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The stable carbon isotope composition of animal tissues represents the weighted sum of the variety of food sources eaten. If sources differ in digestibility, tissues may overrepresent intake of more digestible items and faeces may overrepresent less digestible items. We tested this idea using whole blood and faeces of goats (Capra hircus L., 1758) fed different food mixtures of [C.sub.3] lucerne (Medicago sativa L.) and [C.sub.4] grass (Themeda triandra Forssk.). Although blood and faecal δ[sup.13]C values were broadly consistent with diet, results indicate mismatch between consumer and diet isotope compositions: both materials overrepresented the [C.sub.3] (lucerne) component of diets. Lucerne had lower fibre digestibility than T. triandra, which explains the results for faeces, whereas underrepresentation of dietary [C.sub.4] in blood is consistent with low protein content of the grass hay. A diet switch experiment revealed an important difference in [sup.13]C-incorporation rates across diets, which were slower for grass than lucerne diets, and in fact equilibrium states were not reached for all diets. Although more research is needed to link digestive kinetics with isotope incorporation, these results provide evidence for nonlinear relationships between consumers and their diets, invoking concerns about the conceptual value of 'discrimination factors' as the prime currency for contemporary isotope ecology. La composition en isotopes stables de carbone dans les tissus animaux represente la somme ponderee de la variete des sources de la nourriture consommee. S'il y a des differences de digestibilite entre les sources, les tissus peuvent fournir une surrepresentation de l'ingestion des aliments plus digestibles et les feces une surrepresentation des aliments moins digestibles. Nous avons teste cet enonce par l'analyse du sang et des feces de chevres (Capra hircus L., 1758) nourries de divers melanges de luzerne (Medicago sativa L.; une plante [C.sub.3] )etd'herbes [C.sub.4] (Themeda triandra Forssk.). Bien que les valeurs de δ[sup.13]C du sang et des feces correspondent globalement au regime alimentaire, les resultats indiquent un mesappariement entre les compositions isotopiques du consommateur et de son regime alimentaire; les deux materiaux surrepresentent la composante [C.sub.3] (luzerne) du regime. La digestibilite des fibres de luzerne est plus faible que celle de T. triandra, ce qui explique les resultats obtenus avec les feces, alors que la sous-representation du [C.sub.4] alimentaire dans le sang correspond au faible contenu proteinique du foin d'herbe. Une experience de changement de regime montre une importante difference dans les taux d'incorporation de [sup.13]C entre les regimes; ceux-ci sont plus lents pour les regimes d'herbe que de luzerne et l' etat d' equilibre n' est pas atteint dans tous les regimes. Bien que des recherches additionnelles soient necessaires pour relier la cinetique de la digestion a l' incorporation des isotopes, nos resultats fournissent des preuves que les relations entre les consommateurs et leur regime alimentaire n'est pas lineaire, ce qui genere des doutes sur la valeur conceptuelle des << facteurs de discrimination >> comme outils de change couramment utilises dans l'ecologie actuelle des isotopes. [Traduit par la Redaction], Introduction Stable isotope analysis is a common approach to study animal diets and nutrient flow in food webs (Peterson and Fry 1987; Newsome et al. 2007; Crawford et al. 2008). [...]

The process of nutrient transfer through an ecosystem is an important determinant of production, food-chain length, and species diversity. The general view is that the rate and efficiency of nutrient transfer up the food chain is constrained by herbivore-specific capacity to secure N-rich compounds for survival and production. Using feeding trials with artificial food, we show, however, that physiological stress-response of grasshopper herbivores to spider predation risk alters the nature of the nutrient constraint. Grasshoppers facing predation risk had higher metabolic rates than control grasshoppers. Elevated metabolism accordingly increased requirements for dietary digestible carbohydrate-C to fuel-heightened energy demands. Moreover, digestible carbohydrate-C comprises a small fraction of total plant tissue-C content, so nutrient transfer between plants and herbivores accordingly becomes more constrained by digestible plant C than by total plant C:N. This shift in herbivore diet to meet the altered nutrient requirement increased herbivore body C:N content, the C:N content of the plant community from which grasshoppers select their diet, and grasshopper fecal C:N content. Chronic predation risk thus alters the quality of animal and plant tissue that eventually enters the detrital pool to become decomposed. Our results demonstrate that herbivore physiology causes C:N requirements and nutrient intake to become flexible, thereby providing a mechanism to explain context dependence in the nature of trophic control over nutrient transfer in ecosystems. ecological stoichiometry | metabolism | nutrient balance | physiological stress | predator-prey interaction doi/ 10.1073/pnas.1009300107

A central paradigm in the field of plant--herbivore interactions is that the diversity and complexity of secondary compounds in plants have intensified over evolutionary time, resulting in the great variety of secondary products that currently exists. Unfortunately, testing of this proposal has been very limited. We analyzed the volatile chemistry of 70 species of the tropical plant genus Bursera and used a molecular phylogeny to test whether the species' chemical diversity or complexity have escalated. The results confirm that as new species diverged over time they tended to be armed not only with more compounds/species, but also with compounds that could potentially be more difficult for herbivores to adapt to because they belong to an increasing variety of chemical pathways. Overall chemical diversity in the genus also increased, but not as fast as species diversity, possibly because of allopatric species gaining improved defense with compounds that are new locally, but already in existence elsewhere. Bursera | chemical complexity | chemical diversity | evolution of secondary compounds | coevolution doi/10.1073/pnas.0904456106

