Biocontrol of root-knot nematode infected banana plants by some marine algae

Root-knot nematodes are serious pests that cause losses of a wide range of different crops. Nematodes are controlled mainly by nematicides which cause pollution and have serious effects on all living organisms including human beings. Therefore, discovering alternative methods to control plant parasitic nematodes was attempted during the last few years to avoid pesticides hazards. Four species of marine algae (Ulva lactuca, Jania rubens, Laurencia obtusa and Sargassum vulgare) were tested to control root-knot nematode, (Meloidogyne spp.) infecting banana plants (Musa spp.). All the treatments significantly (p ≤ 0.05) reduced the rate of build-up compared with the check. U. lactuca alga gave the best results in reducing the number of galls (73.68%) and the final population of nematode (56.78%). The chemical analysis of all tested materials revealed that U. lactuca had the highest amount of phenolics (10.39 mg GAE/g dry wt). This may explain the remarkable high capability of U. lactuca to control root-knot nematode infections. Also, the same alga was the best treatment and showed maximum growth when compared with other algae and the check. For instance, shoot weight of U. lactuca surpassed the other treatments, even that of non-nematizied check one, giving high increase percentage.     

Effects of diatom mucilage on the growth and Morphology of marine algae

Germination and growth patterns were studied of germlings and sporelings of eight species of marine algae when grown on diatom mucilage. Whilst growths of green and brown algae were enhanced, growth of the red algae was inhibited. Morphologically abnormal sporelings of Ulva lactuca L. and Gigartina stellata (Stackh.) Batt. were obtained in the presence of the mucilage.     

Phosphorus-31 NMR Studies of Cell Wall-Associated Calcium-Phosphates in Ulva lactuca

Phosphate concentrations in the range 0.1 to 2.0 millimolar induced the formation of extracellular amorphous calcium-phosphates in the cell wall of the marine macro algae Ulva lactuca when they were cultivated in light in seawater at 20°C. A broad resonance representing these compounds as well as resonances for extracellular orthophosphate and polyphosphates could be followed by ³¹P-nuclear magnetic resonance spectroscopy. The presence of the calcium-phosphate made the cells brittle and it inhibited the growth of the macro algae and caused mortality within 1 week. The formation of the calcium-phosphates was influenced by the external phosphate concentration, the extracellular pH and the nature and concentration of the external nitrogen source. Furthermore, no formation of these compounds was observed when Ulva lactuca was cultivated in the dark, at low temperatures (5°C) or in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea. The complex could be removed through washes with ethylenediaminetetraacetate; this treatment did not alter the intracellular pH or the orthophosphate and polyphosphate pools and it restored growth.     

Genetic analysis of the Linnaean Ulva lactuca (Ulvales,Chlorophyta) holotype and related type specimens reveals name misapplications,unexpected origins,and new synonymies

Current usage of the name Ulva lactuca, the generitype of Ulva, remains uncertain. Genetic analyses were performed on the U. lactuca Linnaean holotype, the U. fasciata epitype, the U. fenestrata holotype, the U. lobata lectotype, and the U. stipitata lectotype. The U. lactuca holotype is nearly identical in rbcL sequence to the epitype of U. fasciata, a warm temperate to tropical species, rather than the cold temperate species to which the name U. lactuca has generally been applied. We hypothesize that the holotype specimen of U. lactuca came from the Indo‐Pacific rather than northern Europe. Our analyses indicate that U. fasciata and U. lobata are heterotypic synonyms of U. lactuca. Ulva fenestrata is the earliest name for northern hemisphere, cold temperate Atlantic and Pacific species, with U. stipitata a junior synonym. DNA sequencing of type specimens provides an unequivocal method for applying names to Ulva species.     

