Seasonal Fluctuations In Abundance Research Articles

Population Dynamics and Life Tables of the Mango Mealybug, Rastrococcus invadens Williams, and its Introduced Natural Enemy Gyranusoidea tebygi Noyes in Benin

Life table data for Rastrococcus invadens and its introduced natural enemy Gyranusoidea tebygi were obtained in the field and in the laboratory. The mealybug population's potential rate of increase ranged from 0.066/day to 0.078/day. The potential for increase of the parasitoid was double that of its host. Seasonal fluctuations in abundance of R. invadens were followed from 1988 to 1992 on mango trees in southern Benin. The population density of R. invadens decreased during the rainy seasons and peaked during the dry seasons. Mealybug field sex ratios were extremely variable, and the impact of such variability on the mealybug's potential rate of increase was analyzed. The populations of the exotic encyrtid G. tebygi, introduced into Benin in 1988 for control of the pest, were synchronized with the host populations. The spatial patterns of parasitism distribution in relation to the host population density were either independent or directly density-dependent, both at the tree level and for larger zones. Ho...

Occurrence of Spadella cephaloptera During One Year at Ischia Island (Gulf of Naples)

Abstract. The life cycle of the benthic arrowworm, Spadella cephaloptera, which inhabits the Posidonia meadow at Ischia (Gulf of Naples, Italy), was examined by a one‐year systematic sampling survey and by laboratory culture. The seasonal fluctuations in abundance and the reproductive characteristics indicate that there were two generations of S. cephaloptera in one year; these generations have a different life span. The habitat of S. cephaloptera depends on the growth of the Posidonia meadow; the influence of different factors on the S. cephaloptera population, especially of the Posidonia vagile fauna, is discussed.

Ranging behaviour of feral cattle (Bos taurus) in Doñana National Park, S.W. Spain

The cattle of Doñana (139 individuals in four social groups in 1989) have lived under free‐ranging conditions for centuries. Their ranging behaviour was analysed during a three‐year period. A total of 17,603 locations corresponding to 247 different animals allowed both for the estimation of global and seasonal home ranges of individuals and social groups and for the comparison of movement patterns. Cattle ranging behaviour was not affected by human interference, and was shown to be regulated by a complex interaction of environment, individual and social factors. Habitat structure and seasonal fluctuations in abundance and distribution of resources determined general patterns of ranging behaviour: the greater the concentration of resources, the smaller the home ranges of individuals and social groups. These patterns were modified at an individual level by the sex of the animal and its reproductive status if male. Social influences on ranging behaviour were important because these implied the segregation of home ranges among dominant bulls and among social groups. As a result, there was a great variability in space use and home‐range behaviour.

Seasonal Fluctuations and Diversity of Bark and Wood-boring Beetles in Lowland Forest: Implications for management Practices

SYNOPSIS The phenology and diversity of wood-living beetles attacking Cedrela mexicana, Khaya nyasica and Milicia excelsa were observed for one year with weekly window-flight-trap collections. A total of 150 species (10 known to be common pests of timber) were collected, most of them occurring yearround and a few indicating seasonal fluctuations in abundance. The flight patterns and low catches depicted by some primary attackers could have some management implications in Kimboza or similar areas.

Recruitment of White Mullet in Lake Maracaibo, Venezuela

White mullet Mugil curema forms the basis ofan important artisanal fishery in Lake Maracaibo. I examined recruitment dynamics of juvenile white mullets in Lake Maracaibo to evaluate the potential effects of further anthropogenic habitat alterations. Recruitment was analyzed for seasonal and spatial variation at two stations from 1987 to 1989, by means of beach seines and cast nets. Seasonal fluctuation in abundance was substantial. Evidence suggests that white mullets spawn inside the lake and that salinity and associated factors, such as rainfall and transparency, may greatly influence abundance of juvenile white mullets in Lake Maracaibo. A strong association of juvenile white mullets with the surface, regardless of light phase, was demonstrated. Juvenile white mullets longer than 150 mm total length were uncommon in the coastal waters of Lake Maracaibo. The Lake Maracaibo basin is under extensive development pressure, which has led to extensive modification of coastal areas and loss of mangroves. The proposed establishment of farms for culture of shrimp Penaeus spp. could lead to serious disturbances of the coastal areas through which immature white mullets must migrate. Initiatives for the protection of the white mullet fishery should restrict shrimp farms to zones as far as possible from the coastal areas, limit their number and size, and protect areas near inlets from human-induced changes.

