Showing papers in "Oecologia in 1989"

Abstract: The photosynthetic capacity of leaves is related to the nitrogen content primarily bacause the proteins of the Calvin cycle and thylakoids represent the majority of leaf nitrogen. To a first approximation, thylakoid nitrogen is proportional to the chlorophyll content (50 mol thylakoid N mol-1 Chl). Within species there are strong linear relationships between nitrogen and both RuBP carboxylase and chlorophyll. With increasing nitrogen per unit leaf area, the proportion of total leaf nitrogen in the thylakoids remains the same while the proportion in soluble protein increases. In many species, growth under lower irradiance greatly increases the partitioning of nitrogen into chlorophyll and the thylakoids, while the electron transport capacity per unit of chlorophyll declines. If growth irradiance influences the relationship between photosynthetic capacity and nitrogen content, predicting nitrogen distribution between leaves in a canopy becomes more complicated. When both photosynthetic capacity and leaf nitrogen content are expressed on the basis of leaf area, considerable variation in the photosynthetic capacity for a given leaf nitrogen content is found between species. The variation reflects different strategies of nitrogen partitioning, the electron transport capacity per unit of chlorophyll and the specific activity of RuBP carboxylase. Survival in certain environments clearly does not require maximising photosynthetic capacity for a given leaf nitrogen content. Species that flourish in the shade partition relatively more nitrogen into the thylakoids, although this is associated with lower photosynthetic capacity per unit of nitrogen.

Abstract: A review is made of the ruminant digestive system in its morphophysiological variations and adaptations relating to foraging behaviour, digestive physiology, to interactions between plants and ruminants and to geographic and climatic diversity of ruminants' ecological niches. Evidence is provided for evolutionary trends from an extreme selectivity mainly for plant cell contents and dependence upon a fractionated fore- and hindgut fermentation, to an unselective intake of bulk roughage subjected to an efficient plant cell wall fermentation, mainly in the forestomachs. The review is based on detailed comparative morphological studies of all portions of the digestive system of 65 ruminant species from four continents. Their results are related to physiological evidence and to the classification of all extant ruminants into a flexible system of three overlapping morphophysiological feeding types: concentrate selectors (40%), grass and roughage eaters (25%) and intermediate, opportunistic, mixed feeders (35%). Several examples are discussed how ruminants of different feeding types are gaining ecological advantage and it is concluded that ruminants have achieved high levels of digestive efficiency at each evolutionary stage, (including well-documented seasonal adaptations of the digestive system) and that ruminant evolution is still going on. Deductions made from the few domesticated ruminant species may have, in the past, biased scientific evaluation of the free-ranging species' ecology. The main threat to a continuous ruminant evolution and diversity appears to be man's neglect for essential ecological interactions between wild ruminants and their specific habitats, which he alters or destroys.

Abstract: Ten traits related to life history theory were measured or estimated for 71 freshwater fish species from two locations in the Venezuelan llanos. Multivariate statistics and cluster analysis revealed three basic endpoint patterns bounding a two-dimensional continuum. A suite of attributes associated with parental care and aseasonal reproduction appeared to correspond to an equilibrium strategy. A second group of small fishes was distinguished by traits associated with rapid colonizing ability: early maturation, continuous reproduction, and small clutches. The third basic pattern was associated with synchronized reproduction during the early wet season, high fecundity, absence of parental care, and breeding migrations. A subset of mostly small fishes exhibiting little or no parental care, small clutches, and two to four month reproductive seasons was intermediate between the opportunistic (rapidly colonizing) and seasonal strategies. All ten life history variables showed significant effects of phylogeny. The cluster of species corresponding to the equilibrium group was dominated by siluriform fishes and perciforms of the Cichlidae. The opportunistic cluster was dominated by cyprinodontiform and characiform fishes, whereas the seasonal cluster contained primarily characiform and siluriform fishes. Seven of nine traits were significantly correlated with body length. The three reproductive patterns are interpreted as being adaptative with respect to relative intensity and predictability of temporal and spatial variation in abiotic environmental parameters, food availability, and predation pressure.

Abstract: Deuterated water absorbed by deep roots of Artemisia tridentata appeared in the stem water of neighboring Agropyron desertorum tussocks. This supports the hypothesis that water absorbed by deep roots in moist soil moves through the roots, is released in the upper soil profile at night, and is stored there until it is resorbed by roots the following day. This phenomenon is termed hydraulic lift. The potential for parasitism of the water stored in the upper soil layers by neighboring plant roots is also shown. The effectiveness of water absorption by deep roots was substantially improved with hydraulic lift as indicated by reductions of 25 to 50% in transpiration on days following experimental circumvention of hydraulic lift. This phenomenon has important implications for plant water relations, mineral nutrient uptake, competitive interactions among neighboring plants and aridland hydrology.

