Showing papers in "Oecologia in 1977"

Why Do Males Emerge before Females

Abstract: In butterflies and many other insects there is a general tendency for males to emerge before females. This is known as protandry. In this paper we advance the hypothesis that protandry is a reproductive strategy of males, resulting from competition for mates, and should primarily occur in species maintaining female monogamy. Our hypothesis is corroborated by applying a mathematical treatment to a theoretical population with seven defined properties, all of which are argued to be reasonable assumptions for natural populations.

Limiting effects of low leaf-water content on the nitrogen utilization, energy budget, and larval growth ofHyalophora cecropia (Lepidoptera: Saturniidae).

Abstract: Hyalophora cecropia larvae were reared on leaves of wild cherry,Prunus serotina, which contained variable amounts of leaf water but otherwise did not differ in fiber, total nitrogen, and caloric content. Larvae which were fed leaves low in leaf water grew more slowly and were less efficient at utilizing plant biomass, energy, and nitrogen than those larvae fed leaves which were fully supplemented with water. Experiments were performed using excised leaves under different regimes of relative humidity and leaf water supplementation in climatic control chambers maintained at identical temperatures and photoperiod. Foodplant biomass utilization efficiencies were severely reduced by decreasing amounts of leaf water. Growth rates were halved and the efficiency of conversion of assimilated dry matter into larval biomass was reduced from 82% in the treatment with fully supplemented leaves to 34% in the driest treatment. The nitrogen utilization efficiency (N.U.E.) was reduced from 75–80% to 48%, and the relative accumulation rate of nitrogen (N.A.R.) was suppressed nearly 2-fold for larvae on low-water leaves. Relative maintenance costs (calories expended in respiration/mg tissue/day) of larvae were nearly five times higher on dry leaves than on fully supplemented leaves. Larvae on leaves which were low in water content were themselves more desiccated, and metabolized greater portions of assimilated energy, perhaps in an attempt to supplement body water with metabolic water derived from respiration. The larval rates of consumption of biomass, energy, and nitrogen were the same for all treatments, indicating that leaf water affected larval growth primarily by restricting the efficiency of utilizing these nutrients. Where water was limiting (as in tree leaves), an increased consumption rate did not appear to be a successful means of increasing growth rates. There were daily and seasonal differences in leaf water content between different trees of the same species. Although absolute differences in leaf water exist between different trees and between young and old (fully expanded) leaves of a single tree, these differences are proportional and parallel each other through daily and seasonal cycles. In spite of evolutionary adaptations of herbivores to acquire adequate water and avoid desiccation, the leaf water content naturally encountered by cecropia larvae on cherry leaves may limit their growth, especially if the R.H. is low.

Insect grazing on Eucalyptus in response to variation in leaf tannins and nitrogen.

Abstract: Many species of Eucalyptus, one of the dominant genera in Australian forests and woodlands, contain high levels of tannins and other phenols and are also heavily damaged by grazing insects. These phenols do not appear to affect insect attack because a wide range of concentrations of condensed tannins and other phenols in leaves of 13 Eucalyptus sp. influenced neither feeding rates of Paropsis atomaria larvae, nor their nitrogen use efficiencies. We discuss reasons why tannins may not appreciably reduce the availability of nitrogen (N) to these insects. Performance was directly related to leaf N concentration, and growth rates, N gains, and N use efficiencies all increased as leaf N content increased, although absolute feeding rates remained constant. These relationships differ from those found in insects feeding on other plants, and we suggest that the low N contents common in Eucalyptus leaves may be responsble. We propose that the extensive damage observed in many eucalypts is in part related to the high feeding rates maintained by individual larvae.

Population structure of pierid butterflies : I. Numbers and movements of some montane Colias species

