Trophic ecology and food consumption of fishes in a hypersaline tropical lagoon

This study evaluated the trophic ecology (diet composition, trophic strategy, similarities and overlap between species, feeding period and food consumption) of six benthivorous fish species in Araruama Lagoon, the largest hypersaline tropical lagoon on the east coast of South America, with an area of 210 km² and an average salinity of 52. The burrfish Chilomycterus spinosus fed on Anomalocardia flexuosa shell deposits, ingesting associated fauna. The caitipa mojarra Diapterus rhombeus differed from all other species, having not only the highest proportions of algae and Nematoda, but also feeding on polychaete tentacles. The two mojarras Eucinostomus spp. showed similar trophic strategies, feeding mostly on Polychaeta. The corocoro grunt Orthopristis ruber also fed mainly on Polychaeta, but differed from Eucinostomus spp. in secondary items. The whitemouth croacker Micropogonias furnieri fed mainly on small Crustacea at night, showing a high number of secondary prey items with low frequencies and high prey‐specific abundance. The daily food consumption (g food g^?1 fish mass) for Eucinostomus argenteus was 0·012 and was 0·031 and 0·027 for M. furnieri in two different sampling events. The diet similarities between Araruama Lagoon and other brackish and marine environments indicate that hypersalinity is not a predominant factor shaping the trophic ecology of fishes in this lagoon. The stability of hypersaline conditions, without a pronounced gradient, may explain the presence of several euryhaline fishes and invertebrates well adapted to this condition, resulting in a complex food web.     

The effect of supplementary food on home range of the southern brown bandicoot,Isoodon obesulus (Marsupialia: Peramelidae)

The study investigated the relationship between home range and food abundance in a population of the southern brown bandicoot. Isoodon obesulus, in Western Australia. Home range areas were estimated seven times between 1986 and 1988 by live-trapping, spool-and-line devices and fluorescent pigment tracking. The abundance of invertebrate food was measured simultaneously by placing pitfall traps within the home ranges of individual animals, and by sampling invertebrates in topsoil and litter. Home range areas tended to be negatively correlated with food abundance, especially in the autumn and winter of 1986 and 1987. The influence of food on home range was investigated further in September 1988 by providing eight individual I. obesulus with a supplementary food mixture. Contrary to expectation, the added food caused an increase in home range area, home range overlap and displacement, as well as an influx of new individuals to food stations. In contrast, home range parameters in control (non-fed) individuals changed little during the experiment. The shuffling of home ranges due to feeding suggests that the home range system of I. obesulus is relatively flexible, with individuals monitoring and exploiting resources in an opportunistic manner. In contrast to previous studies, we found no evidence that I. obesulus was territorial. We speculate that individuals may be territorial at low population density if resources are defendable and intruder pressure is low, but occupy overlapping ranges if population density is high.     

Identification of the food sources of sympatric ghost shrimp (Trypaea australiensis) and soldier crab (Mictyris longicarpus) populations using a lipid biomarker,dual stable isotope approach

Fatty acids (FAs) profiles and stable isotope signatures of the ghost shrimp, Trypaea australiensis and the soldier crab, Mictyris longicarpus were determined at an unvegetated sandbank of Southport (Gold Coast, Queensland, Australia), in November 2005 and February 2006. Additionally, the FAs composition of the faeces and feeding pellets of M. longicarpus and the surface sediment at the study site were also analysed. Trypaea australiensis was found to selectively feed principally on benthic diatoms, as revealed by the high contribution of the marker lipid (20:5 (n‐3)) to tissue total FAs and the δ¹³C and δ¹⁵N isotopic signatures of shrimp tissues. Although the diet of T. australiensis did not change between the two sampling periods, the shrimps appeared to reduce their feeding activity in summer, presumably in relation to a restricted metabolism, as revealed by a decrease in the contribution of the microalgal markers in their tissues. The FAs composition of the tissues of the soldier crab indicated that bacteria and diatoms constituted the base of its diet (contributions of branched 15:0 and 17:0, 18:1 (n‐7) and 20:5 (n‐3)). However, the isotopic signatures of the crabs suggested that meiofauna may represent an intermediate link between the crab and these micro‐organisms.     