In vitro and in vivo evaluation of the wound healing properties and safety assessment of two seaweeds (Sargassum ilicifolium and Ulva lactuca)

Seaweeds have been regarded as a reservoir of biologically active molecules that are important in the pharmaceutical industry. The aim of the present study was to explore the wound healing properties and to assess the safety of the seaweed Sargassum ilicifolium and Ulva lactuca. Enhanced cell proliferation and cell migration activities were observed in L929 cells treated with S. ilicifolium extract compared to U. lactuca extract treated cells and the control group. In-vivo experiments were conducted using five groups (10 in each) of Albino mice (BALB/c). Mice in group I and group II were treated (Orally, 100 mg/kg BW/day) with aqueous extracts of S. ilicifolium and U. lactuca, respectively for 14 days. Treatment group III received a topical application of the aqueous extract of S. ilicifolium (25% w/w) and ointment base (75% w/w) (2 g/kg BW/day, for 14 days). Group IV (Control) received an equal amount of distilled water, orally and mice in group V kept without wounds. The extract from S. ilicifolium showed stronger wound healing properties than the one from Ulva lactuca. Histopathological findings also revealed that the healing process was significantly enhanced in the mice group treated orally with S. ilicifolium aqueous extract. These findings show that S. ilicifolium species possess promising wound healing properties in-vitro and in-vivo.     

Antimicrobial activity of some macroalgae of the Veracruzano Reef System (SAV), Mexico

The study of macroalgae antimicrobial agents is limited to Mexico and scarce in the Veracruzano Reef System (SAV). It is necessary to devote efforts towards this field of applied phycology. The aim was to evaluate the antimicrobial activity of some phyla of Rhodophyta, Chlorophyta and Ochrophyta from SAV. Methanolic extracts from 23 marine macroalgae species (7 Chlorophyta, 4 Phaeophyta and 12 Rhodophyta) from the Veracruzano Reef System (SAV) (Mexico) were evaluated for antimicrobial activity. Antibacterial and antifungal activity were assessed by agar diffusion and agar dilution methods. The differences between mean values obtained for experimental groups was done by analysis of variance (ANOVA multifactorial model), p-values of 0.001 or less were considered statistically significant. Two new records are recognized for SAV (Laurencia gracilis and Sebdenia flabellata) and Compsothamnion thuioides for the Gulf of Mexico coasts. 16 species showed antibacterial activity, of which Caulerpa sertularioides, Ulva lactuca and Laurencia obtuse had significant activity on Gram-positive bacteria. 43.7% belong to the phyla Chlorophyta (7 species), 50% Rhodophyta (8 species) and 6.25% Ochrophyta (1 species). This indicates that the extracts of the algae of the Rhodophyta and Chlorophyta are the ones that showed the greatest activity. Regarding the yeasts, 16.6% of the total algae collected were active in the different yeast strains. 43.7% belongs to Chlorophyta species and for Rhodophyta were 60%. The macroalgae with the highest antifungal activity were: Cymopolia barbata, Ulva lactuca and Laurencia gracilis. The macroalgae of the Veracruzano Reef System present antimicrobial activity. This study is the first investigation of macroalgae's bioactive components from SAV, where they could be sources for future medical applications.     

Bioenergy potential of Ulva lactuca: biomass yield, methane production and combustion

The biomass production potential at temperate latitudes (56°N), and the quality of the biomass for energy production (anaerobic digestion to methane and direct combustion) were investigated for the green macroalgae, Ulva lactuca. The algae were cultivated in a land based facility demonstrating a production potential of 45 T (TS) ha⁻¹ y⁻¹. Biogas production from fresh and macerated U. lactuca yielded up to 271 ml CH₄ g⁻¹ VS, which is in the range of the methane production from cattle manure and land based energy crops, such as grass-clover. Drying of the biomass resulted in a 5-9-fold increase in weight specific methane production compared to wet biomass. Ash and alkali contents are the main challenges in the use of U. lactuca for direct combustion. Application of a bio-refinery concept could increase the economical value of the U. lactuca biomass as well as improve its suitability for production of bioenergy.     

Responses to nutrient enrichment,wave action and disturbance in rocky shore communities