Abstract: The numbers, dispersal behavior, aging and residence, and Wrightian neighborhood configurations of three species of Colias butterflies have been studied in central Colorado, using mark-release-recapture techniques as major tools. All populations studied have nonoverlapping generations and mature one brood each year. A brief general review of these species' autecology is given. A system for measuring degree of physical damage to the adults is introduced. This “wear rating” varies with temporal position of any given sample in the course of a brood's flight season, the insects becoming progressively more damaged with time. The sex ratio also changes with brood aging: males eclose before females, and are in the majority early in the flight season, while females may predominate at the end of flight. Local population numbers for the montane grassland species C. alexandra may reach peak levels of 700–900 insects in favorable years, but be much lower in other years as a result of, e.g., drought. Peak densities are no more than 2/ha. The montane bog species, C. scudderi, maintains comparable low density but has much smaller local populations. The subalpine/alpine grassland species C. meadii displays peak local numbers as high as 3000, with peak density as high as 120/hectare. Dispersal varies both among and within species. Those C. alexandra who disperse show an average dispersal radius of about 1.3 km, with a radius for the whole population of about 0.6 km; maximum distance moved was 8 km. Dispersal proportions among recaptures are sharply curtailed by adverse weather, but the dispersal radius of those moving is unaffected by weather. C. scudderi's dispersal is strongly influenced by the geometry of its bog and streamside habitats. Some C. meadii populations approach isolated “island” status, but others show much dispersal. Dispersal radius of those dispersing ranges from 0.3 to 0.7 km in different populations, but the proportion of dispersals varies greatly. The longest observed movement by this species is 1.3 km, although up to 2.6 km could have been detected. Colias normally display constant loss (death plus emigration) rates with average residence expectations of 4–6 days; few insects reach their maximum physiological lifespan of approximately 1 month. Bad weather can increase the loss rate drastically. Females show shorter residence than males, appearently as a result of greater mortality. Total-numbers-per-brood estimates are given for our better studied populations. The reproductive strategy of Colias is such that Wright's models for neighborhood size apply. Neighborhood size for C. alexandra varied sixfold in numbers, and from 3 to 1.3 km in physical extent, between a favorable year and a drought year. One localized C. scudderi habitat is only 200 m in diameter, but a streamside population has a neighborhood length of 4.8 km. In C. meadii, one population of 2000–2500 insects is an 8-ha “island”, while another of similar numbers extends a single neighborhood across 1.9 km distance, 450 m altitude, and a major ecological boundary (timberline). Factors such as weather, individuals' visual cueing, and thermoregulatory behavior can influence population structure. For some Colias populations, selection may be very uniform within neighborhoods, while for others, single neighborhoods cross sharp discontinuities in selective forces. These patterns may differ for different selective forces, and may also vary with stages of the insects' life cycle. these populations will now prove a valuable resource for studying evolutionary population genetics.

Effects of light and temperature on leaf anatomy and photosynthesis in Fragaria vesca.

Abstract: Fragaria vesca, the woodland strawberry, was grown under a series of controlled environments including variations in light intensity, average temperatures, and temperature amplitude around a constant mean. Observations on CO2 exchange capacities, leaf anatomy, and cell ultrastructure were made for each treatment to determine relationships between these variables. With increasing light intensity, leaf thickness, leaf density, and mesophyll cell surface area and volume per leaf surface area increased. Net photosynthesis (NPS) per leaf weight decreased with increasing light pretreatment while NPS per area increased from low to medium intensity, then decreased at the highest intensity. Depression of photosynthesis at the highest light pretreatment may have been due to massive starch accumulation in the chloroplasts associated with the sodium vapor lamps used. Correlation of all anatomical variables was highly significant with dark respiration and NPS per dry weight but insignificant for NPS per leaf area. In the variable temperature treatments, photosynthetic acclimation occurred with a shift in optimum temperature for NPS in the direction of prevailing growth temperature. Absolute rates were highest at moderate pretreatment temperatures and were reduced by extreme growth temperatures. Thick leaves with low density mesophyll became thinner and more dense with increasing growth temperature corresponding to an increase in maximum net photosynthetic rates. Leaves became thicker and more dense at the highest temperatures, but with an increase in cell damage and indications of changes in metabolic pathways. Highest correlations for gas exchange rates were with specific leaf weight (weight per area). Correlation with other anatomical variables were scattered or insignificant. It was concluded that adaptation to a range of environmental conditions cannot be consistently attributed to changes in mesophyll cell volume or surface area.

Desiccation tolerant vascular plants of southern Africa.

Abstract: Drought tolerance limits are given for 36 new 'resurrection plants', sufficient to double the number of desiccation tolerant plants reported from southern Africa. Tolerance limits for angiosperm examples are usually better than those for ferns. Air-dry foliage survives for 1/2 to 5 years or more, unless stored in humidities above 50% RH Abbreviation: RH = relative humidity . Dehydration is sufficiently slow (usually 2-3 days) to allow the possibility of a tolerance induction process, like that found in Borya nitida. Rehydration after rain is usually complete in 1/2 to 1 day. A significant proportion of rain is absorbed through the leaf surface, but there is no evidence of appreciable rehydration from dew.Resurrection plants are usually pioneers in xeroseres, but they often lack xeromorphic characteristics. Anthocyanin pigmentation during drying is a reliable indicator of viability in some species.