Home Range and Movement Patterns of White-lipped Peccary (Tayassu pecari) Herds in the Northern Brazilian Amazon1

Two white-lipped peccary (Tayassu pecari) herds were radio-tracked for 5 and 13 mo, respectively, on Maracá Island Ecological Reserve, Roraima, Brazil. Home range size was 109.6 km² for the larger herd (130 animals) and 21.8 km² for the smaller herd (53 animals). Neither herd migrated or moved nomadically during the study period. The herd with the longer observation period increased its home range size during the flooded season by including new sites not used in the nonflooded season and continuing to use the nonflooded season sites. This pattern of simultancously using distinct seasonal ranges also occurred between the rainy and dry periods and the herd regularly and predictably returned to favored feeding sites. Population declines and disappearances in this study and others may have been caused by in situ mortality rather than by long-distance movements.     

An alien in an archipelago: Spathodea campanulata and the geographic variability of its moth (Lepidoptera) communities in the New Guinea and Bismarck Islands

Aim This analysis of moth (Lepidoptera) communities colonizing an alien tree invading secondary rain forest vegetation in Melanesia examines the predictability of insect herbivorous communities across distances of tens to thousands of km and the effect of dispersal barriers on community composition in the tropics. Location Six secondary rain forest sites were studied within four equidistant yet distinct geographic areas of the New Guinea mainland and the Bismarck Archipelago, including two watershed areas (Madang and Sepik) on mainland New Guinea and the adjacent large island of New Britain and small island of Unea. Methods The analysis is based on feeding records obtained by quantitative sampling and rearing of caterpillars from the alien host Spathodea campanulata (Bignoniaceae). It examines the variation in Lepidoptera community composition at six study sites distributed on three adjacent islands ranging in size from 30 to 865,000 km². Results Spathodea campanulata was colonized by 54 folivorous species of Lepidoptera. Most of them were generalists, feeding on > 1 native plant family. However, the three most abundant species representing 83% of all individuals (Acherontia lachesis, Hyblaea puera complex and Psilogramma menephron) were relatively host specific, feeding predominantly on a single native family that is not the Bignoniaceae. Most of the 23 species analysed in detail had a wide geographic distribution, including 13 species spanning the entire 1000‐km study transect. While the Lepidoptera in two New Guinea areas 280 km apart were similar to each other, there was a discontinuity in species composition between New Guinea and the smaller islands. However, no negative effect of small islands on species richness was detected. Main conclusions Spathodea campanulata was rapidly colonized by folivorous Lepidoptera communities with species richness and dominance structure indistinguishable from the assemblages feeding on native hosts, despite its phylogenetic isolation from the native vegetation. Although most species were generalists, the highest population densities were reached by relatively specialized species, similar to the communities on native hosts. The species turnover across distances from 10 to 1000 km was relatively low as most of the species had wide geographic ranges.     

Feedback between zebra mussel selective feeding and algal composition affects mussel condition: did the regime changer pay a price for its success?