Terrestrial biodiversity is dominated by plants and the herbivores that consume them, and they are one of the major conduits of energy flow up to higher trophic levels. Here, we address the processes that have generated the spectacular diversity of flowering plants (>300,000 species) and insect herbivores (likely >1 million species). Long-standing macroevolutionary hypotheses have postulated that reciprocal evolution of adaptations and subsequent bursts of speciation have given rise to much of this biodiversity. We critically evaluate various predictions based on this coevolutionary theory. Phylogenetic reconstruction of ancestral states has revealed evidence for escalation in the potency or variety of plant lineages' chemical defenses; however, escalation of defense has been moderated by tradeoffs and alternative strategies (e.g., tolerance or defense by biotic agents). There is still surprisingly scant evidence that novel defense traits reduce herbivory and that such evolutionary novelty spurs diversification. Consistent with the coevolutionary hypothesis, there is some evidence that diversification of herbivores has lagged behind, but has nevertheless been temporally correlated with that of their host-plant clades, indicating colonization and radiation of insects on diversifying plants. However, there is still limited support for the role of host-plant shifts in insect diversification. Finally, a frontier area of research, and a general conclusion of our review, is that community ecology and the long-term evolutionary history of plant and insect diversification are inexorably intertwined. coevolution | herbivory | insect host range | phylogenetic analyses | plant defense theory doi/10.1073/pnas.0904106106

Temperature has strong, predictable effects on metabolism. Through this mechanism, environmental temperature affects individuals and populations of poikilotherms by determining rates of resource use, growth, reproduction, and mortality. Predictable variation in metabolic processes such as growth and reproduction could affect the strength of species interactions, but the community-level consequences of metabolic temperature dependence are virtually unexplored. I experimentally tested the hypothesis that plant-herbivore interaction strength increases with temperature using a common species of marine macroalga (Sargassum filipendula) and the grazing amphipod Ampithoe longimana. Increasing temperature increased per capita interaction strength in two independent experiments and reversed a positive effect of temperature on plant growth. Temperature did not alter palatability of plant tissue to herbivores or average herbivore feeding rate. A predictable effect of temperature on herbivore-plant interaction strength could provide key information toward understanding local food web responses to changing temperatures at different spatial and temporal scales. Efforts to extend the effects of physiological mechanisms to larger scale patterns, including projections of the ecological effects of climate change, must be expanded to include the effects of changing conditions on trophic interactions. Key words: algae; amphipods; Ampithoe longimana; herbivore; interaction strength; metabolic scaling; metabolic theory of ecology; photosynthesis; respiration; Sargassum filipendula; temperature.

The distance that mammalian herbivores can travel without interrupting food processing corresponds to a distance threshold (d*) in plant spacing where change occurs in the mechanisms regulating the functional response. The instantaneous rate of food consumption is controlled by food encounter rate when plant spacing exceeds d*. Below this threshold, food processing in the mouth controls instantaneous intake rate. The distance threshold provides a mechanistic definition of the scale of heterogeneity of the food resource. Recent work indicates that d* should scale positively with the body mass of mammalian herbivores. Here I evaluated the empirical evidence for this positive scaling by investigating (1) herbivores consuming only alfalfa (Medicago sativa), (2) grazers, and (3) herbivores consuming any kind of vegetation. Overall, I found greater evidence for a negative than for a positive scaling of d*. Out of the three groups, only herbivores consuming alfalfa could yield a positive covariation between d* and body mass. However, even this positive scaling became negative when herbivores consumed bites of alfalfa that were only a fraction of their maximum size. Finally, d* also scaled negatively among herbivores foraging in similar food patches. Overall, differences in foraging decisions among mammalian herbivores seem more likely to have been shaped by a negative than a positive scaling of d*. Key words: allometry; foraging mechanisms; functional response; intake rate; mammalian herbivores; plant spacing; spatial scale.