The relative use of abandoned farm clearings and old forest habitats by primates and a forest antelope at Tiwai, Sierra leone, West Africa

West Africa's high canopy forests have largely been replaced by a mosaic of active and abandoned agricultural fields. Use of the regenerating habitats by local fauna has not been well documented. I investigated the relative value of young successional forests, aged 5–12 years, and high forest, to primates and ungulates at Tiwai in West Africa. Four primates, Cercopithecus campbelli, Cercopithecus petaurista, Cercocebus atys, and Pan troglodytes, selected regrowth habitats more often than expected, and three primates, Cercopithecus diana, Colobus polykomos, and Procolobus badius, selected high forest habitat. The Maxwell's duiker Cephalophus monticola used both habitats equally. The Cercopithecus spp. exhibited seasonal fluctuations in abundance in the two habitats, presumably in response to different fruit availabilities. The old forest supported a greater diversity and biomass of primates per unit area compared to regrowth habitats. The high forest was more valuable to the primate community, but young forests were also used by resident fauna, suggesting potential for management as wildlife habitat.

Variations in bird abundance in tropical arid and semi‐arid habitats

Temporal variation in bird abundance was studied during a complete annual cycle in a thorn scrub, a thorn woodland and a deciduous forest in northeastern Venezuela. Abundance of site‐attached and transient birds from different feeding guilds was determined by mist‐netting at 2‐week intervals. Diets were investigated by regurgitated samples. The overall avifauna was characterized by a low number of species but they were present all year despite showing strong seasonal fluctuations in abundance. The number of bird species and individuals peaked before and after the reproductive period. These high values probably were associated with movement of species feeding on plant food during the late dry season and the post‐breeding dispersion of juveniles. Bird richness and abundance were lowest during the breeding season and in the early dry season when food abundance was low. Birds from different feeding guilds showed distinct patterns of seasonal abundance which tended to be similar at all three sites. Transient birds represented a large portion of the avifauna, particularly in nectarivores, frugivores and granivores during the dry season. We used a canonical correspondence analysis to demonstrate that bird abundance was correlated with breeding activity, rainfall seasonality and food abundance, with the influence of each parameter varying according to feeding guilds, spatial behaviour of individuals and habitats. Despite a great turnover in the occurrence of the diverse food types available, species composition remained strikingly constant during the year, with birds responding to seasonal changes primarily through a generalist feeding habit and a highly variable rate of transience.

Ecological studies on two intertidal New Zealand fishes,Acanthoclinus fuscusandForsterygion nigripenne robustum

Abstract Population density, seasonal abundance fluctuations, and habitat preferences of Acanthoclinus fuscus and Forsterygion nigripenne robustum were studied in the rocky intertidal zone at Kaikoura, New Zjaland, from August 1988 to June 1989. Monthly recaptures of marked fishes showed that A. fuscus was common on rocky platforms with small shallow pools; F. n. robustum occurred under larger stones and in deeper channels or larger pools. Most captured A. fuscus were juveniles and adolescents; no seasonal fluctuation in abundance was recorded. The intertidal A. fuscus populations at Kaikoura and Auckland were similar in growth rate and condition factor but differed in age structure. The intertidal population of F. n. robustum was dominated by mature fish; the highest abundance was recorded during the winter spawning season. Each monthly sample of A. fuscus included 40% recaptures, significantly more than in F. n. robustum samples. 31% of displaced A. fuscus returned to their original pool within 1 day an...