1. We investigated the role of algal composition on pumping, clearance, assimilation, pseudofaeces and faeces production, feeding time budgets, and condition of zebra mussels from spring to autumn at two sites in Saginaw Bay (Lake Huron) and one site in western Lake Erie. Size‐fractioned chlorophyll was used to distinguish between feeding on small (<53 μm) and large (>53 μm) size fractions, and mussel feeding behaviour was quantified by video observations. 2. Mussel pumping, clearance and assimilation rates varied among sites, particularly during summer, when phytoplankton composition varied considerably among sites. Lowest values were seen at the inner‐bay site of Saginaw Bay, low to moderate values at the outer‐bay site of Saginaw Bay, and high values at the Lake Erie site. Clearance, pumping and assimilation rates were all highly positively correlated (R² = 0.76) with per cent contribution of flagellates to total algal biomass and negatively correlated with per cent of Microcystis aeruginosa (R² = 0.63). The negative effects on pumping rate (as determined by clearance rate on the <53 μm fraction) of Microcystis, which occurred in the >53 μm fraction, could be mitigated by the presence of flagellates in the <53 μm fraction. 3. Visual observations of mussel feeding showed evidence for poor seston quality during summer negatively affecting feeding rates. High faeces production during times of low assimilation rate was suggestive of poor assimilation efficiency and/or viable gut passage of grazing resistant algae. Long periods of time not filtering by the mussels during some Microcystis blooms and lack of production of a filtering current during one experiment were suggestive of intoxication from microcystin or other secondary compounds. 4. Clearance and feeding rates of the mussels in Saginaw Bay were high during spring and autumn and very low in summer, particularly at the inner‐bay site. Condition of the mussels (mass : length ratio) was highest in spring and lowest during summer. This seasonal variation probably reflected high food assimilation rate during autumn and spring and low assimilation rate and reproduction during summer. The condition of mussels throughout the year was higher at the outer‐bay than the inner‐bay site, reflecting better feeding conditions at the former. Mussel selective feeding may have been responsible for the poor quality of food at the inner bay site; therefore, we postulate that a regime shift in phytoplankton composition promoted by the mussels fed back into lowered condition of the mussels.     

Cumaceans (Crustacea) from the Bellingshausen Sea and off the western Antarctic Peninsula: a deep-water link with fauna of the surrounding oceans

During the austral summers of 2003 and 2006, two cruise were carried out in the Bellingshausen Sea and west off Antarctic Peninsula on board of RV Hespérides. Samples were collected at 26 stations with a multinet Macer-GIROQ sled. A total of 557 cumaceans belonging to 36 species of five families were collected. Nannastacidae was the most abundant and speciose family. Hemilamprops pellucidus and Cyclaspis gigas were the most frequently collected species (38.5% of sampling stations). Cumella asutralis reached the highest density (514.7 individuals/1,000 m² at stn 7). Maximum species richness (S = 15) and diversity (H′ = 3.53) was observed at one of the deepest station. Positive correlations were found between the cumacean distribution and the organic content and percentage of coarse sand of the sediments. Predominance of Nannastacidae in front of other cumaceans could be explained by their type of feeding (i.e. predators or scavengers), which may be more successful in the deep seafloor of an oligotrophic sea such as studied herein. The presence in the deepest sampling sites of species shared with faunas of surrounding oceans suggests a link between these faunas and those of deep Antarctic waters.     

Predicting the Competitive Regime of Female <Emphasis Type="Italic">Colobus vellerosus</Emphasis> from the Distribution of Food Resources

We examined the spatial and temporal distribution of the foods of ursine colobus (Colobus vellerosus) at Boabeng-Fiema, Ghana as a means to predict the monopolizablity and usurpability of their food resources. Recent evidence suggests that food may not be limiting for folivorous primates, and that male sexual coercion may be a more important influence on folivore social organization. To address the question, we collected focal data on the feeding behavior of adult females and males over 11 mo (September 2000-August 2001) on 2 groups: WW (n = 31–33 individuals) and B (n = 8–16 individuals). We also conducted phenological monitoring and a tree survey of the two-group home ranges to establish food availability and distribution. We used 2 behavioral or organism-defined indicators of feeding behavior to assess potential resource contestability: food site residence time and distance moved between food sites. The colobus fed on a high diversity of species, most of their food trees were not clumped in distribution, within-tree interfood distances were short, and food trees were large. The only condition associated with the potential for monopolization was low food tree density. However, low food tree density may be offset by the colobus’ use of large trees. Taken together, the ecological and behavioral indicators suggest the food resources of Colobus vellerosus had a low potential for monopolization. Our results also indicate mature leaves had the longest food site residence time, which may suggest they should be the most usurpable plant part, though their presumed low quality and high abundance probably counteracted the effect. The pattern implied the potential for direct feeding competition among Colobus vellerosus at Boabeng-Fiema was low and agonistic interactions over food are not expected. Instead, a group size effect on feeding efficiency should be a more predominant influence on feeding efficiency, if food is limiting for the species.     

