Effects of group size and personality on social foraging: the distribution of sheep across patches

Group cohesion in social animals foraging in patchy environmentsdepends on 2 opposite forces, intraspecific competition, andattraction. The decision to leave or stay in a group may varyaccording to the individual personality. We investigated therole of personality when feeding competition increases as aresult of increasing group size. Individuals referred as "bold"and "shy" were identified from an indoor exploration test accordingto their propensity to leave the group to explore a novel environment,using 12 novel objects placed at increasing distances from thegroup. Groups of 2, 4, 6, or 8 shy or bold sheep were testedin 45 x 5–m grass arenas, with one 5 x 5–m patchof preferred vegetation at each end. Sheep grazed on or closeto these patches, but the number grazing the patches seldomreached more than 4–5 individuals, suggesting that crowdingmight affect foraging at the highest densities. The smallestgroups grazed together on the same patch, but there was an increasinglikelihood of splitting into subgroups as group size increased,with equal-sized subgroups most commonly grazing the 2 patchessimultaneously. This effect was greatest in bold sheep, whichtended to split into subgroups at smaller group sizes than shysheep. This study provides new insight into the mechanisms bywhich group-living herbivores distribute themselves across patchyresources in a way that minimizes interference competition anddemonstrates the importance of individual variability for spatialorganization at the level of the group.     

Behavior, Diet, and Movements of the Sulawesi Crested Black Macaque (Macaca nigra)

We present the first field study of activity budgets, diet and ranging patterns of the Sulawesi crested black macaque, Macaca nigra, one of seven macaque species endemic to Sulawesi, Indonesia. We studied three crested macaque groups, ranging in size from 50 to 97 individuals, for 18 months in the Tangkoko-DuaSudara Nature Reserve, North Sulawesi. They spent 59% of the day moving and procuring food, especially fruits, and 41% of the day resting and socializing. Their diet is composed of more than 145 species of fruit (66% of observed feeding bouts), vegetative material (2.5%), invertebrates (31.5%), and occasional vertebrate prey. Group differences were more pronounced than seasonal or diurnal differences. Specifically, the largest group moved farther during the day, moved at a faster and more uniform rate, ate less fruit, rested more, and socialized less than the smaller groups did. The largest group had the largest home range, but it included less primary forest and more disturbed habitat than the ranges of smaller groups. There are individual differences in activity budgets of adult males and females in time spent moving, resting, feeding, and socializing that may reflect differences in reproductive strategies of males versus females. The behavior of large juveniles is more similar to that of adults than to that of small juveniles. Daily movements and use of home range are correlated with diet. Macaques moved shorter distances as the proportion of time spent feeding on fruit increased, and the top four dietary items accounted for most of the variance in entry into hectare blocks of home range.     

Whole genome comparison of six Crocosphaera watsonii strains with differing phenotypes

Crocosphaera watsonii, a unicellular nitrogen‐fixing cyanobacterium found in oligotrophic oceans, is important in marine carbon and nitrogen cycles. Isolates of C. watsonii can be separated into at least two phenotypes with environmentally important differences, indicating possibly distinct ecological roles and niches. To better understand the evolutionary history and variation in metabolic capabilities among strains and phenotypes, this study compared the genomes of six C. watsonii strains, three from each phenotypic group, which had been isolated over several decades from multiple ocean basins. While a substantial portion of each genome was nearly identical to sequences in the other strains, a few regions were identified as specific to each strain and phenotype, some of which help explain observed phenotypic features. Overall, the small‐cell type strains had smaller genomes and a relative loss of genetic capabilities, while the large‐cell type strains were characterized by larger genomes, some genetic redundancy, and potentially increased adaptations to iron and phosphorus limitation. As such, strains with shared phenotypes were evolutionarily more closely related than those with the opposite phenotype, regardless of isolation location or date. Unexpectedly, the genome of the type‐strain for the species, C. watsonii WH8501, was quite unusual even among strains with a shared phenotype, indicating it may not be an ideal representative of the species. The genome sequences and analyses reported in this study will be important for future investigations of the proposed differences in adaptation of the two phenotypes to nutrient limitation, and to identify phenotype‐specific distributions in natural Crocosphaera populations.     