Abstract: Published studies of consumer feeding preferences using foods that experience autogenic change in mass, numbers, area, etc., on the time scale of a feeding trial fail to employ appropriate statistical analyses to incorporate controls for those food changes occurring in the absence of the consumer. The studies that run controls typically use them to calculate a constant “correction factor”, which is subtracted prior to formal data analysis. This procedure constitutes a non-rigorous suppression of variance that overstates the statistical significance of observed differences. The appropriate statistical analysis for preference tests with two foods is usually a simple t-test performed on the between-food differences in loss of mass (or numbers, area, etc.) comparing the results of experimentals with consumers to controls without consumers. Application of this recommended test procedure to an actual data set illustrates how low replication in controls, which is typical of most studies of feeding preference, inhibits detection of an apparently large influence of previous mechanical damage (simulated grazing) in reducing the attractiveness of a brown alga to a sea urchin.

Abstract: Are plants at high altitudes short in nutrients? In order to answer this question the mineral nutrient content of leaves from over 150 plant species from 9 different mountain areas of all major climatic zones were analyzed (Kjeldahl nitrogen in all, phosphate in half of the samples, K, Mg, Mn, Ca in the Alps only). The majority of data are from herbaceous perennials, but shrubs and trees were studied as well. N-partitioning was studied in 45 herbaceous species from contrasting altitudes in the Alps. The survey falls into three categories: (1) comparisons of whole communities of species from contrasting altitudes, (2) analysis of altitudinal gradients, and (3) additional collections from high altitude sites alone. Unlike the other mineral nutrients, nitrogen content follows consistent altitudinal and latitudinal trends. The higher altitude sample always had higher N content per unit leaf area, irrespective of life form, wherever comparable plants (the same or related species) were investigated at contrasting altitudes. N content per unit dry weight (%) increased with altitude in herbaceous plants (in some species >4%), but was remarkably stable in evergreen woody plants (around 1%). The mean fraction of total plant N allocated to leaves of herbaceous plants in the Alps was the same at low and high altitude (1/3 of total). Leaf N (%) from the regional upper limits of higher plant life reveals a latitudinal decrease from subarctic to equatorial mountains, which may be related to the duration of annual leaf activity. Since mean N content per leaf area hardly differs between the uppermost sites, life span expectation (sink-duration) seems to control carbon investments rather than N input per leaf area. The growth of leaves at high altitude seems to be controlled in a way that leads to comparatively high nutrient contents, which in turn support high metabolic activity. Inherent developmental growth constraints inhibit nutrient dilution in the plant body and thus defy the application of classical concepts of plant-nutrient versus soil-nutrient relations developed for lowlands and in particular for cultivated plants. The results re-emphasize the global significance of links between nitrogen content, leaf sclerophylly, leaf longevity and photosynthetic capacity.

Abstract: In this study we propose the hypothesis that ecosystem succession is accompanied by a decrease in the metabolic quotient qCO2 (respiration-to-biomass ratio) of the soil microflora. The qCO2 is calculated from basal respiration (CO2-C·h-1) per unit microbial biomass carbon (Cmier). The hypothesis was tested by studying two primary successions on recessional moraines of the Rotmoos Ferner (Austria) and the Athabasca Glacier (Canada). For both soil seres (0->200 years) it was shown that the qCO2 decreased with time, which corroborated the hypothesis. In addition, the short term development of the qCO2 was demonstrated with a revegetation trial. We observed a rise in qCO2 for the first two years after reclamation, followed by a subsequent decrease.

Abstract: Experiments were conducted in the Patagonian steppe in southern South America to test the following hypotheses: (a) grasses take up most of the water from the upper layers of the soil and utilize frequent and short-duration pulses of water availability; (b) shrubs, on the contrary, take up most of the water from the lower layers of the soil and utilize infrequent and long-duration pulses of water availability. Grasses and shrubs were removed selectively and the performance of plants and the availability of soil resources were monitored. Results supported the overall hypothesis that grasses and shrubs in the Patagonian steppe use mainly different resources. Removal of shrubs did not alter grass production but removal of grasses resulted in a small increase in shrub production which was mediated by an increase in deep soil water and in shrub leaf water potential. The efficiency of utilization of resources freed by grass removal was approximately 25%. Shrubs used water exclusively from lower soil layers. Grasses took up most of the water from upper layers but they were also capable of absorbing water from deep layers. This pattern of water partitioning along with the lack of response in leaf nitrogen to the removal treatments suggested that shrubs may be at a disadvantage to grasses with respect to nutrient capture and led to questions about the role of nutrient recirculation, leaching, and nitrogen fixation in the steppe.