Call differences and calling site segregation in anuran species from central Amazonian floating meadows.

Abstract: The acoustic behaviour of 15 sympatric and synchronically breeding species of frogs in an area of floating meadows near Manaus (Brazil) was studied for a period of 8 months. The calling positions of each species can be identified with certain physiognomic types of vegetation.Sound analyses were used to compare the mating calls. The main variables are dominant frequency, call duration and pulse repetition rate. Each of the 15 species has a distinct mating call and differs from the acoustic behaviour of each other one. Eleven species are separated in their dominant frequency ranges within their specific calling sites. Species sharing emphasised frequency ranges within identical calling sites differ greatly in at least two temporal variables.The roles of calling position, spectral, and temporal features of mating calls in species recognition and premating reproductive isolation are discussed.

Taxonomic and ecological aspects of the distribution of glycinebetaine and related compounds in plants

Abstract: The concentrations of the major inorganic ions and glycinebetaine, choline and proline and the osmotic pressure of extract sap have been determined in eight salt marsh species and four sand dune species from local habitats. These results together with those previously reported on hydroponically grown plants and data assembled from the literature show that glycinebetaine accumulation is a feature of members of the Chenopodiaceae, Amaranthaceae, many Gramineae and some members of the Solanaceae and Compositae, particularly when exposed to conditions of low soil water potential. It is suggested that in these families betaine is employed as a non-toxic cytoplasmic osmoticum when decreased osmotic potentials are required. In some other plant species proline may fulfil a similar function. Another quaternary ammonium compound may be accumulated in the Plumbaginaceae in addition to proline. Some evidence suggests that the differences in the organic osmoticum used may relate to the different inorganic ion contents of the plants. The accumulation of nitrogen dipoles as cytoplasmic osmotica may make heavy demands on the nitrogen economy of the plants and this problem is discussed briefly.

Spacial distribution of photosynthetic capacity and performance in a mountain spruce forest of northern Germany

Abstract: Net photosynthesis of Picea abies was measured in a spruce forest in northern Germany with temperature- and humidity-controlled cuvettes in 4 different crown layers on shoots of different ages. These measurments were performed such that temperature and humidity either followed ambient conditions or were kept constant. Annual courses of light-, temperature-, and humidity-related net photosynthesis were determined. Spruce had a remarkably constant rate of CO2 uptake from April to September for 1-year and older needles. Light saturation was achieved at 25 klx. Current year needles had the highest rates of CO2 uptake in early summer, but these rates decreased by autumn. Photosynthetic capacity decreased with needle age and, on a dry weight basis, it was higher in the shade than in the sun crown. The temperature optimum was between 13 and 23° C. Photosynthesis in spruce decreased when air humidity was low. The effect of the natural weather conditions on photosynthetic capacity was determined. The habitat is characterized by a high frequency of low light intensities (75% of total daytime below 20 klx) and cool temperatures (80% of daytime between 9 and 21° C). Low air humidity was only present when light intensities were high. The major limiting factor for production was low light intensities, which reduced photosynthetic capacity in the sun crown to 42% below maximum possible rates. Adverse temperatures reduced CO2 uptake by 28% and large water vapor pressure deficits reduced rates by only 2% compared with maximum possible rates. The limited adaptation to light is discussed.

Fire and soil-plant nutrient relations in a pine-wiregrass savanna on the coastal plain of North Carolina.

Abstract: Changes in soil and plant nutrient conditions were evaluated following various burn and clip treatments in a longleaf pine-wiregrass savanna in Bladen Co, NC, USA Ground fires were found to add substantial quantities of N, P, K, Ca, and Mg to the soil, though not necessarily in forms immediately available to plants Less than 1% of the total nitrogen in the charred residue (ash) is present as nitrate or ammonium Considerable quantities of all nutrients examined were lost to the atmosphere during burning Green leaf tissue in recently burned areas was consistently higher in N, P, K, Ca, and Mg compared to unburned areas Howerver, when compared to similar tissues from clipped plots, burned area tissues were significantly higher in N, Ca, and Mg only Data presented here suggest that tissue age significantly affects nutrient content and must be considered in any analysis of tissue nutrient content following burning Within 4–6 months following fire, burned-area tissue nutrient content decreases to concentrations found in the unburned area Burning resulted in initial enrichment of available soil nutrients including PO4, K+, Ca++, and Mg++, however, NO3 -, and NH4 + concentrations in burned soil were not significantly different from unbruned soil Soil and plant nutrient changes in an area burned two years in succession indicate that repeated burning may diminish nutrient availability Plant response to various nutrient enrichment treatments of the soil indicated that nitrogen is limiting growth in both burned and unburned soils and that burning may alter some factors other than nutrients which may retard plant growth in unburned areas

