Early Spring Species Research Articles

Advanced recruitment and accelerated population development in Arctic calanoid copepods of the North Water

Abstract The timing of copepodite recruitment and population development of copepods in spring and early summer (April–July) were compared between the North Water polynya and Barrow Strait, a non-polynya region in the Canadian Archipelago. In the North Water, young copepodites (CI–CIII) of calanoid herbivores were concentrated in the cold and chlorophyll-rich water at the base of the Arctic surface layer, while later stages (CIV–CV) invaded the warmer surface layer. The phytoplankton bloom and the recruitment of the first cohort of copepodites of Calanus hyperboreus , C. glacialis , and Pseudocalanus spp started in May–June, some 1.5–3 months earlier than in Barrow Strait. Consistent with a precocious summer recruitment, population stage structure of these species in early spring (April–May) was more advanced in the North Water than in Barrow Strait. The recruitment in June of CI of the omnivore Metridia longa was advanced by at least 5 weeks in the polynya relative to Barrow Strait. We found no evidence for an acceleration of the population development of the small Microcalanus pygmaeus , Oithona similis or Oncaea borealis in the polynya. Once the recruitment of young copepodites had started, recruitment success (i.e. % of young copepodites in the population) increased primarily with Chl a concentration for C. hyperboreus , with both sea-surface temperature and Chl a for C. glacialis , and with temperature only for Pseudocalanus spp. Hence, depending on the species, both greater food availability and higher temperature resulting from reduced ice cover contributed to improve reproductive success in herbivorous copepods in the North Water relative to Barrow Strait. A climate-induced reduction of ice cover duration is predicted to favour the population growth of the predominant large calanoid copepods and Pseudocalanus on Arctic shelves.

Population trends of Finnish Lepidoptera during 1961-1996

Based on a query and on a literature review, the population trends of Finnish Lepidoptera since Kaisila's (1962) thorough overview are analysed. Changes in the belt of three coastal biogeographical provinces (V-EK) show significant correlations with those in three inland provinces (St-ES). Furthermore, positive trends in these belts are reflected as new provincial finds north of them. The spatial synchrony is supposedly caused by spatially conelated climatic conditions. This is supported by evidence of synchronous trends in species grouped according to their overwintering stages (Marttila 1991, Bruun 1992). The increased migration rate, indicated by the new provincial finds, is probably a consequence of high population densities, and does not explain the synchrony itself. Kaisila's division into expansive and fluctuant species is considered to be a historical rather than a biological characterization. During the 19th century, the reporting of new lepidopteran species was delayed by about 50 years if they were night-active vs. day-active. The low numbers of observers and slow development of collecting methods have caused further analytical uncertainties. Some of Kaisila's expansive species may actually have been inhabitants of Finland for long periods of time. At present, drainage of peatlands and overgrowth of meadows are the most adverse environmental changes causing a decline of lepidopterans, particularly of the butterflies. Increase of bushiness and reeds appear to have positively affected many geometrid and noctuid species. The high incidence of new provincial finds and of species new to the country in the 1990s as well as positive trends in late-autumn and early-spring species supposedly reflect the ongoing climatic change. The Finnish lepidopteran fauna is undergoing a dynamic phase: around 30 recent invaders and 40 older expansive species are spreading, while fewer are retreating; the declining species are mainly habitat specialists while the expansive ones are generalists, mainly feeding on bushes and trees. Fewer expansions are evident among micro- than macrolepidopterans.

Epidemiology of abomasal nematodes of dairy cattle in Hokkaido, northern Japan.

The prevalence and intensity of infection with abomasal nematodiasis was studied in dairy cattle of Hokkaido, northern Japan, for successive two years. During the period of March in 1985 to September in 1987, a total number of 393 abomasa of Holstein-Friesian cows was examined for nematode parasites. Nematodes were detected from 75% of the cows. The prevalence of nematode species detected was Ostertagia ostertagi 250 (63.6%), Mecistocirrus digitatus 181 (46.1%), Trichostrongylus axei 85 (21.6%) and Haemonchus sp. 1 (0.3%). The prevalence and population composition of each growth stage varied seasonally in O. ostertagi and M. digitatus. The large percentage of arrested larvae, early L4 O. ostertagi and immature L5 M. digitatus, detected during the mid-winter and the increasing percentage of matured adult populations of both species in early spring revealed the occurrence of the autumn associated arrested development (hypobiosis) phenomenon in bovine abomasum nematodes of Japan.

