Seasonal Changes In Distribution Research Articles

Seasonal Changes in Distribution of Intercepted Photosynthetically Active Radiation for Layer and Dry Matter Production in Spring Wheat Canopy.

In order to understand the relationship between solar radiation and biomass production within crop canopies, penetration, reflection, and interception of photosynthetically active radiation (PAR) were measured in the canopy of a spring wheat variety called Haruyrutaka. The relationship was evaluated by looking at the plant and canopy architecture, the amount of intercepted PAR, the crop growth rate (CGR), and the conversion of PAR into dry matter (EPAR). The interception (%) of PAR increased rapidly from seedling emergence to flag leaf emergence. It was more than 90% from flag leaf emergence to maturity. Within the canopy, the interception of PAR by the ear was more than 30% after anthesis. The interception of the flag leaf increased from anthesis to milk ripe stage as the flag leaf reclined from an erect to a horizontal position. Interception decreased from the milk ripe stage to maturity as the flag leaf further drooped. Two regression lines fit the relationship between the amount of intercepted PAR by the living plant and the CGR for canopy. The slope of the line after heading was higher than the one before heading. This is because the ear covered the upper layer of the canopy so that assimilation increased under high PAR conditions and consumption increased under low PAR conditions. EPAR changed throughout the growing season as the plant and canopy configuration changed.

Seasonal changes in distribution and habitat differences among dolphins in the eastern tropical Pacific

Large-scale patterns of dolphin distribution and oceanography were studied from research-vessel surveys conducted in the pelagic eastern tropical Pacific dunng June to November 1982, 1986 and 1987. Substantial changes were observed in relation to previously reported winter distributions for spotted and/or spinner dolphin schools (Stenella attenuata and/or S. 1ongirostris)and for striped dolphin schools (S. coeruleoalba). These dolphin species were sighted in abundance west of 120W along 10N coincident with seasonal shoaling of a thermocline ridge. No seasonal distribution changes were observed for common dolphin schools (Delphinus delphis); as in the winter, they occupied upwelling-modified waters of the region. Highest-density areas for the 3 school types were clearly separated spatially, and the thermocline depths and sigma-t's of sighting localities were statistically different between spottedlspinner dolphin schools and common dolphin schools. Striped dolphin schools could not be discriminated from the other 2 types based on these habitat variables, indicating other factors or processes contribute to the observed spatial separation of the 3 distributions.

Seasonal Distribution and Abundance of Dugongs in the Western-Gulf-of-Carpentaria

Aerial surveys of coastal waters (27 216 km2) in the western Gulf of Carpentaria during the dry season of 1984 and wet season of 1985 indicated no major seasonal changes in distribution and relative abundance of dugongs. Minimum population size in the dry season was estimated as 16 816 � 2946 (standard error), with a relative density of 0.62 k 0.11 km-2, and that for the wet season 16 846 + 3257, with a relative density of 0.62 � 0.12 km-2. The estimates exclude 5% of observations which could have been either dugongs or Irrawaddy dolphins, and were corrected for submerged dugongs and those missed on the surface. Dugongs were unevenly distributed over the study area, and neither mean group size nor proportion of calves varied between seasons. Dugong abundance was correlated with area of available seagrass. The catch rate of dugongs by Aboriginal people off Numbulwar decreased six-fold between the 1960s and 1985 (60 to 10 p.a.), possibly due to excessive hunting.

Food Habits and Distribution of Wintering Canvasbacks, Aythya valisineria, on Chesapeake Bay

Baltic clams (Macoma balthica) were the predominant food items of 323 canvasbacks (Aythya valisineria) collected throughout Chesapeake Bay during 1970–1979. Natural vegetation constituted 4% of the food volume. Widgeongrass (Ruppia maritima) and redhead grass (Potamogeton perfoliatus) constituted the greatest percent volume and frequency of occurrence among the plant species, whereas wild celery (Vallisneria americana) constituted only a trace of the food volume. These results contrast with historical records of food habits of canvasbacks in Chesapeake Bay. Canvasback population estimates during the 1970’s were examined to detect annual and seasonal changes in distribution. Linear regression analyses of winter canvasback populations in the bay showed a significant decline in the upper-bay and middle-bay populations, but no significant changes in the lower-bay and Potomac River populations. The changes in winter distribution and abundance of the canvasback appear related to changes in natural food availability, which is the result of altered environmental conditions.

Insect size tactics and developmental strategies.