Growth- and feeding-related isotopic dilution and enrichment patterns in young-of-the-year yellow perch (Perca flavescens)

1. Isotopic signatures (δ¹⁵N and δ¹³C) from young‐of‐the‐year (YOY) yellow perch (Perca flavescens) were collected over the initial 4 month summer growing period from three separate and distinctive sites in northern Alberta, Canada. Data were analysed to test the hypotheses that there are within‐ and among‐population differences in the patterns of isotopic δ¹⁵N and δ¹³C change over the growing season, and that observed isotopic dilution and/or enrichment patterns were influenced by site‐specific physical and chemical factors. 2. Increases in δ¹⁵N relative to spawned egg masses were observed in immediate posthatch (emergent) YOY and attributed to enrichment associated with the assimilation of yolk during embryonic development. 3. Posthatch dilution of YOY δ¹⁵N signatures associated with ontogenetic dietary shifts from yolk to exogenous feeding and zooplanktivory to benthivory occurred at all sites and was associated at most sites with a concomitant increase in δ¹³C. 4. The rate and pattern of δ¹⁵N dilution and δ¹³C enrichment observed for the study populations varied between and within sites and depended on maternal trophic status and timing of ontogenetic dietary shifts, as determined by prey availability and site‐specific biogeochemical factors. 5. Comparisons of isotopic dilution patterns among species, using results from this study and literature‐derived values, indicated that dilution rates and patterns are species dependent and may vary in relation to key life‐history events. 6. Seasonal and spatial isotopic variability among populations and between species complicates field sampling. In particular, the connectivity to site‐specific conditions found here suggests that for locally resident juvenile fishes, spatial, as well as temporal variability must be included in isotopic sampling programmes designed to characterise littoral zone foodweb relationships.     

Length–weight relationship and a relative condition factor equation for lake sturgeon (Acipenser fulvescens) from the St Clair River system (Michigan, USA)

Several USA state, federal, and Canadian agencies study lake sturgeon (Acipenser fulvescens) within the St Clair River and Lake St Clair, collectively referred to hereafter as the St Clair River (SCR) system. Previously, there has been no set standard for determining condition for SCR system lake sturgeon. Condition measures the variation from the expected weight for length as an indicator of fatness, general well‐being, gonad development, etc. The aim of this project was to determine the length–weight relationship of lake sturgeon caught from the SCR system, from which a relative condition factor (K_n) equation could be derived. Total length (TL, mm) and weight (W, kg) were measured for 1074 lake sturgeon (101 males and 16 females were identifiable) collected by setline and bottom trawl from the SCR system in May–September, 1997–2002. Analysis of covariance found no difference in the length–weight relationship between sampling gear or sex. Least‐squares regression of log₁₀W × log₁₀TL produced the overall equation logW = 3.365logTL ? 9.320. Using the exponential form of the slope and y‐intercept, relative condition factor for lake sturgeon from the SCR system can be calculated as K_n = W/[(4.786 × 10^?10)(TL^3.365)]. Equations for males and females were also developed. Overall, body condition was significantly correlated with both age and girth; no significant difference in K_n by sex was found. In general, the SCR lake sturgeon population was near the upper ends of growth and condition ranges listed in the literature, comparable with those populations that are at similar latitudes. Although condition factors should be interpreted with caution, proper use of a standard equation provides a non‐lethal measure of overall fish health that can be used by biologists and managers in ongoing efforts to restore lake sturgeon throughout the Great Lakes.     