Regression Trees for Survival Data — an Approach to Select Discontinuous Split Points by Rank Statistics

Regression trees allow to search for meaningful explanatory variables that have a non linear impact on the dependent variable. Often they are used when there are many covariates and one does not want to restrict attention to only few of them. To grow a tree at each stage one has to select a cut point for splitting a group into two subgroups. The basis for this are the maxima of the test statistics related to the possible splits due to every covariate. They or the resulting P-values are compared as measure of importance. If covariates have different numbers of missing values, ties, or even different measurement scales the covariates lead to different numbers of tests. Those with a higher number of tests have a greater chance to achieve a smaller P-value if they are not adjusted. This can lead to erroneous splits even if the P-values are looked at informally. There is some theoretical work by Miller and Siegmund (1982) and Lausen and Schumacher (1992) to give an adjustment rule. But the asymptotic is based on a continuum of split points and may not lead to a fair splitting rule when applied to smaller data sets or to covariates with only few different values. Here we develop an approach that allows determination of P-values for any number of splits. The only approximation that is used is the normal approximation of the test statistics. The starting point for this investigation has been a prospective study on the development of AIDS. This is presented here as the main application.     

Characterization of two morphological groups of isolates ofPythium ultimum var.ultimum in a vegetable field

Comparisons were made between two morphological groups ofPythium ultimum var.ultimum strains isolated in a vegetable field in Japan. The groups were distinguished as having smaller or larger sexual organs by the sizes of their antheridia and oogonia. Morphological study indicated that the two groups comprised a single taxon,P. ultimum var.ultimum, by the current taxonomical keys. The smaller group grew faster in the lower temperature range of 4–15°C, whereas the larger group grew faster in the higher temperature range of 25–37°C. Random amplified polymorphic DNA (RAPD) and isozyme analyses revealed genetic dissimilarity between the two groups. Cluster analysis of the isozyme banding patterns with four otherPythium spp. demonstrated that the genetic dissimilarity between the two groups was equivalent to species level. In the field survey, the smaller group was frequently detected in February, May and September but not in July, while the larger group was detected mainly in July and September. The two groups were not distinguishable by their pathogenicity to spinach seedlings.     

Effects of Joint Space Use and Group Membership on Contact Rates Among White-Tailed Deer

Abstract: Establishment and spread of infectious diseases are controlled by the frequency of contacts among hosts. Although managers can estimate transmission coefficients from the relationship between disease prevalence and age or time, they may wish to quantify or compare contact rates before a disease is established or while it is at very low prevalence. Our objectives were to quantify direct and indirect contacts rates among white-tailed deer (Odocoileus virginianus) and to compare these measures of contact rate with simpler measures of joint space use. We deployed Global Positioning System (GPS) collars on 23 deer near Carbondale, Illinois, USA, from 2002 to 2005. We used location data from the GPS collars to measure pairwise rates of direct and indirect contact, based on a range of proximity criteria and time lags, as well as volume of intersection (VI) of kernel utilization distributions. We analyzed contact rates at a given distance criterion and time lag using mixed-model logistic regression. Direct contact rates increased with increasing VI and were higher in autumn—spring than in summer. After accounting for VI, the estimated odds of direct contact during autumn—spring periods were 5.0–22.1-fold greater (depending on the proximity criterion) for pairs of deer in the same social group than for between-group pairs, but for direct contacts during summer the within:between-group odds ratio did not differ significantly from 1. Indirect contact rates also increased with VI, but the effects of both season and pair-type were much smaller than for direct contacts and differed little as the time lag increased from 1–30 days. These results indicate that simple measures of joint space use are insufficient indices of direct contact because group membership can substantially increase contacts at a given level of joint space use. With indirect transmission, however, group membership had a much smaller influence after accounting for VI. Relationships between contact rates and season, VI, and pair-type were generally robust to changes in the proximity criterion defining a contact, and patterns of indirect contacts were affected little by the choice of time lag from 1–30 days. The use of GPS collars provides a framework for testing hypotheses about the form of contact networks among large mammals and comparing potential direct and indirect contact rates across gradients of ecological factors, such as population density or landscape configuration.     

A computer simulation study on the number of loci and trees required to estimate genetic variability in cacao (Theobroma cacao L.)

