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Grazers
Kinds of Grazers Terms modified by Grazers Selected AbstractsGrazer and virus-induced mortality of bacterioplankton accelerates development of Flectobacillus populations in a freshwater communityENVIRONMENTAL MICROBIOLOGY, Issue 3 2007Karel, imek Summary We present a detailed analysis of the effects of distinct bacterial mortality factors, viral lysis and heterotrophic nanoflagellates (HNF) bacterivory, associated with the development of filamentous Flectobacillus populations. Reservoir bacterioplankton communities were subjected to additions of both HNF and viruses together, or HNF alone, and then incubated in situ in dialyses bags. For distinct bacterial groups, mortality or growth stimulation was analysed by examining bacterial prey ingested in HNF food vacuoles with fluorescence in situ hybridization (FISH) and via FISH with microautoradiography (MAR-FISH). We also developed a semi-quantitative MAR-FISH-based estimation of relative activities of Flectobacillus populations (targeted by the R-FL615 probe). Bacterial groups vulnerable to HNF predation (mainly clusters of Betaproteobacteria), or discriminated against (Actinobacteria), were detected. Bacterial lineages most vulnerable to virus-lysis (mainly the Betaproteobacteria not targeted by the R-BT065 probe, of the Polynucleobacter cluster) were identified by comparing treatments with HNF alone to HNF and viruses together. Filaments affiliated with the Flectobacillus cluster appeared in both treatments, but were about twice as abundant, long and active as in incubations with viruses and HNF as compared with HNF alone. Viruses appeared to selectively suppress several bacterial groups, perhaps enhancing substrate availability thus stimulating growth and activity of filamentous Flectobacillus. [source] Direct and indirect effects of a potential aquatic contaminant on grazer,algae interactionsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2009Michelle A. Evans-White Abstract Contaminants have direct, harmful effects across multiple ecological scales, including the individual, the community, and the ecosystem levels. Less, however, is known about how indirect effects of contaminants on consumer physiology or behavior might alter community interactions or ecosystem processes. We examined whether a potential aquatic contaminant, an ionic liquid, can indirectly alter benthic algal biomass and primary production through direct effects on herbivorous snails. Ionic liquids are nonvolatile organic salts being considered as an environmentally friendly potential replacement for volatile organic compounds in industry. In two greenhouse experiments, we factorially crossed four concentrations of 1-N-butyl-3-methylimidazolium bromide (bmimBr; experiment 1: 0 or 10 mg/L; experiment 2: 0, 1, or 100 mg/L) with the presence or absence of the snail Physa acuta in aquatic mesocosms. Experimental results were weighted by their respective control (no bmimBr or P. acuta) and combined for statistical analysis. When both bmimBr and snails were present, chlorophyll a abundance and algal biovolume were higher than would be expected if both factors acted additively. In addition, snail growth rates, relative to those of controls, declined by 41 to 101% at 10 and 100 mg/L of bmimBr. Taken together, these two results suggest that snails were less efficient grazers in the presence of bmimBr, resulting in release of algae from the grazer control. Snails stimulated periphyton primary production in the absence, but not in the presence, of bmimBr, suggesting that bmimBr also can indirectly alter ecosystem function. These findings suggest that sublethal contaminant levels can negatively impact communities and ecosystem processes via complex interactions, and they provide baseline information regarding the potential effects of an emergent industrial chemical on aquatic systems. [source] Grazing impact and phenology of the freshwater sponge Ephydatia muelleri and the bryozoans Plumatella emarginata and Fredericella sultana under experimental warmingFRESHWATER BIOLOGY, Issue 5 2009ANDREAS VOHMANN Summary 1.,Both the clearance rates (CR) and abundances of the freshwater sponge Ephydatia muelleri and the bryozoans Plumatella emarginata and Fredericella sultana were investigated from autumn to spring under different temperature regimes. The experiments were performed in bypass channels of the River Rhine (Cologne, Germany) in which temperature could be manipulated. 2.,The impact of temperature increase on CRs depends upon the grazer: E. muelleri showed a clear increase in CRs with increasing temperature whereas P. emarginata was not significantly affected by experimental warming. 3.,Distinct differences in food preference were found for the sponge (which is an efficient grazer of bacteria and small algae) and for the bryozoan P. emarginata (which feeds primarily on large algae, and with no significant grazing on bacteria). 4.,In contrast to their temperature-related patterns in CR, respiration of both P. emarginata and E. muelleri increased with temperature between 19 and 32 °C, suggesting that the risk of experiencing energy deficiency at high temperatures due to increased metabolic rates is particularly high for the bryozoan. 5.,A temperature elevation of 3 °C above the natural Rhine temperature resulted in a delay in the disappearance of active tissue and formation of resting stages for E. muelleri in autumn. This delay ranged from 8 (beginning of gemmulation) to 22 days (termination of gemmulation). In contrast, there was no distinct effect of warming on the disappearance of active zooids of the two bryozoan species in autumn. However, warming can positively affect the maintenance of active zooids during winter in F. sultana. In spring, the appearance of active zooids of P. emarginata was clearly stimulated by temperature elevations, whereas the hatching of both F. sultana and E. muelleri was hardly affected by warming. 6.,The study demonstrated different patterns in the thermal ecology of the two freshwater bryozoans and the sponge in comparison to other filter feeders, particularly mussels. Such patterns need to be considered when predicting the impact of temperature on pelagic-benthic coupling in aquatic habitats. [source] Life history and production of Agapetus quadratus (Trichoptera: Glossosomatidae) in a temporary, spring-fed streamFRESHWATER BIOLOGY, Issue 6 2005MARUXA ÁLVAREZ Summary 1. The life history and trophic basis of production of the caddisfly grazer Agapetus quadratus were studied in the torrent Gorg Blau, a spring-fed stream on the island of Majorca that dries annually during summer. 2. Quantitative random samples were taken every 2,3 weeks during an annual surficial flow period, from November 2000 to mid-July 2001. Instars of field-collected larvae were determined by measurements of head width and pronotum length, and the sex of all pupae was determined to study sexual dimorphism and sex ratio. 3. Stage-frequency histograms suggested a trivoltine population, with an average cohort time of 4 months. Larval development was asynchronous, with continuous growth and overlapping generations. Recruitment peaks were identified in mid-November, early March and late June, indicative of winter, spring and summer generations. On average, females were larger than males and the mean sex ratio was 2 : 3 (females : males). Population densities and biomasses derived from the field data were used to calculate production and turnover rate. 4. Annual production of A. quadratus in the torrent Gorg Blau (4.80 g dry mass m,2 year,1) was the highest ever reported for the genus, being comparable with that estimated for some insects with rapid development and multiple cohorts. 