Seasonal Development and Morphological Variability of Cyclotella ocellata (Bacillariophyceae) in the Eutrophic Lake Dagow (Germany)

The development of Cyclotella ocellata Pantocsek was studied systematically in the eutrophic, dimictic hardwater Lake Dagow from March to October, 1994. Cyclotella ocellata was the most important centric diatom in the lake with a maximum cell density of 6 × 10⁶ cells 1⁻¹. The seasonal development, characterized by a spring and a summer maximum, is considered in relation to environmental factors and the succession of the phytoplankton community. The amount of Cyclotella ocellata biomass as a proportion of the total phytoplankton biomass varied from 0.5 to 35%. In addition, seasonal changes in cell size and feature associated with sexual reproduction of Cyclotella ocellata were documented. Light and electron microscopic investigations demonstrate an extremely wide range of morphological variability of this natural population.     

Population dynamics of the West Indian sweetpotato weevil Euscepes postfasciatus (Fairmaire): a simulation analysis

The West Indian sweetpotato weevil Euscepes postfasciatus (Fairmaire) is a major pest of the sweet potato Ipomoea batatas (L.) Lam. and this weevil is a target of an eradication program using the Sterile Insect Technique in Okinawa Prefecture, Japan. Understanding the population ecology is essential in the planning of an eradication program; hence, a host‐plant infestation survey and light trap survey have been conducted to monitor the population dynamics of the weevil on Kume Island (Okinawa Prefecture), which is the target area of the trial weevil eradication project. Seasonal tendencies of weevil density were found in these field surveys, but the tendency found in the host‐plant infestation survey was not seen every year, and the effectiveness of the light trap is somewhat suspect. To confirm the reliability of the tendency observed in these field surveys, the present study attempted to explain the tendency by a seasonal temperature change using a temperature‐based model of weevil population dynamics. The seasonal changes of weevil density differed according to host plants and host‐plant fields. The seasonal changes of weevil density inside the host plant Ipomoea indica and outside the host plants in I. indica fields were consistent with those predicted by the model. However, those inside the host plant Ipomoea pes‐caprae in the host‐plant infestation survey were contrary to the predicted ones, and those observed outside host plants in I. pes‐caprae fields by the light trap survey were not in good agreement with the predicted ones. It was concluded that the seasonal change of the weevil density observed in I. indica and I. indica fields can be explained by a seasonal temperature change, but factors other than seasonal temperature change are needed to explain those in I. pes‐caprae and I. pes‐caprae fields.     

Structure and annual biomass production of Nymphoides peltata (Gmel.) O. Kuntze (Menyanthaceae)

In 1980, the monthly changes in biomass and plant surface area, together with aspects of production of Nymphoides peltata (Gmel.) O. Kuntze were studied in a backwater of the river Waal (The Netherlands). Furthermore, the seasonal changes in the vertical stratification of the biomass were studied in concrete tanks. These seasonal changes were studied with the harvest method, while the estimation of the net primary production was based upon biomass data and turnover rates of various plant parts. The data thus obtained are compared with those of other water plants, especially other floating-leaved macrophytes. In 1980, N. peltata reached its peak biomass in August being 372 g AFDW m⁻² (ash-free dry weight). The annual net productivity of Nymphoides was estimated to be 1036 g AFDW m⁻². The leaf blades and their petioles contributed most to the production.     

The infestation and dispersion patterns of Carcinonemertes spp. (Nemertea) on their crab hosts

Seasonal changes in the infestation and dispersion patterns of egg predatory nemerteans on their crab hosts were analyzed. Marked differences in the seasonal patterns of infestation were noted between worm species, yet, common patterns in the aggregation of the worms were found. Worm aggregation increased at the onset of the reproductive seasons of the hosts, and at the nadirs of the reproductive seasons for those hosts with year round breeding. The aggregation patterns of two worm species fluctuated with the physical environment of their estuarine hosts. Salinity changes as a result of seasonal rains may have caused changes in the underlying dispersion patterns of Carcinonemertes epialti on Hemiarapsus oregonensis, and C. mitsukurii on Portunus pelagicus. Lastly, the embryogenic cycle of the host species was significant in shaping the infestation and aggregation patterns of C. epialti on Cancer anthonyi and C. regicides on Paralithodes camtschaticus. Worm immigration and emigration were linked to crab embryogenesis and directly influenced the dispersion patterns of the worms.     