Colour Polymorphism in Relation to Spatial Distribution in Some Intertidal Isopods in Northern Spain

The hypothesis that the level of chromatic polymorphism in intertidal isopods is related to their distribution and seasonal fluctuations in abundance was examined in northern Spain. Four species were used,Dynamene bidentata, Dynamene magnitorata, Cymodoce truncataandCymodoce emarginata. Only forDynamenespecies were results consistent with initial hypothesis. The most common colour morph inDynamene bidentatawasuniformiswhich is the most flexible phenotype, allowing effective concealment in most of the environments where the species occurs.Dynamene bidentatais the most abundant species of isopod in northern Spain, where it is abundant along the shore and throughout the year. Distribution of D.magnitorata, Cymodoce truncataand C.emarginatais restricted to macroalgal assemblages at low tidal levels. Seasonality is also important in D.magnitorataand C.truncata. The number of colour morphs and phenotypic diversity was larger in D.magnitoratathan inD. bidentata. Only one colour morph was found in C.truncataand four in C.emarginata.

The zooplankton of the north sea

This review summarizes available knowledge on herbivorous and omnivorous zooplankton of the North Sea. After an introductory chapter on history and general approach of zooplankton studies, the four main contributions review distribution patterns, cycles and trends in temporal variation, trophic interactions and population dyamics and production. The distribution of zooplankton species in relation to hydrography and origin of watermasses is described for copepods. It highlights the influence of Atlantic Ocean influx from the northwest, which to a large extent dominates the species composition and its seasonal variation in the summer-stratified waters. In contrast, the more neritic communities in the southeast region mainly depend on the local populations of the species abundant in coastal mixed waters. The chapter on cycles and trends in temporal variation discusses the differences in seasonal variation with respect to species, area, and community structure in terms of herbivores, omnivores and carnivores. The year-to-year changes are considered as dependent on the overwintering stocks and strategies. Patterns in long-term variation appearing from long-term data series are related to climatic changes, leading to two hypotheses with respect to the effects of changes in wind regime. The chapter on trophic interactions deals with the utilization of primary particulate production by planktonic herbivores and its variation in time and space. Emphasis is put on differences between north and south, which are partly due to differences in species composition, community structure and seasonal variation already discussed in foregoing chapters. The various aspects of copepod grazing are reviewed, but also the role of microzooplankton as both grazers and food organisms is brought to attention. The last chapter deals with population dynamics and production of key species. Seasonal fluctuations in abundance and biomass are discussed and related to underlying population processes and characteristics such as reproduction and life strategy, growth and development, and mortality. Secondary-production estimates inferred from biomass and growth rate estimates are discussed.

Distribution and seasonal occurrence of the hyporheic fauna in a northern California stream

The surface and hyporheic fauna of a second-order reach of a northern California Coast Range stream (Big Canyon Creek, Lake Co., CA, USA) was examined using substrate colonization samplers (i.e. hyporheic pots) during both the wet and dry seasons in the prevailing Mediterranean climate of the region. In terms of total number of macroinvertebrate taxa, the surface (0 cm to −5.0 cm within the stream substrate) level had higher richness than any level within the hyporheic (−5.1 cm to −15.0 cm, −15.1 cm to −25.0 cm, or −25.1 cm to −35.0 cm) from the beginning of the dry season (May) to the beginning of the wet season (October); during this period the surface was not subject to disturbance from wet-season storms. During the wet season, richness at the surface was similar to that observed at any of the three hyporheic levels examined. Macroinvertebrate density at the surface was substantially reduced during the wet season; however, mean surface densities always exceeded those found within the hyporheic zone (from 25% to 78% of total macroinvertebrate numbers were found at the surface). Seasonal fluctuations in abundance of total macroinvertebrates and density of many constituent populations were less within the hyporheic zone than at the surface. Apparently, early instars of abundant surface taxa do not penetrate the interstices, and substrate disturbance due to spates is less in deeper levels. Compared with many hyporheic faunas described from other temperate-zone sites, this hyporheic community shows reduced numerical dominance by the Chironomidae.

