Overwintering by the western thatch ant, Formica obscuripes (Hymenoptera, Formicidae)

Seed preferences of Lumbricus terrestris L.

Seston in the impounded North Anna River (NAR) was analyzed and compared to that in the free-flowing South Anna River (SAR) in Virginia, U.S.A. A wet filtration technique was used to separate seston into five size classes. The overall quantity of organic seston was much lower in the NAR than in the SAR. The seston in the NAR was composed of more living organisms, in particular zooplankters in the medium large (234–864 µm) and small (105–234 µm) size classes and diatoms and other algae in the fine (43–105 µm) and very fine (25–43 µm) size classes. The percentage of zooplankton declined sharply before reaching the downstream study site (32 km). The seston in the NAR tended to consist of slightly larger particles, but 80–85% of the seston in both rivers was in the ultrafine (0.45–25 µm) size class, which was almost entirely composed of detritus. One indication of seston food quality, the organic/inorganic ratio, was considerably higher for the medium large and small size classes in the NAR immediately below the dam and for the fine and very fine size classes farther downstream. Another indication of food quality, the usable caloric content, showed that the seston in the NAR contained considerably less total assimilable energy as far as 32 km downstream from the dam, but that the medium large and small size classes were rich in assimilable energy immediately below the dam because of zooplankton released from the reservoir. Thus, the overall quantity and quality of seston was lower in the NAR, but the quality of the seston, for at least a short distance below the dam, was higher in a well-defined size range that can be effectively utilized by certain filter feeders.

We monitored mortality and recruitment annually for six years for all trees >5 cm diameter at breast height in four 1-ha plots in second-growth, lowland rain forests in northeastern Costa Rica. Stands initially ranged in age from 12 to 25 years since aban- donment of cattle pastures. In younger stands, abundance decreased 10-20% in the small size class (5-9.9 cm dbh), but increased 49-100% in the large size class (?25 cm dbh). In the two youngest plots, 45.0% and 27.6% of the common tree species showed annual population increases of 3% or more, whereas 10% showed annual decreases of 4% or more. Annual rates of tree mortality for all size classes and recruitment into the 5-cm size class varied significantly among years, and mortality rates of trees 5-9.9 cm dbh were higher in younger than in older stands. Tree mortality was highest during the 1997-1998 El Nifio Southern Oscillation (ENSO) year; on average, 5.6%, 3.5%, and 1.4% of trees died in the small, intermediate, and large size classes, respectively. Mortality rates during the ENSO year were 1.9 times higher for trees ?10 cm dbh compared to non-ENSO years. Annual mortality rates for trees >10 cm dbh decreased significantly with increasing dry-season rainfall, but not with total annual rainfall during the census periods. Tree mortality (par- ticularly for trees -25 cm dbh) in these secondary forests was highly sensitive to dry- season rainfall, even during non-ENSO years. Increased tree mortality during ENSO years is likely to accelerate forest dynamics and successional change in wet tropical second- growth forests.

Summary The diet composition was quantified of year-0 Scaphirhynchus sturgeons during sampling years (2004–2008) from the Middle Mississippi River to evaluate trends in diet. River stage height varied among years and seasons. Water temperature differed among seasons but did not differ among years. The presence of empty stomachs was evident across years, seasons, and size classes of sturgeon. The overall Multivariate Analysis of Variance for frequency of occurrence was significant, suggesting that macroinvertebrate taxa (e.g. Ephemeroptera, Diptera pupae, Chironomidae, ‘Other’) differed among size classes of sturgeon, but not seasons or years. Furthermore, Tukey's pairwise comparisons indicated Ephemeroptera frequency of occurrence differed between medium and large size classes; Diptera pupae differed between small and medium size classes and small and large size classes; Chironomidae differed between small and large size classes and medium and large size classes; the macroinvertebrate taxa category ‘Other’ differed between small and large size classes. Ultimately, because of the link between diet and growth of year-0 Scaphirhynchus sturgeon, the early life history may affect eventual recruitment to adult stages.