Carbon balance, productivity, and water use of cold-winter desert shrub communities dominated by C3 and C4 species.

Abstract: Common generalizations concerning the ecologic significance of C4 photosynthesis were tested in a study of plant gas exchange, productivity, carbon balance, and water use in monospecific communities of C3 and C4 salt desert shrubs. Contrary to expectations, few of the hypotheses concerning the performance of C4 species were supported. Like the C3 species, Ceratoides lanata, the C4 shrub, Atriplex confertifolia, initiated growth and photosynthetic activity in the cool spring months and also exhibited maximum photosynthetic rates at this time of year. To compete successfully with C3 species, Atriplex may have been forced to evolve the capacity for photosynthesis at low temperatures prevalent during the spring when moisture is most abundant. Maximum photosynthetic rates of Atriplex were lower than those of the C3 species. This was compensated by a prolonged period of low photosynthetic activity in the dry late summer months while Ceratoides became largely inactive. However, the annual photosynthetic carbon fixation per ground area was about the same in these two communities composed of C3 and C4 shrubs. The C4 species did not exhibit greater leaf diffusion resistance than the C3 species. The photosynthesis/transpiration ratios of the two species were about the same during the period of maximum photosynthetic rates in the spring. During the warm summer months the C4 species did have superior photosynthesis/transpiration ratios. Yet, since Ceratoides completed a somewhat greater proportion of its annual carbon fixation earlier in the season, the ratio of annual carbon fixation/transpiratory water loss in the two communities was about the same. Atriplex did incorporate a greater percentage of the annual carbon fixation into biomass production than did Ceratoides. However, this is considered to be a reflection of properties apart from the C4 photosynthetic pathway. Both species displayed a heavy commitment of carbon to the belowground system, and only about half of the annual moisture resource was utilized in both communities.

The effect of grazing by the detritivore Orchestia grillus on Spartina litter and its associated microbial community.

Abstract: Orchestia grillus efficiently feeds upon microorganisms attached to ingested Spartina alterniflora litter, but does not digest litter itself. Microorganisms respond to Orchestia grazing with increased metabolic activity, reflected in accelerated decomposition of the nitrogen fraction of litter and increased microbial biomass. Increased microbial activity may be partly a function of ammonia excretion and higher diffusion rate due to animal movement, but mainly it is a direct response to grazing. Microbial biomass increases with grazing because the pool of available nitrogen becomes larger. A model postulating interactions between Orchestria, Spartina litter and attached microorganisms is presented.

Water relations and photosynthesis of a barrel cactus, Ferocactus acanthodes, in the Colorado desert.

Abstract: The structural characteristics, water relations, and photosynthesis of Ferocactus acanthodes (Lemaire) Britton and Rose, a barrel cactus exhibiting Crassulacean acid metabolism (CAM), were examined in its native habitat in the western Colorado desert. Water storage in its succulent stem permitted nighttime stomatal opening ot continue for about 40 days after the soil water potential became less than that of the stem, a period whe the plant would be unable to extract water from the soil. After 7 months of drought and consequent unreplenished water loss from a plant, diurnal stomatal activity was not observed and the stem osmotic pressure was 6.4 bars, more than double the value measured during wet periods with nighttime stomatal opening. F. acanthodes had a shallow root system (mean depth of 8 cm) which responded within 24 h to rainfall. When the nocturnal stem surface temperature was raised from 8.0° C to 35.0° C, the stomatal resistance increased 4-fold, indicating that cool nighttime temperatures are advantageous for gas exchange by F. acanthodes. Moreover, the optimal temperature for CO2 uptake in the dark was only 12.6° C. CO2 uptake at night became maximal for 3.0 mEinsteins cm-2 of photosynthetically active radiation incident during the preceding day, and the minimum number of incident quanta absorbed per CO2 fixed was 68. The transpiration ratio (mass of water transpired/mass of CO2 fixed) had the relatively low value of 70 for an entire year, consistent with values obtained for other CAM plants. The total amount of water annually diverted to the floral structures was about 6% of the stem wet weight. The annual growth increment estimated from the net CO2 assimilation corresponded to about 10% of the stem mass for barrel cacti 34 cm tall, in agreement with measured dimension changes, and indicated that such plants were about 26 years old.