The zebraperch, Hermosilla azurea Jenkins and Evermann, a warm-temperate marine fish species with a strictly macroalgal diet, has a relatively long digestive tract with an enlarged hindgut and an associated blind caecum (HC). In zebraperch sampled off Santa Catalina Island, California (33[degrees]19'42'N; 118[degrees]18'37'W) in years 1995 through 2001, direct cell counts, gut epithelium assessment of bacterial attachment, and short-chain fatty acid (SCFA) analyses verified that the zebraperch HC possesses a dense and morphologically diverse, fermentative microbiota. Bacterial cell counts and morphological diversity were significantly higher in HC contents compared to anterior gut regions, suggesting that microbial populations were growing along the digestive tract. Similarly, electron micrographs of the HC epithelium revealed attached microbes, further supporting the possibility that these organisms constitute resident microbiota. Five different SCFAs were detected in all three regions of the digestive tract, but levels were up to three times greater in HC contents. Acetate was consistently the prevailing SCFA in all gut regions. Sequence analysis of bacterial 16S rDNA was used to identify predominant bacterial groups in HC contents. Of the seven main bacterial types identified, Enterovibrio spp. were the dominant bacteria in HC contents followed by species of Bacteroides, Faecalibacterium, and Desulfovibrio. Taken together, our findings show that the zebraperch HC harbors a consortium of microbes that appears to assist in the breakdown of algal polysaccharides in the herbivorous diet of the fish., Introduction A diverse microbiota occurs in the digestive tracts of numerous species of herbivorous fishes representing several mainly tropical families (Clements 1991; Clements and Choat 1995; Mountfort et al. 2002). [...]

Leaf herbivores potentially reduce plant fitness by increasing fruit abortion. The impact of leaf herbivory on fruit abortion, however, may vary with branch height in trees because of differential investment in reproduction among branches, differences among branches in exposure to solar radiation and the mobility, of resource movement among branches following defoliation. Here we describe spatial patterns in abundance of lepidopteran herbivores and resultant damage in the canopy of mature white oak trees, Quercus alba. The effect of foliar damage on fruit abortion for upper and lower canopy branches was also examined. A significant positive correlation occurred between foliar damage and spring herbivore abundance. Damage measured at the end of the season was unevenly distributed throughout the canopy, varying from 10-20% leaf area loss. A significant positive correlation between percent herbivore damage and percent fruit abortion also existed. Moreover, upper canopy branches had a higher percentage of fruit abortion for a given damage level than lower canopy branches, even though herbivore damage did not differ significantly with canopy height. These results suggest that early season leaf-chewing herbivores negatively affected fruit production, but the impact on fruit abortion depended upon the location of the damaged branch. Resources apparently did not move from lesser-damaged branches to more heavily damaged branches to reduce reproductive losses.

Effects of individual terpenes on alfalfa pellet intake by lambs were examined in four experiments. Forty-five lambs (nine lambs/treatment) were individually fed alfalfa pellets sprayed with either camphene, myrcene, caryophyllene oxide, or [beta]-pinene at one of five concentrations (one terpene per experiment). Treatments (0, 0.5, 1, 2, and 10x) were multiples of the concentration (x) of a specific terpene in tarbush. Terpenes were applied to alfalfa pellets (0.64 kg. [lamb.sup.-1]*[d.sup.-1], DM basis), and consumption was measured during a 20-min interval for 5 d. Lambs were maintained and fed alfalfa pellets in one group (except during 20-min tests) at a mean total daily intake of 4.7% of BW (DM basis). Camphene and caryophyllene oxide tended to decrease intake (linear contrasts were P = .0651 and P = .0504, respectively), whereas myrcene and [beta]-pinene exerted no effect on the consumption of alfalfa pellets by lambs. Camphene and caryophyllene oxide may be involved in the differential herbivory of individual tarbush plants by livestock. Key Words: Food Intake, Food Preferences, Herbivores, Sheep, Terpenoids

Many plants induce defenses against herbivores following initial attack. Maternal effects associated with herbivory could mediate induced defenses across generations of plants if damaged plants produce more resistant progeny than undamaged plants. I report that wild radish plants (Raphanus raphanistrum) damaged by herbivores (Pieris rapae) or treated with a chemical elicitor of induced resistance (jasmonic acid) during the vegetative growth stage, induced resistance of the plants' progeny compared to controls. Conversely, clipping of leaves with scissors, which results in loss of photosynthetic area but not induced resistance, tended to increase susceptibility of progeny plants to P. rapae compared to controls. Progeny plants exhibited further induced resistance when damaged as seedlings, although maternally induced plants were less inducible than maternal-control plants. Herbivory in the maternal generation also affected the growth of progeny plants in two ways: (1) seed mass, which was influenced by maternal herbivory, strongly positively correlated with early plant growth; and (2) when seed mass was accounted for, maternal herbivory still had an effect on plant growth, but these effects varied by plant family. Taken together, these results demonstrate that the defensive phenotype of plants is determined, in part, by the maternal environment, and that this allocation can affect the growth trajectories of progeny. Key words: herbivory and maternal effects; jasmonic acid; Pieris rapae; plant-insect interactions; transgenerational adaptive plasticity; wild radish (Raphanus raphanistrum).

Light availability and consumer pressure are fundamental factors that structure aquatic communities, but their integrated effects are rarely studied in marine benthic systems. Using a factorial experiment, I investigated the effects of light availability and grazing by limpets (Lottia digitalis) to determine the relative influence of each on the growth and abundance of producers and consumers in a rocky intertidal community during the winter. Light reduction via shading reduced the abundance of filamentous algae and reduced the abundance of the herbivorous periwinkle Littorina sitkana. The effects of limpet grazing reduced the abundance of filamentous algae, Porphyra spp., and diatom mats. Higher limpet densities were also associated with significantly lower densities of adult, but not juvenile, Littorina spp. Light and limpet density interacted to determine Lottia growth, which was high in unshaded, single-limpet enclosures but was negligible in plots with two limpets, shades, or both. Variation in bottom-up (resource-driven) and top-down (consumer-driven) forces are important determinants of abundance at both trophic levels, but the effects are complex, taxon-specific, and, for littorine snails, size-specific. Because the study species accomplish most of their growth and reproduction during the winter, the interplay of light and herbivory during this season will likely influence long-term community dynamics.