Abstract: Fruit-eating animals deposit viable seeds in patterns that determine the conditions under which seeds and seedlings live or die. Many tree species are scatter-dispersed by birds, bats, or other small frugivores that regurgitate, defecate, or drop seeds singly or in pairs. These scatterdispersed plant species normally recruit as isolated individuals, and are unlikely to evolve exceptional resistance to herbivores, pathogens, or to other sources of density-dependent seed or seedling mortality. Other tree species are clump-dispersed by larger terrestrial or arboreal frugivores that defecate seeds in masses which produce bouquets of seedlings. Because their seeds invariably germinate in close proximity to other seedlings, clump-dispersed species necessarily evolve chemical or mechanical defenses against seed predators, pathogens, and herbivores that act in a densitydependent manner.Population and genetic attributes should reflect this basic dichotomy in the conditions of seedling recruitment. I predict that seedlings of scatter-dispersed species rarely survive near parents or in dense aggregations under frugivore roosts. Seed dispersal should be mandatory, often to light gaps or other special habitats. Outbred adults and juveniles are expected to exist at low densities in loose aggregations or random distributions. Seedlings of clump-dispersed trees are pre-adapted for survival in dense aggregations near parents, as well as in fecal clumps. Substantial recruitment of juveniles and young adults should occur from undispersed seeds under and near parent trees. Such species should be common, highly aggregated, and show strong genetic family structure. Because recruitment requires dispersal, scatter-dispersed plant species should be especially vulnerable to loss of dispersal agents. Because offspring consistently recruit near parents, clump-dispersed plants should be less vulnerable to temporary loss of dispersal agents.

Abstract: Within the high arctic of Canada, Salix arctica, a dioecious, dwarf willow exhibits significant spatial segregation of the sexes. The overall sex ratio is female-biased and female plants are especially common in wet, higher nutrient, but lower soil temperature habitats. In contrast, male plants predominate in more xeric and lower nutrient habitats with higher soil temperatures that can be drought prone. Associated with the sex-specific habitat differences were differences in the seasonal and diurnal patterns of water use as measured by stomatal conductance to water vapor and the bulk tissue water relations of each gender. Within the wet habitats, female plants maintained higher rates of stomatal conductance (g) than males when soil and root temperatures were low (<4° C). In contrast, within the xeric habitats, male plants maintained higher g and had lower leaf water potentials Ψleaf at low soil water potentials and a high leaf-to-air vapor pressure gradient (Δw) when compared to females. Female plants had more positive carbon isotope ratios than males indicating a lower internal leaf carbon dioxide concentration and possibly higher water use efficiency relative to males. Tissue osmotic and elastic properties also differed between the sexes. Male plants demonstrated lower tissue osmotic potentials near full tissue hydration and at the turgor loss point and a lower bulk tissue elastic modulus (higher tissue elasticity) than female plants. Males also demonstrated a greater ability to osmotically adjust on a diurnal basis than females. These properties allowed male plants to maintain higher tissue turgor pressures at lower tissue water contents and Ψsoil over the course of the day. The sex-specific distributional and ecophysiological characteristics were also correlated with greater total plant growth and higher fecundity of females in wet habitats, and males in xeric habitats respectively. The intersexual differences in physiology persisted in all habitats. These results and those obtained from growth chamber studies suggest that sex-specific differences have an underlying genetic basis. From these data we conjecture that selection maintaining the intersexual differences may be related to different costs associated with reproduction that can be most easily met through physiological specialization and spatial segregation of the sexes among habitats of differing conditions.

Abstract: Numerous studies have demonstrated a negative relationship between increasing habitat complexity and predator foraging success. Results from many of these studies suggest a non-linear relationship, and it has been hypothesised that some “threshold level” of complexity is required before foraging success is reduced significantly. We examined this hypothesis using largemouth bass (Micropterus salmoides) foraging on juvenile bluegill sunfish (Lepomis macrochirus) in various densities of artificial vegetation. Largemouth foraging success differed significantly among the densities of vegetation tested. Regression analysis revealed a non-linear relationship between increasing plant stem density and predator foraging success. Logistic analysis demonstrated a significant fit of our data to a logistic model, from which was calculated the threshold level of plant stem desity necessary to reduce predator foraging success. Studies with various prey species have shown selection by prey for more complex habitats as a refuge from predation. In this stydy, we also examined the effects of increasing habitat complexity (i.e. plant stem density) on choice of habitat by juvenile bluegills while avoiding predation. Plant stem density significantly effected choice of habitat as a refuge. The relationship between increasing habitat complexity and prey choice of habitat was found to be positive and non-linear. As with predator foraging success, logistic analysis demonstrated a significant fit of our data to a logistic model. Using this model we calculated the “threshold” level of habitat complexity required before prey select a habitat as a refuge. This density of vegetation proved to be considerably higher than that necessary to significantly reduce predator foraging success, indicating that bluegill select habitats safe from predation. Implications of these results and various factors which may affect the relationships described are discussed.