Seasonality and its physiological regulation in three neotropical insect taxa from Barro Colorado Island, Panama

Seasonal activity and environmental and hormonal regulation of development and diapause were studied in three different orders of tropical insects at Barro Colorado Island (9°N), Panama. The seed bug, Jadera aeola, reproduces in the late dry season coincident with mass production of its food, seeds of Sapindaceae. Newly emerged adults enter diapause. Population density and food, but not photoperiod, appear to be involved in diapause regulation. Juvenile hormone analogue (JHA) stimulates sexual maturation in both sexes. The fungus beetle, Stenotarsus rotundus, aggregates at the base of a palm tree where it remains in imaginai diapause for up to 10 months. In addition to daylength (Tanaka et al., 1987), humidity plays an important role in regulating diapause termination. Gonad and flight muscle development occur more rapidly at high humidity than at low humidity. Beetles treated with JHA initiate oocyte and flight muscle development but not testis development. 20-hydroxyecdysone has no effect on diapause termination. Flesh flies (Sarcophagidae), when monitored with a meat-baited trap, show striking seasonal fluctuations in abundance. Yet, we found no evidence for diapause in three fly species reared in the laboratory under a range of photoperiod and temperature conditions.

Seasonal changes in abundance and spatial distribution of the soil arthropods in a Japanese cedar (Cryptomeria japonica D.Don) plantation, with special reference to collembola and acarina

AbstractSeasonal changes in abundance and distribution pattern of soil micro‐arthropods were studied in connection with a few environmental factors in a Japanese cedar (Cryptomeria japonicaD. Don) plantation. The soil arthropods were sampled from three different depths at intervals of two months for two years. Of the collected animals (total 51000–155000 m−2), Collembola (20000–76000 m−2), oribatid mites (19000–55000 m−2) and carnivorous mites (6200–21000 m−2) were the numerically dominant animal groups. Low seasonal variations in abundance indicated their seasonal stability in population levels. The trends in seasonal fluctuation were similar among these groups and between the two years, showing bimodal pattern with little peaks in early summer and winter. The pattern of seasonal fluctuation in abundance of carnivorous mites (Pd) was significantly synchronized with that in the total abundance of Collembola and oribatid mites (Pτ). Thus, the number‐ratios (Pd/Pτ) were fairly constant, ranging from 0.10 to 0.25. Seasonal changes in vertical distribution of the three animal groups showed a similar pattern for both years. The downward migrations were shown to be more affected by low temperatures in winter accompanied by snow coverage rather than by the desiccation of the surface soil in summer. All the three groups demonstrated as a whole slightly aggregated patterns of horizontal distribution throughout the two years. Temporal increases in the patchiness indices were observed from summer to autumn when the moisture content of the surface soil was low.

Reproductive patterns of harpacticoid copepods on intertidal macroalgae (Ascophyllum nodosum and Fucus vesiculosus) in Nova Scotia, Canada

Harpacticoid copepods generally showed marked seasonal variation in abundance on intertidal macroalgae (Ascophyllum nodosum, Fucus vesiculosus) on a moderately exposed rocky shore. In some species (Nitocra typica, Mesochra spp., Harpacticus sp., Heterolaophonte spp.) the sex ratio was unbiased, or biased towards males, at peak population densities in summer and fall, but became biased towards females as density decreased towards winter. In other species (Thalestris purpurea, Parastenhelia spinosa, Amphiascopsis sp.) there was no consistent trend in sex ratio. Most species have a protracted period of reproductive activity between spring and fall, as indicated by the occurrence of ovigerous females and copepodites. Some species (Harpacticus sp., Heterolaophonte discophora, Thalestris purpurea) that were absent from macroalgae during winter reappeared with ovigerous females and copepodites in the spring. Tisbe spp. showed no seasonal fluctuation in abundance or sex ratio: ovigerous females and copepodites occurred throughout the year, suggesting continuous reproduction. Reproductive patterns of harpacticoid species on intertidal macroalgae may be related to seasonal variation in temperature and food supply.