Hyperaccumulation of Ni by plants is hypothesized to function as an elemental defense against herbivores and pathogens. Laboratory experiments have documented toxic effects to herbivores consuming high-NJ plant tissues, but this paper reports the first experiment to examine the defensive effectiveness of Ni hyperaccumulation under field conditions. The experiment was conducted at an ultramafic soil site naturally inhabited by the Ni hyperaccumulator Streptanthus polygaloides (Brassicaceae). Experimental treatments examined the response of herbivores to hyperaccumulated Ni using exclosure and insecticide treatments to divide herbivores into groups based primarily upon herbivore size. Three soils (Ni-amended greenhouse soil, unamended greenhouse soil, ultramafic soil), three exclosure treatments (exclosure, control exclosure, no exclosure), and a systemic insecticide treatment were combined in a fractional factorial experimental design. Streptanthus polygaloides plants were grown in a greenhouse for 2 mo, transplanted into the field by inserting potted plants into holes dug on the experimental site, and periodically examined for herbivore damage during a 41-d period. Initial surveys showed greater amounts of insect damage to plants with low tissue Ni levels, confirming the defensive effect of Ni against some insect herbivores, but large herbivores (probably vertebrates) later consumed entire plants regardless of plant Ni status. We concluded that Ni was not an effective defense against these large herbivores, probably because their diets mix high-Ni S. polygaloides foliage with that of associated non-hyperaccumulating species. We suggest that such dietary dilution is one mechanism whereby some herbivores can circumvent elemental plant defenses. Key words: Brassicaceae; elemental defense; heavy metals; herbivory; Ni hyperaccumulation; plant defense; Streptanthus polygaloides.

Research has been conducted on the gut microbiota. The role of the gut microbiota in the energy metabolism of the marine herbivorous fish and the kinetics of the short-chain fatty acid production and utilization in the guts have been investigated and the results are discussed.

The effects of herbivores on plant production and fitness may not relate directly to the quantity of biomass removed because folivory may alter photosynthetic rates at a considerable distance from the damaged tissue [Welter, S. C. (1989) in Insect-Plant Interactions, ed. Bernays, E. A. (CRC, Boca Raton), pp. 135-151.]. An impediment to understanding the effects of leaf damage on photosynthesis has been an inability to map photosynthetic function within a single leaf. We developed an instrument for imaging chlorophyll fluorescence and used it to map the effects of caterpillar feeding on whole-leaf photosynthesis in wild parsnip. The adverse effects of caterpillar feeding on photosynthesis were found to extend well beyond the areas of the leaflet in which caterpillars removed tissue. These 'indirectly' affected areas remained impaired for at least 3 days after the caterpillars were removed and were six times as large as the area directly damaged by the caterpillars. Although photosynthesis in indirectly affected areas was reduced and not eliminated, these areas accounted for three times as much of the overall reduction in photosynthesis as the area removed by the caterpillars. The size of the indirect effects was positively correlated with defense-related synthesis of furanocoumarins, suggesting that costs of chemical defense may be one factor that accounts for the indirect effects of herbivory on plants.

Research has been conducted on the food preferences of the generalist herbivores for juvenile and adult brown algae tissues. Results indicate that the juvenile algae is not a preferred food for the herbivores.

Research was conducted on the genetic variation in tolerance to herbivore damage in a mixed model consisting of scarlet gilia full-sib family members. Results show that tolerance traits are influenced by herbivore-imposed natural selection and is limited by the genetic variation and selection constraints in the population.

The diets of Girella cyanea, Girella elevata and Kyphosus bigibbus were analyzed to determine the relationship between diet composition and mode of digestion in fishes. The three Girella species subsisted mostly on phaeophytes, chlorophytes and rhodophytes. Analysis of the intestines of Kyophosus species indicated the presence of short-chain fatty acids that are characteristic products of microbial fermentation. On the other hand, the short chain fatty acids were not detected in the herbivorous Girella species.