5. Estimates of production of A. quadratus were combined with foregut content analysis to estimate the fraction of total production derived from the principal food sources: algae and organic detritus. Algae supported a major proportion of the production of this grazer. 6. The low density of predators characteristic of many temporary streams, and the small amplitudes in discharge and temperature during most of the wet period that characterise the spring habitats might allow high levels of grazer production in this particular Mediterranean stream. [source] How a mega-grazer copes with the dry season: food and nutrient intake rates by white rhinoceros in the wildFUNCTIONAL ECOLOGY, Issue 2 2006A. M. SHRADER Summary 1Few studies have investigated how free-ranging wild herbivores adjust their food intake rate and nutrient gains during the dry season. Our study focused on the largest extant grazer, the white rhinoceros (Ceratotherium simum Burchell 1817). Field measurements were made on changes in bite mass, bite rate and nutrient concentrations of food eaten during the dry season. 2As the dry season progressed, the quality and availability of food resources declined. During this time white rhinos foraged mainly in high-quality short and woodland grasslands. Late in the dry season they also used flushes of green grass in previously burnt Themeda grasslands. 3Bite mass increased linearly with increasing sward height, while bite rate declined. Intake rate was determined primarily by bite mass and thus tended to increase linearly with sward height. Maximum bite mass and intake rate was obtained in swards >20 cm. 4White rhinos did not compensate for seasonal declines in food quality by adjusting their food intake rate or diet breadth. We suggest that white rhinos mobilize fat reserves to help meet their nutritional needs during the dry season. [source] Contrasting effects of cattle and wildlife on the vegetation development of a savanna landscape mosaicJOURNAL OF ECOLOGY, Issue 5 2010Kari E. Veblen Summary 1.,Through their effects on plant communities, herbivores can exert strong direct and indirect effects on savanna ecosystems and have the potential to create and maintain savanna landscape heterogeneity. Throughout much of sub-Saharan Africa, periodic creation and abandonment of livestock corrals leads to landscape mosaics of long-term ecosystem hotspots that attract both cattle and large ungulate wildlife. 2.,The development and maintenance of vegetation in these types of hotspots may be controlled in part by herbivory. Cattle and wildlife may have different, potentially contrasting effects on plant succession and plant,plant interactions. We ask how cattle and wild herbivores affect the maintenance and vegetation development of corral-derived landscape heterogeneity (0.25,1.0 ha treeless ,glades') in Laikipia, Kenya, through their effects on long-term successional and short-term plant,plant dynamics. 3.,We used the Kenya Long-term Exclosure Experiment to exclude from glades different combinations of cattle, large ungulate wildlife (i.e. zebras, gazelles and other antelopes), and mega-herbivore wildlife (i.e. giraffes and elephants). We first assessed long-term changes in cover of the dominant grass species, Cynodon plectostachyus and Pennisetum stramineum (the early- and late-dominant species, respectively). We then used a neighbour removal experiment to test the effects of different herbivores on competition and facilitation between the two glade grass species. 4.,In the long-term experiment, we found that large ungulate wildlife reinforced landscape heterogeneity over time by helping maintain glades in their early C. plectostachyus -dominated form. Cattle and mega-herbivore wildlife, on the other hand, appeared to reduce the positive effects through forage preference for C. plectostachyus. 5.,In the neighbour removal experiment, we found that each grass species benefited from facilitation when it was the preferred forage for the dominant grazer. Facilitation of C. plectostachyus by P. stramineum was strongest when cattle co-occurred with wildlife, whereas facilitation of P. stramineum by C. plectostachyus was strongest when cattle were absent. 6.,Synthesis. Our results demonstrate that different combinations of cattle and wildlife have different effects, largely via contrasting forage preferences, on the persistence of landscape heterogeneity in this savanna landscape. More generally, we provide evidence for contrasting effects of cattle and wildlife on short-term plant interactions (facilitation) and successional processes within the herbaceous plant community. [source] A PCR-based method for diet analysis in freshwater organisms using 18S rDNA barcoding on faecesMOLECULAR ECOLOGY RESOURCES, Issue 1 2010EMMANUEL CORSE Abstract The development of DNA barcoding from faeces represents a promising method for animal diet analysis. However, current studies mainly rely on prior knowledge of prey diversity for a specific predator rather than on a range of its potential prey species. Considering that the feeding behaviour of teleosts may evolve with their environment, it could prove difficult to establish an exhaustive listing of their prey. In this article, we extend the DNA barcoding approach to diet analysis to allow the inclusion of a wide taxonomic range of potential prey items. Thirty-four ecological clade-specific primer sets were designed to cover a large proportion of prey species found in European river ecosystems. Selected primers sets were tested on isolated animal, algal or plant tissues and thereafter on fish faeces using nested PCR to increase DNA detection sensitivity. The PCR products were sequenced and analysed to confirm the identity of the taxa and to validate the method. The methodology developed here was applied to a diet analysis of three freshwater cyprinid species that are assumed to have similar feeding behaviour [Chondrostoma toxostoma toxostoma (Vallot 1837), Chondrostoma nasus nasus (Linnaeus, 1758) and Barbus barbus, (Linneaus 1758)]. These three species were sampled in four different hydrographic basins. Principal Component Analysis based on prey proportions identified distinct perilithon grazer and benthophagous behaviours. Furthermore, our results were consistent with the available literature on feeding behaviour in these fish. The simplicity of the PCR-based method and its potential generalization to other freshwater organisms may open new perspectives in food web ecology. [source] Mixotrophy in the Phototrophic Harmful Alga Cochlodinium polykrikoides (Dinophycean): Prey Species, the Effects of Prey Concentration, and Grazing ImpactTHE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 5 2004HAE JIN JEONG ABSTRACT We first reported here that the harmful alga Cochlodinium polykrikoides, which had been previously known as an autotrophic dinoflagellate, was a mixotrophic species. We investigated the kinds of prey species and the effects of the prey concentration on the growth and ingestion rates of C. polykrikoides when feeding on an unidentified cryptophyte species (Equivalent Spherical Diameter, ESD = 5.6 ,m). We also calculated grazing coefficients by combining field data on abundances of C. polykrikoides and co occurring cryptophytes with laboratory data on ingestion rates obtained in the present study. Cocholdinium polykrikoides fed on prey cells by engulfing the prey through the sulcus. Among the phytoplankton prey offered, C. polykrikoides ingested small phytoplankton species that had