Trophic ecology of the black drum,Pogonias cromis (Sciaenidae), in Mar Chiquita coastal lagoon (Argentina)

This is the first documentation on the feeding habits of the black drum, Pogonias cromis, in waters of South America. The aim of the investigation was to determine the trophic ecology of P. cromis in the Mar Chiquita coastal lagoon (37°32′–37°45′S; 57°19′–57°26′W) from stomach content analyses of 109 P. cromis specimens. Samples in various sizes were collected monthly using various types of fishing gear. The results showed that this species is a benthic predator focusing on bivalves and crabs. permanova results indicated significant seasonal differences in the diet. This pattern reflected seasonal changes in prey abundance and availability, which produced changes in both foraging strategy and trophic niche breadth. This indicates that P. cromis is a versatile predator, adapting its feeding strategy in response to a seasonal shift of prey abundance, and indicating an opportunist behavior.     

Demography of Carex brevicuspis (Cyperaceae) rhizome populations: a wetland sedge that produces both elongated and shortened rhizomes

The wetland sedge Carex brevicuspis reproduces vegetatively by producing short rhizomes to form clumping ramets phalanx) and long rhizomes to form spreading ramets (guerrilla), resulting in a combined growth form. As an initial step towards understanding the adaptation of Carex growth strategies to seasonal fluctuations in wetland habitats, we investigated the density and composition of C. brevicuspis rhizome populations immediately after flooding (November), in winter (January), in spring (March), and before flooding (May) in the Dongting Lake wetlands, China. The total rhizome density peaked in winter and was lowest before flooding. A large rhizome population in winter may enable C. brevicuspis to survive the seasonal cold weather and recruit a shoot population in the spring. A small rhizome population before flooding may optimize reproductive allocations and be a strategy for enduring the long flooding season. Regardless of date, short rhizomes comprised the majority of the rhizome population (73.0% in March to 98.2% in May). This indicates that C. brevicuspis primarily uses a phalanx growth strategy to utilize locally abundant resources in wetlands. The percentage of long rhizomes in the rhizome population varies significantly between seasons (1.8% in May to 27.0% in March), indicating that growth form also changes with seasonal fluctuation of wetland habitats. The results show that C. brevicuspis may adapt to seasonal changes in wetland habitats through changes in demography of rhizome populations.     

Seasonal effects on metabolism and thermoregulation abilities of the Red-winged Starling (Onychognathus morio)

Basal metabolic rate (BMR) of birds is beginning to be viewed as a highly flexible physiological trait influenced by environmental fluctuations, and in particular changes in ambient temperatures (T_a). Southern Africa is characterized by an unpredictable environment with daily and seasonal variation. This study sought to evaluate the effects of seasonal changes in T_a on mass-specific resting metabolic rate (RMR), BMR and body temperature (T_b) of Red-winged Starlings (Onychognathus morio). They have a broad distribution, from Ethiopia to the Cape in South Africa and are medium-sized frugivorous birds. Metabolic rate (VO₂) and T_b were measured in wild caught Red-winged Starlings after a period of summer and winter acclimatization in outdoor aviaries. RMR and BMR were significantly higher in winter than summer. Body mass of Starlings was significantly higher in winter compared with summer. The increased RMR and BMR in winter indicate improved ability to cope with cold and maintenance of a high T_b. These results show that the metabolism of Red-winged Starlings are not constant, but exhibit a pronounced seasonal phenotypic flexibility with maintenance of a high T_b.     

A biometric study of seasonal variation in worker wasps (Hymenoptera: Vespidae)

The seasonal changes in some morphometric characters of worker wasps of Vespula vulgaris and Vespula germanica are described and discussed in relation to colony populations and economics.     

Influence of Pluchea lanceolata (Asteraceae) on selected soil properties

Allelopathic interference may operate simultaneously, sequentially, and/or in combination with other mechanisms of interference such as nutrient interference. It is hypothesized that under field conditions, allelopathic plants may cause changes in chemical characteristics of soils in addition to qualitative and quantitative changes in the allelochemical status of soil infested with the allelopathic plant. To test this hypothesis, the perennial allelopathic weed Pluchea lanceolata was selected. A comparative study of P. lanceolata-infested soils, and soils 10, 20, 30, and 40 m away from the weed was undertaken to examine soil characteristics and quantitative and qualitative variation in soil phenolics. Impact of seasonal weather on the biotic and chemical characteristics of P. lanceolata, and quantitative variation in phenolics of weed-infested soils was also studied. Growth experiments were conducted to study the seasonal impact on allelopathic interference of P. lanceolata toward certain crop plants. Results indicate that P. lanceolata influences soil properties in addition to causing variation in soil phenolics. Two-way tests (i.e., analyzing allelopathic and nutrient interference) should be run regardless of whether one is studying allelopathy or nutrient interference and it is important to test allelopathy in all studies dealing with nutrient interference.     