Feeding strategies and elemental composition in Ponto‐Caspian peracaridans from contrasting environments: can stoichiometric plasticity promote invasion success?

1. Ponto‐Caspian peracaridans, and mysids and amphipods in particular, are among the most successful aquatic invaders. However, species differ in the trophic‐status range of ecosystems they can invade while establishment rates and impacts can vary substantially between habitats. There is limited knowledge of the environmental factors and species characteristics that drive such variation in invasion success. 2. Here we test how trophic level and body stoichiometry vary among peracaridan species and in relation to body size. The amphipod Pontogammarus robustoides and the mysids Limnomysis benedeni and Paramysis lacustris were investigated in ecosystems differing considerably in productivity and nutrient supply, namely an N‐limited eutrophic lagoon and P‐limited mesotrophic lakes. 3. As revealed by stable isotope (¹⁵N/¹⁴N) analysis, herbivory was inferred to be the main feeding mode of L. benedeni. In contrast, the mysid P. lacustris and the amphipod P. robustoides displayed a higher propensity for predatory feeding at larger body sizes, a pattern that was more pronounced in the eutrophic lagoon than in the mesotrophic lakes. 4. Their mean stoichiometric composition (P. robustoides C:N:P 108:20:1, L. benedeni 92:21:1 and P. lacustris 93:22:1) demonstrates that these peracaridans are rich in nutrients, especially nitrogen. They all exhibited the same ontogenetic pattern of reduced stoichiometric regulation during juvenile stages and stricter homoeostasis at older stages. 5. The higher P content in juveniles of all peracaridan species from the lagoon indicates higher potential somatic and population growth rates than those in the mesotrophic lakes. Such a difference may explain the substantially faster rates of invader establishment observed in the lagoon in comparison with lakes of low trophy. 6. Due to differences in ontogenetic and habitat‐induced variation, the study species differed significantly in stoichiometric variability, which was lowest in L. benedeni and highest in P. robustoides. The ranges of species‐specific variation in stoichiometric ratios corresponded to the trophic (by chlorophyll a) and nutrient stoichiometry (N:P) ranges of lentic waters successfully invaded by these species in Lithuania. 7. Stoichiometric plasticity, which should be associated with flexibility of feeding strategy, may enhance the potential of peracaridan species to successfully invade habitats with differing trophy and nutrient supply. The optimal feeding strategy should be omnivory with a propensity for predatory feeding, which can be adjusted with respect to ontogenetic nutrient demands and resource availability. Invading species may have a stronger effect on the local biota in ecosystems with high P levels, which promote growth, and N limitation that should favour predation.     

Home ranges and densities of medium-sized carnivores in south-east Finland, with special reference to rabies spread

Home ranges and densities of medium-sized carnivores were studied in south-east Finland by radio tracking. The species studied included potential vectors of rabies: the raccoon dogNyctereutes procyonoides (Gray, 1834), red foxVulpes vulpes (Linnaeus, 1758), European badgerMeles meles (Linnaeus, 1758) and domestic catFelis silvestris catus (Schreber, 1777). Home ranges of badgers were largest (mean 14.7 km²) and those of cats smallest (1.5 km²). Home ranges overlapped largely, both within and between species. Most home ranges were larger and population densities lower in south-east Finland compared with those in Western Europe. The pooled density of medium-sized carnivores with overlapping home ranges was, however, high, which may indicate a high risk of a rabies epizootic in this multi-host community. Rabies might also spread rapidly to new areas, because of the large home ranges and, consequently, long dispersal distances.     