Based on the monitoring data from the plots of Changbai Mountains in the temperate zone (CBS), Guandi Mountain in the warm temperate zone (GDS), Heishiding Mountain in the subtropical zone (HSD), we analyzed the spatial distribution of tree species from three families (Pinaceae, Fagaceae, Rosaceae) and their correlation using paired correlation function g(r). The results showed that the individual number and size class structural characteristics of the trees from the three families varied among different regions. Pinaceae had high population density and a bimodal size-class structure in GDS plot but a small number and skewed normal size-class structure in CBS and HSD plots. Fagaceae had low abundance and a bimodal, skewed normal size-class structure respectively in CBS and GDS plots but a large number and an inverted J-type diameter distribution in HSD plot. Rosaceae had high abundance and a L-type size structure in GDS plot but relatively low abundance and a L-inverted and J-type size class distribution respectively in HSD and CBS plots. The trees from those three families showed different spatial distribution patterns in three different forest plots. The large size class individuals of Pinaceae were regularly distributed at small scale in CBS and GDS plots but aggregated in HSD plot, the middle and small size class ones were consis-tently aggregated in three plots. Fagaceae trees were mainly characterized by large size class and approximately distributed at random in CBS plot, but mainly characterized by middle or small size class and aggregated in GDS and HSD plots. The trees of Rosaceae were aggregated in three plots. The aggregation degree of trees from three families decreased with the increases of spatial scales. The large size class individuals of Fagaceae were negatively associated at small scale or uncorrelated with Pinaceae trees in CBS and HSD plots. The middle or small size class individuals of Fagaceae were negatively associated with Pinaceae ones in CBS and GDS plots but positively associated with Pinaceae ones in HSD plot. Trees from Pinaceae were negatively correlated with trees from Rosaceae in three plots. The middle or small size class individuals of Fagaceae were positively correlated with individuals of Rosaceae in CBS and GDS plots but negatively correlated with trees of Rosaceae in HSD plot. In conclusion, the spatial distribution patterns and associations of the trees from three families changed with the size class, research scale and had different patterns among three plots.

Analysis of stomach contents for Dasyatis chrysonota revealed that diet varied with size and habitat. The diet of all size classes in the surf zone was comprised primarily of Callianassa spp., Donax spp. and unidentified polychaete species. The medium and large size classes fed primarily on Donax spp., whereas the very large size class fed mainly on Callianassa spp. Polychaetes were of secondary importance as prey for the medium size class. The diet of D. chrysonota in the nearshore zone consisted mainly of Balanoglossus capensis and Callianassa spp. Balanoglossus capensis decreased from an index of relative importance (IRI) of 75.3% for the medium size class to 59.9% for the very large size class, whereas Callianassa spp. increased from 22.8% to 39.4% between the medium and the very large size classes. The offshore zone was the only area in which small size class D. chrysonota were caught. The diet of these small D. chrysonota was primarily polychaetes and amphipods. Polychaetes increased in importance in the medium size class, but declined in each successively larger size class. Conversely, Pterygosquilla armata capensis became the single most important prey item for the very large size class, comprising an IRI of 50.9%. The behaviour pattern used by D. chrysonota to locate and extract prey is described.

Evaluation of different tags on survival, growth and stress response in the flatfish Senegalese sole

Grass pickerel (Esox americanus vermiculatus) was collected from 16 streams and rivers in Indiana for diet analysis to determine the effects of this small-bodied esocid on lotic ecosystems. The 128 fish used in the analysis were divided among three size classes- 57–95 mm, 96–150 mm, and > 150 mm. Grass pickerel exhibited an ontogenetic shift in prey type with increasing size. The small size class had a diet dominated by fish, the intermediate size class had a diet dominated by both fish and crayfish, and the large size class had a diet dominated by crayfish. Insects also made up 22% of the volume of small and 29% of the volume of the intermediate size classes, whereas the large size class consumed only 1% insects by volume. Calculated relative importance index (RI) showed that grass pickerel diet shifted from one dominant in fish (RI = 53) at the small size class to one dominated by crayfish (RI = 57) at the large size class. The grass pickerel was opportunistic in its diet choices and fed on increasingly larger items as its total length increased. This choice by grass pickerel in small streams suggests that it is feeding as a top predator and structuring the fish communities in these ecosystems.

