitudinal gradient. 4Nation-wide trends in communities coincided with known gradients of increased homogeneity of habitat mosaics and agricultural intensification. However, more work is required to understand fully how communities are controlled by the interaction of crops with changes in landscape structure at different spatial scales. 5We conclude that crop type is a powerful determinant of carabid biodiversity, but that it cannot be considered in isolation from other components of the landscape for optimal conservation policy. [source]

Mammal community structure in relation to disturbance and resource gradients in southern Africa

AFRICAN JOURNAL OF ECOLOGY, Issue 1 2009
Märtha Wallgren
Abstract The arrangements of mammals differ along environmental gradients, such as of disturbance and resources. We examined how mammal community composition in the Kalahari, Botswana, varied in relation to disturbance and resource gradients. We predicted that livestock-keeping villages are disturbances and pans are resources for wildlife, that the responses of mammals to disturbance and resources depend on their functional types and that increased disturbance over time has reduced the numbers and distributions of wildlife. The methods involved road-side counts of mammals >0.2 kg and trapping of small mammals, <0.2 kg. The disturbance gradient was more important than the resource gradient for explaining the distribution of mammals >0.2 kg. Communities in low disturbance-high resource areas were most diverse regarding species and functional types. Small mammal species richness and abundances were unaffected by villages, but increased with distance from pans. Villages were particularly deterring to large wild herbivores, functionally similar to livestock. Most large wild herbivores had decreased since 1975,1983. We conclude that large and medium-sized mammals are highly affected by large-scale disturbance gradients, while small mammals are most dependent on small-scale variation in resources, probably shelter and food. Increased disturbance over time leads to decreasing ranges and numbers of the large wild herbivores. Résumé Les associations de mammifères diffèrent selon des gradients environnementaux tels que ceux des perturbations et des ressources. Nous avons examiné comment la composition de la communauté de mammifères variait dans le Kalahari, au Botswana, en fonction des gradients de perturbations et de ressources. Nous avions prédit que les villages qui gardent du bétail sont des perturbations, et les pans des ressources pour la faune sauvage, que les réponses des mammifères à ces deux facteurs dépendaient de leur type de fonctionnement, et que les perturbations croissant avec le temps avaient réduit l'abondance et la distribution de la faune sauvage. Les méthodes employées comprenaient les comptages le long de la route de tous les mammifères de plus de 0,2 kg et le piégeage des petits mammifères de moins de 0,2 kg. Le gradient de perturbation était plus important que celui des ressources pour expliquer la distribution des mammifères >0,2 kg. Les communautés vivant dans les zones de faibles perturbations et d'abondantes ressources étaient plus diverses au point de vue du nombre d'espèces et de types fonctionnels. La richesse en espèces de petits mammifères et leur abondance n'étaient pas affectées par les villages mais augmentaient avec la distance par rapport au pan. Les villages étaient particulièrement dissuasifs pour les grands herbivores sauvages qui étaient, fonctionnellement, semblables au bétail. La plupart des grands herbivores sauvages ont diminué depuis 1975,1983. Nous concluons que les herbivores grands et moyens sont fort affectés par les gradients de perturbations à grande échelle alors que les petits mammifères sont surtout dépendants des variations à petite échelle des ressources, probablement les abris et la nourriture. Les perturbations croissant avec le temps entraînent une réduction des domaines vitaux et du nombre des grands herbivores sauvages. [source]

Resource distribution and soil moisture content can regulate bait control in an ant assemblage in Central Amazonian forest

AUSTRAL ECOLOGY, Issue 3 2010
FABRICIO BEGGIATO BACCARO
Abstract Resources influence population growth, interspecific interactions, territoriality and, in combination with moisture content, affect terrestrial arthropod distribution and abundance. Ants are usually described as interactive and compete in transitive hierarchies, where the dominants behaviourally exclude subordinate species from food resources. In this study, we evaluated the effects of (i) dominant ants, soil moisture and an artificial resource gradient on the number of ant species attracted to baits; and (ii) how soil moisture and an artificial resource gradient change the number of controlled baits in a Central Amazonian rain forest. We sampled 30 100-m-long transects, located at least 200 m apart. The transects were established with six different bait densities varying between six and 41 baits and the soil moisture content was measured at 10 points for each transect. Six ant species were considered dominant, and had negative correlations with the number of species at baits (r2 = 0.186; F1,28 = 6.419; P = 0.017). However, almost half of the transects showed low abundance of dominant species (<30%), and relatively high number of species (mean of 20.1 ± 8.75). Resource availability and soil moisture had negative and positive correlations, with number of controlled baits. These results suggest that, even though the dominance is relatively poorly developed on the floor of this tropical forest, both resource availability and soil moisture affect resource control, and thus, the number of species that use baits. [source]