Spacial distribution of photosynthetic capacity and performance in a mountain spruce forest of Northern Germany : III. The significance of the evergreen habit.

Abstract: Growth and CO2 uptake in the crown of a spruce tree is described and the production processes of this evergreen conifer are compared with those of a deciduous beech. Spruce had 60% lower rates of net photosynthesis per dry weight than beech. But, beech had a 30% shorter growing season and a 84% smaller biomass than spruce. The annual CO2 gain was 40% lower in beech than it was in spruce.An analysis shows the following conclusions for this habitat. (1) The effect of a prolonged growing season is small. The annual CO2 gain of spruce would be reduced only by 9% if the growing season was the same length as for beech. (2) The annual CO2 gain would increase 14% if all needles in spruce were deciduous, because the current year needles have a higher average rate of CO2 uptake than 3-year old and older needles, but a lower average rate than 1- and 2-year old ones. However, the carbon balance of the tree shows that spruce could not afford to produce the existing needle biomass (14 t ha-1) each year. (3) If spruce were to produce the same deciduous foliage biomass during the same growing season as beech then total production by spruce would be reduced 67%. (4) The annual CO2 uptake by evergreen spruce was higher than deciduous beech not because of a long growing season, but because of the longevity of its needles, which during their total life time (an average of 5 years) have a two to three times greater CO2 uptake than a deciduous leaf in one summer season. The relatively small investment in current year needles produces an annually low, but long lasting assimilation of CO2.

Root systems of chaparral shrubs.

Abstract: Root systems of chaparral shrubs were excavated from a 70 m2 plot of a mixed chaparral stand located on a north-facing slope in San Diego County (32°54' N; 900 m above sea level). The main shrub species present were Adenostoma fasciculatum, Arctostaphylos pungens, Ceanothus greggii, Erigonum fasciculatum, and Haplopappus pinifolius. Shrubs were wired into their positions, and the soil was washed out beneath them down to a depth of approximately 60 cm, where impenetrable granite impeded further washing and root growth was severely restricted. Spacing and interweaving of root systems were recorded by an in-scale drawing. The roots were harvested in accordance to their depths, separated into diameter size classes for each species, and their dry weights measured. Roots of shrubs were largely confined to the upper soil levels. The roots of Eriogonum fasciculatum were concentrated in the upper soil layer. Roots of Adenostoma fasciculatum tended to be more superficial than those from Ceanothus greggii. It is hypothesized that the shallow soil at the excavation site impeded a clear depth zonation of the different root systems. The average dry weight root:shoot ratio was 0.6, ranging for the individual shrubs from 0.8 to 0.4. The root area always exceeded the shoot area, with the corresponding ratios ranging from 6 for Arctostaphylos pungens to 40 for Haplopappus pinifolius. The fine root density of 64 g dry weight per m2 under the canopy was significantly higher than in the unshaded area. However, the corresponding value of 45 g dry weight per m2 for the open ground is still high enough to make the establishment of other shrubs difficult.

Nitrogen uptake : Apparent pattern during old field succession in Southeastern U.S.

Abstract: Nitrogen uptake from applied nutrient solutions was evaluated in two old fields, in a pine plantation, and in a hardwood stand, to test the idea that plant communities become more efficient trappers and retainers of plant nutrients during succession. Uptake was estimated as the difference between nutrient concentrations in water collected from beneath soil profiles with and without roots by lysimeters within each successional stage. Results suggest that nitrate uptake decreased while ammonia uptake increased with succession. This apparent shift from a nitrate to an ammonia nitrogen economy during succession has been reported by other workers and is evolutionarily significant as an energy, nitrogen, and cation saving mechanism.

Detecting two-dimensional spatial structure in biological data.