Fish monitoring gears rarely capture all available fish, an inherent bias in monitoring programs referred to as catchability. Catchability is a source of bias that can be affected by numerous aspects of gear deployment (e.g., deployment speed, mesh size, and avoidance behavior). Thus, care must be taken when multiple surveys—especially those using different sampling methods—are combined to answer spatio-temporal questions about population and community dynamics. We assessed relative catchability differences among four long-term fish monitoring surveys from the San Francisco Estuary: the Bay Study Otter Trawl (BSOT), the Bay Study Midwater Trawl (BSMT), the Fall Midwater Trawl (FMWT), and the Suisun Marsh Otter Trawl (SMOT). We used generalized additive models with a spatio-temporal smoother and survey as a fixed effect to predict gear-specific estimates of catch for 45 different fish species within large and small size classes. We used estimates of the fixed effect coefficients for each survey (e.g., BSOT) relative to the reference gear (FMWT) to develop relative measures of catchability among taxa, surveys, and fish-size classes, termed the catch-ratio. We found higher relative catchability of 27%, 22%, and 57% of fish species in large size classes from the FMWT than in the BSMT, BSOT, or SMOT, respectively. In the small size class, relative catchability was higher in the FMWT than the BSMT, BSOT, or SMOT for 50%, 18%, and 25% of fish species, respectively. As expected, relative catchability of demersal species was higher in the otter trawls (BSOT, SMOT) while relative catchability of pelagic species was higher in the midwater trawls (FMWT, BSMT). Our results demonstrate that catchability is a source of bias among monitoring efforts within the San Francisco Estuary, and assuming equal catchability among surveys, species, and size classes could result in significant bias when describing spatio-temporal patterns in catch if ignored.

Fish monitoring gears rarely capture all available fish, an inherent bias in monitoring programs referred to as catchability. Catchability is a source of bias that can be affected by numerous aspects of gear deployment (e.g., deployment speed, mesh size, and avoidance behavior). Thus, care must be taken when multiple surveys—especially those using different sampling methods—are combined to answer spatio-temporal questions about population and community dynamics. We assessed relative catchability differences among four long-term fish monitoring surveys from the San Francisco Estuary: the Bay Study Otter Trawl (BSOT), the Bay Study Midwater Trawl (BSMT), the Fall Midwater Trawl (FMWT), and the Suisun Marsh Otter Trawl (SMOT). We used generalized additive models with a spatio-temporal smoother and survey as a fixed effect to predict gear-specific estimates of catch for 45 different fish species within large and small size classes. We used estimates of the fixed effect coefficients for each survey (e.g., BSOT) relative to the reference gear (FMWT) to develop relative measures of catchability among taxa, surveys, and fish-size classes, termed the catch-ratio. We found higher relative catchability of 27%, 22%, and 57% of fish species in large size classes from the FMWT than in the BSMT, BSOT, or SMOT, respectively. In the small size class, relative catchability was higher in the FMWT than the BSMT, BSOT, or SMOT for 50%, 18%, and 25% of fish species, respectively. As expected, relative catchability of demersal species was higher in the otter trawls (BSOT, SMOT) while relative catchability of pelagic species was higher in the midwater trawls (FMWT, BSMT). Our results demonstrate that catchability is a source of bias among monitoring efforts within the San Francisco Estuary, and assuming equal catchability among surveys, species, and size classes could result in significant bias when describing spatio-temporal patterns in catch if ignored.

Island ecosystems provide habitat for many endemic species that may be threatened by nonnative species introductions. We examined nonnative freshwater turtle occurrences and diets to examine potential predation effects on native species in Kawai Nui Marsh, Oahu, Hawaii. No freshwater turtles are native to the Hawaiian Archipelago. The Pond Slider (Trachemys scripta) and Chinese Softshell (Pelodiscus sinensis) were the only turtles found in the marsh after 767 trap days. Trachemys scripta stomachs (n = 50) contained mostly the nonnative plant Commelina diffusa and nonnative snails (Pomacea sp.), whereas Pelodiscus sinensis stomachs (n = 5) contained mostly snails. Interspecific dietary overlap was low and intersexual dietary overlap in the sliders was high, with more diverse female diets. Small, medium, and large size classes of T. scripta stomachs contained different proportions of plant and animal matter, with the small size class containing less plant matter than the medium size class, and the large size class containing a greater volume of animal than plant matter. No native species were found in the stomach contents of the turtles sampled except a freshwater sponge (Heteromyenia baileyi). This lack of native species in their diets may have more to do with the degraded state of the marsh and lack of native taxa than with a preference for nonnative taxa. A potential concern could be nonnative freshwater turtle presence in pristine wetland habitats in Hawaii, because of the higher abundances of native species in those areas.