ESD's , 11 ,m (e.g. the prymnesiophyte Isochrysis galbana, an unidentified cryptophyte, the cryptophyte Rhodomonas salina, the raphidophyte Heterosigma akashiwo, and the dinoflagellate Amphidinium carterae). It did not feed on larger phytoplankton species that had ESD's , 12 ,m (e.g. the dinoflagellates Heterocapsa triquetra, Prorocentrum minimum, Scrippsiella sp., Alexandrium tamarense. Prorocentrum micans, Gymnodinium catenatum, Akashiwo sanguinea, and Lingulodinium polyedrum). Specific growth rates of C. polykrikoides on a cryptophyte increased with increasing mean prey concentration, with saturation at a mean prey concentration of approximately 270 ng C ml,1 (i.e. 15,900 cells ml,1)- The maximum specific growth rate (mixotrophic growth) of C. polykrikoides on a cryptophyte was 0.324 d,', under a 14:10 h light-dark cycle of 50 ,E m,2 s,1, while its growth rate (phototrophic growth) under the same light conditions without added prey was 0.166 d,. Maximum ingestion and clearance rates of C. polykrikoides on a cryptophyte were 0.16 ng C grazer,1d 1 (9.4 cells grazer 1d,1) and 0.33 ,1 grazer 1h,1, respectively. Calculated grazing coefficients by C. polykri koides on cryptophytes were 0.001,0.745 h,1 (i.e. 0.1,53% of cryptophyte populations were removed by a C. polykrikoides population in 1 h). The results of the present study suggest that C. polykrikoides sometimes has a considerable grazing impact on populations of cryptophytes. [source] Avoidance by grazers facilitates spread of an invasive hybrid plantECOLOGY LETTERS, Issue 2 2010E. Grosholz Ecology Letters (2010) 13: 145,153 Abstract Biological invasions greatly increase the potential for hybridization among native and non-native species. Hybridization may influence the palatability of novel hybrids to consumers potentially influencing invasion success; however, the palatability of non-native hybrids relative to the parent species is poorly known. In contrast, studies of native-only hybrids find they are nearly always more palatable to consumers than the parent species. Here, I experimentally demonstrate that an invasive hybrid cordgrass (Spartina) is dramatically less palatable to grazing geese than the native parent species. Using field and aviary experiments, I show that grazing geese ignore the hybrid cordgrass and preferentially consume native Spartina. I also experimentally demonstrate that reduced herbivory of the invasive hybrid may contribute to faster spread in a California estuary. These results suggest that biological invasions may increase future opportunities for creating novel hybrids that may pose a greater risk to natural systems than the parent species. [source] Trading off the ability to exploit rich versus poor food qualityECOLOGY LETTERS, Issue 5 2002Alan 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] Basin geochemistry and isotopic ratios of fishes and basal production sources in four neotropical riversECOLOGY OF FRESHWATER FISH, Issue 3 2007David B. Jepsen Abstract,,, We analysed stable carbon and nitrogen isotopic ratios of dissolved inorganic carbon (DIC), plants, detritus and fishes to estimate the relative importance of dominant production sources supporting food webs of four Venezuelan rivers with divergent geochemical and watershed characteristics. Based on samples taken during the dry season at each site, fishes from two nutrient-poor, blackwater rivers had significantly lower ,13C values (mean = ,31.4, and ,32.9,) than fishes from more productive clearwater and whitewater rivers (mean = ,25.2, and ,25.6, respectively). Low carbon isotopic ratios of fishes from blackwaters were likely influenced by low ,13C of DIC assimilated by aquatic primary producers. Although floodplains of three savanna rivers supported high biomass of C4 grasses, relatively little carbon from this source appeared to be assimilated by fishes. Most fishes in each system assimilated carbon derived mostly from a combination of microalgae and C3 macrophytes, two sources with broadly overlapping carbon isotopic signatures. Even with this broad overlap, several benthivorous grazers from blackwater and whitewater rivers had isotopic values that aligned more closely with algae. We conclude that comparative stable isotopic studies of river biota need to account for watershed geochemistry that influences the isotopic composition of basal production sources. Moreover, isotopic differences between river basins can provide a basis for discriminating spatial and temporal variation in the trophic ecology of fishes that migrate between watersheds having distinct geochemical characteristics. [source] Population ecology of cave armoured catfish, Ancistrus cryptophthalmus Reis 1987, from central Brazil (Siluriformes: Loricariidae)ECOLOGY OF FRESHWATER FISH, Issue 2 2007E. Trajano Abstract,,, The population ecology of Ancistrus cryptophthalmus (Reis 1987) was studied by mark,recapture technique in caves from the São Domingos karst area, State of Goiás, northeastern Brazil. Total population sizes estimated for Angélica and Passa Três Caves were 20,000 and 1000 individuals, respectively. Densities around 1.0 individuals per m2 in Angélica, Bezerra and São Vicente I Streams, and 0.6 individuals per m2 in the smaller Passa Três Stream may be considered high for cavefish standards, as well as for epigean loricariids. As expected for benthic grazers, cave catfish are highly sedentary. The distribution of size classes did not differ among caves and within the same cave throughout the studied dry seasons; on the contrary, the condition factor decreased throughout this period probably because of the progressive depletion of organic matter available as food. Low proportions of mature individuals, low growth rates (average = 0.5 mm month,1) with cases of negative growth and high longevities (8,10 years) point to a precocial lifestyle, typical of troglobitic species. [source] Use of stable isotope-labelled cells to identify active grazers of picocyanobacteria in ocean surface watersENVIRONMENTAL MICROBIOLOGY, Issue 2 2009Jorge Frias-Lopez Summary Prochlorococcus and Synechococcus are the two most abundant marine cyanobacteria. They represent a significant fraction of the total primary production of the world oceans and comprise a major fraction of the prey biomass available to phagotrophic protists. Despite relatively rapid growth rates, picocyanobacterial cell densities in open-ocean surface waters remain fairly constant, implying steady mortality due to viral infection and consumption by predators. There have been several studies on grazing by specific protists on Prochlorococcus and Synechococcus in culture, and of cell loss rates due to overall grazing in the field. However, the specific sources of mortality of these primary producers in the wild remain unknown. Here, we use a modification of the RNA stable isotope probing technique (RNA-SIP), which involves adding labelled cells to natural seawater, to identify active predators that are specifically consuming Prochlorococcus and Synechococcus in the surface waters of the Pacific Ocean. Four major groups were identified as having their 18S rRNA highly labelled: Prymnesiophyceae (Haptophyta), Dictyochophyceae (Stramenopiles), Bolidomonas (Stramenopiles) and Dinoflagellata (Alveolata). For the first three of these, the closest relative of the sequences identified was a photosynthetic organism, indicating the presence of mixotrophs among picocyanobacterial predators. We conclude that the use of RNA-SIP is a useful method to identity specific predators for picocyanobacteria in situ, and that the method could possibly be used to identify other bacterial