Abstract: Cliff and Ord (1973) made versatile methods available for the direct utilization of location data in the analysis of dispersion patterns, but their monograph has as yet seen little use in the ecological literature. Application of their weighted forms of Geary's c and Moran's I indices of spatial autocorrelation to some marine benthos data demonstrates a diversity of population structure not anticipated on the basis of more common measures of pattern. These indices provide objective means to evaluate numerous recent spatial models and hypotheses in geographical ecology and genetics. The procedures are particularly attractive because (1) they efficiently utilize data which are often wasted (i.e., sample coordinates), (2) their application puts few constraints on sampling designs which would otherwise be employed, and (3) they reveal and quantify pattern differences which are not obvious to the untrained eye.

Breeding site specificity in the domestic species of Drosophila

Abstract: The emergences of domestic Drosophila species from fruits and vegetables in a market are analysed by partitioning the species diversity. Confidence limits are determined for the components of diversity.

Chemical composition of halophytes from the Neusiedler Lake region in Austria

Abstract: The ionic relations in halophytes from the region east of Neusiedler Lake in Austria have been investigated. The study encompasses the following compounds: Na, K, Mg, Ca; Cl, SO4, phosphate, nitrate, and organic acids.

Carbon cycling in a loblolly pine plantation.

Abstract: The carbon cycle of a loblolly pine plantation in North Carolina was examined during its 12th through 16th years from planting. Net primary production during the study period averaged 2056 g C m-2 year-1. With autotrophic respiration equal to 2068 g C, the calculated gross production was 4124 g C m-2 year-1. Heterotrophic respiration of 694 g C m-2 year-1 resulted in net ecosystem production of 1362 g C m-2 year-1. In carbon cycle comparisons between forest ecosystems, autotrophic respiration rates were found to be closely coupled to regional temperature.

Role of temperature in the germination ecology of three summer annual weeds.

Abstract: Ambrosia artemisiifolia L., Chenopodium album L., and Amaranthus retroflexus L. are three summer annual weeds that occur in disturbed habitats. In nature, the peak germination season for A. artemisiifolia and C. album is in early to mid-spring, while in A. retroflexus the peak germination season is late spring to early summer. Furthermore, seeds of A. artemisiifolia germinate only in spring, while seeds of C. album and A. retroflexus germinate throughout the summer. In an attempt to explain the differential germination behavior of these three species in nature, changes in their germination responses to temperature during burial in a non-heated greenhouse from October 1974 to October 1975 were monitored. A high percentage of the seeds of all three species after-ripened during winter. Seeds of A. artemisiifolia and C. album germinated at temperatures characteristic of those in the field in early and mid-spring, but seeds of A. retroflexus required the higher temperatures of late spring and early summer for germination. Seeds of all three species germinated to higher percentages in light than in darkness. Non-dormant seeds of A. artemisiifolia that did not germinate in spring entered secondary dormancy. On the other hand, seeds of C. album and A. retroflexus that did not germinate when temperatures first became favorable for germination, did not enter secondary dormancy and, thus, retained the ability to germinate at summer field temperatures during summer. Thus, temporal differences in the germination behavior of these three species are caused by the differential reaction of the seeds to temperature during the annual temperature cycle.

Spacial distribution of photosynthetic capacity and performance in a mountain spruce forest of Northern Germany : I. Biomass distribution and daily CO2 uptake in different crown layers.

Abstract: Biomass distribution and diurnal CO2 uptake under natural conditions were investigated on Picea abies in a mountainous climate (Solling, Northwest Germany). Spruce has a remarkable variability in leaf characteristics. Even on a single branch in the lower sun crown, needle dry weight and surface area change considerably from the branch base to the tip and accoring to exposure. Only about 18% of the total biomass of the tree was current year's growth, about 40% of the needles were 4 years and older reaching a maximal age of 12 years. The main growing zone was at the border of upper shade and lower sun crown and the main accumulation of dry weight was at a greater tree height than was observed for maximal growth of needle numbers or surface area. The annual, new growth shifted toward the upper sun crown. Maximal daily CO2 uptake was highest in the lower sun crown on days with variable cloud cover when temperatures were moderate and water vapor pressure deficits were low. Also the annual CO2 uptake was highest in the lower sun crown, where 4-year-old and older needles contributed about 35% to the annual CO2 uptake of the tree. Current year growth contributed about 15% of the total CO2 gain. The upper and lower sun crowns produce about 70% of the total carbon gain. The carbon balance of spruce and the distribution of the production process in relation to needle age and crown level are discussed.

The energy balance of leaves of the evergreen desert shrub Atriplex hymenelytra.