Muscle fiber hypertrophic growth can lead to an increase in the myonuclear domain (MND), leading to greater diffusion distances within the cytoplasmic volume that each nucleus services. We tested the hypothesis that hypertrophic growth in the white muscle of fishes was associated with increases in the mean DNA content of nuclei, which may be a strategy to offset increasing diffusion constraints. DAPI-stained chicken erythrocytes standards and image analysis were used to estimate nuclear DNA content in erythrocytes and muscle fibers from 17 fish species. Mean diploid (2C) values in fish erythrocytes ranged from 0.78 to 7.2pg. Erythrocyte 2C values were used to determine ploidy level in muscle tissue of small and large size classes of each species. Within each species, mean muscle fiber diameter was greater in the large size class than the small size class, and MND was significantly greater in larger fibers for 11 of the 17 species. Nuclear DNA content per species in muscle ranged from 2 to 64C. Fiber-size dependent increases in ploidy were observed in nine species, which is consistent with our hypothesis and indicates that endoreduplication is occurring during fiber growth. However, two species exhibited significantly lower ploidy in the larger size class, and the mechanistic basis and potential advantage of this ploidy shift is unclear. These results suggest that increases in ploidy may be a common mechanism to compensate for increases in MND associated with fiber hypertrophy in fishes, although it is likely that other factors also affect ploidy changes that occur in muscle during animal growth.

The breadth, correspondence and overlap of the diets of the small and large size classes of the three native species (Galaxias occidentalis, Bostockia porosa and Edelia vittata) and two introduced species (Gambusia holbrooki and Perca fluviatilis) of fishes found in the shallows of the main channel and in the tributary creeks of a south-western Australian river have been compared in each season. Classification and ordination were used to examine the overall interrelationships of the diets across species, size groups, seasons and the location where the fish were caught (channel or creek). The smaller fish had a narrower dietary breadth than larger fish in the spring and summer, presumably reflecting the size limit imposed on prey size by their possession of a relatively small mouth in these seasons. Intraspecific dietary overlap between large and small size classes was usually high in G. occidentalis, but generally low in G. holbrooki and P. fluviatilis, and also in B. porosa and E. vittata when the difference between the lengths of the two size groups was greatest. Dietary overlap was least in autumn when the main prey taxa were most abundant. During winter, the diets of the three native species in the tributaries converged, probably reflecting a relatively low faunal diversity in these highly seasonal water bodies. The only relatively consistent interspecific overlap in diet was between B. porosa and E. vittata. Classification and ordination of the dietary samples separated G. occidentalis (which fed extensively on terrestrial organisms from the water surface) from the smaller P. fluviatilis (that concentrated on copepods in the plankton) and from B. porosa and E. vittata (which ingested primarily benthic organisms). Furthermore, B. porosa tended to ingest larger prey taxa than E. vittata. The diet of Gambusia holbrooki is sometimes dominated by terrestrial insects and at other times by benthic organisms, demonstrating that this species is an opportunistic carnivore. It is concluded that food partitioning by the three native and two introduced fish species in the Collie River is likely to be one of the principal factors facilitating the coexistence of substantial populations of these species in this system.

The mechanistic basis of differences in adult body size between two closely related freshwater amphipod species (Hyalella spp.) are investigated. The study populations, Duck Lake and George Pond, are representative of two sibling species found in southeast Michigan, U.S.A that differ in adult body size and life history. An analysis of relative growth rates across size classes indicated that growth rates were similar in small size classes, but divergent at larger size classes, with higher growth rates in Hyalella from George Pond. Because the timing of the divergence coincides with the onset of reproduction in the Duck Lake population, which reaches sexual maturity at a smaller body size than individuals in the George Pond population, tradeoffs in allocation of resources between growth and reproduction probably contribute substantially to population differences in adult body size. Resource consumption rates were similar between populations in small and intermediate size classes, but large Duck Lake adults had lower consumption rates than George Pond individuals of similar size. Thus, differences in resource consumption rate may also contribute to differences in adult growth rate and body size.

Groups of year 0 and year 2 brown bullhead (Ictalurus nebulosus) that had concluded the summer's growth, were exposed to six different temperatures between 5 and 30 °C for 8 weeks. For both size classes, ration (grams of food per fish per day) increased with temperature. Instantaneous growth (percent body weight per day) was best at 20–30 °C. In the small size class it was higher at 30 °C than at 20–25 °C. Conversion efficiency results were highest at 10–30 °C and 15–25 °C for the small and large size classes, respectively. Relative to seasonal water temperatures in Lake Opinicon, the period of greatest expected growth was June to September. Instantaneous growth (percent total length per day) was high from June to August in the field population. Times of greatest prey biomass, however, were in May and September. Despite the times of maximum temperature and growth not coinciding with that of greatest prey abundance, the field growth rates were comparable to laboratory values. This suggested that food was not limiting in Lake Opinicon and that the brown bullheads achieved their potential growth relative to length of the growth season.