Insect size tactics or developmental strategies are discussed in relation to decisions individuals make about when to mature. Such decisions carry with them costs and benefits in terms of that individual's reproductive success. Whenever size affects fitness, selection should act such that individuals evaluate the costs and benefits due to changes in size and should mature when the ratio of benefit to cost is maximized.Predictions about seasonal changes in adult sizes within a population are tested on two species of mole cricket, Scapteriscus acletus and vicinus. Specifically, individuals maturing in the fall should be larger than average because there is no cost associated with delayed reproduction since reproduction occurs only during spring months. Smaller than average individuals should remain in juvenile stages and get larger before reproducing. Also it is predicted that as the spring reproductive season progresses a greater proportion of smaller individuals should mature because the costs due to delaying reproduction increase. The changes in seasonal distribution of adult sizes of mole crickets support the predictions and suggest that individuals make decisions about when to mature based on costs and benefits associated with changes in size.

Effects of agricultural drainage on streamflow in the Middle Thames River, Ontario, 1949–1980

The effects of surface and subsurface agricultural drainage on streamflow in the Middle Thames River have been studied through the analysis of changes in the volumetric response, changes in the seasonal distribution of streamflow volumes, and changes in the time distribution of runoff response of the Middle Thames in the period 1949–1980.The results indicated that only small changes in streamflow behaviour occurred in the Middle Thames for the period studied. There is evidence of a reduction of less than 25% in the time-to-peak of storm hydrographs on the watershed, but with little change in peak flow rate or centroid-to-centroid lag time. This is consistent with increased channel velocities in hydraulically improved municipal drains, coupled with an increased proportion of storm flow being diverted from overland runoff to rapid subsurface runoff through subsurface pipe drainage. There is no evidence of appreciable changes in volumes of runoff for individual storms or as annual total streamflow or changes in seasonal distribution of streamflow. Key words: agricultural drainage, streamflow, unit hydrograph, storm runoff.

Ecology of a Population of Crocodylus acutus at a Power Plant Site in Florida

This paper presents the status and ecology of a population of Crocodylus acutus associated with the Turkey Point power plant in Florida. Distribution, habitat preference, repro- duction, population size and structure, and recruitment and dispersal are discussed. Nesting occurs on spoil berms in the cooling canal system. The Turkey Point population con- tributes 10% of the annual production of hatchlings in southern Florida. Crocodiles have exploited previously unavailable, man-altered nesting habitat in approximately 4 years. The resident population consists of a minimum of 19 adult, subadult and juvenile crocodiles. This population exhibits differential habitat preferences according to size class, and shows seasonal changes in distribution. Salinity regime is a factor in these trends. Ecology and population structure are similar to those of the population residing in the more pristine habitat of Everglades National Park. Long distance dispersal and recruitment into the Turkey Point population are documented. The long-term outlook for the population in this man-altered habitat is for growth and expansion.

Occurrence, distribution, and feeding habits of juvenile lumpfish, Cyclopterus lumpus L. in the Bay of Fundy

Juvenile lumpfish (< 55 mm length) occur in near-surface waters of the Bay of Fundy from July to September. Samples collected simultaneously with neuston and subsurface nets indicate that the juveniles occur primarily in the top few centimetres of the water column. Seasonal changes in distribution may be related to wind drift of surface waters and the residual circulation of the inner Bay. The length–weight relationship (W = 8.7 L3.36 × 10−6) indicates allometric growth up to 50 mm, at which time lumpfish probably leave surface waters and adopt a pelagic or benthic existence. Juvenile lumpfish feed on a wide range of near-surface plankton, shifting with growth from harpacticoid copepods (particularly Harpacticus chelifer) to the amphipods Calliopius laeviusculus and Parathemisto gaudichaudi.

Seasonal variation in the distribution of white clover (Trifolium repensL.) stolons among 3 horizontal strata in 2 grazed swards

Abstract White clover stolon material from pasture under rotational grazing by cattle (RGC) and set stocking by sheep (SSS) was dissected into 3 classes: aerial stolon, surface stolon, and buried stolon. The length and dry weight of stolon in each class were measured. Stolon length and weight measurements showed the same trends. The amount of stolon in each class varied markedly with time of sampling and grazing management. The pattern of seasonal change in distribution among the classes was similar for both grazing managements. Aerial stolon peaked in March and then decreased to very low levels in winter and spring. Surface stolon peaked in summer-autumn and was at a minimum in winter and spring. Buried stolon contributed a large proportion of total stolon weight at all times of the year, but varied markedly with season, ranging from a minimum of 30% and 40% in late summer to 87% and 99% in early spring in RGC and SSS swards respectively. There was a sudden decrease by 50% in the size of the buried-stolo...

Resource partitioning by small mammals in lowland heath communities of south-eastern Australia

Habitat selection by seven species of small mammals was investigated in three areas of heathland in Victoria. A total of 12 120 trapnights over 22 months was used to assess preference for different vegetation groups formed by clustering trap sites on (a) floristic and (b) structural criteria. Rattus lutreolus proved to have both floristic and structural requirements. Seasonal changes in distribution in relation to rainfall appeared to be dependent on soil type. Greatest movement occurred on sandy podzol soils. Pseudomys shortridgei selected the most diverse vegetation types. Rattus fuscipes preferred wet, structurally complex vegetation. Mus musculus appeared to fill the niche of Antechinus minimus and partially replace A. stuartii and A. flavipes when Antechinus spp. were absent. M. musculus seems to commonly fill three niches in these heathlands: fossorial insectivore, scansorial insectivore and immediate post-fire omnivore. A small mammal community structure of five major food niches may be common to both heathland and forest communities of south-eastern Australia.