Abstract: Atriplex hymenelytra is an evergreen shrub distributed in the hot deserts of parts of Mexico and the southwestern United States. The leaves of the species have a number of characteristics that are adaptive in a hot, dry environment, some of which change seasonally. Steeply angled leaves reduce midday solar interception, yet result in relatively high interception when solar angles are low and vapor pressure deficits are at a minimum. The leaves substantially reduce their absorptance of incident radiation during the hot periods of the year by changing their moisture and hence dissolved salt contents. At these times the light intensity required for saturation of photosynthesis is low and a reduction in the radiation absorbed by the leaves therefore results in a greater water-use efficiency.

The uptake of lead, zinc, cadmium, and copper by the pulmonate mollusc, Helix aspersa muller, and its relevance to the monitoring of heavy metal contamination of the environment

Abstract: The occurrence of lead, zinc, cadmium, and copper in individuals of Helix aspersa from two sites of varying degrees of contamination was studied. Zinc, cadmium, and copper were shown to increase in a linear fashion with animal weight. The rate of uptake for zinc and cadmium in particular was significantly greater at the more contaminated site. Statistical analysis of the data, using correlation and regression techniques provided information on apparent intermetallic effects. It is concluded that because metal uptake and body weight show a positive linear relationship only the use of animals of similar weight and/or size can be used for monitoring purposes. Even then, different patterns of uptake into different organs and interactions between metal uptakes are such as to seriously question the use of Helix, and other molluscs, for monitoring purposes unless specific organs from comparably sized and/or aged animals are used.

Shifts of thermogenesis in the prairie vole (Microtus ochrogaster) : Strategies for survival in a seasonal environment.

Abstract: The weight-specific oxygen consumption ([Formula: see text]) of prairie voles caught in winter is 24% higher at 27.5° C and 29% higher at 7.5° C than that of summer animals, thus affording a higher weight-specific thermogenesis in winter than in summer which may allow tolerance to lower thermal exposures. Coincident with the increase in weight-specific rates of oxygen consumption is a decrease in body weight. When total energetic cost to maintain an animal per unit time is calculated, the cost at 27.5° C is the same for both summer and winter animals. Further, the cost to maintain an animal at 7.5° C is less in winter than in summer. Arguments are presented suggesting that prairie voles compensate for increased weight-specific thermogenesis in winter by lowering body weight. The responses to thermal acclimation are quite different in summer and winter animals, thus implying different sorts of metabolic organization. Acclimation to 5° C effects a 26% increase in [Formula: see text] at 27.5° C of winter voles, and acclimation to 30° C does not change [Formula: see text]. In contrast, [Formula: see text] at 27.5° C of summer animals is unaffected by 5° C acclimation, and depressed 20% by 30° C acclimation. Thus, the animals are capable of considerable physiological adjustment to varying thermal conditions in different seasons.

The dependence of reproductive rate on cell size and temperature in freshwater ciliated protozoa.

Abstract: Reproductive rates have been calculated for ten species of ciliated protozoa in defined conditions. Interspecific double log regressions of generation time vs. cell volume have been computed at each of three temperatures (8.5° C, 15° C, and 20° C) indicating a significant dependence of reproductive rate on cell size. Recorded generation times varied from 6.38 h in Vorticella microstoma at 20° C to 1004 h in Spirostomum teres at 8.5° C. These values correspond to a range in r m (day)-1 of 2.607 to 0.017 and λ (day)-1 of 13.554 to 1.017. The relationship between these data and similar published data for marine ciliates is examined and the value of such regressions in ecological studies of the protozoa is discussed.

Ecophysiological investigations on lichens of the Negev desert : V. A model to simulate net photosynthesis and respiration ofRamalina maciformis.

Abstract: Previous publications have reported on investigations of CO2 exchange in the desert lichenRamalina maciformis both in its natural habitat in the Negev and in the laboratory. Utilizing laboratory data, net photosynthesis and dark respiration were expressed as mathematical functions of the most important environmental factors. Based on these relationships, a model is developed that allows one to predict CO2 exchange of the plant. Input data are light intensity, temperature, and water content of the thallus, together with a measure of the rate of the seasonal change of photosynthetic and respiratory activity. The validity of the model is tested by comparing simulated daily courses of CO2 uptake and release of the lichen with independent results of CO2 exchange measurements conducted in the field during and after the condensation of dew. The sensitivity of the model is shown by simulating changes in the input data of temperature and water content of the lichen.