A high degree of resistance against nutrient enrichment has previously been demonstrated for macroalgal-dominated rocky shore communities in the presence of moderate to large amounts of macroinvertebrate grazers. To experimentally examine, under controlled conditions, the possible roles for this resistance of two other factors, i.e. disturbance (presence/absence of the macroalgal canopy itself) and wave action, the canopy algae and associated algal and animal assemblages were removed by scraping from approximately one third of the area of eight littoral mesocosms, subjected to two different wave action regimes. After this, excessive nutrients were added to four mesocosms with the factor nutrients fully crossed with the factor wave action with two replicate mesocosm basins of each nutrient/wave treatment combination. Disturbance was added to the design as a within-basin factor thus making up a split-plot experiment. The abundance of grazers was allowed to vary freely and under the influence of the treatments. After 11 summer weeks, there were significant differences in community structure between nutrient enrichment levels for both algal and animal assemblages when examined by multivariate statistical techniques. Univariate analyses confirmed a significantly stimulated colonisation by green algae, mainly Ulva lactuca, in both disturbed (scraped) and undisturbed areas of nutrient-enriched mesocosms. In un-enriched mesocosms, the green algae were absent from undisturbed areas and rare in disturbed areas, where mainly brown Ectocarpus spp. and red algae had settled. Among the macrofauna, the total abundance of grazers was stimulated in nutrient-enriched mesocosms with individuals of the amphipod genus Gammarus and the isopod genus Jaera being especially numerous. With regard to wave action, no significant differences occurred in community structure, although there were indications of significant nutrient × wave effects for both the amount of exported red algae and the amount of accumulated brown algae. The study shows that eutrophication-related community shifts on rocky shores may occur very rapidly, regardless of the level of wave-energetic stress and the abundance of grazers, if the nutrient concentrations are high and the colonisation and growth of opportunistic algae are facilitated by disturbance such as (naturally or anthropogenically driven) canopy gap forming processes.     

Cultivation of Ulva lactuca with manure for simultaneous bioremediation and biomass production

The potential of liquid manure as sole nutrient source for cultivation of Ulva lactuca was investigated with the perspective of utilizing the produced biomass for feed and/or energy. Algae grown with manure demonstrated equal growth rates to algae grown with standard f/2-medium. The optimum manure concentration, expressed as ammonium concentration, was 25?μM. At these conditions, the biomass produced was potentially suitable for anaerobic digestion, due to a relative high carbon/nitrogen ratio (approximately 19). At higher manure concentrations, tissue concentrations of nitrogen, phosphorus, proteins, and amino acids increased, making the biomass less suitable for anaerobic digestion but potentially interesting as a feed supplement. Cultivating U. lactuca with manure as nutrient source has potential in terms of bioremediation as well as production of bioenergy and protein-feed.     

Responses to nutrient enrichment,wave action and disturbance in rocky shore communities

A high degree of resistance against nutrient enrichment has previously been demonstrated for macroalgal-dominated rocky shore communities in the presence of moderate to large amounts of macroinvertebrate grazers. To experimentally examine, under controlled conditions, the possible roles for this resistance of two other factors, i.e. disturbance (presence/absence of the macroalgal canopy itself) and wave action, the canopy algae and associated algal and animal assemblages were removed by scraping from approximately one third of the area of eight littoral mesocosms, subjected to two different wave action regimes. After this, excessive nutrients were added to four mesocosms with the factor nutrients fully crossed with the factor wave action with two replicate mesocosm basins of each nutrient/wave treatment combination. Disturbance was added to the design as a within-basin factor thus making up a split-plot experiment. The abundance of grazers was allowed to vary freely and under the influence of the treatments. After 11 summer weeks, there were significant differences in community structure between nutrient enrichment levels for both algal and animal assemblages when examined by multivariate statistical techniques. Univariate analyses confirmed a significantly stimulated colonisation by green algae, mainly Ulva lactuca, in both disturbed (scraped) and undisturbed areas of nutrient-enriched mesocosms. In un-enriched mesocosms, the green algae were absent from undisturbed areas and rare in disturbed areas, where mainly brown Ectocarpus spp. and red algae had settled. Among the macrofauna, the total abundance of grazers was stimulated in nutrient-enriched mesocosms with individuals of the amphipod genus Gammarus and the isopod genus Jaera being especially numerous. With regard to wave action, no significant differences occurred in community structure, although there were indications of significant nutrient × wave effects for both the amount of exported red algae and the amount of accumulated brown algae. The study shows that eutrophication-related community shifts on rocky shores may occur very rapidly, regardless of the level of wave-energetic stress and the abundance of grazers, if the nutrient concentrations are high and the colonisation and growth of opportunistic algae are facilitated by disturbance such as (naturally or anthropogenically driven) canopy gap forming processes.     