Abstract: Root proliferation in nutrient-rich soil patches is an important mechanism facilitating nutrient capture by plants. Although the phenomenon of root proliferation is well documented, the specific timing of this proliferation has not been investigated. We studied the timing and degree of root proliferation for three perennial species common to the Great Basin region of North America: a shrub, Artemisia tridentata, a native tussock grass, Agropyron spicatum, and an introduced tussock grass, Agropyron desertorum. One day after we applied nutrient solution to small soil patches, the mean relative growth rate of Agropyron desertorum roots in these soil patches was two to four times greater than for roots of the same plants in soil patches reated with distilled water. Most of the increased root growth came from thin, laterally branching roots within the patches. This rapid and striking root proliferation by Agropyron desertorum occurred in response to N-P-K enrichment as well as to P or N enrichment alone. A less competitive bunchgrass, Agrophyron spicatum, showed no tendency to proliferate roots in enriched soil patches during these two-week experiments. The shrub Artemisia tridentata proliferated roots within one day of initial solution injection in the N-enrichment experiment, but root proliferation of this species was more gradual and less consistent in the N-P-K and P-enrichment experiments, respectively. The ability of Agropyron desertorum to proliferate roots rapidly may partly explain both its general competitive success and its superior ability to exploit soil nutrients compared to Agropyron spicatum in Great Basin rangelands of North America.

Abstract: Abundance and flower visitation rate of the pollinators of Lavandula latifolia (Labiatae), an insect-pollinated shrub, were studied over a 6-year period. The objective was to elucidate interspecific patterns in the “quantity” component of the plant-pollinator interaction. A total of 54 insect taxa are considered in the analyses, including hynenopterans, dipterans and lepidopterans. Most pollinators were comparatively scarce, with a few taxa acounting collectively for the majority of individuals. Pollinators differed broadly in flower visitation rate (0.2–30 flowers/min). Most of this variation was explained by differences in flower handling time (HT). Regardless of proboscis length, hymenopterans had intrinsically shorter handling times than lepidopterans. Within each group, HT decreased exponentially with increasing proboscis length. Abundance and visitation rate were uncorrelated across pollinator taxa. The total number of visits that each pollinator contributed to the plant (NFV) was estimated as the product of abundance x visitation rate. NFV values spanned four orders of magnirade. A small, taxonomically diverse group of species (1 moth, 1 butterfly, 4 bees) accounted for most visits and thus could effectively exert some selection on floral features. Nevertheless, the morphological diversity represented in this group of dominant pollinators probably constrains plant specialization, as they will most likely select for different floral features or in opposing directions on the same traits.

Abstract: Emergence and survival of honey mesquite (Prosopis glandulosa var.glandulosa Torr.) seedlings was quantified on sites with contrasting grazing histories: long-term continuous grazing (LTG) and long-term protection (LTP) from grazing by cattle. On each site, different levels of heroaceous defoliation were imposed at monthly intervals (no defoliation=ND, moderate=MD and heavy=HD). The two weeks following seed dissemination appeared to be the most critical toProsopis establishment on LTP-ND plots. Openings in the herbaceous layer created by moderate defoliation of grasses on the LTP site increased germination and/or survival 7-to 8-fold during this period. However, increasing the degree of defoliation from moderate to heavy did not stimulate additional emergence on either the LTP or LTG site. Emergence from scarified seed placed in cattle dung (17 to 30%) was lower than that of bare seed placements in various microhabitats (43–60%). However, deposition of scarifiedProsopis seed in dung in conjunction with graminoid defoliation may be the most likely combination of events when livestock are present. Emergence from seeds transported into grasslands by other fauna likely would be low, unless seeds were deposited in areas where grasses had been defoliated.Prosopis survival was comparably high in dung and bare seed placements after one growing season. survival of seedlings present two weeks after seed dissemination ranged from 74 to 97% at the end of the second growing season. Seedling survival and shoot development (biomass, leaf area and height) were similar on LTP and LTG sites, regardless of the level of herbaceous defoliation or seed placement. In addition, the magnitude and patterns of net photosynthesis, stomatal conductance and xylem water potential were comparable among one-year-old seedtings on ND, MD and HD plots, even though differences in herbaceous species composition and above- and below-ground biomass between these treatments were substantial. Such data suggest competition for soil resources between grasses andProsopis may be minimal early in the life cycle ofProsopis. High rates ofProsopis emergence and establishment on LTP-MD plots are counter to the widespread assumption that long-term and/or heavy grazing is requisite forProsopis encroachment into grasslands. Results are discussed with regard to factors contributing to the recent, widespread invasion of this woody legume into grasslands of southwestern North America.