McNab (1986, 1988) has hypothesized that mammals using food with low energy content should exhibit basal metabolic rates (BMR) lower than those expected on the basis of their body mass ([m.sub.b]). That is, those species that exploit food with low energy content and/or high cost of digestion tend to have low, mass-independent metabolic rates. To date there is not an experimental test of this pattern. The aim of this work was to examine experimentally the effect of diet quality on BMR, digestive efficiency, and the relationship between digestion and energy expenditure in a small herbivorous mammal. We used as a model the herbivorous caviomorph burrowing rodent Octodon degus ([m.sub.b] nearly 200 g), an inhabitant of semi-arid and mediterranean communities of northem and central Chile. Individuals maintained during 27 wk with a diet high in dietary fiber showed significantly lower BMRs (28%) than those feeding on low fiber. Daily food intake and ingestion rates (energy and dry matter) of individuals under a high-fiber diet were significantly higher than animals maintained with a low-fiber diet. The same pattern was obtained for total feces production and rate of feces production. The total intake and rate of ingestion of proteins were not significantly different between treatments. However, a significantly higher amount of protein was excreted by the individuals exposed to a high-fiber diet. Apparent digestibility of dry matter, energy, and protein were consistently lower in individuals maintained with high fiber. However, nonsignificant differences were observed between gut contents in the two treatments (P > .58), but a significantly higher digesta turnover rate was observed in animals exposed to a high-fiber diet (P < .05). A significant correlation was found between digestibility and the basal metabolic rate of individuals ([r.sub.s] = 0.781, P < .01), suggesting that elevated digestibilities on high-quality diets allow increased basal rates of metabolism. We suggest that, although small mammals like degus may select sparsely distributed plants of high quality in their habitat, their capability to drop their metabolic demands may help them meet their nutritional and energy requirements when nutritional conditions in the environment deteriorate.

Herbivorous insects are responsible for a portion of foliar litterfall in forest ecosystems. There is little information on the nutrient content of this litterfall despite speculation that herbivores regulate nutrient cycles. We quantified herbivore-caused 'greenfall' (green leaves falling as a direct result of herbivore feeding activity) in four Appalachian watersheds and analyzed samples for total nitrogen. Concentrations of nitrogen in greenfall fluctuated significantly from May through September and were always higher than concentrations of nitrogen in autumn senesced leaves. Annual inputs of greenfall nitrogen ranged from 0.08-0.18 g centered dot m to the -2 centered dot yr to the -1 and resulted in 3.2% to 6.5% of total nitrogen transferred to the forest floor in autumn foliar litterfall. Greenfall is viewed as a high-quality substrate supplying nitrogen to decomposer organisms and is thus a potential mechanism by which herbivorous insects speed nutrient cycling.

The phenology and demographics of the opisthobranch Placida dendritica, a specialist herbivore found in marine intertidal regions, were examined. The study was conducted from1984-89 in several sites along the central coast of Oregon. P. dendritica fed mainly on the green algae Codium setchellii, C. fragile and Bryopsis corticulans. Newly metamorphosed individuals were rapidly recruited in wave-protected areas, and sexual maturity is attained one month after larval settlement. Efficient, continous larval settlement and adult movement allows persistent colonization of algal hosts.

The idea that plant polyphenols act as digestibility-reducing compounds is well entrenched. This hypothesis has recently been countered with the proposal that the presence of surfactants in the gu fluids of herbivores may preclude the digestibility-reducing effects of plant polyphenols. We examined three marine isopods, three limpets, and a rock lobster, and established that surfactant are present in the digestive fluids of all of these organisms. However, further determinations of the efficacy with which these surfactants can prevent the complexation of proteins by brown-algal polyphenols in vitro revealed substantial differences between species. Moreover, in cases where the surfactants were ineffective, polyphenols reduced in vitro digestibility in a dose-dependent manner. We therefore conclude that the presence of gut surfactants does not necessarily preclude protein precipitation by polyphenols in vivo. Thus polyphenols might still be regarded as digestability-reducing compounds, since gut surfactants only counter these effects in some cases. Key words: brown algae; chemical defenses; digestibility-reducing; gut surfactants; herbivory; polyphenols.

The existence of elevated metabolic loads associated with the detoxification of plant allelochemicals has been proposed to be an important selective force in the evolution of dietary specialization of herbivorous insects. In this study we have examined the effects of one host plant toxin (nicotine) and three nonhost plant toxins (xanthotoxin, precocene II, and canavanine) on the growth and energy metabolism of the tobacco hornworm, Manduca sexta (Lepidoptera: Sphingidae). Although M. sexta has three mechanisms for reducing the toxic effects of nicotine, nicotine has a dose-dependent growth-inhibiting effect on third-instar larvae at dietary concentrations ranging from 0.25 to 8.0%. Thus, herbivory by adapted species, as well as nonadapted species, can potentially select for higher levels of defensive chemicals in plants. At higher concentrations, where the effects of nicotine are most pronounced, growth reduction is associated with reduced consumption (which reduces the amount of food assimilated) and an increase in the duration of the instar (which increases the amount of the assimilate pool that must be allocated to maintenance metabolism, thus leaving less assimilate for allocation to growth. The respiration rates of larvae on diets containing up to 1% nicotine are the same as the respiration rates of larvae on nicotine-free diets, while the respiration rates of larvae on diets containing 4 to 8% nicotine are lower than those of larvae on the nicotine-free diet. Thus, the processing of nicotine does not pose a significant metabolic cost on M. sexta larvae, and it is invalid to infer increased metabolic costs of detoxification from the observation of concomitant decreases in growth rate (GR or RGR) and the efficiency of conversion of digested food (ECD) of larvae on toxin-containing diets. In a manner similar to nicotine, the growth-reducing effects of the nonhost plant toxins (xanthotoxin, precocene II, and canavanine) can be explained on the basis of their effects on consumption and the duration of the third instar. In no case is growth reduction a consequence of an increase in metabolic rate. Instead, reductions in growth result from the diversion of assimilate from growth to energy metabolism mandated by a longer instar, and from decreases in the size of the assimilate pool resulting from decreases in consumption and/or assimilation. Thus, the effects of allelochemicals on the energy budget of M. sexta result from their activity as metabolic toxins and feeding deterrents reducing rates of growth and consumption, and not from their diversion of energy from growth to allelochemical processing. We conclude that (1) the processing of host plant allelochemicals does not impose a significant energy demand on Manduca sexta and (2) the energy costs of allelochemical processing are unlikely either to constrain the expansion or to drive the contraction of the host plant range of M. sexta. Therefore, we suggest that the concept of metabolic load is not a useful one in understanding the effects of plant allelochemicals on the growth and efficiency of food utilization or in explaining the evolution of dietary specialization of lepidopteran herbivores. Key words: detoxification; herbivory; host plant specialization; host plant toxins; Lepidoptera; Manduca sexta; metabolic cost; metabolic load; plant-insect interactions.