Current methods for measures of genetic diversity of populations and germplasm collections are often based on statistics calculated from molecular markers. The objective of this study was to investigate the precision and accuracy of the most common estimators of genetic variability and population structure, as calculated from simple sequence repeat (SSR) marker data from cacao (Theobroma cacao L.). Computer simulated genomes of replicate populations were generated from initial allele frequencies estimated using SSR data from cacao accessions in a collection. The simulated genomes consisted of ten linkage groups of 100 cM in length each. Heterozygosity, gene diversity and the F statistics were studied as a function of number of loci and trees sampled. The results showed that relatively small random samples of trees were needed to achieve consistency in the observed estimations. In contrast, very large random samples of loci per linkage group were required to enable reliable inferences on the whole genome. Precision of estimates was increased by more than 50% with an increase in sample size from one to five loci per linkage group or 50 per genome, and up to 70% with ten loci per linkage group, or equivalently, 100 loci per genome. The use of fewer, highly polymorphic loci to analyze genetic variability led to estimates with substantially smaller variance but with an upward bias. Nevertheless, the relative differences of estimates among populations were generally consistent for the different levels of polymorphism considered.     

Metabolism of Serine in Growing Rats and Chicks at Various Dietary Protein Levels

The metabolic fate of the carbon skeleton of l-serine-U-¹⁴C has been investigated, in vivo and in vitro, in growing rats and chicks fed the diets with various protein calories percents (PC%) at 410 kcal of metabolizable energy.

The incorporation of ¹⁴C into body protein at 12 hr after the injection of serine-¹⁴C was about 49% of the injected dose in rats fed the 10 or 15 PC % diet, though the value was reduced in rats fed lower and higher protein diets. The ¹⁴CO₂ production was smaller in rats fed the 10 and 15 PC% diet, and it showed an inverse pattern to that of the ¹⁴C incorporation into body protein. Urinary excretion of ¹⁴C was higher in rats fed 10 and higher PC% diets, whose growth rate and net body protein retention were maximum.

In contrast to the case of rats, the incorporation of ¹⁴C into body protein of chicks at 6 hr after the injection was rather reduced in the 15 PC% group. The proportion of ¹⁴C excreted as uric acid was remarkably increased above the 10 PC% group, and about 19% of the injected dose was recovered in the 50 PC% group.

The catabolic rate of serine in the liver slices of rats and chicks was increased by high protein diets.

These results support the concept that the nutritional significance of metabolism of the carbon skeleton of serine in growing rats and chicks is different from each other, especially at high protein diets.     

Studies on the Critical Micellar Concentration and Phase Transitions of Stearoylcarnitine

The critical micellar concentration (CMC) of stearoylcarnitine was determined at different pH values at room temperature by fluorescence spectroscopy, monitoring the spectral changes of 8-anilinonaphthalene-1-sulfonate (ANS). The CMC was found to vary with pH, increasing from about 10 μM at pH 3.0 to ca. 25 μM at pH 7.0, but decreasing slightly with further increase in pH to approximately 19 μM at pH 10.0. Differential scanning calorimetry (DSC) shows that stearoylcarnitine dispersed in water at low concentration undergoes a broad thermotropic phase transition at 44.5°C, with a transition enthalpy of 15.0 kcal/mol. The transition temperature (T _t) shifts to ca. 50.5°C in the presence of 1 mM EDTA or when the concentration is increased significantly. The turbidity of aqueous dispersions of stearoylcarnitine was found to be considerably high at low temperatures, which decreases quite abruptly over a short temperature range, indicating that a transition occurs from a phase of large aggregates to one of much smaller aggregates, most likely micelles. The phase transition temperature was determined as 29.1°C at pH 3.0, which increased with increasing pH up to a value of 55.3°C at pH 8.6 and remains nearly constant thereafter up to pH 11.2. The pH dependence of CMC and T _t suggest that the pK _a of the carboxyl group of long chain acylcarnitines shifts to higher temperatures upon aggregation (micelles or bilayer membranes).     