Abstract: In ants, there are two main processes of colony founding, the independent and the dependent modes. In the first case young queens start colony founding without the help of workers, whereas in the second case they are accompanied by workers. To determine the relation between the mode of colony founding and the physiology of queens, we collected mature gynes of 24 ant species. Mature gynes of species utilizing independent colony founding had a far higher relative fat content than gynes of species employing dependent colony founding. These fat reserves are stored during the period of maturation, i.e. between the time of emergence and mating, and serve as fuel during the time of colony founding to nurture the queen and the brood. Gynes of species founding independently but non claustrally were found to have a relative fat content intermediate between the values found for gynes founding independently and those founding dependently. This suggests that such gynes rely partially on their fat reserves and partially on the energy provided by prey they collect to nurture themselves and the first brood during the time of colony founding. Study of the fat content of mature gynes of all species has shown that it gives a good indication of the mode of colony founding.

Abstract: Seasonal patterns of insect damage to reproductive tissue of the legume Baptisia australis were studied for three years in native tallgrass priairie. Contrasting seasonal patterns of damage were associated with the major species of insect consumers. The moth Grapholitha tristegana (Olethreutidae) and the weevil Tychius sordidus (Curculionidae), which together infested 80-100% of developing fruits (pods), consistently damaged more seeds on average in early than in late maturing pods. But while late opening flowers were less subject to attack from moths and weevils, they were more subject to attack from chewing insects, particularly blister beetles (Epicauta fabricii, Meloidae), which destroyed >80% of all flowers and developing young pods (including moth and weevil larval inhabitants). The blister beetles arrived late in the flowering season and fed particularly on young reproductive tissue, allowing larger, older pods that had developed from early opening flowers to escape destruction. The relative abundances and impacts of blister beetles, moths, and weevils varied from year to year. Adding to the uncertainty of reproductive success of the host plant were the large and variable amounts of damage to immature buds inflicted by insects (including the blister beetles and weevil adults) and late killing frosts. Thus, timing of flowering is critical to success in seed production for B. australis. The heavy impacts of insects and weather can result in a very narrow window in time (which shifts from year to year) during which B. australis can flower with any success. The opposing pressures exerted by insects and weather on floral reproductive success may act in concert with other features of the plant's biology to foster the maintenance of considerable diversity in flowering times among individuals in local populations of B. australis.

Abstract: The value of a leaf to a plant depends on the fate of its exported assimilates. When these are translocated and used in the growth of new leaves they contribute to further carbon assimilation. The result is that their value to the plant is greatest while they are young. In contrast, when assimilates are translocated to storage, assimilates produced early and late in the life of a leaf are of equal value. This arguments is developed in relation to the optimal distribution of mineral resources and defenses during the life of leaves.

Abstract: In the humid tropics of SE Asia there are some 14 myrmecophytic species of the pioneer tree genus Macaranga (Euphorbiaceae). In Peninsular Malaysia a close association exists between the trees and the small, non-stinging myrmicine Crematogaster borneensis. These ants feed mainly on food bodies provided by the plants and have their colonies inside the hollow internodes. In a ten months field study we were able to demonstrate for four Macaranga species (M. triloba, M. hypoleuca, M. hosei, M. hulletti) that host plants also benefit considerably from ant-occupation. Ants do not contribute to the nutrient demands of their host plant, they do, however, protect it against herbivores and plant competition. Cleaning behaviour of the ants results in the removal of potential hervivores already in their earliest developmental stages. Strong aggressiveness and a mass recruiting system enable the ants to defend the host plant against many herbivorous insects. This results in a significant decrease in leaf damage due to herbivores on ant-occupied compared to ant-free myrmecophytes as well as compared to non-myrmecophytic Macaranga species. Most important is the ants' defense of the host plant against plant competitors, especially vines, which are abundant in the well-lit pioneer habitats where Macaranga grows. Ants bite off any foreign plant part coming into contact with their host plant. Both ant-free myrmecophytes and non-myrmecophytic Macaranga species had a significantly higher incidence of vine growth than specimens with active ant colonies. This may be a factor of considerable importance allowing Macaranga plants to grow at sites of strongest competition.

Abstract: Measurements of litter fall and litter removal by crabs, in conjunction with estimates of litter decay by microbes and tidal export of litter from three high-intertidal mangrove forests were made during a year-long study in tropical northeastern Australia. In forests dominated by Ceriops tagal and Bruguiera exaristata, litter standing stocks remained low on the forest floor (mean 6 g·m-2), although litter fall was high; 822 and 1022 g·m-2·y-1, respectively. Sesarmid crabs removed 580 (Ceriops) and 803 (Bruguiera) g·m-2·y-1, or 71 and 79%, of the total annual litter fall from the forest floor. Relative to the rate of litter removal by crabs, microbial turnover of whole, unshredded litter was insignificant, accounting for 75 times the rate of microbial decay alone, thus facilitating the high sediment bacterial productivity in these forests. The importance of litter processing by crabs increases with height in the intertidal in tropical Australia, in contrast to New World mangrove forests, where the reverse is true.