Migratory Orientation of Blackcaps (Sylvia atricapilla): Population-specific Shifts of Direction during the Autumn

The population-specific orientation of two groups of blackcaps (Sylvia atricapilla), one from southwest Germany, the other from easternmost Austria, was studied outdoors in Emlen funnels. We investigated whether a seasonal shift in the migratory direction — as expected for the Austrian birds from ringing recoveries — occurs under experimental conditions and in a seasonally constant magnetic field. The West German birds, for which no shift was expected, oriented southwest during the entire season. The Austrian birds oriented southeast in October and southsouthwest in November. The clockwise shift by about 60° occurred within a 10-day period. The results indicate that in this species seasonal changes of migratory direction are probably based on an endogenous program, occur without the birds actually migrating and are independent of changes in the magnetic field. Our results provide further evidence that directional shifts in Sylvia warblers may be controlled by a different mechanism than in pied flycatchers (Ficedula hypoleuca).     

Intraspecific differentiation of social behavior and shelter selection in Mesobuthus gibbosus (Brullé, 1832) (Scorpiones: Buthidae)

We compared seasonal shelter selection and social behavior of Mesobuthus gibbosus from autumn to mid-summer in two similar phryganic ecosystems, in continental Greece (near Volos city) and in insular Greece (eastern Crete), and in the laboratory under simulated abiotic conditions. Our results showed that shelter selection is a critical indicator of the seasonal social behavior of the species. The abrupt climatic changes in spring caused a differentiation in shelter selection between the cold period (November–February) and the warm period (March–June) at both sites. Sociality was exhibited only during winter in the field and was more extensive under cold conditions in the laboratory. Co-occurrence of scorpions proved to be age-specific, facilitated by population density and by harsh abiotic conditions during winter, and negatively influenced by intraspecific competition, which was higher in continental Greece. The response of scorpions to changes of abiotic factors reveals synchronization of seasonal shelter selection with climatic changes.     

Reproduction in Coquerel's dwarf lemur (Mirza coquereli)

Most nocturnal Malagasy primates, as well as many diurnal species, are highly endangered in their natural habitat. Captive breeding programs have been established for many species, but detailed information on reproduction is only available for three nocturnal taxa: the mouse lemur (Microcebus murinus), the dwarf lemur (Cheirogaleus medius), and the greater dwarf lemur (Cheirogaleus major). In this study, we present data for another nocturnal Malagasy primate, Coquerel's dwarf lemur (Mirza coquereli), which has been propagated since 1982 at the Duke University Primate Center. Unlike all other Malagasy primates bred in captivity, M. coquereli cycles throughout the year, and is clearly less seasonal in its birth distribution than is C. medius or M. murinus. Estrous intervals ranged between 19 and 30.5 days. Estrus lasted no longer than 1 day. After an average gestation length of 89.2 days, litters of one or two were born. Females cycled for the first time between 8 and 15 months of age, and gave birth for the first time between 12.8 and 33.5 months of age. The earliest mating of a male leading to conception was observed at the age of 17 months. For males and females, an increase in daylength appears to trigger pubertal development. Males had seasonal changes in testicular volume which were not explained by covariation with body weight. Maximum testis size occurred in spring, when breeding activity was highest. The occurrence of year-round reproduction in M. coquereli, and the absence of seasonal fattening and/or hibernation, along with their specialized winter diet, may be correlated. © 1995 Wiley-Liss, Inc.     

DISTRIBUTION AND TAXONOMIC REAPPRAISAL OF CTENOCLADUS (CHLOROPHYCEAE: CHAETOPHORALES)1,2

The distribution of the rare filamentous green alga Ctenocladus Borzi was examined on a world-wide basis. All the collection sites are restricted to specific inland habitats. Most of these locations are in arid regions of North America with a few scattered sites in Peru, Sicily, and Siberia. This alga has been referred to 2 genera, either Ctenocladus or Lochmiopsis Woronochin & Popova, for the past 45 years. Based on field observations, laboratory cultures, and herbarium material, Lochmiopsis is considered synonymous with Ctenocladus. The response of vegetative cell dimensions to seasonal changes (i.e., osmotic potential and temperature) in 3 saline habitats in British Columbia was also investigated. Results from the study, along with laboratory dilutions of natural saline waters, showed that cell dimensions arc not valid criteria for separating species of Ctenocladus as proposed by some authors. Consequently Ctenocladus is considered a monotypic genus with physiological variants responding to seasonal environmental conditions.     