Preliminary assessment of Greenland halibut diet in Cumberland Sound using stable isotopes

We provide preliminary carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotope assessment of the Greenland halibut (Reinhardtius hippoglossoides) diet in Cumberland Sound, with focus on two possible prey sources: pelagic represented by capelin (Mallotus villosus) and epibenthic represented by shrimp (Lebbeus polaris). The δ¹³C for the Greenland halibut stock indicated a pelagic carbon source in Cumberland Sound while stable isotope mixing models, IsoSource and MixSIR, indicated a 99% dietary composition of capelin relative to the shrimp. The δ¹⁵N did not vary across Greenland halibut size ranges and placed them at a fourth trophic position relative to a primary herbivore. This study provides the starting point for more elaborate Cumberland Sound research on the local Greenland halibut feeding ecology by confirming pelagic feeding and establishing relative trophic position as well as identifying stable isotopes as a useful tool for the study of diet in cold water fish species.     

Feeding Preferences in Greylag Geese and the Effect of Activated Charcoal

ABSTRACT Greylag geese (Anser anser) can cause serious damage to agricultural fields near wetlands that are attractive for resting and nesting but not for feeding. Alternative plantings or spraying fields may prevent goose damage. We randomly designed 64 plots in spring 2004 and prepared plantings of white clover (Trifolium repens), white clover with perennial ryegrass (Lolium perenne; mixture), fertilized perennial ryegrass (grass), or unfertilized perennial ryegrass. We measured goose-dropping densities in plots as a measure of feeding preference in autumn 2004 (7 weeks), spring 2005 (6 weeks), and autumn 2005 (7 weeks) following removal of a protective fence and vegetation sampling for content analysis in 2004. We also sprayed activated charcoal (20 kg/ha) in a suspension on 32 plots (8/planting) to deter geese in autumn 2004 only. In a second experiment we examined pairs of greylag geese in cages for preferences between grass treated with or without activated charcoal. Charcoal did not deter geese in either experiment. However, dropping density averaged highest for clover (1.01/m²), followed by the mixture (0.65/m²), then fertilized (0.23/m²) and unfertilized grass (0.16/m²). Preferences were consistent in all 3 experimental periods. Fertilized grass reached 31.8 cm in height on average in spring, whereas clover measured 15.4 cm. Crude protein and water-soluble carbohydrate content (g/kg dry matter) was 294 and 49, respectively, in white clover and 183 and 139, respectively, in fertilized grass. We found a positive partial correlation independent of vegetation type between dropping densities and crude protein and a negative correlation with water-soluble carbohydrate content. Thus, to prevent grazing damage to agricultural fields, we recommend planting white clover, strongly preferred by feeding geese, in areas (fallow agricultural or nonagricultural) adjacent to their habitat and not in agricultural fields under production.     

Inter-strain differences in nitrogen use by the coccolithophore Emiliania huxleyi, and consequences for predation by a planktonic ciliate

Four strains of the coccolithophore Emiliania huxleyi (CCMP strains 370, 373, 374, 379) were tested for their ability to grow on various nitrogen sources. All strains grew on ammonium, nitrate, and urea, although growth of CCMP379 on urea was low. Responses to other dissolved organic nitrogen (DON) sources varied. CCMP379 did not grow on any DON source other than urea. All other strains grew on one of the two tested amino acids: CCMP370 and CCMP373 on glutamine, and CCMP374 on alanine. All three of these strains also grew on hypoxanthine; in addition, two grew well on acetamide and one on ethanolamine. E. huxleyi strains also differed in their susceptibility to predation by the ciliate Strobilidium sp. CCMP374 was ingested at substantially higher rates than CCMP373 regardless of E. huxleyi growth condition. Ciliate feeding rates also depended on E. huxleyi growth condition. For CCMP374, feeding rates were 2× higher on growing E. huxleyi cells than on non-growing cells (average 27.5 versus 15.6 cells ciliate⁻¹ h⁻¹, respectively). For CCMP373, a relationship between E. huxleyi growth rate and ciliate feeding rate was not evident, but E. huxleyi grown on some N sources (ammonium, nitrate, urea) were ingested at consistently higher rates than E. huxleyi grown on other sources (ethanolamine, glutamine). Interstrain differences in the ability to utilize DON and resist predation may contribute to maintenance of high genetic diversity within this cosmopolitan, bloom-forming species.     