Abstract: Ecological studies have been made of all 5 European species of Maculinea. These confirm that M. nausithous and M. rebeli live underground in Myrmica ant nests for 10 months of the year, as has long been known for the other 3 species. The main discovery was that each Maculinea species depends on a single, and different, host species of Myrmica. This specificity contradicts previous papers and scientific reviews of the relationship between Maculinea and ants. Therefore, early records are re-examined and 3 reasons are given to explain why most are misleading when applied to wild populations. Dependence on a single, rather than any, species of Myrmica explains why Maculinea populations exist in only a small minority of biotopes where their foodplants and Myrmica ants abound. It also explains the puzzling disappearance of Maculinea populations from apparently suitable sites. The discovery that M. alcon and M. rebeli depend on separate species of Myrmica that are not even closely related strengthens the argument that these butterflies are good species.

Abstract: We have analyzed seasonal shifts of energy and time allocation in a population of golden-mantled ground squirrels (Spermophilus saturatus) by directly measuring total daily energy expenditure (DEE) with an isotopic technique ("doubly labeled water"=dlw), and by estimating components of total DEE through an integration of field behavioral observations with laboratory-measured rates of energy expenditure (oxygen consumption) associated with major behavioral and physiological states. Hibernation laster about 7 1/2 months, and the 4 1/2-month activity season consisted of mating, a 28-d gestation of 3-5 young, 5 1/2 weeks of postnatal growth building to a peak in lactation just before the young emerged above ground, an additional 2-3-week period of maternal care before dispersal, and finally restoration of body mass preceding hibernation. Although the hibernation season comprised nearly two-thirds of the year, it involved only 13-17% of annual energy expenditure, leaving about 85% of energy expenditure for the active season. Ground squirrels were actually present on the surface for only about 11% of the year's time, and the foraging time required to obtain the total annual energy supply amounted to only about 2% of the year's time. The squirrels fed mainly on herbs in the early season and hypogeous fungi later; both were used extensively during peak lactation when female energy expenditure and demand were maximal. Average daily foraging time increased steadily throughout the season to a maximum of 28% of aboveground time as availability of greens diminished and fungus predominated in the diet; time availability did not limit foraging since the animals sat on average for 65% of the daily surface time of about 7 h. Timing of reproduction is apparently optimized such that peak reproductive energy demands are matched with maximal food availability and moderate thermal conditions that minimize energy demand. Despite the greater body mass of males, the greatest total DEE (measured by dlw) of any squirrels at any time of year was that of females during peak lactation. For production of young and lactation through above-ground emergence of an average litter of 2.7, females required a total energy increase of 24% above annual nonreproductive metabolism. Yearling females all bred and performed similarly to older females, yet some costs were greater because the yearlings began and ended hibernation at smaller mass, compensated by giving birth later, and finally showed a greater absolute increase in body mass over the active season than older females. Annual metabolic energy expenditure of breeding males was about 18% greater than that of females, due to greater male body mass. Yet the annual energy intake requirement for both sexes was essentially identical (about 42MJ) due to the greater reproductive export by females in the form of newborn and milk. During the mating season males showed wide-ranging exploratory behavior and social interactions, including aggression, that involved considerable locomotory energy expenditures. Although we did not directly account for the energetics of these specific reproductive behaviors, they are critical to male reproductive success and on a daily basis they probably involved much greater energy expenditure than sperm production. Some yearling males avoided these costs by foregoing testicular development, yet they allocated four times as much energy to growth as older males, thereby increasing somatic condition for the future.

Abstract: In the Constant Frequency portions of the orientation calls of various Rhinolophus and Hipposideros species, the frequency with the strongest amplitude was studied comparatively. (1) In the five European species of the genus Rhinolophus call frequencies are either species-specific (R. ferrumequinum, R. blasii and R. euryale) or they overlap (R. hipposideros and R. mehelyi). The call frequency distributions are approximately 5–9 kHz wide, thus their ranges spead less than ±5% from the mean (Fig. 1). Frequency distributions are considerably narrower within smaller geographic areas. (2) As in other bat groups, call frequencies of the Rhinolophoidea are negatively correlated with body size (Fig. 3). Regression lines for the genera Rhinolophus and Rhinolophus, species from dryer climates have on the average higher call frequencies than species from tropical rain forests. (4) The Krau Game Reserve, a still largely intact rain forest area in Malaysia, harbours at least 12 syntopic Rhinolophus and Hipposiderso species. Their call frequencies lie between 40 and 200 kHz (Fig. 2). Distribution over the available frequency range is significantly more even than could be expected from chance alone. Two different null hypotheses to test for random character distribution were derived from frequency-size-relations and by sampling species assemblages from a species pool (Monte Carlo method); both were rejected. In particular, call frequencies lying close together are avoided (Figs. 4, 5). Conversely, the distribution of size ratios complied with a corresponding null hypothesis. This even distribution may be a consequence of resource partitioning with respect to prey type. Alternatively, the importance of these calls as social signals (e.g. recognition of conspecifics) might have necessitated a communication channel partitioning.