Phytosociological and geographical survey of Mesohromion communities in Western Europe

A survey is given of the floristic composition and geographical distribution of limestone grasslands assigned to the Mesobromion ereeti, in Western Europe.This survey is based upon 800 vegetation relevés from various investigators throughout the area. Relevant tables have been summarized into a synoptic table with 30 columns. Each column represents a community described as an association or a subassociation.The synoptic table shows a division into a NW European group (Ireland, England, Denmark, and South Sweden) and a Central-W European group (Germany, The Netherlands, Belgium, France, and Switzerland). Associations belonging to the former have, as a rule, a smaller distribution area than the latter.In the latter group only two associations can be distinguished: Mesobrometum erecti and Antherico-Brometum ass. nov. The Mesobrometum is widespread and includes many subassociations. The Antherico-Brometum shows a transition towards the Xerobromion erecti.According to Barkman et al., (1976) the often used name Gentiano-Koelerietum has to be seen as a not-correct synonym for the Mesobrometum erecti.The Mesobromion grasslands can, in general, not be divided based upon their agricultural management system.An attempt is made to interpret the gradual transition in floristic composition of the limestone grasslands from NW to SE, with climatological data.Plant nomenclature follows Heukels & Van Ooststroom (1975) or, else, Clapham et al. (1968) for phanerogams and Vander Wijk et al. (1969) for bryophytes.I am much indebted to Prof. Dr. J. J. Barkman, who encouraged me to tackle the present study and stimulated me throughout its duration.     

Changes in group size and composition of the blue monkeys (Cercopithecus mitis stuhlmanni) between 1984 and 2009 at Ngogo,Kibale National Park,Uganda

Group counts were conducted on five groups of blue monkeys at the Ngogo study site, Kibale National Park, Uganda between January and June 2009. Group sizes were compared with those obtained using similar methods at the same site during 1983‐84 by Tom Butynski. During the present study, group size ranged from 16 to 28 monkeys. The results show that the group size of blue monkeys (Cercopithecus mitis stuhlmanni) has increased significantly between 1984 and 2009. Mean group size has increased over two‐fold from 9 after the fission of group 33 during Butynski s study to 21.6 animals per group in 2009. These results strongly suggest that the density of blue monkeys at Ngogo has increased although census data indicate that group density has remained more or less the same.     

The effect of brain size evolution on feeding propensity,digestive efficiency,and juvenile growth

One key hypothesis in the study of brain size evolution is the expensive tissue hypothesis; the idea that increased investment into the brain should be compensated by decreased investment into other costly organs, for instance the gut. Although the hypothesis is supported by both comparative and experimental evidence, little is known about the potential changes in energetic requirements or digestive traits following such evolutionary shifts in brain and gut size. Organisms may meet the greater metabolic requirements of larger brains despite smaller guts via increased food intake or better digestion. But increased investment in the brain may also hamper somatic growth. To test these hypotheses we here used guppy (Poecilia reticulata) brain size selection lines with a pronounced negative association between brain and gut size and investigated feeding propensity, digestive efficiency (DE), and juvenile growth rate. We did not find any difference in feeding propensity or DE between large‐ and small‐brained individuals. Instead, we found that large‐brained females had slower growth during the first 10 weeks after birth. Our study provides experimental support that investment into larger brains at the expense of gut tissue carries costs that are not necessarily compensated by a more efficient digestive system.     

Myonuclear apoptosis occurs during early posthatch starvation

Apoptosis is a naturally occurring process; it is important for the final shape and size of developing tissues, and it is characterized by some morphological features such as plasma membrane blebbing, nuclear breakdown, chromosomal fragmentation and apoptotic bodies followed by phagocytosis. The objective of the study was to evaluate the occurrence of apoptosis in chickens immediately posthatch under fed and starved conditions. Male broiler chickens were or were not provided feed for the first 3 days posthatch. Chickens were killed immediately after hatch, at 1 day of age, at 2 days of age and at 3 days of age. The Pectoralis thoracicus was removed, fixed, dehydrated, cleared and embedded in paraffin. Muscle sections were labeled using terminal deoxynucleotidyl transferase (TdT)-mediated dUTP Nick-End Labeling (TUNEL) for detection of apoptotic nuclei. Body weights were lower (P<0.05) in the starved compared to the fed group at 2 and 3 days posthatch. Myofiber cross-sectional area was only smaller (P<0.05) in the starved compared to the fed birds at 3 days posthatch. TUNEL-positive nuclei were present at all days for the fed and starved groups. The proportion of TUNEL-positive nuclei was higher (P<0.05) for the starved group at day 2 and day 3 posthatch compared to the fed group at 3 days posthatch. Apoptosis is a mechanism that contributes to the smaller myofiber size observed at 3 days posthatch.     