Additive Interactions of Maternal Prepregnancy BMI and Breast‐feeding on Childhood Overweight

Objective: To examine the interactions of maternal prepregnancy BMI and breast‐feeding on the risk of overweight among children 2 to 14 years of age. Research Methods and Procedures: The 1996 National Longitudinal Survey of Youth, Child and Young Adult data in the United States were analyzed (n = 2636). The weighted sample represented 51.3% boys, 78.0% whites, 15.0% blacks, and 7.0% Hispanics. Childhood overweight was defined as BMI ≥95th percentile for age and sex. Maternal prepregnancy obesity was determined as BMI ≥30 kg/m². The duration of breast‐feeding was measured as the weeks of age from birth when breast‐feeding ended. Results: After adjusting for potential confounders, children whose mothers were obese before pregnancy were at a greater risk of becoming overweight [adjusted odds ratio (OR), 4.1; 95% confidence interval (CI), 2.6, 6.4] than children whose mothers had normal BMI (<25 kg/m²; p < 0.001 for linear trend). Breast‐feeding for ≥4 months was associated with a lower risk of childhood overweight (OR, 0.6; 95% CI, 0.4, 1.0; p = 0.06 for linear trend). The additive interaction between maternal prepregnancy obesity and lack of breast‐feeding was detected (p < 0.05), such that children whose mothers were obese and who were never breast‐fed had the greatest risk of becoming overweight (OR, 6.1; 95% CI, 2.9, 13.1). Discussion: The combination of maternal prepregnancy obesity and lack of breast‐feeding may be associated with a greater risk of childhood overweight. Special attention may be needed for children with obese mothers and lack of breast‐feeding in developing childhood obesity intervention programs.     

Nuclear introgression without mitochondrial introgression in two turtle species exhibiting sex‐specific trophic differentiation

Despite the presence of reproductive barriers between species, interspecific gene introgression has been documented in a range of natural systems. Comparing patterns of genetic introgression in biparental versus matrilineal markers can potentially reveal sex‐specific barriers to interspecific gene flow. Hybridization has been documented in the freshwater turtles Graptemys geographica and G. pseudogeographica, whose ranges are largely sympatric. Morphological differentiation between the species is restricted to females, with female G. geographica possessing large heads and jaws compared to the narrow heads of G. pseudogeographica females. If hybrid females are morphologically intermediate, they may be less successful at exploiting parental feeding niches, thereby limiting the introgression of maternally inherited, but not biparental, molecular markers. We paired sequence data with stable isotope analysis and examined sex‐specific genetic introgression and trophic differentiation in sympatric populations of G. geographica and G. pseudogeographica. We observed introgression from G. pseudogeographica into G. geographica at three nuclear loci, but not at the mitochondrial locus. Analysis of ?¹⁵N and ?¹³C was consistent with species differences in trophic positioning in females, but not males. These results suggest that ecological divergence in females may reduce the opportunity for gene flow in this system.     

Interactions in a tritrophic acarine predator-prey metapopulation system III: effects of Tetranychus urticae (Acari: Tetranychidae) on host plant condition

Spider mites are serious pests on many economically important plant species, because they may reduce plant productivity and, at high mite densities, overexploit and even kill the host plants. We have conducted a series of greenhouse experiments to quantify the effects of two-spotted spider mites (Tetranychus urticae) on host plants (Phaseolusvulgaris). The average amount of chlorophyll per cm² leaf area was used as a measure of plant condition. It was shown that chlorophyll concentration decreases with plant age and intensity of spider mite feeding. Damage caused by spider mites was assessed visually, using the Leaf Damage Index (LDI) defined by, and a mathematical relationship between the visual measurements and the amount of chlorophyll/cm² was fitted to data. The relationship may serve as a short-cut to estimate overall plant injury, expressed as the relative loss of chlorophyll/cm² leaf area caused by spider mites (D). D takes values between 0 (no injury) and 1 (all leaves dead). A highly significant positive relationship between the instantaneous spider mite density and D was found, even though D is expected to reflect the cumulated density of mites (mite-days). A model of plant growth incorporating information about plant age and D predicts that plant area has a maximum when plant age is about 60 days, and that plant area decreases exponentially with an increase in D. This revised version was published online in July 2006 with corrections to the Cover Date.     