Abstract: We demonstrate here the existence of a range of size-independent reproductive tactics in teleostean fish involving the allocation of a size-dependent reproductive effort between fecundity and egg size. Despite considerable evidence that larger eggs and the larvae hatching from them are more likely to survive than smaller ones, we found no evidence of evolutionary trends towards greater egg sizes. Fish with pelagic eggs tend to spawn many, and therefore small, eggs, whereas demersal spawners tend to produce large, and therefore few, eggs. Maximizing egg number should increase the number of eggs hatching in suitable locations in the patchy pelagic environment and, hence, increase the reproductive success of pelagic spawners. On the other hand, the reproductive success of demersal spawners, which reduce the variance in growing conditions experienced by the off spring, should be more dependent on the survival of the individual larvae, which increases as egg size increases.

Abstract: Foliar samples were obtained from symbiotic nitrogen-fixers and control plants (non-fixers) along elevational and primary successional gradients in volcanic sites in Hawai'i. Most control plants had negative δ15N values (range-10.1 to +0.7‰), while most nitrogen-fixers were near 0‰. Foliar 15N in the native tree Metrosideros polymorpha did not vary with elevation (from sea level to tree-line), but it did increase substantially towards 0‰ on older soils. The soil in an 197-yr-old site had a δ15N value of approximately-2‰, while in a ∼67000-yr-old site it was +3.6‰. We suggest that inputs of 15N-depleted nitrogen from precipitation coupled with very low nitrogen outputs cause the strongly negative δ15N values in non-nitrogen-fixing plants on early successional sites.

Abstract: Three high marsh communities on the Chesapeake Bay were exposed to a doubling in ambient CO2 concentration for one growing season Open-top chambers were used to raise CO2 concentrations ca 340 ppm above ambient over monospecific communities of Scirpus olneyi (C3) and Spartina patens (C4), and a mixed community of S olneyi, S patens, and Distichlis spicata (C4) Plant growth and senescence were monitored by serial, nondestructive censuses Elevated CO2 resulted in increased shoot densities and delayed sensecence in the C3 species This resulted in an increase in primary productivity in S olneyi growing in both the pure and mixed communities There was no effect of CO2 on growth in the C4 species These results demonstrate that elevated atmospheric CO2 can cause increased aboveground production in a mature, unmanaged ecosystem

Abstract: We compared seasonal trends in photosynthesis of two naturalized exotic shrubs (Rhamnus cathartica and Lonicera X bella) and two native shrubs (Cornus racemosa and Prunus serotina) in open and understory habitats in southern Wisconsin. We examined the relationships between resource availability and leaf photosynthetic performance in these four species. All four species had similar relationships between leaf nitrogen (N) content and photosynthetic rate, but the species differed in absolute leaf N content and therefore in photosynthetic rates. Maximum daily photosynthetic rates of all species were significantly correlated with leaf N content in the open habitat, but not in the understory, where low light availability was the major limitation to photosynthesis. Extended leaf longevity was important in the forest understory because it allowed shrubs to take advantage of high light availability at times when the overstory canopy was leafless. Early leaf emergence was more important than late senescence: from 27% to 35% of the annual carbon gain of P. serotina, R. cathartica, and L. X bella occurred prior to leaf emergence of C. racemosa, the species with the shortest leaf life span. Extended leaf longevity of exotic shrubs may help explain their persistence in the understory habitat, but it contributed relatively less to their annual carbon gain in the open habitat.