Pareuchiloglanis (Teleostei: Sisoridae) from the Pearl River,China with description of three new species

We describe three new species of Pareuchiloglanis. Based on a comparison of 17 valid species of Pareuchiloglanis, the genus can be divided into two groups contingent on their gill opening size and the anus position. One group, which we call the large gill opening group, has a large gill opening extending to the base of the first pectoral-fin element; the anus is obviously closer to pelvic-fin insertion than the anal-fin origin; this group includes five species distributed in the Red and Pearl Rivers, China. The other group has a small gill opening extending only to the middle base of the pectoral-fin elements; the anus is usually located at the midpoint of the pelvic-fin insertion to the anal-fin origin or slightly behind. This group includes the other 12 species, which are distributed in the Mekong and Yangtze Rivers. The large-gill-opening group can be divided into two sub-groups based on the length of the caudal peduncle. One sub-group has a long caudal-peduncle and the distance from the anal-fin origin to caudal-fin base is greater than distance from the pelvic-fin insertion. This sub-group is only distributed in the Pearl River drainage. Another sub-group has a short caudal peduncle and the distance from the anal-fin origin to the caudal-fin base is typically smaller than the distance from the pelvic-fin insertion. This sub-group is only distributed in the Red River basin of China and Vietnam. The former will be called the large-gill-opening group with long caudal peduncle in the text and only includes one species P. longicauda. During our ongoing taxonomic work of specimens collected from Nanpan-jiang and Beipan-jiang (upper Pearl River drainage in Yunnan, China), some Pareuchiloglanis specimens that had the characters of the large-gill-opening group with long caudal peduncle represent three undescribed species.     

Behavioral modifications in northern bearded saki monkeys (<Emphasis Type="Italic">Chiropotes satanas chiropotes</Emphasis>) in forest fragments of central Amazonia

We investigated behavioral differences among seven groups of northern bearded saki monkeys (Chiropotes satanas chiropotes) living in five forest fragments and two areas of continuous forest at the Biological Dynamics of Forest Fragments Project study area, located approximately 80 km north of Manaus, Brazil. We collected data in six research cycles from July–August 2003 to January 2005–April 2006. When bearded saki monkeys were present in a study area, we followed the group from dawn until dusk for three consecutive days. Every 5 min, we conducted behavioral scans of all visible individuals. There was a positive relationship between forest size and group size, but animals in the small forest fragments lived at greater densities. Bearded saki monkeys in the smaller fragments spent more time resting, less time traveling, and less time vocalizing, but there was no relationship between forest size and the amount of time spent feeding. Our results indicate that the main behavioral differences among the groups are related to the amount of forest resources (e.g., fruit trees, space) available to the monkeys in the smaller fragments, as well as the resulting smaller group sizes. We stress the need to preserve large tracts of forest and provide connectivity between forest patches.     

Population Dynamics of a Single-Stage Sulfidogenic Bioreactor Treating Synthetic Zinc-Containing Waste Streams

Waste streams from industrial processes such as metal smelting or mining contain high concentrations of sulfate and metals with low pH. Dissimilatory sulfate reduction carried out by sulfate-reducing bacteria (SRB) at low pH can combine sulfate reduction with metal-sulfide precipitation and thus open possibilities for selective metal recovery. This study investigates the microbial diversity and population changes of a single-stage sulfidogenic gas-lift bioreactor treating synthetic zinc-rich waste water at pH 5.5 by denaturing gradient gel electrophoresis of 16S rRNA gene fragments and quantitative polymerase chain reaction. The results indicate the presence of a diverse range of phylogenetic groups with the predominant microbial populations belonging to the Desulfovibrionaceae from δ-Proteobacteria. Desulfovibrio desulfuricans-like populations were the most abundant among the SRB during the three stable phases of varying sulfide and zinc concentrations and increased from 13% to 54% of the total bacterial populations over time. The second largest group was Desulfovibrio marrakechensis-like SRB that increased from 1% to about 10% with decreasing sulfide concentrations. Desulfovibrio aminophilus-like populations were the only SRB to decrease in numbers with decreasing sulfide concentrations. However, their population was <1% of the total bacterial population in the reactor at all analyzed time points. The number of dissimilatory sulfate reductase (DsrA) gene copies per number of SRB cells decreased from 3.5 to 2 DsrA copies when the sulfide concentration was reduced, suggesting that the cells' sulfate-reducing capacity was also lowered. This study has identified the species present in a single-stage sulfidogenic bioreactor treating zinc-rich wastewater at low pH and provides insights into the microbial ecology of this biotechnological process.     