Mammal community structure in relation to disturbance and resource gradients in southern Africa

AFRICAN JOURNAL OF ECOLOGY, Issue 1 2009
Märtha Wallgren
Abstract The arrangements of mammals differ along environmental gradients, such as of disturbance and resources. We examined how mammal community composition in the Kalahari, Botswana, varied in relation to disturbance and resource gradients. We predicted that livestock-keeping villages are disturbances and pans are resources for wildlife, that the responses of mammals to disturbance and resources depend on their functional types and that increased disturbance over time has reduced the numbers and distributions of wildlife. The methods involved road-side counts of mammals >0.2 kg and trapping of small mammals, <0.2 kg. The disturbance gradient was more important than the resource gradient for explaining the distribution of mammals >0.2 kg. Communities in low disturbance-high resource areas were most diverse regarding species and functional types. Small mammal species richness and abundances were unaffected by villages, but increased with distance from pans. Villages were particularly deterring to large wild herbivores, functionally similar to livestock. Most large wild herbivores had decreased since 1975,1983. We conclude that large and medium-sized mammals are highly affected by large-scale disturbance gradients, while small mammals are most dependent on small-scale variation in resources, probably shelter and food. Increased disturbance over time leads to decreasing ranges and numbers of the large wild herbivores. Résumé Les associations de mammifères diffèrent selon des gradients environnementaux tels que ceux des perturbations et des ressources. Nous avons examiné comment la composition de la communauté de mammifères variait dans le Kalahari, au Botswana, en fonction des gradients de perturbations et de ressources. Nous avions prédit que les villages qui gardent du bétail sont des perturbations, et les pans des ressources pour la faune sauvage, que les réponses des mammifères à ces deux facteurs dépendaient de leur type de fonctionnement, et que les perturbations croissant avec le temps avaient réduit l'abondance et la distribution de la faune sauvage. Les méthodes employées comprenaient les comptages le long de la route de tous les mammifères de plus de 0,2 kg et le piégeage des petits mammifères de moins de 0,2 kg. Le gradient de perturbation était plus important que celui des ressources pour expliquer la distribution des mammifères >0,2 kg. Les communautés vivant dans les zones de faibles perturbations et d'abondantes ressources étaient plus diverses au point de vue du nombre d'espèces et de types fonctionnels. La richesse en espèces de petits mammifères et leur abondance n'étaient pas affectées par les villages mais augmentaient avec la distance par rapport au pan. Les villages étaient particulièrement dissuasifs pour les grands herbivores sauvages qui étaient, fonctionnellement, semblables au bétail. La plupart des grands herbivores sauvages ont diminué depuis 1975,1983. Nous concluons que les herbivores grands et moyens sont fort affectés par les gradients de perturbations à grande échelle alors que les petits mammifères sont surtout dépendants des variations à petite échelle des ressources, probablement les abris et la nourriture. Les perturbations croissant avec le temps entraînent une réduction des domaines vitaux et du nombre des grands herbivores sauvages. [source]

Maximum size distributions in tropical forest communities: relationships with rainfall and disturbance

JOURNAL OF ECOLOGY, Issue 3 2008
Lourens Poorter
Summary 1The diversity and structure of communities are partly determined by how species partition resource gradients. Plant size is an important indicator of species position along the vertical light gradient in the vegetation. 2Here, we compared the size distribution of tree species in 44 Ghanaian tropical forest communities, using data from 880 one-hectare plots and over 118 000 trees belonging to more than 210 species. 3The size distribution of forest species showed a continuous normal or log-normal distribution, with many canopy species and a few large species, and varied from community to community. Multiple regression showed that this variation is related to rainfall and to disturbance. 4Size distributions in wet forests were less skewed than those in dry forests, with a smaller proportion of big species and a smaller size range. At the same time they exhibited tighter species packing, resulting in higher species richness. Communities with high disturbance have less species packing and lower species richness. 5Synthesis. We conclude that the factors that constrain organism size and species coexistence in these tropical forest tree communities differ from those known to operate on a number of well-studied animal communities. [source]

Seedling growth and morphology of three oak species along field resource gradients and seed mass variation: a seedling age-dependent response