Organic matter quality and management effects on enrichment of soil organic matter fractions in contrasting soils in Zimbabwe

Spatial variability of soil total nitrogen (N), available N (KCl extractable NH₄⁺ and NO₃⁻), and spatial patterns of N mineralization and nitrification at a stand scale were characterized with geostatistical and univariate analysis. Two extensive soil spatial samplings were conducted in an evergreen broadleaf forest in Sichuan province, southwestern China in June and August 2000. In a study area of 90 × 105 m², three soil samples were collected from each 5 × 5 m² plot (n = 378) in June and August, and were analyzed for total N and available N contents. Net N mineralization and nitrification were measured by in situ core incubation and the rates were estimated based on the difference of NH₄⁺ and NO₃⁻ contents between the two sampling dates. Total N, NH₄⁺, and NO₃⁻ were all spatially structured with different semivariogram ranges (from high to low: NH₄⁺, NO₃⁻, and total N). The semivariograms of mineralization and nitrification were not as spatially structured as available N. NH₄⁺ was the dominant soil inorganic N form in the system. Both NH₄⁺ and NO₃⁻ affected spatial patterns of soil available N, but their relative importance switched in August, probably due to high nitrification as indicated by greatly increased soil NO₃⁻ content. High spatial auto-correlations (>0.7) were found between available N and NH4⁺, available N and NO₃⁻ on both sampling dates, as well as total N measurements between both sampling dates. Although significant, the spatial auto-correlation between NH₄⁺ and NO₃⁻ were generally low. Topography had significant but low correlations with mineralization (r = −0.16) and nitrification (r = −0.14), while soil moisture did not. The large nugget values of the calculated semivariograms and high-semivariance values, particularly for mineralization and nitrification, indicate that some fine scale (<5 m) variability may lie below the threshold for detection in this study.     

Ecological attributes recorded in stable isotope ratios of arboreal prosimian hair

Carbon and nitrogen stable isotope ratios were measured in hair samples from two species of Galago from Gedi Ruins National Monument in eastern Kenya and from Lepilemur leucopus from Beza Mahafaly Special Reserve in southern Madagascar. Forest structure was generally similar in the two areas but average rainfall was lower in Madagascar. Species average ¹³C values varied with feeding height in the forest canopy and with average rainfall level as expected from reported variation in plant ¹³C values. G. garnettii, which feeds higher in the forest canopy, had less negative ¹³C values than G. zanzibaricus, which spends more time below 5 m. L. leucopus, from a drought-afflicted forest, had less negative hair ¹³C values than the two galago species. The values within the Lepilemur sample showed a positive linear relation with percent dependence on a CAM tree species and with xeric conditions within the species reserve. Nitrogen stable isotope ratios varied with trophic level of feeding and with time spent feeding on leguminous plants. The insectivorous galagos had significantly more positive ¹⁵N values than the folivorous L. leucopus. Within the Lepilemur sample, ¹⁵N values varied inversely with the percent of feeding time spent on leguminous plants. The range of ¹⁵N and ¹³C values in each of the prosimian species is larger than reported for animals fed monotonous diets and for New World monkey species. The monkey species feed as groups of individuals whereas the prosimians have solitary feeding habits. The ranges in the prosimian species apparently reflect the greater variation in diet among individual prosimians compared to individual monkeys. The isotope data reported here are equivalent, on average, to those reported for other arboreal species from similar forest habitats and with similar dietary habits. This supports the use of such data for paleoecological reconstruction of forest and woodland systems and diet reconstruction of extinct primate populations and species. Received: 18 April 1997 / Accepted: 11 August 1997