Potential use of green macroalgae Ulva lactuca as a feed supplement in diets on growth performance,feed utilization and body composition of the African catfish,Clarias gariepinus

This study aimed to evaluate the effects of diet containing the green macroalgae, Ulva lactuca, on the growth performance, feed utilization and body composition of African catfish Clarias gariepinus. Four experimental diets were formulated: D1 as a control group and D2, D3 and D4 which included 10%, 20% and 30% U. lactuca meal, respectively. 180 African catfish, weighing 9.59 ± 0.43 g, and with an average length of 11.26 ± 0.21, (mean ± SE) were divided into four groups corresponding to the different feeding regimes. The final body weight of the fish showed insignificant differences (P > 0.05) between the control and fish fed D2, whereas, there was a significant difference (P < 0.05) between these two diets compared with D3 and D4, with weights of 70.52, 60.92, 40.57 and 35.66 g recorded for D1, D2, D3 and D4, respectively. In the same trend significant differences were also evident in weight gain, specific growth rate and feed utilization. Fish fed with a diet containing 20% or 30% U. lactuca meal had poorer growth performance and feed utilization. Protein productive value, protein efficiency ratio, daily dry feed intake and total feed intake were also significantly lower in fish fed with D3 and D4 than in the control D1 and D2.Overall, the results of the experiment revealed that African catfish fed a diet with U. lactuca included at 20% and 30% levels showed poorer growth and feed utilization than the control group and fish fed diets containing 10% of U. lactuca.     

Partial inclusion of Ulva lactuca and Gracilaria parvispora meal in balanced diets for white leg shrimp (Litopenaeus vannamei)

The algae Ulva lactuca and Gracilaria parvispora are abundant in the Gulf of California, rich in nutrients, and may be used as a source of protein in balanced diets for shrimp. This study tests whether their meal, as a partial inclusion in diets for juvenile Litopenaeus vannamei, is feasible. Percentages of inclusion were 5, 10, and 15 %. Results showed that final weight, weight gain, and specific growth rate varied significantly among diets (P?U. lactuca (P?G. parvispora (P?>?0.05). In general, better results were obtained when using G. parvispora compared with U. lactuca. When compared to the control diet (without inclusion), diets that included 10 and 15 % U. lactuca meal yielded a significantly lower growth (P?U. lactuca 5 % meal (P?>?0.05), suggesting the feasibility of inclusion to this limited percentage. No significant differences were detected between the control and the three treatments with G. parvispora, suggesting the possibility of using higher percentages of inclusion. We conclude that both seaweeds may be used as a component in preparing feed for juvenile L. vannamei.     

Purification and characterization of cellulase from a marine Bacillus sp. H1666: A potential agent for single step saccharification of seaweed biomass

In this study, 115 marine bacterial isolates were screened for cellulase enzymatic activity and enzyme with a molecular mass of 40 kDa was purified from culture supernatant of the marine bacterium Bacillus sp. H1666 using ion exchange and size exclusion chromatography method. Growth of bacterial strain H1666 with efficient cellulase enzyme production was observed on untreated wheat straw and rice bran. The biochemical properties of the extracted cellulase were studied and enzyme was found active over a range of pH 3–9. The optimum cellulase activity was observed at pH 7 and temperature 50 °C. The enzyme was also shown to be slightly thermo-stable with 40% residual activity at 60 °C for 4 h. The potential applicability of enzyme was tested on dried green seaweed (Ulva lactuca) and 450 mg/g increase in glucose yield was obtained after saccharification. MALDI TOF–TOF analysis of cellulase peptide fingerprint showed similarity to the sequence of the glycoside hydrolase family protein.     

<Emphasis Type="Italic">Ulva lactuca</Emphasis>: A potential seaweed for tumor treatment and immune stimulation

This is the first report on the antitumor and immunostimulating activities ofUlva lactuca. Using the WSM (water-soluble fraction of a methanol extract fromUlva lactuca), a concentration of 140 g/mL was found to inhibit 50% of the human leukemia cell line U937 in growth, while splenocyte growth was stimulated up to a concentration of 100 μg/mL. In addition, NO production by a macrophage cell line (RAW 264.7) and alkaline phosphatase activity in mouse splenocytes were both stimulated with 10 μg/mL of WSM. Dose-dependent patterns were observed on all three cell-lines. Accordingly, the current results indicate thatUlva lactuca may be useful as a natural antitumor and immunostimulating agent.     

Chemical and physical-chemical characteristics of dietary fibres from Ulva lactuca (L.) Thuret and Enteromorpha compressa (L.) Grev.