We compared sodium and potassium content of plants with the dietary levels of low sodium and high potassium that stimulate hypertrophy of the zona glomerulosa of the adrenal gland of Microtus pennsylvanicus. The zona glomerulosa typically enlarges in animals subjected to severe sodium shortage or potassium overload. Among voles maintained on several low sodium diets, the relative size of the zona glomerulosa was elevated significantly only on the lowest sodium diet (0.00043 mol/kg or 10 ppm.) This level of sodium is extremely low for plant sodium contents in nature. Dietary potassium levels [is greater than or equal to]0.614 mol/kg or 24,000 ppm induced significant increases in size of zona glomerulosa; few plant species we analyzed had potassium levels below these early in the growing season. From our results, we suggest that potassium excess may play a more central role than sodium deficiency in the seasonal mineral-balance dynamics of this herbivore species.

Populations of feral donkeys, Equus asinus, in northern Australia are limited by density-dependent mortality during the first 6 mo of individuals' lives. A female's ability to raise her offspring successfully increases with age and is dependent on her maintaining high levels of stored mineral nutrients (calcium, phosphorus, and sodium). A low proportion of offspring was successfully raised in a population at carrying capacity where females had low levels of stored mineral nutrients. Females in a growing population that had been reduced to 45% of carrying capacity had high levels of stored minerals and successfully raised a higher proportion of offspring. Females in the population at carrying capacity ingested a species-poor diet (predominantly a grass, Sehima nervosa) containing low levels of nitrogen and mineral nutrients, and high levels of crude fibre. Females in the growing population ingested a more species-rich diet with higher levels of nitrogen and minerals, and less crude fibre. Levels of calcium, phosphorus, and potassium in the faeces of females in the population at carrying capacity were higher than those in the food ingested. The reverse was true for females in the growing population. At the time of sampling (early dry season), 17% of females in the population at carrying capacity and 0% of females in the growing population were eating or had recently eaten clay. Increased salivary secretion and gastrointestinal irritation caused by high-fibre diets (even when lubricated by clay) may be responsible for mineral depletion of females at carrying capacity, and hence population limitation through the inability of females to raise offspring.

We document through correlative and experimental analyses sex-biased herbivory in the arroyo willow, Salix lasiolepis. Male willows typically support higher densities of five species of tenthredinid sawflies than do female willows. Significant intersexual variation in sawfly densities exists in naturally occurring willow clones and in clones grown in a common garden. Arroyo willow is sexually dimorphic in leafing phenology and in aspects of leaf chemistry. Male willows have significantly longer vegetative shoots than do females at the time of sawfly oviposition (P = .01). Males also have significantly higher foliar concentrations of nitrogen, phosphorus, and potassium than do females. Female willows have a marginally significant (P = .093) higher concentration of total phenols. Of the dimorphic traits, only variation in leaf phenology is a consistent predictor of variation in sawfly densities among willow clones.

The multicuspid molariform teeth in crocodyliform fossils dating from the Lower Cretaceous in China show that the structure of the teeth is similar to that of postcanine teeth of tritylodontid synapsids, having back-to-front motion during jaw closing. Certain features indicate its close relation to the Notosuchidae from the Cretaceous of Gondwana. This new crocodyliform appears to have been herbivorous.

A study examines the effect of plant chemical iridoid glycoside (IG) content variations in a generalist aposematic herbivore Parasemia plantaginis on its warning signal expression. Results indicate that the level of IG content obtained from the diet of its larvae and adults does not affect larval coloration, but causes differences in reproductive output and warning signal of females through coloration variations in their wings.

Analyses of countrywide insect-host catalogs, field studies of local herbivore communities and comparative studies at different spatial scales are presented. Methods of community phylogenetic analysis, complex networks, spatial and among-host diversity partitioning, and metacommunity models present approaches for future work.