predators important in the microbial food-web. [source] Direct and indirect effects of a potential aquatic contaminant on grazer,algae interactionsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2009Michelle A. Evans-White Abstract Contaminants have direct, harmful effects across multiple ecological scales, including the individual, the community, and the ecosystem levels. Less, however, is known about how indirect effects of contaminants on consumer physiology or behavior might alter community interactions or ecosystem processes. We examined whether a potential aquatic contaminant, an ionic liquid, can indirectly alter benthic algal biomass and primary production through direct effects on herbivorous snails. Ionic liquids are nonvolatile organic salts being considered as an environmentally friendly potential replacement for volatile organic compounds in industry. In two greenhouse experiments, we factorially crossed four concentrations of 1-N-butyl-3-methylimidazolium bromide (bmimBr; experiment 1: 0 or 10 mg/L; experiment 2: 0, 1, or 100 mg/L) with the presence or absence of the snail Physa acuta in aquatic mesocosms. Experimental results were weighted by their respective control (no bmimBr or P. acuta) and combined for statistical analysis. When both bmimBr and snails were present, chlorophyll a abundance and algal biovolume were higher than would be expected if both factors acted additively. In addition, snail growth rates, relative to those of controls, declined by 41 to 101% at 10 and 100 mg/L of bmimBr. Taken together, these two results suggest that snails were less efficient grazers in the presence of bmimBr, resulting in release of algae from the grazer control. Snails stimulated periphyton primary production in the absence, but not in the presence, of bmimBr, suggesting that bmimBr also can indirectly alter ecosystem function. These findings suggest that sublethal contaminant levels can negatively impact communities and ecosystem processes via complex interactions, and they provide baseline information regarding the potential effects of an emergent industrial chemical on aquatic systems. [source] Bacterivorous grazers facilitate organic matter decomposition: a stoichiometric modeling approachFEMS MICROBIOLOGY ECOLOGY, Issue 2 2009Hao Wang Abstract There is widespread empirical evidence that protist grazing on bacteria reduces bacterial abundances but increases bacteria-mediated decomposition of organic matter. This paradox has been noted repeatedly in the microbiology literature but lacks a generally accepted mechanistic explanation. To explain this paradox quantitatively, we develop a bacteria-grazer model of organic matter decomposition that incorporates protozoa-driven nutrient recycling and stoichiometry. Unlike previous efforts, the current model includes explicit limitation, via Liebig's law of minimum, by two possible factors, nutrient and carbon densities, as well as their relative ratios in bacteria and grazers. Our model shows two principal results: (1) when the environment is carbon limiting, organic matter can always be decomposed completely, regardless of the presence/absence of grazers; (2) when the environment is nutrient (such as nitrogen) limiting, it is possible for organic matter to be completely decomposed in the presence, but not absence, of grazers. Grazers facilitate decomposition by releasing nutrients back into the environment, which would otherwise be limiting, while preying upon bacteria. Model analysis reveals that facilitation of organic matter decomposition by grazers is positively related to the stoichiometric difference between bacteria and grazers. In addition, we predict the existence of an optimal density range of introduced grazers, which maximally facilitate the decomposition of organic matter in a fixed time period. This optimal range reflects a trade-off between grazer-induced nutrient recycling and grazer-induced mortality of bacteria. [source] Palatability of macrophytes to the invasive freshwater snail Pomacea canaliculata: differential effects of multiple plant traitsFRESHWATER BIOLOGY, Issue 10 2010PAK KI WONG Summary 1.,By selective grazing, invasive grazers can alter macrophyte-herbivore relationships in shallow freshwater bodies. Evaluating the palatability of macrophytes and understanding the determinants of plant palatability can help predict grazing impact. In no-choice feeding assays, we tested the palatability of 21 species of freshwater macrophytes to the invasive freshwater apple snail Pomacea canaliculata. 2.,Daily feeding rate varied greatly with plant species, ranging from 1.1 to 22% of snail body mass. We assessed six plant properties and examined their correlation with feeding rate. Total nitrogen content was positively related, and C:N ratio and dry matter content (DMC) negatively related, to snail feeding rate. There was no significant correlation between snail feeding rate and plant phenolic content, but the feeding rate on Myriophyllum aquaticum (the plant with the highest phenolic content) was very low. 3.,We repeated the feeding assays for 15 species that were not palatable as fresh leaves with reconstituted plant tissues formed by mixing ground up dried leaves with agar. The feeding rate still differed greatly among macrophyte species. Phragmites australis and Vallisneria natans (two species with the highest DMC) were eaten much more as reconstituted plant than as fresh leaves, indicating that structure (i.e. DMC) may be important in their defence against snail herbivory. For two plants (M. aquaticum and Alternanthera philoxeroides) that had moderate amounts of nitrogen/phosphorus but were consumed very little as fresh and reconstituted tissues, we incorporated their extracts into a palatable agar-based food. The extracts from both species greatly reduced snail feeding rate, indicating the presence of chemical defences in these two species. 4.,These results indicated that feeding was affected by several plant traits. The snail favoured plants with a high nitrogen content and avoided plants with a high DMC. Only a few plants possessed chemical feeding deterrents that were effective against this snail. Given the invasive spread of P. canaliculata in Asia, ecologists and managers should consider plant palatability when selecting plants for use in wetland restoration and when predicting the impact of further invasion by this species. [source] Fatty acid analyses reveal high degrees of omnivory and dietary plasticity in pond-dwelling tadpolesFRESHWATER BIOLOGY, Issue 7 2010MATT R. WHILES Summary 1.,Understanding the trophic relationships of consumers is central to ecology, but constructing meaningful food webs is often difficult because of a lack of detailed information on consumption versus assimilation and high degrees of omnivory. 2.,We used fatty acid analyses to examine the trophic relationships of three common larval anurans (Pseudacris crucifer, Lithobates catesbeianus and Lithobates clamitans) that are often classified as grazers or detritivores. Tadpoles and potential food sources were sampled in four ponds in southern Illinois and analysed for fatty acid composition. Single linkage cluster analysis was then used to compare fatty acid profiles among tadpole gut contents, tadpole muscle tissues and available food resources. 3.,Diets varied among species and within species among ponds, but organic sediments consistently contributed most to the fatty acid composition of the gut contents of all species. Fatty acid profiles also indicated that larval insects and phytoplankton were consumed by both L. catesbeianus and L. clamitans in one pond, while L. clamitans and P. crucifer consumed mainly periphyton along with sediments in another pond, and these diet differences appeared linked to physical differences among ponds, with periphyton and/or phytoplankton contributing more to tadpole diets in less shaded ponds. 