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Size Spectra (size + spectrum)
Selected AbstractsPutting the meio- into stream ecology: current findings and future directions for lotic meiofaunal researchFRESHWATER BIOLOGY, Issue 1 2000A. L. Robertson Summary 1There is a paucity of research on epigean freshwater lotic meiofauna. This may result from a previous emphasis on interstitial (groundwater and hyporheic) meiofauna and/or a reliance on sampling methodologies in lotic systems which are inappropriate for meiofauna. 2Meiofauna contribute much to the diversity of lotic ecosystems. Species lists for seven streams reveal that meiofauna contribute 58,82% of total species numbers, with rotifers and chironomids dominating most systems. The absence of taxonomic keys for most meiofaunal taxa in large areas of the world precludes a wider analysis of their contribution to lotic diversity and an assessment of biogeographical patterns and processes. 3The trophic and functional role of meiofauna in lotic ecosystems is unclear. There are few estimates of meiofaunal production in freshwaters and biomass spectra have produced conflicting results for lotic meiofauna. Present static estimates suggest that the contribution of meiofauna to lotic productivity and biomass is small to moderate, but further studies incorporating a temporal component may provide a more realistic picture of the total contribution of meiofauna to biomass size spectra. 4Meiofauna differ from macroinvertebrates in several respects apart from size and conceptual models for lotic ecosystems should include all metazoans if they are to be truly representative. 5Information on the basic ecology of certain lotic meiofauna (i.e. nematodes, tardigrades, microturbellarians) is urgently required. For those groups whose distributional patterns are better understood (e.g. microcrustaceans), the mechanisms underpinning these patterns should be explored. It is essential that the importance of meiofauna is recognised by lotic ecologists; the only realistic way forward is for greater collaboration among meiofaunal ecologists and taxonomists and other lotic scientists. [source] Measurement of body size and abundance in tests of macroecological and food web theoryJOURNAL OF ANIMAL ECOLOGY, Issue 1 2007SIMON JENNINGS Summary 1Mean body mass (W) and mean numerical (N) or biomass (B) abundance are frequently used as variables to describe populations and species in macroecological and food web studies. 2We investigate how the use of mean W and mean N or B, rather than other measures of W and/or accounting for the properties of all individuals, can affect the outcome of tests of macroecological and food web theory. 3Theoretical and empirical analyses demonstrate that mean W, W at maximum biomass (Wmb), W when energy requirements are greatest (Wme) and the W when a species uses the greatest proportion of the energy available to all species in a W class (Wmpe) are not consistently related. 4For a population at equilibrium, relationships between mean W and Wme depend on the slope b of the relationship between trophic level and W. For marine fishes, data show that b varies widely among species and thus mean W is an unreliable indicator of the role of a species in the food web. 5Two different approaches, ,cross-species' and ,all individuals' have been used to estimate slopes of abundance,body mass relationships and to test the energetic equivalence hypothesis and related theory. The approaches, based on relationships between (1) log10 mean W and log10 mean N or B, and (2) log10 W and log10 N or B of all individuals binned into log10 W classes (size spectra), give different slopes and confidence intervals with the same data. 6Our results show that the ,all individuals' approach has the potential to provide more powerful tests of the energetic equivalence hypothesis and role of energy availability in determining slopes, but new theory and empirical analysis are needed to explain distributions of species relative abundance at W. 7Biases introduced when working with mean W in macroecological and food web studies are greatest when species have indeterminate growth, when relationships between W and trophic level are strong and when the range of species'W is narrow. [source] Application of chemical and biological agents for the management of frosty pod rot (Moniliophthora roreri) in Costa Rican cocoa (Theobroma cacao)ANNALS OF APPLIED BIOLOGY, Issue 2 2005R.P. Bateman Abstract This article describes two field trials carried out at La Lola, Costa Rica, to assess control measures against frosty pod rot of cocoa (Theobroma cacao) caused by Moniliophthora (Crinipellis) roreri. In the first, factorial, trial the control agents were applied using motorised mistblowers (MMs) and hydraulic sprayers fitted with a narrow angle cone nozzle. There was an interaction between agents and application methods; together with previous application data for the most active fungicide (copper hydroxide), these trials indicate that best yields are achieved with sprays that maximise deposits on pods. We describe the droplet size spectra produced by a Stihl SR400 MM under a range of conditions because this has become the standard method of fungicide application in this series of trials at La Lola. The factor that had the largest effect on droplet size spectrum was the presence or the absence of a detachable baffle plate in front of the air-shear nozzle. In both trials described here, MMs were fitted with baffle plates, a formulation pump and restrictor transmitting 550 mL min,1 to deliver an estimated equivalent of 190 L ha,1. Copper hydroxide as prophylactic applications at 1500 g a.i. ha,1 have, to date, shown the most consistent (but incomplete) improvement in healthy pod yield. Use of copper fungicides may be cost effective when farm-gate cocoa prices exceed approximately $1.25 kg,1. In these trials, isolates of the hyperparasitic fungi Clonostachys byssicola and Trichoderma asperellum and two off-patent triazole fungicides (bitertanol and triadimenol) made no significant improvement to healthy yields. The systemic oxathiin fungicide flutolanil, at a dosage of 300 g a.i. ha,1, appears to protect pods substantially at early stages but gives proportionately less control of M. roreri than copper at later stages of pod development. [source] Linking herbivore-induced defences to population dynamicsFRESHWATER BIOLOGY, Issue 3 2006IRENE VAN DER STAP Summary 1.,Theoretical studies have shown that inducible defences have the potential to affect population stability and persistence in bi- and tritrophic food chains. Experimental studies on such effects of prey defence strategies on the dynamics of predator,prey systems are still rare. We performed replicated population dynamics experiments using the herbivorous rotifer Brachionus calyciflorus and four strains of closely related algae that show different defence responses to this herbivore. 