Seasonal changes in distribution of intertidal macrofauna in the lower Mersey Estuary, U.K.

The distribution of intertidal macrofauna on the east shore of the Mersey Estuary changes from season to season. Principal components analysis identified a faunal gradient in winter which is oriented partly long-shore and partly down-shore. This pattern is simplified in spring and summer when distribution is graded everywhere perpendicular to the shore but this breaks down in autumn with the return of a long-shore gradient. The continual re-adjustment of the intertidal community is related to the seasonal change in the proportion of very fine sand and mud. The physical properties of the estuary which determine turbidity and sedimentation on the east shore are discussed with regard particularly to organic pollution associated with the sediments.

Determinants of Spatial Distribution of Rocky Mountain Bighorn Sheep

Determinants of Spatial Distribution of Rocky Mountain Bighorn Sheep

Population Biology of Alewives, Alosa pseudoharengus, in Lake Michigan, 1949–70

Alewives were unknown in Lake Michigan before 1949, but became extremely abundant in the 1960s and soon exceeded the carrying capacity of the lake. In 1967 they were decimated by a lakewide mass mortality, and have since been less abundant as "adults" (≥120 mm long), although numerous young were produced in 1967–70 and the adult population appeared to be gradually increasing. Alewives were studied intensively during 1962–70 on the basis of collections made primarily with bottom trawls. Principal considerations in the population study include effects of seasonal changes in distribution on length composition of young and adults, sex and maturity in relation to size and age at recruitment into adult stocks, and changes in age, growth, condition, and population structure that accompanied the drastic changes in abundance.A substantial increase in the age of adults in the bottom stocks and on the spawning grounds was among the important population changes after the 1967 die-off. Growth of older adults also increased appreciably immediately after the die-off, and a sharp increase in average weight (16–26%) over a standard range of lengths was maintained in 1968–70. Selective depletion of zooplankton by alewives was evidence that overabundance decreased the food supply, depressed growth, and caused the poor condition that made alewives vulnerable to excessive mortality in 1967. Although poor condition in fall undoubtedly increased winter and spring mortality in the mid-1960s, alewives apparently were stressed by below-average temperature in the winter of 1969–70, and experienced a light die-off through May 1970 despite their good condition and relatively low population density the preceding fall.The population upsurge that preceded the 1967 die-off was reflected by a fivefold increase of adults in the fall index catch (in trawls) from 1962 to 1965 and 1966. The index catch then dropped 70% in fall 1967. Mortality among the 1960–64 year-classes, as represented by annual losses from age III to age IV in the index catch during 1964–68, ranged from 40% in 1965 to 89% in 1967, and averaged 68%. Assessment of mortality from the index catches was difficult because the age of alewives at full recruitment into bottom stocks increased from III in the mid-1960s to IV or older in 1968–70, when alewives remained longer at midlevels, possibly because of a delay in sexual maturity. Annual mortality after the fifth year of life, on the basis of average percentage age composition of the trawl catches in 1964–70, was tentatively estimated as 79–80%. The number of alewives recruited to the adult population from the 1962–67 year-classes over several ages in the fall index catch was inversely related to the abundance of their parents in the fall immediately preceding the year in which each year-class was spawned.Annual commercial production in the 1960s (peak in 1967, 42 million lb) may not have exceeded 7.7–18.6% of the bottom stocks, on the basis of the estimated weights of alewives available to trawls in the spring of 1964 and 1969. Yield per recruitment to the commercial fishery was low because of slow growth and high natural mortality.

A population study on larvae of the damselfly Pyrrhosoma nymphula (Sulzer) (Odonata: Zygoptera)

1. Data on population density, mortality rates and seasonal changes in distribution in larvae of the damselflyPyrrhosoma nymphula (Sulzer) (Odonata: Zygoptera) are described. Field work was carried out between July 1966 and July 1968 in a small weedy pond near to Durham City. 2. Samples were taken using a standard net sweep, and converted to numbers per m2 using a conversion factor. 3. Larvae made pronounced movements during development, one consequence of which was the virtual complete separation of senior and junior age-classes into different areas of the pond throughout development. This may have been important in preventing predation by large larvae on smaller individuals. 4. Mortality rates were constant within year-classes but varied between year-classes, being 99.5, 78 and between 60 and 70 percent per annum in the 1965, 1966 and 1967 year-classes respectively. 5. Larval population densities varied markedly between year-classes. Thus, there were approximately 340 and 110 newly hatched larvae per m2 in July 1966 and 1967 respectively, and 2 and 23 final instars per m2 prior to emergence in May 1967 and 1968 respectively. 6. An independent check on the population data was possible at emergence. Complete collections of exuvia yielded estimates of the number of larvae emerging from the pond that were 24 percent more in 1967 and 34 percent less in 1968 than the calculated number of larvae present prior to emergence.