4.,The fatty acid composition of muscle tissues of L. clamitans, the dominant tadpole in these systems, indicated that plant detritus and bacteria, which were the dominant components of organic sediments in the ponds, were common components of the assimilatory diet. 5.,Results demonstrate the utility of fatty acid analyses for assessing both consumption and assimilation. The tadpole assemblages we examined derive much of their energy from heterotrophic and allochthonous sources and exhibit high dietary plasticity. This information will allow for more accurate and comprehensive assessments of trophic interactions in freshwater habitats, as well as aid in amphibian conservation, management and captive propagation efforts. [source] The role of light for fish,zooplankton,phytoplankton interactions during winter in shallow lakes , a climate change perspectiveFRESHWATER BIOLOGY, Issue 5 2009METTE ELISABETH BRAMM Summary 1.,Variations in the light regime can affect the availability and quality of food for zooplankton grazers as well as their exposure to fish predation. In northern lakes light is particularly low in winter and, with increasing warming, the northern limit of some present-day plankton communities may move further north and the plankton will thus receive less winter light. 2.,We followed the changes in the biomass and community structure of zooplankton and phytoplankton in a clear and a turbid shallow lake during winter (November,March) in enclosures both with and without fish and with four different light treatments (100%, 55%, 7% and <1% of incoming light). 3.,In both lakes total zooplankton biomass and chlorophyll- a were influenced by light availability and the presence of fish. Presence of fish irrespective of the light level led to low crustacean biomass, high rotifer biomass and changes in the life history of copepods. The strength of the fish effect on zooplankton biomass diminished with declining light and the effect of light was strongest in the presence of fish. 4.,When fish were present, reduced light led to a shift from rotifers to calanoid copepods in the clear lake and from rotifers to cyclopoid copepods in the turbid lake. Light affected the phytoplankton biomass and, to a lesser extent, the phytoplankton community composition and size. However, the fish effect on phytoplankton was overall weak. 5.,Our results from typical Danish shallow eutrophic lakes suggest that major changes in winter light conditions are needed in order to have a significant effect on the plankton community. The change in light occurring when such plankton communities move northwards in response to global warming will mostly be of modest importance for this lake type, at least for the rest of this century in an IPCC A2 scenario, while stronger effects may be observed in deep lakes. [source] Stoichiometric relationships in vernal pond plankton communitiesFRESHWATER BIOLOGY, Issue 7 2008CARLA E. CÁCERES Summary 1. The light-nutrient hypothesis (LNH) predicts that changes in light supply can alter the balance of nutrient and energy limitation in primary producers. We tested this prediction by examining temporal changes in vernal forest ponds, which are highly dynamic systems with respect to seasonal change in light and nutrient supply. In three vernal ponds that differ in productivity, we measured changes in light, total and seston nitrogen and phosphorus, and seston carbon and chlorophyll during the spring, before and after tree leaf-out. We also quantified changes in the population dynamics of the major zooplankton grazers in these systems. 2. In each pond, nutrient levels increased and light levels declined, creating a temporal shift in light-nutrient supply to the plankton. Results generally supported predictions of stoichiometric theory and the LNH, but there were notable exceptions. 3. Seston C : N : P ratios rapidly changed in response to dramatic increases in N and P supply rates. However, seston N : P was typically lower than values for total N : P in the water. Furthermore, as predicted, we observed a decline in seston C : P as the light : nutrient ratio declined, but seston C : N simultaneously increased. These results suggest an unexpected shift towards potential nitrogen limitation. Alternatively, this change in nutrient ratios may be driven by a seasonal change in phytoplankton composition or nutritional mode. 4. Seston carbon concentrations remained stable despite seasonal changes in grazing intensity associated with the phenology of large-bodied Daphnia grazers. However, chlorophyll concentrations declined dramatically as the season progressed, resulting in a simultaneous decline in the C : Chlorophyll ratio of seston. Both pond shading and increased grazing probably contributed to the decline in chlorophyll. [source] Effects of increased temperature and nutrient enrichment on the stoichiometry of primary producers and consumers in temperate shallow lakesFRESHWATER BIOLOGY, Issue 7 2008M. VENTURA Summary 1. We studied the effects of increased water temperatures (0,4.5 °C) and nutrient enrichment on the stoichiometric composition of different primary producers (macrophytes, epiphytes, seston and sediment biofilm) and invertebrate consumers in 24 mesocosm ecosystems created to mimic shallow pond environments. The nutrient ratios of primary producers were used as indicative of relative nitrogen (N) or phosphorus (P) limitation. We further used carbon stable isotopic composition (,13C) of the different primary producers to elucidate differences in the degree of CO2 limitation. 2. Epiphytes were the only primary producer with significantly higher ,13C in the enriched mesocosms. No temperature effects were observed in ,13C composition of any primary producer. Independently of the treatment effects, the four primary producers had different ,13C signatures indicative of differences in CO2 limitation. Seston had signatures indicating negligible or low CO2 limitation, followed by epiphytes and sediment biofilm, with moderate CO2 limitation, while macrophytes showed the strongest CO2 limitation. CO2 together with biomass of epiphytes were the key variables explaining between 50 and 70% of the variability in ,13C of the different primary producers, suggesting that epiphytes play an important role in carbon flow of temperate shallow lakes. 3. The ratio of carbon to chlorophyll a decreased with increasing temperature and enrichment in both epiphytes and seston. The effects of temperature were mainly attributed to changes in algal Chl a content, while the decrease with enrichment was probably a result of a higher proportion of algae in the seston and epiphytes. 4. Macrophytes, epiphytes and seston decreased their C : N with enrichment, probably as an adaptation to the different N availability levels. The C : N of epiphytes and Elodea canadensis decreased with increasing temperature in the control mesocosms. Sediment biofilm was the only primary producer with lower C : P and N : P with enrichment, probably as a result of higher P accumulation in the sediment. 5. Independently of nutrient level and increased temperature effects the four primary producers had significantly different stoichiometric compositions. Macrophytes had higher C : N and C : P and, together with epiphytes, also the highest N : P. Seston had no N or P limitation, while macrophytes and epiphytes may have been P limited in a few mesocosms. Sediment biofilm indicated strong N deficiency. 