A discussion on several behavioral and physiological offenses used by herbivorous terrestrial vertebrates is presented. New avenues for research in the area of plant-animal interactions in the future include genomic and standardized functional assays.

Research has been conducted on annual plant Arabidopsis thaliana. The authors have investigated the joint evolution of tolerance and resistance to rabbit herbivory in A. thaliana, and they suggest that tolerance and resistance to rabbit herbivory are related to the difference in size, architectural and phenological traits.

Microorganisms can alter the direction and magnitude of plant-herbivore interactions. However, how they affect the susceptibility of the host plant and their impact on the herbivore may vary depending on the scale of the interaction such as among locations, individual plants, and parts of the plant. Positive preference-performance relationships for insects in general, and for sedentary insects such as leafminers in particular, would predict that there would be negative selection pressure against females ovipositing in low-performance sites. Thus, where the presence of microorganisms causes reduced performance, selection would favor oviposition in sites where the microbes are absent. However, this assumes that ovipositing females can detect the microbes and respond by avoidance, or that females can use cues that predict the future presence of microbes and use these predictors to respond by avoidance. We used the Cameraria sp. leafminer-Quercus emoryi system and the associated fungal endophyte species that share the leaves of the host to test the hypothesis that leafminer ovipositional preference and therefore distribution are negatively associated with endophyte distribution at scales where endophytes mediate insect antagonism and where endophyte distribution is predictable. We censused fungal endophyte distribution and abundance on [is greater than] 20 trees over three growing seasons at the following scales: among trees, among positions within trees, among leaves, and between and within seasons. In addition, we censused leafminer distribution and abundance and used data on leafminer distributions at different spatial scales collected over the past decade from other studies in this system to determine how they are associated with endophytes. We found that leafminers and fungal endophytes were negatively associated at two spatial scales where endophytes have been shown to affect leafminer performance negatively and where endophyte distribution and abundance were predictable. Endophytes and leafminers were not associated at one spatial scale where endophytes do not affect leafminers, and distribution and abundance was not predictable. Leafminer growth and endophyte infection were positively associated over time as both increase over the season. The results demonstrate that leafminer ovipositional preference may have been selected by avoidance of fungal endophytes and associated endophyte-mediated antagonism, but that avoidance is reliant on predictable patterns of infection. Key words: Arizona; Cameraria sp.; fungal endophytes; leafminers; oviposition; preference-performance; Quercus emoryi; scale.

Animals of a wide range of orders or classes have a portion of their digestive system adapted to accommodate a fermentation, which assists in digestion as well as providing a variety of other benefits. Because of the refractory nature of the plant cell wall and the difficulty in digesting it, herbivores have anatomical and physiological adaptations of the digestive tract to allow assimilation of this material. Herbivorous reptiles, birds, and mammals usually have enlarged or elongated digestive tracts, often including fermentation chambers or sacs in the foregut and hindgut. Cecum-colon (hindgut) fermentors represent an older differentiation than foregut fermentors which, in turn, are older than ruminants. Advances in our understanding of fermentative digestion have tended to obscure the vital role that the gastrointestinal microbiota plays in the normal physiological, immunological and protective functions of the host animal. The association of microbes with tissues of the gastrointestinal tract of animals during evolution has resulted in a balanced relationship between resident microbes and the host. In fact, all animals including humans are adapted to life in a microbial world. Numerous biochemical, physiological and immunological features that are considered intrinsic characteristics of animal species are actually responses by the animal to the physical presence and metabolic activities of the normal indigenous microbiota. This microbial challenge has modified the course of evolution in animals resulting in the selection of animal-microbe relationships which are complex and which vary tremendously ranging from competition to cooperation. Its high population density, wide diversity and complexity of interactions characterize the gastrointestinal microbial community.

There has been much discussion and some controversy regarding the role of nutrient enrichment versus other factors, such as altered rates of herbivory, in the degradation of coral reef ecosystems. The resolution of this controversy has been hampered by the lack of manipulative field studies testing the effects of ecologically relevant levels of nutrient enrichment on coral reef communities. We present a new method for adding ecologically relevant levels of nutrients to experimental substrates on coral reefs. The method elevates nutrients for sustained periods of time ([is greater than] 41 d without replenishment of nutrients) and allows for testing interactions of nutrients and altered levels of herbivory. Results from an offshore reef in Key Largo, Florida, show strong effects of excluding large herbivorous fishes, negligible effects of nutrient enrichment--or effects that are opposite of predictions, and no interaction between nutrient levels and herbivory in affecting algal abundance. Patterns observed for this reef did not confirm predictions of previously proposed models that frondose macroalgal or crustose algal abundance would be enhanced with nutrient enrichment or that dominance of filamentous turfs would be greater in unenriched conditions. In contrast to previous predictions, the abundance of larger macroalgae at this site was not increased by elevating nutrients above predicted threshold response levels of 1.0 [micro]M for total inorganic nitrogen or 0.10 [micro]M for soluble reactive phosphate. Also conflicting with some models, filamentous, nitrogen-fixing cyanobacteria were enhanced, rather than suppressed, by nutrient enrichment.