Seasonal changes in distribution of the African armyworm,Spodoptera exempta(Wlk.) (Lep., Noctuidae), with special reference to eastern Africa

Emigration of moths of the NoctuidSpodoptera exempta(Wlk.) from their developmental sites occurred within a few hours of emergence, and captive moths have lived in semi-outdoor conditions for several weeks. Flight has been recorded at all times of night in the Kenya highlands, and has shown a very marked association, seasonally, nightly and even hourly, with rain; it has been observed at temperatures down to 13°C, and inferred at temperatures several degrees lower, so that over the greater part of eastern Africa flight activity is very unlikely to be restricted by low temperatures.The breeding season ofS. exemptadiffers markedly and consistently in different parts of eastern Africa; outbreaks of larvae recorded over the past forty years in Kenya, Tanzania and Uganda have been confined to November-July (very largely to December-May), alternating with those recorded over the past twenty years in Ethiopia, which have been confined to March-December (very largely April to August). The progressive establishment of a network of fifty light-traps in these countries since late 1962 has repeatedly recorded the arrival of invading moths before the first infestations of larvae, and has also provided evidence of a strikingly complete seasonal evacuation of much of the region; all traps in Kenya and most of those in Tanzania have revealed a period of several months in every year without a single moth ofS. exempta.Seasonal successions of moth catches and outbreaks of larvae have provided repeated evidence of a progressive northward movement of populations ofS. exempta, developing in March in Tanzania and Kenya, and extending across Ethiopia, in some years as far as northern Eritrea by June. The extent of these inferred displacements is consistent with the evidence so far available on behaviour and other factors affecting range of flight, which has been examined in as much detail as the limited data permit.Evidence of a return migration southwards to Kenya and Tanzania is relatively scanty. There are some indications of a north to south sequence of moth catches and outbreaks; the heaviest infestations in Kenya and Tanzania during the four-year period of detailed study were preceded by the largest catches so far recorded at the relevant time of year in Ethiopia; and in several years the first moths arriving in Kenya and Tanzania, in November-December, have appeared with the onset of the north-east monsoon, representing the southward movement of the intertropical convergence zone. Conversely, appearances of moths towards the northern limits of their inferred seasonal migration, in Ethiopia and around the Gulf of Aden in June, have shown an analogous association with the establishment of the south-west monsoon,i.e., with the northward movement of the intertropical convergence zone. Brief reference is made to evidence of seasonal migration in other parts of Africa; possibly in some years the eastern African populations may be supplemented by migrants from the south.Two recorded moth ‘ swarms ’ have been associated with weather systems characterised by particularly vigorous wind-convergence. It is suggested that wind-convergence may have contributed to the density of the ‘ swarms ’ and of the subsequent infestations of larvae.The overall effect of the seasonal changes in distribution which have been demonstrated is to bring the population into areas experiencing seasonal rains. Such a pattern of seasonal migration is likely to be of particular survival value for grass-eating insects, and such concentration of the insects as may be attributable to the associated wind-convergence may be significant in relation to the status of such insects as pests of cereal crops.Records in the literature of long-range geographical displacements of some other Lepidoptera have been found to be associated in a similar manner with analogous systems of wind and weather in other parts of the world.

Diurnal and seasonal changes in distribution of two planktonic ostracods, Conchoecia elegans and Conchoecia alata minor: McHardy R. A. and B. McK. Bary, 1965. J. Fish. Res. Bd., Canada, 22 (3): 823–840.

Diurnal and seasonal changes in distribution of two planktonic ostracods, Conchoecia elegans and Conchoecia alata minor: McHardy R. A. and B. McK. Bary, 1965. J. Fish. Res. Bd., Canada, 22 (3): 823–840.

Observations on Anopheles gambiae and other mosquitoes at Wadi Halfa

Summary Owing to the position of Wadi Halfa on the Nile route, the control of A. gambiae is important to prevent it from travelling northward. Conditions affecting this and other species are described at some length because the Aswan Dam may be raised and produce further problems. The mosquito fauna is discussed in relation to the zoogeographical position of the area. Notes on each species and on seasonal changes in distribution of A. gambiae are given. It is probable that this species has occurred at Wadi Halfa for many years and that it winters in the Second Cataract. Methods of control, particularly of A. gambiae , are described, with special reference to the possible effect of the prevailing wind.