6. Consumers had strongly homeostatic stoichiometric compositions in comparison to primary producers, with weak or no significant treatment effects in any of the groups (insects, leeches, molluscs and crustaceans). Among consumers, predators had significantly higher N content and lower C : N than grazers. [source] Selectivity and competitive interactions between two benthic invertebrate grazers (Asellus aquaticus and Potamopyrgus antipodarum): an experimental study using 13C- and 15N-labelled diatomsFRESHWATER BIOLOGY, Issue 2 2005N. ABERLE Summary 1. Tracer experiments with two diatoms labelled with 13C (Nitzschia palea) and 15N (Fragilaria crotonensis), were conducted to investigate feeding selectivity and interspecific competition between the grazers Asellus aquaticus (Isopoda, Crustacea) and Potamopyrgus antipodarum (Hydrobiidae, Gastropoda). Conventional methods, such as cell counts and estimated biovolume, were used first to detect feeding preferences within the different grazer treatments. 2. The results revealed a significant decline in algal biovolume in all grazer treatments and no indications of active selectivity were observed. In contrast to conventional methods, measurements based on isotope signatures showed strong differences in tracer uptake, thus indicating different degrees of assimilation and digestion by the two grazers. 3. The selectivity index Q, which provides information on the uptake ratio of 13C to 15N, showed a significant time effect for both grazer species and a significant difference between single- and mixed-grazer treatments for P. antipodarum. Thus, this technique enabled the direct quantification of the uptake by grazers and, therefore, served as an ideal tool for the detection of passive selectivity. 4. Our results indicate a shift in feeding preferences related to between-species competition and a potential divergence of trophic niches when species coexist. [source] Does high nitrogen loading prevent clear-water conditions in shallow lakes at moderately high phosphorus concentrations?FRESHWATER BIOLOGY, Issue 1 2005María A. González Sagrario Summary 1. The effect of total nitrogen (TN) and phosphorus (TP) loading on trophic structure and water clarity was studied during summer in 24 field enclosures fixed in, and kept open to, the sediment in a shallow lake. The experiment involved a control treatment and five treatments to which nutrients were added: (i) high phosphorus, (ii) moderate nitrogen, (iii) high nitrogen, (iv) high phosphorus and moderate nitrogen and (v) high phosphorus and high nitrogen. To reduce zooplankton grazers, 1+ fish (Perca fluviatilis L.) were stocked in all enclosures at a density of 3.7 individuals m,2. 2. With the addition of phosphorus, chlorophyll a and the total biovolume of phytoplankton rose significantly at moderate and high nitrogen. Cyanobacteria or chlorophytes dominated in all enclosures to which we added phosphorus as well as in the high nitrogen treatment, while cryptophytes dominated in the moderate nitrogen enclosures and the controls. 3. At the end of the experiment, the biomass of the submerged macrophytes Elodea canadensis and Potamogeton sp. was significantly lower in the dual treatments (TN, TP) than in single nutrient treatments and controls and the water clarity declined. The shift to a turbid state with low plant coverage occurred at TN >2 mg N L,1 and TP >0.13,0.2 mg P L,1. These results concur with a survey of Danish shallow lakes, showing that high macrophyte coverage occurred only when summer mean TN was below 2 mg N L,1, irrespective of the concentration of TP, which ranged between 0.03 and 1.2 mg P L,1. 4. Zooplankton biomass and the zooplankton : phytoplankton biomass ratio, and probably also the grazing pressure on phytoplankton, remained overall low in all treatments, reflecting the high fish abundance chosen for the experiment. We saw no response to nutrition addition in total zooplankton biomass, indicating that the loss of plants and a shift to the turbid state did not result from changes in zooplankton grazing. Shading by phytoplankton and periphyton was probably the key factor. 5. Nitrogen may play a far more important role than previously appreciated in the loss of submerged macrophytes at increased nutrient loading and for the delay in the re-establishment of the nutrient loading reduction. We cannot yet specify, however, a threshold value for N that would cause a shift to a turbid state as it may vary with fish density and climatic conditions. However, the focus should be widened to use control of both N and P in the restoration of eutrophic shallow lakes. [source] Herbivory in an acid streamFRESHWATER BIOLOGY, Issue 4 2000Mark E. Ledger Summary 1Spatial and temporal variation in the distribution and feeding of non-predatory macroinvertebrates was investigated in a first-order, acid stream in the Ashdown Forest, southern England. 2Stonefly (Nemouridae) and chironomid (Orthocladiinae) larvae were abundant on the upper surfaces of mineral substrata of three sizes (small stones, large stones, bedrock). The density of larvae in each taxonomic group did not vary among substrata of different sizes, although strong seasonal variation existed. 3Nemourids and chironomids (H. marcidus) collected from the upper surfaces of substrata exhibited generalist feeding habits, consuming algae (diatoms, coccoid and filamentous green algae), detritus (biofilm matrix material and fine particulate organic matter (FPOM)) and inorganic debris. 4There was spatial variation in the gut contents of nemourids. The proportion of algae in the guts of larvae often increased with the size of the substratum from which they were collected. Strong temporal variation in the composition of the diet also existed. Nemourids ingested a large quantity of attached algae and biofilm matrix from the biofilm in spring and winter, but consumed loose FPOM and associated microflora in summer and autumn. 5We conclude that, in this acid stream, the trophic linkage between algae and grazers is maintained by ,detritivorous' stonefly and chironomid species. The relationship between the feeding habits of these larvae and other life-history attributes, such as mouthpart morphology and mobility, is discussed. [source] Leaf dry matter content as an integrative expression of plant palatability: the case of freshwater macrophytesFUNCTIONAL ECOLOGY, Issue 1 2003A. Elger Summary 1We examined the possibility of using the dry matter content (DMC) of macrophytes (the ratio of dry mass to wet mass) as an integrative variable to predict their palatability to generalist invertebrate grazers. 2We assessed the palatability of 20 macrophyte species, using the snail Lymnaea stagnalis (L.) in non-choice feeding experiments. Three of the species were studied at two different dates in the year, at two or four sites. 