The effect of diet quality on gut anatomy in British voles (Microtinae)

Three species of British voles, the bank vole Clethrionomys glareolus, the field vole Microtus agrestis and the water vole Arvicola terrestris were maintained on diets of seed and plant leaf material to investigate changes in gut anatomy. C. glareolus and M. agrestis showed significant changes in most regions of the gut; they developed longer and heavier tracts when on a highfibre diet. This response may be important in enabling these animals to withstand seasonal changes in diet quality.     

The Decapod Custacean Community of the Guadalquivir Estuary (SW Spain): Seasonal and Inter-Year Changes in Community Structure

Monthly samples were taken from May 1997 to March 2002 at three sampling sites within the last 32 km of the Guadalquivir Estuary. Twenty-four decapod crustacean species were recorded of which Crangon crangon (Linnaeus), Melicertus kerathurus (Forskal), and Palaemon spp. represented 99% of all collected individuals. These three dominant species showed a similar seasonal density pattern even though peaks in M. kerathurus were lower. Their densities were positively correlated (p < 0.01) with water temperature and salinity, but negatively with turbidity. The highest correlation corresponded to temperature in Palaemon spp. and to salinity in C. crangon and M. kerathurus. Therefore, the total estuarine decapod density also showed a regular seasonal pattern having the lowest figures in late autumn and winter and the highest in spring and summer. In addition, it was positively correlated with water temperature and salinity, but negatively with turbidity. Density decreased upstream, mainly due to the higher density of C. crangon and M. kerathurus in more saline waters. Non-metric multi-dimensional scaling ordination of samples also indicated a regular seasonal change in the community, even though inter-year differences between dry and rainy winters were especially great. The first ordination axis was significantly correlated with environmental variables, while the second axis seemed to split samples up following seasonal community changes in species’ composition and dominance.     

Diel and seasonal variation of Striped Cuckoo (Tapera naevia) vocalizations revealed using automated signal recognition

Studying seasonal changes in the vocal activity of birds may shed light on the function of avian vocalizations and the phenology of life history events. Our current knowledge regarding the seasonality of the vocal behaviour of tropical birds in general, and avian brood parasites in particular, is very limited. Here, we employed passive acoustic monitoring with automated signal recognition to monitor the vocal behaviour of the Striped Cuckoo Tapera naevia over a complete annual cycle in the Brazilian Pantanal. We evaluated whether the pattern of vocal activity differed between the two main vocalizations of the species (sem-fim and wee-series songs) and whether vocal activity varied with time of day and season. The diel pattern of vocal activity for both vocalization types showed a bimodal pattern, with the first peak of vocal activity in the few hours after sunrise and the second peak before sunset, in agreement with prior studies in other cuckoos. The sem-fim song was also produced during the night, while the wee-series song was produced only during the day. Both vocalization types showed clear seasonality and were produced between mid-June and mid-February. Seasonal changes in vocal activity suggest that the Striped Cuckoo breeds during the dry season and leaves the study area during the flooding period. The seasonal pattern of the wee-series song showed strong seasonality, with 90% of these calls detected in September and October, whereas the sem-fim song showed weaker seasonality, with 80% of the calls detected during the July–October period. Our study indicates that automated signal recognition might be a reliable tool for monitoring cuckoos. Further research could evaluate whether the different seasonal patterns of the sem-fim and wee-series songs of the Striped Cuckoo are related to different functions.     