Dietary fibres from Ulva lactuca (L.) Thuret (sea lettuce) and Enteromorpha compressa (L.) Grev. (A.O. nori) were measured according to a ‘standard’ method and a ‘physiological’ protocol simulating the gastric and intestinal environments. U. lactuca contained 15.8–8.0% soluble and 24.2–32.6% insoluble fibres according to the ‘standard’ and ‘physiological’ methods, respectively. For E. compressa, these values were 14.9–15.9 and 21.6–28.7%, respectively. For both algae, the composition suggests that the soluble fibres were xylorhamnoglycuronans sulphates and insoluble fibres were essentially composed of glucans. No marked chemical compositional variation was observed between soluble fractions extracted under the simulated gastric and intestinal conditions. Fibres in both algae are hydrophilic but the water holding capacities were higher after extraction of soluble fibres (5.5–9.5 g g⁻¹ for the dry algae; 14.0–16.0 g g⁻¹ for the standard insoluble fibres). Water soluble fibres demonstrated low intrinsic viscosities at 37 °C in buffers, particularly those from E. compressa (36.0–36.5 ml g⁻¹), and was affected by pH for those of U. lactuca (147.5 ml g⁻¹ at pH 3.0 and 175.0 ml g⁻¹ at pH 7.3).     

Biological activities of two macroalgae from Adriatic coast of Montenegro

In the present investigation the acetone extracts of macroalgae Ulva lactuca and Enteromorpha intestinalis were tested for antioxidant, antimicrobial and cytotoxic potential. Antioxidant activity was evaluated by measuring the scavenging capacity of tested samples on DPPH and superoxide anion radicals, reducing the power of samples and determination of total phenolic and flavonoid compounds in extracts. As a result of the study, U. lactuca extract was found to have a better free radical scavenging activity (IC₅₀ = 623.58 μg/ml) than E. intestinalis extract (IC₅₀ = 732.12 μg/ml). Moreover, the tested extracts had effective ferric reducing power and superoxide anion radical scavenging. The total content of phenol in extracts of U. lactuca and E. intestinalis was 58.15 and 40.68 μg PE/mg, while concentrations of flavonoids were 39.58 and 21.74 μg RE/mg, respectively. Furthermore, among the tested species, extracts of U. lactuca showed a better antimicrobial activity with minimum inhibitory concentration values ranging from 0.156 to 5 mg/ml, but it was relatively weak in comparison with standard antibiotics. Bacillus mycoides and Bacillus subtilis were the most susceptible to the tested extracts. Contrary to this Aspergillus flavus, Aspergillus fumigatus and Penicillium purpurescens were the most resistant. Finally, cytotoxic activity of tested extracts was evaluated on four human cancer cell lines. Extract of E. intestinalis expressed the stronger cytotoxic activity towards all tested cell lines with IC₅₀ values ranging from 74.73 to 155.39 μg/ml.     

Ethanol production from marine algal hydrolysates using Escherichia coli KO11

Algae biomass is a potential raw material for the production of biofuels and other chemicals. In this study, biomass of the marine algae, Ulva lactuca, Gelidium amansii,Laminaria japonica, and Sargassum fulvellum, was treated with acid and commercially available hydrolytic enzymes. The hydrolysates contained glucose, mannose, galactose, and mannitol, among other sugars, at different ratios. The Laminaria japonica hydrolysate contained up to 30.5% mannitol and 6.98% glucose in the hydrolysate solids. Ethanogenic recombinant Escherichia coli KO11 was able to utilize both mannitol and glucose and produced 0.4 g ethanol per g of carbohydrate when cultured in L. japonica hydrolysate supplemented with Luria-Bertani medium and hydrolytic enzymes. The strategy of acid hydrolysis followed by simultaneous enzyme treatment and inoculation with E. coli KO11 could be a viable strategy to produce ethanol from marine alga biomass.     