Cooperative Breeding in the Lake Tanganyika Cichlid Julidochromis ornatus

Cooperative breeding has been described for several cichlids from the genus Julidochromis (Perciformes: Cichlidae) under laboratory conditions, but field evidence is scarce. Here we describe the breeding system of the cichlid Julidochromis ornatus (Boulenger) in Lake Tanganyika (Zambia). Groups defended a breeding shelter under a large flat stone. Smaller group members stayed and fed under or close to the stone, actively guarded by the larger group members. Six out of 28 groups were newly established by breeders, joined by subordinates from a large pool of independent fish (comprising 50–70% of the total population), and four groups were seen to dissolve during a total of 77 observation days. Breeding groups consisted of a large breeding male and female with zero to five smaller subordinates (average 2). Larger breeders and subordinates were found in larger groups. All group members participated in territory defence and -maintenance, but the breeders were only present at the shelter 48% of the time, in contrast to the subordinates which guarded the breeding shelter 94% of the time. Smaller group members showed submissive behaviours to larger group members. We conclude subordinates in J. ornatus are helpers, but we did not find evidence that helpers increased the group’s current reproductive success. Personal observations combined with a literature review revealed at least 19 species of Lake Tanganyika cichlids show evidence of cooperative breeding, entirely confined to the substrate breeding tribe of the Lamprologini (24% of 80 species in total): 2 Chalinochromis spp., 5 Julidochromis spp., 12 Neolamprologus spp. More effort should be put into detecting cooperative breeding in American and Asian substrate breeding cichlid species.     

Properties of protease-treated cytochrome c oxidase from beef heart

Summary About 45% of the protein can be removed from oxidized cytochrome c oxidase by treatment with proteolytic enzymes under a variety of conditions, leading to an increased heme to protein ratio.The principal spectroscopic parameters of cytochrome c oxidase are retained in the protease-treated enzyme.Of the overall catalytic activity 20% remained after digestion; the electron-transfer reactions were impaired but the affinity for cytochrome c appeared unchanged.Proteolysis resulted in removal of the hydrophobic subunit III and most of the smaller hydrophilic subunits, leaving a core, which basically consists of the two largest subunits I and II.The subunits I and/or II carry the prosthetic groups of the enzyme and at least one of the cytochrome c binding sites. The smaller subunits, however, are essential for optimal electron transfer and possibly have other functions as well.     

Higher mortality of smaller sika deer fawns

Bodyweight, breast girth and hind-foot length were compared in sika deer fawns (Cervus nippon Temminck) that were shot or had died naturally. The study site was Mount Goyo, in northern Japan. Samples were collected in January and February every year from 1982 to 1991 for the dead fawns and from 1990 to 1992 for the living fawns. The average bodyweight and the variation in bodyweight was significantly smaller in the dead fawns than in the living ones, suggesting a higher mortality rate in smaller fawns. The mean breast girth and hind-foot length were also significantly smaller in the dead fawns. Two possibilities are suggested: (i) the smaller fawns were born later than the larger fawns and grew at normal rates; or (ii) the smaller and larger fawns were born in a similar period but grew at different rates thereafter.     

Effects of temperature and food level on growth and development of a planktonic water mite

We analysed the relative effects of food availability and temperature on rates of growth and development of a predatory planktonic water mite, Piona exigua. Growth in length of mites fed Daphnia, Ceriodaphnia and Chydorus was analysed by Gompertz or von Bertalanffy curves; these curves were compared by parallel curve analysis. Growth rates of nymphs and adult female mites increased with temperature; the duration of the imagochrysalis stage decreased. Females grown at 10 °C were smaller at final size than females grown at 15 °C, 18 °C or 22 °C. Females reared at food levels of 15 or 30 prey l⁻¹ grew more slowly and were smaller than those provided with 60 or 120 prey l⁻¹. Nymphs grew more slowly when Daphnia were the only prey, than when smaller prey were available. Food level did not affect nymph growth at 10 °C or 15 °C, but growth at 18 °C or 22 °C may have been slowed at the lowest food levels. Synergistic effects of temperature and food level on nymph growth were apparent only from analysis of growth curves and not from stage duration data.