2.,We observed herbivore populations to fluctuate at a higher frequency when feeding on small undefended algae. During these fluctuations minimum rotifer densities remained sufficiently high to ensure population persistence in all the replicates. The initial growth of rotifer populations in this treatment coincided with a sharp drop in algal density. Such a suppression of algae by herbivores was not observed in the other treatments, where algae were larger due to induced or permanent defences. In these treatments we observed rotifer population densities to first rise and then decline. The herbivore went extinct in all replicates with large permanently defended algae. The frequency of herbivore extinctions was intermediate when algae had inducible defences. 3.,A variety of alternative mechanisms could explain differential herbivore persistence in the different defence treatments. Our analysis showed the density and fraction of highly edible algal particles to better explain herbivore persistence and extinctions than total algal density, the fraction of highly inedible food particles or the accumulation of herbivore waste products or autotoxins. 4.,We argue that the rotifers require a minimum fraction and density of edible food particles for maintenance and reproduction. We conjecture that induced defences in algae may thus favour larger zooplankton species such as Daphnia spp. that are less sensitive to shifts in their food size spectrum, relative to smaller zooplankton species, such as rotifers and in this way contributes to the structuring of planktonic communities. [source] Application of chemical and biological agents for the management of frosty pod rot (Moniliophthora roreri) in Costa Rican cocoa (Theobroma cacao)ANNALS OF APPLIED BIOLOGY, Issue 2 2005R.P. Bateman Abstract This article describes two field trials carried out at La Lola, Costa Rica, to assess control measures against frosty pod rot of cocoa (Theobroma cacao) caused by Moniliophthora (Crinipellis) roreri. In the first, factorial, trial the control agents were applied using motorised mistblowers (MMs) and hydraulic sprayers fitted with a narrow angle cone nozzle. There was an interaction between agents and application methods; together with previous application data for the most active fungicide (copper hydroxide), these trials indicate that best yields are achieved with sprays that maximise deposits on pods. We describe the droplet size spectra produced by a Stihl SR400 MM under a range of conditions because this has become the standard method of fungicide application in this series of trials at La Lola. The factor that had the largest effect on droplet size spectrum was the presence or the absence of a detachable baffle plate in front of the air-shear nozzle. In both trials described here, MMs were fitted with baffle plates, a formulation pump and restrictor transmitting 550 mL min,1 to deliver an estimated equivalent of 190 L ha,1. Copper hydroxide as prophylactic applications at 1500 g a.i. ha,1 have, to date, shown the most consistent (but incomplete) improvement in healthy pod yield. Use of copper fungicides may be cost effective when farm-gate cocoa prices exceed approximately $1.25 kg,1. In these trials, isolates of the hyperparasitic fungi Clonostachys byssicola and Trichoderma asperellum and two off-patent triazole fungicides (bitertanol and triadimenol) made no significant improvement to healthy yields. The systemic oxathiin fungicide flutolanil, at a dosage of 300 g a.i. ha,1, appears to protect pods substantially at early stages but gives proportionately less control of M. roreri than copper at later stages of pod development. [source] Leaf litter breakdown in Patagonian streams: native versus exotic trees and the effect of invertebrate sizeAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 2 2002R. J. Albariño Abstract 1.Nothofagus native forest in the Southern Andes is being progressively substituted by forestation with rapid growth of the exotic trees, mainly species of Pinaceae. The effect on stream processing dynamics is explored through in situ experiments. 2.The effects of leaf litter quality and macroinvertebrate size on in situ litter breakdown were analysed. Experiments were run in litter bags which allowed access of macroinvertebrate fauna in streams running through a dense forest of the deciduous Nothofagus pumilio. 3.In Experiment 1, the decay rates of N. pumilio leaves and Pinus ponderosa needles were measured during an autumn-winter period. N. pumilio decayed twice as fast as P. ponderosa (P<0.01). Shredders fed only on N. pumilio leaves. The total abundance of macroinvertebrates colonizing both treatments was similar; however, the biomass was higher in the N. pumilio treatment. Large shredders were only found colonizing N. pumilio leaves. Since no decay due to shredders was observed in P. ponderosa, the presence of macroinvertebrates in these litter bags was related to refuge and feeding on FPOM-biofilm resources. 4.In Experiment 2, N. pumilio leaf litter was exposed in order to allow (open bags) or restrict (closed bags) access of invertebrates. The invertebrate assemblage in open bags showed the similar pattern observed for N. pumilio in the first experiment. Gathering-collectors were generally smaller and dominant in number while shredder biomass was higher in open bags as a result of high individual biomass. N. pumilio decayed faster when the whole size spectrum of macroinvertebrates colonized the bags (P<0.01). However, feeding signs of small shredders were observed in closed bags, therefore their role on leaf litter breakdown in Andean streams should not be neglected. 5.The combined results of both experiments lead to the conclusion that the whole litter processing mechanism would be affected as a consequence of the substitution of native forest by exotic pine forestation. Copyright © 2002 John Wiley & Sons, Ltd. [source] | ||||||||||