Many emydid species, such as Trachemys scripta, undergo an ontogenetic shift from carnivory in juveniles to herbivory in adults. Chelydrid species, such as Chelydra serpentina, are carnivorous throughout life. The sensitivity of growth rate to increased levels of dietary protein may be influenced by the difference in lifetime protein intake between these two foraging ecologies. Hatchling T. scripta and C. serpentina were raised for twelve weeks on diets of various protein concentrations to determine the optimal level for growth in each species. Housing in T. scripta was also manipulated to determine the effect of social interaction on growth rate. At week ten, the diets tested had a significant effect on growth in C. serpentina. Neither diet nor social interaction had a significant effect on growth rate in T. scripta. C. serpentina growth was sensitive to increases in dietary protein above the optimal level for T. scripta. The preliminary results suggest that the life-long carnivore has the physiological capacity to assimilate higher levels of dietary protein than the animal with an ontogenetic shift from carnivory to herbivory.

Marine herbivores survive and grow on low quality, often chemically or structurally defended food in which the nutrients are locked inside relatively indigestible cell walls. Questions arise: What does it take to be a herbivore? What are their morphological, physiological and biochemical specializations for processing plant and algal material? Deeper understanding at all steps of the digestive process and at different levels of organization is required to answer these questions. For fishes, structural and kinematic studies of the pharyngeal jaws will help show how cell walls are disrupted, and how mucus-mediated absorption may occur in some herbivores. Use of tracer molecules to examine algal cell porosity in a low pH environment ought to reveal the role of acid lysis in digestion. Enzyme- and immuno-histochemistry will allow precise localization of enzyme activity, and in situ hybridization holds promise for localizing gene expression sites of digestive enzymes. Identification of biochemical pathways involving microbial fermentation of various polysaccharides should reveal vital information about digestive processes, energy sources and neutralization of secondary metabolites in many marine herbivores.

Furanocoumarins are plant secondary compounds toxic or deterrent to a number of herbivores. The parsnip webworm, Depressaria pastinacella (Lepidoptera: Oecophoridae), however, feeds only on three genera of Umbelliferae, all of which contain furanocoumarins. The purpose of this study was to determine the tolerance of D. pastinacella to furanocoumarins occurring in its hosts, and to evaluate the adaptive significance of polysubstrate mono-oxygenases (PSMOs) in enabling this specialist to feed on plants chemically inaccessible to most other herbivores. The D. pastinacella larvae were offspring of adults collected as pupae on parsnips in the wild. The larvae were reared to pupation on a semidefined artificial diet with and without the furanocoumarins xanthotoxin and angelicin, under conditions of UV light appropriate to photoactivate xanthotoxin. Bioassays were performed on pupal mass for xanthotoxin and angelicin, and tested using one-way and two-way ANOVAs, respectively. No effect on larval growth and survivorship by xanthotoxin, a linear furanocoumarin toxic to polyphagous herbivores, was detected. PSMOs in the microsomal fraction of the midgut possess a high specific activity for this furanocoumarin. The importance of these enzymes in the detoxification of xanthotoxin was further suggested by the observation that xanthotoxin induces microsomal enzymes that in turn metabolize this allelochemical. Enzymatic adaptation to xanthotoxin allows D. pastinacella to feed on plants unavailable to many generalist herbivores. Moreover, no effect of angelicin, an angular furanocoumarin, was found on parsnip webworm growth. Angelicin is toxic to at least one other herbivore adapted to feeding on xanthotoxin. Although the mechanism of the parsnip webworm's adaptation to angelicin was not determined, the ability to tolerate this compound further suggests that D. pastinacella is a specialist on furanocoumarin-containing hosts.

Plants can vary substantially among species in morphological and physiological traits that influence their resistance to herbivores and their quality for herbivore growth and development. Seeds of the desert trees Cercidium floridum and C. microphyllum vary within and among populations in their resistance to, and suitability for, growth and development of larvae of the seed beetle, Stator limbatus. We examined how this variation influences the magnitude of natural selection on the size of eggs laid by beetles and tested whether female beetles can distinguish between seeds of more vs. less suitable trees (within species). We found that selection favoring large eggs differed substantially between the two tree species (greater on C. floridum) and varied substantially among populations of C. floridum and among trees (within populations) of both C. floridum and C. microphyllum. In general, the magnitude of selection favoring large eggs correlated positively with seed coat resistance between tree species, among populations within species, and among trees within populations. Female S. limbatus are capable Of distinguishing seeds of the two host species and respond to species differences in selection by laying larger eggs on seeds of C. floridum than on seeds of C. microphyllum. However, despite large variation in seed suitability within populations of trees, females did not preferentially lay eggs on seeds of less resistant trees, nor did they adjust egg size in response to variation in resistance among trees. Key words: body-size; Cercidium; development time; egg-size; natural selection; oviposition preference; paloverde; selection intensity; Stator limbatus; survivorship.