Niche relations among dung-inhabiting beetles.

Abstract: The whole dung-inhabiting (adult) beetle community living in southern Finland was studied with reference to the seasonal (6 summer months), macrohabitat (open field, half-open pine forest and closed spruce forest) and successional (30 days) gradients. The material comprised 50 coprophagous and 129 carnivorous species, represented by 26,650 and 35,850 individuals, respectively. The most important characteristics of each species are given in an Appendix.In the coprophages the species-abundance relations fitted the lognormal distribution well, but in the carnivores the distribution was strikingly less even. A great number of other differences (see below) apparent between the two trophic groups were explained as the result of a difference in the degree of specialization, apart from the difference in their trophic position: coprophages are microhabitat (dung) and food specialists, while carnivores are microhabitat generalists (and therefore their "critical" niche space was not completely covered in this study).In the coprophages, two important species guilds were observed: the first occurred at the very geginning of the succession (mean position 2.5 days), and consisted mainly of true dung specialists; the second guild contained species with wider utilization along the successional dimension (mean position 6.5 days), and species of more generalist nature (saprophages). The utilization of carnivores along the successional gradient was more continuous, probably because of their more diversified food resources. The total niche width among the coprophages increased from early successional species to species occurring mainly later on, but was more constant in carnivores. The environmental dimensions proved to be totally independent of each other among the carnivores, while the coprophages showed a clear supplementary relationship along them. Among the carnivores, a spherical niche shape dominated, but among the coprophages elongated and disk-liked shapes were also well represented, especially in specialist species. In both groups, a significant positive correlation existed between niche width and dominance, but not between niche width and abundance. It is suggested that the patchy distribution and transient occurrence of suitable microhabitats contributes to the coexistence of many ecologically similar species.

Thermal conditions for successful breeding in Great Tits (Parus major L.) : II. Thermal properties of nests and nesthoxes and their implications for the range of temperature tolerance of Great Tit broods.

Abstract: A model is described in which the thermal properties of nests and nestboxes are integrated with allometric equations describing the metabolic properties of Great Tit broods. These allometric equations were presented and discussed in the preceding paper.The effect of changing certain dimensions of the nest and the nestbox and the size of the brood is discussed in relation to the over-all conductance of the whole system and the influence of these factors on the range of temperature tolerance of Great Tit broods. It seems likely that the over-all conductance of the nest and nestbox system, and consequently the rate of heat loss of the brood, are roughly proportional to the 2/3 power of the brood weight. This is explained by the fact that the value of the over-all conductance is mainly determined by the heat transport due to radiation and convection from the upper surface of the brood. The fact that Great Tits build their nests mainly of moss is discussed in relation to special properties of this nest material by which the upper limit of the range of temperature tolerance can rise under conditions of heat stress.

Adjustment of the components of energy balance in response to temperature change in Ostrea edulis.

Abstract: 1. Routine oxygen consumption (VO2μl 285 mg-1 h-1) by specimens of Ostrea acclimated to temperatures between 5° and 25°C increases with exposure temperature throughout much of the range 5 to 30°C. 2. There is little evidence of a relative suppression of the acutely-measured rate: temperature curves for routine oxygen consumption following warm acclimation. Energetic costs in Ostrea thus rise sharply with increase of environmental temperature. 3. The clearance rate (V w ,ml 285 mg-1 h-1) of Phaeodactylum measured synchronously shows a marked thermal optimum within the range 15-28°C, followed by a decline towards high exposure temperatures. 4. Maximal clearance rates of 600-750 ml water h-1 occur approximately 5°C above the temperature to which the animals have been acclimated and are adjusted according to environmental temperature. 5. The changes in filtration efficiency (V w /VO2, ml/μl) in Ostrea following thermmal acclimation are controlled by compensatory responses of the irrigation rate rather than by a relative reduction of energy losses from metabolism. 6. Because the clearance rate declines in animals acclimated to 25°C, whereas the metabolic losses increase throughout the temperature range 5 to 30°C, maximum filtration efficiency is achieved at 20°C. 7. Calculation of the energetic cost of filtration suggests that the improvement of filtration following warm acclimation offsets metabolic energy losses even at low food concentrations in Ostrea. Even if energy losses not accounted for in this study were substantial, a positive index of energy balance could be maintained during the summer months at ration levels which commonly occur in inshore waters.