3The average dry mass consumed by L. stagnalis ranged widely between species, and was negatively correlated to plant DMC. At the intraspecific level, the dry mass consumed varied over time but was not related to site location. Again, the dry mass consumed was negatively correlated to plant DMC. 4The DMC of the macrophytes studied explained about 30% of interspecific variability, and >80% of seasonal variability, in snail consumption rate. Therefore this trait could be used as a shortcut to predict variations in macrophyte palatability, especially at the intraspecific level. At the interspecific level, the relationship between DMC and palatability might be weakened by the presence in some plants of low molecular weight chemical deterrents. [source] Diversity and species composition of West African ungulate assemblages: effects of fire, climate and soilGLOBAL ECOLOGY, Issue 6 2008Erik Klop ABSTRACT Aim, Anthropogenic fires are a major component of the ecology of rangelands throughout the world. To assess the effects of these fires on the diversity patterns of herbivores, we related gradients in fire occurrence, climate and soil fertility to patterns in alpha and beta diversity of African ungulates. Location, West Africa. Methods, We used a survey-based approach for ungulates in 37 protected areas in desert, savanna and rain forest habitats throughout West Africa, combined with satellite images of fire occurrence and digital maps of actual evapotranspiration and soil fertility. Alpha diversity was related to the environmental variables using conventional and spatial regression models. We investigated beta diversity using partial Mantel tests and ordination techniques, and by partitioning the variance in assemblage composition into environmental and spatial components. Results, The species richness of grazers showed a quadratic relationship with actual evapotranspiration, whereas that of browsers and frugivores showed a linear relationship. However, in the multiple regression models fire occurrence was the only variable that significantly correlated with the species richness of grazers. Soil fertility was weakly related to overall beta diversity and the species richness of browsers, but was non-significant in the multiple regression models. Fire occurrence was the most important variable explaining species composition of the overall species set and of grazers, whereas the assemblage composition of browsers and frugivores was explained mostly by actual evapotranspiration. Main conclusions, In contrast to previous studies, our analyses show that moisture and nutrients alone fail to adequately predict the diversity patterns of grazing ungulates. Rather, the species richness and assemblage composition of grazers are largely governed by anthropogenic fires that modify the quality and structure of the grass sward. Diversity patterns of browsers and frugivores are markedly different from grazers and depend mainly on the availability of moisture, which is positively correlated with the availability of foliage and fruits. Our study highlights the importance of incorporating major human-induced disturbances or habitat alterations into analyses of diversity patterns. [source] The role of trout in stream food webs: integrating evidence from field surveys and experimentsJOURNAL OF ANIMAL ECOLOGY, Issue 2 2006KRISTIAN MEISSNER Summary 1We evaluated the effects of brown trout on boreal stream food webs using field surveys and enclosure/exclosure experiments. Experimental results were related to prey preference of uncaged trout in the same stream, as well as to a survey of macroinvertebrate densities in streams with vs. without trout. Finally, we assessed the generality of our findings by examining salmonid predation on three groups of macroinvertebrate prey (chironomid midges, epibenthic grazers, invertebrate predators) in a meta-analysis. 2In a preliminary experiment, invertebrate predators showed a strong negative response to trout, whereas chironomids benefited from trout presence. In the main experiment, trout impact increased with prey size. Trout had the strongest effect on invertebrate predators and cased caddis larvae, whereas Baetis mayfly and chironomid larvae were unaffected. Trout impact on the largest prey seemed mainly consumptive, because prey emigration rates were low and independent of fish presence. Despite strong effects on macroinvertebrates, trout did not induce a trophic cascade on periphyton. Uncaged trout showed a strong preference for the largest prey items (predatory invertebrates and aerial prey), whereas Baetis mayflies and chironomids were avoided by trout. 3Densities of invertebrate predators were significantly higher in troutless streams. Baetis mayflies also were less abundant in trout streams, whereas densities of chironomids were positively, although non-significantly, related to trout presence. Meta-analysis showed a strong negative impact of trout on invertebrate predators, a negative but variable impact on mobile grazers (mainly mayfly larvae) and a slightly positive impact on chironomid larvae. 4Being size-selective predators, salmonid fishes have a strong impact on the largest prey types available, and this effect spans several domains of scale. Discrepancies between our experimental findings and those from the field survey and meta-analysis show, however, that for most lotic prey, small-scale experiments do not reflect fish impact reliably at stream-wide scales. 5Our findings suggest that small-scale experiments will be useful only if the experimental results are evaluated carefully against natural history information about the experimental system and interacting species across a wide array of spatial scales. [source] Ungulate foraging strategies: energy maximizing or time minimizing?JOURNAL OF ANIMAL ECOLOGY, Issue 2 2001Carita M. Bergman Summary 1,Many classical models of ungulate foraging are premised on energy maximization, yet limited empirical evidence and untested currency assumptions make the choice of currency a non-trivial issue. The primary constraints on forage intake of ungulates are forage quality and availability. Using a model that incorporates these two constraints, we predicted the optimal biomass of forage patches for ungulate grazers using an energy maximizing vs. a time minimizing strategy. 2,We tested these predictions on wood bison (Bison bison athabascae Rhoads) grazing naturally occurring sedge (Carex atherodes Spreng). The digestive constraint was determined by a series of ad libitum feeding trials using sedge at different stages of growth. Sedge digestibility declined with biomass. Ad libitum intake of sedge by bison declined with sedge digestibility and thus decreased with sedge biomass. On the other hand, short-term sedge intake rates of wood bison increased with biomass. 3,Incorporation of these constraints resulted in the prediction that daily energy gain of bison should be maximized by grazing patches with a biomass of 10 g m,2, whereas a bison could minimize daily foraging time needed to fulfil its energy requirement by cropping patches with a biomass of 279 g m,2. 4,To test these quantitative predictions, we used a staggered mowing regime to convert even-aged stands of sedge to a mosaic of patches varying in quality and quantity. Observations of bison grazing these mosaics indicated that patches of biomass below 120 g m,2 were avoided, while patches of biomass 156 and 219 g m,2 were highly preferred, with the greatest preference for the latter. 5,These results indicate that bison were behaving as time minimizers rather than energy maximizers. Daily cropping times of free-ranging bison from the literature corroborate our results. [source] How important is climate?JOURNAL OF APPLIED ECOLOGY, Issue 5 2003Effects of warming, fish on phytoplankton in shallow lake microcosms, nutrient addition Summary 1Climate is changing. Predictions are for at least a 3 °C rise in mean temperature in northern Europe over the next century. Existing severe impacts of nutrients and inappropriate fish stocking in freshwater systems remain. 2Effects of warming by 3 °C above ambient, nutrient addition and the presence or absence of sticklebacks Gasterosteus aculeatus were studied in experimental microcosms dominated by submerged plants, mimicking shallow lake ecosystems. 