High interannual variation in the diet of a tropical forest frugivore (Hylobates lar)

Frugivores must deal with seasonal changes in fruit availability and changes from year to year, as most species of tropical forest fruiting trees have considerable interannual variation in phenology and many are mast fruiters. We quantified seasonal and interannual changes in the fruit diet in a frugivore and important seed disperser, the white‐handed gibbon, Hylobates lar, in Thailand. We used 40‐d following data during April and May replicated in six consecutive years to study interannual variability in the diet and compared it with seasonal changes measured in monthly samples of the same size collected in three successive years. The 40‐d periods of following also allowed us to measure the decline in dietary similarity with time over a finer scale. We measured fruit diet similarity between replicated 5‐d periods using the percentage overlap (Renkonen's) index and Jaccard's similarity index. Seasonally, average dietary overlap between adjacent months was low, and similarity approached zero after four months. Average rate of decline in similarity exceeded 20 percent per 5‐d period. Variation in fruit species in the diet between years was high and was correlated with interannual variation in fruiting phenology. The strongest correlation occurred in the case of Nephelium melliferum, a highly preferred species that dominated the diet in good fruiting years. It is difficult to separate changes in food species preference from changes in availability from year to year. We devised a relative measure of preference that depends on the degree to which the gibbons rely on prior knowledge to find sources.     

Feeding ecology of the shortnose greeneye Chlorophthalmus agassizi Bonaparte, 1840 (Pisces: Chlorophthalmidae) in the eastern Ionian Sea (eastern Mediterranean)

The feeding ecology of Chlorophthalmus agassizi from the North Ionian Sea was examined in specimens caught during daylight hours on a seasonal basis from December 1996 to November 1997, at depths between 250 and 800 m (92 stations, total). Chlorophthalmus agassizi showed a mixed feeding strategy, exploiting a wide range of prey including mesopelagic, benthic and endobenthic organisms. Crustaceans and fishes were dominant food items in the diet year round. Diet composition showed slight seasonal fluctuations; these variations were correlated with food availability and reproductive activity. However, ontogenetic changes in the diet were relatively clear, despite the high overlap observed between small, medium and large individuals. Larger individuals are more efficient hunters that exhibit selection of prey with good swimming capabilities; smaller individuals consume prey with low mobility. Chlorophthalmus agassizi seem to be adapted to a food‐scarce environment, as typified in the deep‐water habitats of the Ionian Sea, and exploit all available niches.     

Seasonal photosynthetic performance of the endemic antarctic red algaPalmaria decipiens (Reinsch) Ricker

 A male gametophyte of the endemic Antarctic red macroalga Palmaria decipiens (Reinsch) Ricker was cultivated under fluctuating daylengths, simulating the seasonal changes at the site of collection (King George Island, Antarctica). The plant was maintained at 0±1°C, an irradiance of 25 μmol m^-2 s^-1 and under growth-saturating nutrient conditions. Samples were taken at intervals of 3–6 weeks to measure growth, photosynthesis, dark respiration and pigment content. The growth optimum in spring coincided with a higher photosynthetic activity. Whereas dark respiration was constantly low over the year, there was a rapid increase in maximum photosynthetic rate (P_max) in conditions corresponding to September and October. This was correlated with a change in the initial slope (α) of the photosynthesis versus irradiance (P vs I) curve. Higher activity in photosynthesis mainly resulted from higher Chl a and phycobilin concentrations during Antarctic spring, an indication of an increase in absorption cross-section areas of photosynthetic reaction centres. These changes in physiology are discussed in relation to the seasonal growth “strategy” of the species, which is controlled by seasonal variation in daylength. Received: 27 February 1995/Accepted 3 October 1995     

Seasonal changes in glomerular filtration rate in Antechinus stuartii (Marsupialia: Dasyuridae)

The small marsupial Antechinus stuartii experiences a synchronised life cycle that culminates in complete male mortality (within 3 weeks) following the 1 week mating period in mid-August (late winter). There are pronounced physiological changes in male A. stuartii over the life cycle and renal function was assessed for correlation with these changes. Glomerular filtration rate and urine and plasma electrolytes were determined in male and female A. stuartii in February, May, July and August. Females showed little change in glomerular filtration rate, except for pre-mating values in August which decreased. In contrast, glomerular filtration rate of males decreased significantly in July and August. Plasma sodium and chloride levels were higher in males than females and were higher in animals in July and August than in February and May. Plasma potassium levels dropped in both males and females in July and August. Plasma osmolality was higher in animals in February compared to animals from May and August. However, there were no significant sex or seasonal differences in urine electrolytes, although urea concentration was higher in females than males. Urine osmolality was higher in both sexes in July and August. There were no significant differences in total excretory rates of sodium, potassium or chloride between sexes or between seasons. Many of the alterations in renal function are correlated with known physiological and hormonal profiles in A. stuartii. This is the first observation of seasonal changes in glomerular filtration rate that are unrelated to dietary and water stresses. Accepted: 8 September 1997