SEASONAL OCCURRENCE OF XYLEM EMBOLISM IN SUGAR MAPLE (ACER SACCHARUM)

Xylem embolism, the reduction of water flow by air‐filled vessels, was measured in a stand of 5‐ to 8‐year‐old sugar maple (Acer saccharum Marsh.) saplings growing in a nursery bed in northwestern Vermont. Embolism was quantified as percentage loss in hydraulic conductivity of trunk and branch segments relative to maximum values obtained by removing air from vessels by repeated high pressure (173 kPa) perfusions. Ten segments per tree were cut from 6 trees for each of 11 measurement periods spaced at roughly monthly intervals from May 1986 to June 1987. During the 1986 growing season, embolism increased significantly from 11 to 31% in the larger branches and trunk (segment diameter #8805;0.5 cm), but remained at about 10% in twigs (segment diameter <0.5 cm). This was unexpected because the greatest water stess and thus potential for embolism occurs in twigs. During the winter, embolism increased throughout the trees and the trend with diameter was reversed; by February, small twigs were 84% embolized vs. 69% for larger branches and trunk. Dye perfusions showed that winter embolism in trunks was localized on the south side; this may have resulted from water loss by sublimation or evaporation in the absence of water uptake. Beginning in late March, embolism decreased throughout the trees to approximately 20% in June. This decrease was associated with positive xylem pressure of at least 16 kPa which may have originated in the roots, because weather conditions at the time were unfavorable for the generation of stem pressures characteristic of Acer species in early spring.

Influence of Microclimate and Growth Form on Plant Temperatures of Early Spring Species in a High-elevation Prairie

The influence of microhabitat, growth form and leaf morphology on plant temperatures was investigated for nine species (five families) that were first to appear in early spring at a high-elevation, shortgrass prairie site in SE Wyoming. Aboveground plant growth prior to the measurement period was restricted to S-facing slopes, and all species, except one, had leaf temperatures that were substantially higher than air temperature during the daytime. Maximum increases (> 15 C) above ambient air temperature occurred in a cushion plant (Haplopappus acaulis) and a broadleaf species (Penstamon eriantherus) that had relatively large leaves in close contact with the soil surface. Leaf temperatures over 10 C above air temperature also occurred for two species (Hymenoxys acaulis and Gutierrezia sarothrae) whose current-year growth was sheltered by old vegetative growth. Artificially disturbing microsite and growth characteristics resulted in major reductions in plant temperatures to within about + 2 C of ambient air temperature. Only one (Zigadenus venenosus) of the nine species that first appeared in early spring did not have elevated leaf temperatures or any apparent growth characteristics that would contribute to such elevations. Thus, variation in microsite, growth form and leaf morphology in these early spring species appears to contribute substantially to the avoidance of low temperatures during a portion of the season when growth may be limited by temperature. INTRODUCTION Plants can potentially avoid the effects of extreme environments by occupying favorable microsites or by adaptations in growth form or leaf morphology which affect their energy balance. An alternative to avoidance is physiological adaptation or tolerance (Levitt, 1980). Little is known regarding the relative numbers of avoider vs. tolerator species within communities and, thus, the apparent prevalence of one adaptive strategy over the other. Furthermore, avoidance mechanisms of species in low temperature environments have received little attention compared to tolerance mechanisms (Levitt, 1980) or in comparison to high temperature avoidance mechanisms (Turner and Kramer, 1980). The purpose of this study was to compare the influence of microhabitat or microsite preference, growth form and leaf morphology on leaf temperatures of the species appearing first in early spring in a high-elevation prairie of southeastern Wyoming. Comparisons were made when aboveground vegetative growth was just beginning on southern aspects and was entirely absent on northern aspects. Nine species from five families, representing a variety of growth forms and leaf morphologies, were monitored. Microclimatic measurements were compared for a representative northern and southern aspect, as well as for numerous microsites on the southern aspect. The number of species occupying favorable microsites was evaluated by comparing soil surface temperatures immediately adjacent to individual plants with mean surface temperatures. Also, the relative number of avoiders and tolerators was evaluated by assessing the number of species with growth forms and leaf morphologies that contributed to substantial elevations in leaf temperature above air temperature. The observed avoidance mechanisms are compared according to their ability to elevate leaf temperature above air temperature.