Seed dormancy and germination in Dodonaea viscosa (Sapindaceae) from south-western Saudi Arabia

Dodonaea viscosa (Sapindaceae) is widespread in the mountainous highlands of the southwestern part of Kingdom of Saudi Arabia, where it is a medicinally important species for the people in Saudi Arabia. Seeds of this species were collected from Mount Atharb in Al-Baha region, at an altitude of 2100 m. The aims of this study were to determine if the seeds of D. viscosa have physical dormancy (i.e. a water-impermeable seed coat) and, if so, what treatments would break dormancy, and what conditions promote germination after dormancy has been broken. The dormancy-breaking treatments included: soaking of seeds in concentrated sulfuric acid (H₂SO₄) for 10 min, immersion in boiling water for 10 min and exposure to 50 °C for 1 min. After seeds had been pre-treated with H₂SO₄, to break dormancy, they were incubated at constant temperatures from 5 to 35 °C, under 12-h photoperiods or in continuous darkness, and germination recorded. Salinity tolerance was investigated by incubating acid-scarified seeds in different concentrations of mM NaCl in the light at 25 °C.Untreated seeds had low final germination 30%. Seeds that had been acid-scarified, immersed in boiling water or exposed to 50 °C all achieved 91% subsequently when incubated at 25 °C. Thus, seeds of this species in Saudi Arabia have physical dormancy, which can be broken by all three treatments designed to increase the permeability of the testa. After pre-treatment, there was a broad optimum constant temperature for germination that ranged between 5 and 25 °C but germination was inhibited by higher temperatures (30 and 35 °C). Light had little effect on this germination response. Scarified seeds were also sensitive to salinity, with the highest germination in distilled water and complete inhibition in 400 mM NaCl. Seeds that failed to germinate in saline treatments were mostly able to germinate on transfer to distilled water, suggesting osmotic inhibition.     

The habitat and feeding preferences of Littorina obtusata (L.) and L. mariae sacchi et rastelli

The vertical zonation of the flat periwinkles Littorina obtusata (L.) and L. mariae Sacchi et Rastelli is different, but overlaps. At a sheltered location on the Isle of Cumbrae, Scotland, L. obtusata, although most abundant on Fucus vesiculosus L. and Ascophyllum nodosum (L.) Le Jol. on the midshore, ranged over the entire shore from the Pelvetia zone down to the upper limits of Laminaria. Littorina mariae exhibited a much more restricted distribution being associated predominantly with Fucus serratus L. on the lower shore. In laboratory trials with adult plants, flat periwinkles found fucoid algae both more attractive and more palatable than other seaweeds. Littorina obtusata also preferred the reproductive receptacles of fucoid algae to their vegetative tissue. Tiny germlings of a diversity of seaweeds were readily consumed by L. obtusata. In choice experiments germling Ulva lactuca L. was preferred to adult U. lactuca, whereas adult Fucus serratus was preferred to germling F. serratus. Contrasting foraging behaviours between different species of flat periwinkle are discussed in relation to differences in their radular dentition.     

Differential toxic effects of Ulva lactuca (Chlorophyta) on the herbivorous gastropods,Littorina littorea and L. obtusata (Mollusca)

Members of the genus Ulva are widespread and abundant in intertidal and shallow subtidal areas but there are conflicting data regarding susceptibility to herbivory. While some studies have documented that Ulva spp. were favored by a diversity of marine herbivores, other work has revealed herbivore deterrence. We investigated grazing and growth rates of the littorinid species, Littorina littorea and L. obtusata, when offered Fucus vesiculosus, Ascophyllum nodosum, Ulva lactuca, and Chondrus crispus, highlighting distinctive vulnerabilities to toxic effects of U. lactuca. Ulva lactuca was the preferred food of L. littorea, while L. obtusata showed no grazing on this ephemeral algal species. In contrast, F. vesiculosus was highly preferred by L. obtusata. Although L. littorea demonstrated a grazing preference for U. lactuca, growth rate of this gastropod species was nearly 3× greater when fed F. vesiculosus, suggesting a non‐lethal, negative effect of U. lactuca on L. littorea with long‐term exposure. Mortality of L. obtusata ranged from 0% to 100% when held in the presence of various Ulva densities for 1 week, and Ulva exudate depressed herbivory of this gastropod. We conclude that the water‐soluble, toxic exudate produced by U. lactuca in response to herbivory had allelochemical properties, and may contain a cleavage product (acrylic acid) of dimethylsulfoniopropionate or reactive oxygen species (i.e., H₂O₂). Observed differences in susceptibility to Ulva toxicity by the littorinid species may be related to generalist versus specialist feeding and habitat strategies.