Dynamics of hydra populations in Lake Zürich, Switzerland, and Lake Maggiore, Italy

Hydra populations were sampled every two weeks for three years in Lake Zurich and for one year in Lake Maggiore.Hydra fusca was most abundant followed byH. circumcincta andH. attenuata. The first two species showed strong seasonal fluctuations in abundance. Most of the reproduction occurred by budding. In all species, approximately one third of the individuals carried buds while the proportion of individuals carrying gametes was 1.6% inH. fusca and 13% inH. circumcincta in Lake Zurich. In Lake Maggiore very few sexual individuals were found. The ciliate commensalsKerona polyporum andTrichodina pediculus were observed on approximately one third of the individuals.

A Seasonal Analysis of Bird Communities in Southern Nevada

Bird communities were studied on 3 sites in southern Nevada for a period of 15 months, including 2 breeding seasons. Study sites ranged from 975 m to about 1220 m elevation. Vegetation varied from low desert shrub dominated by creosote (Larrea tridentata) and Mohave yucca (Yucca schidigera) to sparse pinyon pine (Pinus monophylla) - California juniper (Juniperus californica) woodland. Twenty-three species bred on 1 or more study sites during 1975 and 1976. Species richness and density of individuals was directly related to elevation in all seasons. Monthly fluctuations in species richness followed a similar pattern on all 3 sites; fluctuations in density were more variable among sites. Spring migration was characterized by more species and individuals than was fall migration; few or no migrants were recorded from the 2 lowest sites in fall. Density and number of species was lowest in winter, particularly January. Seasonal fluctuations in abundance of individuals within major trophic groups differed among groups, probably in response to food availability.

Continuous plankton records: relationships between species of phytoplankton and zooplankton in the seasonal cycle

Seasonal fluctuations in abundance and their geographical variations in the north-east Atlantic Ocean and the North Sea for 49 taxa of both phytoplankton and zooplankton have been studied by multivariate techniques. Most of the observed variability in both seasonal and geographical fluctuations in abundance can be attributed to differences between the taxa with respect to population growth rates modulated by temperature coupled with the distribution of overwintering stocks, with the overall pattern also influenced by the timing of the establishment and breakdown of vertical stability in the water column. The observations indicate that for any species, the similarity between its seasonal cycles in the various areas, which represent a wide range of hydrographic regimes, is appreciably greater than any differences induced by interaction between the species in any particular area.

The influence of fish predation on the abundance cycles of an algal turf invertebrate fauna.

A fauna of small invertebrates in a perennial algal turf habitat showed marked seasonal fluctuations in abundance. These were characterised by a summer (December) peak in the abundance of gammarid amphipods and an autumn (April) peak in polychaete densities. Invertebrate abundance was lowest during the period February-March which coincided with an influx of very high densities of juveniles (0+ year class) of the sparid fish Chrysophrys auratus. Both juvenile C. auratus and also the mullid Upeneichthys porosus achieved their highest densities over coralline turf areas and fed on the associated invertebrates. Gammarid amphipods constituted the main food items of each species. All these observations suggested a key role of fish predators in determining the observed seasonal patterns of invertebrate abundance.This hypothesis was investigated by the use of replicated fish exclusion shields and cages which excluded both species from the algal turf and also permitted an assessment of Upeneichthys porosus feeding in the absence of Chrysophrys auratus. The experiment ran from November until June and covered the period of invertebrate and fish abundance changes. Little evidence of a fish predation effect on either the densities of or the timing of abundance peaks of the invertebrate fauna was detected. Sediment analysis of the cage and control experimental sites revealed no evidence of a cage effect on the microhabitat. It is suggested that seasonal changes in the abundance of invertebrates occurs independently of the high densities of predatory fish recorded in this habitat.