Abstract: The many evolutionary modifications to seed biology in response to seed predation do not necessarily imply that seed predators have an important impact on population recruitment. This is because competition between individual plants for rare safe sites can cause an 'oversupply' of seeds so far as a population is concerned. The importance of seed losses to population recruitment at any point in time is related to the abundance of safe sites (Fig. 1): it is zero when safe sites are absent, negligible when safe sites are rare, and greatest when safe sites are numerous enough for recruitment to be limited by seed supply. Here I interpret the impact of severe seed losses on population recruitment in four species of long-lived perennials (Eucalyptus baxteri, Leptospermum juniperinum, Casuarina pusilla and L. myrsinoides) by considering these losses in terms of the overall seed dynamics of the populations. I focus on seed supply and seedling survival, as a measure of the current abundance of safe sites, and the maintenance of seed banks, as a measure of the ability of populations to exploit any future changes in safe site abundance. Insect seed predators destroyed about 95% of total seeds in each case. However, these losses do not necessarily have an important impact on population recruitment, because: (i) in most years recruitment appears to be limited by a rarity of safe sites, and not by seed supply (which was as high as 43 germinable seeds/m2/yr); and (ii) the losses did not prevent the establishment of large seed banks (ranging from >30 to >1000 viable seeds/m2) potentially capable of exploiting temporary conditions favourable for recruitment. In contrast to the situation with many annual plants, patterns of recruitment in stable populations of long-lived perennials are often extremely complex, and the significance of seed losses therefore difficult to determine.

Abstract: To investigate the physiological, behavioral, and genetic contributions to growth rate, we studied the thermal sensitivity of growth rate in hatchlings of the iguanid lizards Sceloporus occidentalis and S. graciosus in the laboratory. We used a cycling thermal regime patterned after thermal environments found in nature. Growth rates increased with duration of access to radiant heat. Thus, variation in the thermal environment can cause phenotypic variation in growth rate and hence body size. The two species differed in both the magnitude and thermal sensitivity of growth rate, and these differences were associated with differences in behavioral thermoregulation. Thus, growth is determined interactively by both behavior and physiology. We found evidence of among-family variation in the growth rates of S. occidentalis, suggesting that growth rate has the genetic potential to evolve. In S. occidentalis, both growth rate and egg size affected body size of hatchlings at several weeks of age. In turn, hatchling size may affect fitness: for example, larger S. occidentalis hatchlings had higher sprint speeds and may therefore be more adept at capturing prey or evading predators. Our results demonstrate that growth rate has genetic, behavioral, and physiological components, and that the resulting effects on body size may have important consequences for ecological performance e.g., sprint speed.

Abstract: We examined the competitive effects of two annual species on soil water potential and blue oak (Quercus douglasii Hook & Arn.) seedling growth and water relations. Two densities of the annual grass Bromus diandrus (Roth.) (100/dm2, 3.6/dm2) and one density of the annual forb Erodium botrys (Cav.) (3.6/dm2) comprised plant neighborhoods around the oak seedlings grown in 1 m deep boxes. Rates of soil water depletion differed among neighborhoods. Soil in the Erodium neighborhoods dried significantly more slowly than did soil in the Bromus neighborhoods at either density. Differences in the rates of soil water depletion were correlated both with the 30% lower root biomass developed by Erodium, and the lower water extraction rates of Erodium relative to Bromus roots at constant root biomass. These results suggest that the annual species are not equivalent competitors for water: fibrous grass roots had greater competitive effect than did forb tap-roots. In a control container without an annual neighborhood, soil water potentials remained high for the duration of the experiment. Oak seedling emergence and growth responses were significantly affected by annual plant density. High density of annual plants suppressed oak root growth and shoot emergence. Only 20% of the acorns planted in high density Bromus neighborhoods showed aboveground shoot growth; 56% of those planted in low density Bromus or Erodium emerged. Ninety percent emerged in the control box. Relative growth rates of oak seedling roots and shoots were directly dependent on soil water potentials. Soil water was also closely correlated with oak seedling predawn water potentials and gas conductance measurements. Higher soil water potentials greater dry weights, and longer growing seasons were found for oak seedlings in the Erodium neighborhood and the container with no annuals than in Bromus neighborhoods of either density. These results suggest that competition for soil water with introduced annual species contributes to the increased rate of blue oak seedling mortality currently observed in California woodland systems.

Abstract: Carbon dioxide concentrations were elevated in three estuarine communities for an entire growing season. Open top chambers were used to raise CO2 concentrations ca. 336 ppm above ambient in monospecific communities of Scirpus olneyi (C3) and Spartina patens (C4), and a mixed community of S. olneyi, S. patens and Distichlis spicata (C4). Nitrogen and carbon concentration (% wt) of aboveground tissue was followed throughout growth and senescence. Green shoot %N was reduced and %C was unchanged under elevated CO2 in S. olneyi. This resulted in a 20%–40% increase in tissue C/N ratio. There was no effect of CO2 on either C4 species. Maximum aboveground N (g/m2) was unchanged in S. olneyi, indicating that increased productivity under elevated CO2 was dependent on reallocation of stored N. There was no change in the N recovery efficiency of S. olneyi in pure stand and a decrease in the mixed community. Litter C/N ratio was not affected by elevated CO2 suggesting that decomposition and N mineralization rates will also remain unchanged. Continued growth responses to elevated CO2 could, however, be limited by the ability of S. olneyi to increase the total aboveground N pool.