3Warming had considerably smaller effects on the phytoplankton community than did fish and nutrients. It had very minor effects on chlorophyll a and total phytoplankton biovolume. However, it significantly decreased the biovolumes of Cryptophyceae (a major component in the controls) and Dinophyceae. Contrary to expectation, warming did not increase the abundance of blue-green algae (cyanophytes). Warming decreased the abundances of Cryptomonas erosa (Cryptophyceae) and Oocystis pusilla (Chlorophycota) and increased those of two other green algae, Tetraedron minimum and Micractinium pusillum. It had no effect on a further 17 species that were predominant in a community of about 90 species. 4Fish and nutrients, either together or separately, generally increased the crops of most of the 21 abundant species and of the algal groups. Exceptions were for diatoms and chrysophytes, which were very minor components of the communities. Fish, but neither nutrients nor warming, increased the number of species of phytoplankton detected. This was probably through removal of zooplankton grazers, and parallels terrestrial studies where the presence of top predators, by controlling herbivores, leads to increased plant diversity. 5There was no particular pattern in the taxonomy or biological characteristics of those species affected by the treatments. In particular, there was no link between organism size (a surrogate for many important biological features of phytoplankton species) and the effects of warming, nutrient addition or presence or absence of fish. However, all species were relatively small and potentially vulnerable to grazing. 6Synthesis and applications. The results suggest that fears of an increasing abundance of cyanophytes with current projections of global warming may be unrealized, at least in shallow unstratified lakes still dominated by macrophytes. However, they emphasize that eutrophication and fish manipulations remain very important impact factors that determine the abundance of phytoplankton and subsequent problems caused by large growths. [source] Applied issues with predators and predation: editor's introductionJOURNAL OF APPLIED ECOLOGY, Issue 2 2002S. J. Ormerod Summary 1,The effects of predation are among the most pervasive in ecology. As parasitoids, parasites, grazers or top carnivores, predators have large influences on the distribution, density, dynamics and evolved traits of other organisms. Effects scale-up to influence community attributes such as species coexistence and ecosystems processes such as production or trophic cascades. 2,Increasingly, however, some of the largest predation issues fall clearly within the scope of applied ecology. They include instances where, due to their ecological attributes and trophic position: (i) predators are valuable to nature conservation, as biocontrol agents, as natural enemies, or as grazers used in rangeland or ecosystem management; (ii) natural or introduced predators are viewed negatively due to effects on conservation, agriculture, forestry, hunting or disease transmission; (iii) predators are affected by human activities such as resource exploitation, or from exposure to factors such as biomagnified pollutants and disturbance; (iv) predators are controversial because different groups view them as either desirable or undesirable. 3,In all these cases, ecologists have a pivotal rôle in facilitating appropriate management. For valued predators, this involves developing sufficient ecological understanding to optimize habitat, increase prey abundance or to reinforce, establish or reintroduce desirable species. For predators considered undesirable, management can involve direct control. In other cases, predation and its consequences can be mitigated by deterrent, exclusion, supplementary feeding, habitat management to favour prey, predator swamping, or by compensating losses financially. These latter strategies are often used where predators are themselves considered too valuable to remove or control. 4,This collection of seven papers illustrates many of these themes by examining contrasting aspects of the applied ecology of Eurasian lynx; by further probing the interaction between predatory birds and red grouse; by exploring the effects of weather on biocontrol; and by illustrating effects on plant species where grazing or seed predation play a dominant rôle. 5,A key lesson from these and other recent papers in the Journal of Applied Ecology is that the successful management of predators depends invariably on understanding adequately the exact ecological context in which predator,prey interactions take place and in which problems arise. With predator-related issues growing rather than diminishing, ecologists will need sufficient resources to maintain current research if they are to provide the understanding required to offer and evaluate sound management. [source] Seasonal variation in forages utilized by the African buffalo (Syncerus caffer) in the succulent thicket of South AfricaAFRICAN JOURNAL OF ECOLOGY, Issue 2 2010Thulani Tshabalala Abstract The succulent thicket of the Eastern Cape, South Africa, is characterized by densely wooded vegetation that is dominated by succulents with little understory of ephemeral and weakly perennial grasses and forbs. Studies have developed around the question: how do bulk grazers such as the African buffalo (Syncerus caffer) survive in the succulent thicket? In this study, the diet of the African buffalo at the Great Fish River Reserve (GFRR) was studied in two seasons (wet and dry). The diet profile was assessed from faecal matter, using the micro-histological analysis method. During the wet season, grass species contributed 72% to the diet while 28% was contributed by browse species. In the dry season there was a significant increase in the intake of browse by 5% (,2 = 19.94, df = 11, P < 0.05). There were species that were neglected in the wet season but became principal dietary items in the dry season, these included Setaria neglecta, Cymbopogon plurinodis, Capparis sepiaria and Portulacaria afra. Diet quality, as estimated from faecal samples, suggested that the buffalo were nutritionally stable; however, the presence of sarcoptic mange in the buffalo suggests nutritional stress. Résumé Le fourré de plantes succulentes de l'Eastern Cape, en Afrique du Sud, se caractérise par une végétation boisée dense dominée par des succulentes avec un peu de sous-bois d'herbes éphémères ou faiblement pérennes. Des études se sont développées au départ de cette question: comment des gros ruminants comme le buffle (Syncerus caffer) peuvent-ils survivre dans le fourré de succulentes ? Dans cette étude, nous avons étudié pendant deux saisons (des pluies et sèche) le régime alimentaire du buffle de la Great Fish River Reserve (GFRR). On a évalué le profil du régime à partir de la matière fécale, en utilisant la méthode de l'analyse micro-histologique. Pendant la saison des pluies, les monocotylédones composaient 72% du régime et les 28% restants étaient composés d'espèces de brout. En saison sèche, il y avait une augmentation significative (5%) des espèces de brout (X²= 19,94, d.f = 11, P < 0,05). Il y avait des espèces qui étaient négligées en saison des pluies mais qui devenaient des éléments principaux du régime en saison sèche. Parmi ceux-ci, citons Setaria neglecta, Cymbopogon plurinodis, Capparis sepiaria et Portulacaria afra. La qualité du régime alimentaire, estimée d'après les matières fécales, suggère que les buffles sont stables au point de vue nutritionnel; toutefois, la présence de gale sarcoptique chez les buffles suggère un stress alimentaire. [source] | ||||||||||||||||||||||||||||||||||