Heteromorphic algal life histories: The seasonal pattern and response to herbivory of the brown crust, Ralfsia californica.

Little is known about the natural history of crustose phases of heteromorphic algae. A qualitative model describing their life history strategies has hypothesized that the morphologies and seasonal occurrences of the two phases evolved largely in response to variable grazing pressure. Crustose phases are predicted to occur when grazing is intense, and erect phases when grazing is reduced. The brown algal crust Ralfsia calfornica, which is the non-obligatory alternate phase of Scytosiphon lomentaria and/or Petalonia fascia, was studied on San Juan Island, Washington, USA. Both phases inhabit pools in the midto upper-intertidal zone, with the crust reaching maximum abundance between 1.8 and 2.3 m. The crust undergoes radical and predictable seasonal fluctuations in abundance, with a maximum in March-April and minimum in August. The erect phases are winter annuals, with maxima in January-April. Thus the crustose and erect phases show high temporal overlap. Colonization studies on new substrata showed that: 1) the crust is ephemeral, with a lifespan of 7-12 months, 2) it reproduces throughout the year and its propagules rapidly colonize new substrata at almost any time, while 3) erect phases appear only during the winter. Manipulations of limpets indicated that they do not directly graze the crust and are not responsible for its seasonal fluctuations in abundance; however, they are crucial to its persistence because they remove potential competitors. The crust fits poorly into models relating morphology to successional status in that it is ephemeral and opportunistic yet is grazer-resistant and grazer-dependent. Furthermore, both the crust and its erect phases are most abundant in the winter, when grazing appears to be least intense. Thus this heteromorphic complex exhibits interesting characteristics not predicted by current models.

Seasonal changes in resident zooplankton sampled by emergence traps in one tree lagoon, great barrier reef

Small resident Zooplankton species which rise from the substratum after sunset were sampled during the winter and summer seasons of 1977 and 1978. Modified emergence traps were used to obtain quantitative overnight samples from five habitats on and around two lagoonal patch reefs: live coral, and coralline rock, both on top of the reefs, sand at undercut and at vertical reef bases, and open sand 1–3 m away from the reef. In summer, at each habitat, many more animals and more species rise off the substratum than in winter. Estimated mean densities of animals rising overnight ranged from 664.9 · m −2 in winter (at undercut reef base) to 5034.7 · m −2 in summer (rock on top of reef). In winter the abundance of animals rising from open sand is significantly lower than that from the top of the reef. A total of 261 taxa was recognized. Samples from all habitats are dominated by copepods, mainly small calanoid and harpacticoid species. The most abundant of these include Stephos sp., Pseudodiaptomus cornutus Nicholls, Peltidium spp., Tisbe sp., and an unidentified thalestrid. In summer, additional copepod and peracarid species become numerous at night over the reef and over open sand. Other major taxonomic groups collected were ostracods, polychaetes, mysids, cumaceans, tanaids, gammarids, and the zoeae of some carid species. Most species appear to have a limited vertical range. Fauna rising from the top of patch reefs is rich compared with that from open sand, and significantly richer in summer than in winter. Faunal analyses indicate the localized distribution of a “coral” fauna and a “sand” fauna. Spatial distribution of these characteristic faunas is more discrete in winter than in summer. The reef base habitats appear to be a transitional faunal zone which contains elements of both “coral” and “sand” faunas. Seasonal fluctuations in abundance, composition and spatial distribution are similar to seasonal trends found in light-trap sampling of resident Zooplankton in the same seasons, and in similar locations, on Heron Reef. Sampling techniques, limitations, and results are compared with those of single-season emergence trap studies in other coral reef regions.