JOURNAL OF VEGETATION SCIENCE, Issue 3 2010
Ignacio M. Pérez-Ramos
Abstract Question: What is the relative importance of seed mass and abiotic factors in species-specific seedling growth and morphology during the first and the second growing season? How do oak species respond along gradients of these factors? Location: Mediterranean oak forest in southern Spain. Methods: We analysed seedling growth components and morphology of three co-occurring Quercus species (two deciduous and one evergreen). Oak seeds with a wide variety of sizes were sown along broad gradients of abiotic conditions. Intra- and inter-specific differences were evaluated by calibrating maximum likelihood estimators of seedling growth during the first two years of life. Results: We found multiple resources and conditions affecting seedling morphology and biomass allocation. However, the integrative variables of seedling growth , total aboveground biomass and relative growth rate (RGR) , were affected by two main factors: seed mass and light conditions. The relative contribution of these two factors depended strongly on seedling age. Seed mass explained most of the growth and morphological variables during the first year, while light conditions were the best predictor in the second growing season. In contrast, soil factors did not play an important role in seedling growth. We found some evidence of regeneration niche partitioning between oak species along the light gradient, a reflection of their distribution patterns as adults at the study site. Conclusions: We conclude that inter-specific differences in seedling growth, arising from seed size variability and microsite heterogeneity, could be of paramount importance in oak species niche segregation, driving stand dynamics and composition along environmental gradients. [source]

Search and navigation in dynamic environments , from individual behaviors to population distributions

OIKOS, Issue 5 2008
Thomas Mueller
Animal movement receives widespread attention within ecology and behavior. However, much research is restricted within isolated sub-disciplines focusing on single phenomena such as navigation (e.g. homing behavior), search strategies (e.g. Levy flights) or theoretical considerations of optimal population dispersion (e.g. ideal free distribution). To help synthesize existing research, we outline a unifying conceptual framework that integrates individual-level behaviors and population-level spatial distributions with respect to spatio-temporal resource dynamics. We distinguish among (1) non-oriented movements based on diffusion and kinesis in response to proximate stimuli, (2) oriented movements utilizing perceptual cues of distant targets, and (3) memory mechanisms that assume prior knowledge of a target's location. Species' use of these mechanisms depends on life-history traits and resource dynamics, which together shape population-level patterns. Resources with little spatial variability should facilitate sedentary ranges, whereas resources with predictable seasonal variation in spatial distributions should generate migratory patterns. A third pattern, ,nomadism', should emerge when resource distributions are unpredictable in both space and time. We summarize recent advances in analyses of animal trajectories and outline three major components on which future studies should focus: (1) integration across alternative movement mechanisms involving links between state variables and specific mechanisms, (2) consideration of dynamics in resource landscapes or environments that include resource gradients in predictability, variability, scale, and abundance, and finally (3) quantitative methods to distinguish among population distributions. We suggest that combining techniques such as evolutionary programming and pattern oriented modeling will help to build strong links between underlying movement mechanisms and broad-scale population distributions. [source]

Patterns and gradients of diversity in South Patagonian ombrotrophic peat bogs

AUSTRAL ECOLOGY, Issue 1 2010
TILL KLEINEBECKER
Abstract Many north-hemispherical mires seemingly untouched by drainage and cultivation are influenced by a diffuse sum of man-made environmental changes, such as atmospherical nitrogen deposition that mask general patterns in species richness and functional group responses along resource gradients. To obtain insights into natural diversity-environment relationships, we studied the vegetation and the peat chemistry of pristine bog ecosystems in southern Patagonia along a west,east transect across the Andes. The studied bog ecosystems covered a floristic gradient from hyperoceanic blanket bogs dominated by cushion building vascular plants via a transitional mixed type to Sphagnum -dominated raised bogs east of the mountain range. To test the influence of resource availability on diversity patterns, species richness and functional groups were related to environmental variables by calculating general regression models and generalized additive models. Species richness showed strong linear correlations to peat chemical features and the general regression model resulted in three major environmental variables (water level, total nitrogen, NH4Cl soluble calcium), altogether explaining 76% of variance. Functional group response illustrated a clear separation along environmental gradients. Mosses dominated at the low end of a nitrogen gradient, whereas cushion plants had their optimum at intermediate levels, and graminoids dominated at high nitrogen contents. Further shifts were related to NH4Cl soluble calcium and water level. The models documented partly non-linear relationships between functional group response and trophical peat properties. Within the three bog types, the calculated models differed remarkably illustrating the scale-dependency of the explanatory factors. Our findings confirmed several general patterns of species richness and functional shifts along resource gradients in a surprisingly clear way and underpin the significance of undisturbed peatlands as reference systems for testing of ecological theory and for conservation and ecological restoration in landscapes with strong human impact. [source]