Showing papers in "Oecologia in 1976"
TL;DR: It appears that the deleterious effects of low temperatures during growth negate the advantages of possessing the C4 pathway in cooler habitats, and high minimum temperatures during the growing season have the strongest correlation with the relative abundance of C4 grass species in a regional flora.
Abstract: A stepwise multiple regression analysis was used in an attempt to correlate statistically the geographic patterns in the abundance of C4 grasses with patterns in climatic variables. The percent of grasses having the C4 pathway was computed for the total grass flora in twenty-seven widely spaced regions of North America. From long-term climatic records seasonal and annual values for solar irradiance, water supply, heat availability, and combinations of these variables were assigned to each of the twentyseven regions. The results of the analysis suggest that high minimum temperatures during the growing season have the strongest correlation with the relative abundance of C4 grass species in a regional flora. It appears that the deleterious effects of low temperatures during growth negate the advantages of possessing the C4 pathway in cooler habitats.
737 citations
TL;DR: Standing crop biomass, energy expenditure and production by large mammalian herbivores in the African savannas show a high degree of correlation with mean annual precipitation and predicted above ground primary production, which possess the potential for predicting carrying capacity and protein production from simple meteorological data.
Abstract: Standing crop biomass, energy expenditure and production by large mammalian herbivores in the African savannas show a high degree of correlation with mean annual precipitation and predicted above ground primary production. These relationships possess the potential for predicting carrying capacity and protein production from simple meteorological data.
615 citations
TL;DR: The effect of forest size on avian diversity was studied in oak forest patches in rural New Jersey and number of bird species continued to increase significantly in old oak woods up through 40 ha.
Abstract: The effect of forest size on avian diversity was studied in oak forest patches in rural New Jersey. Number of bird species continued to increase significantly in old oak woods up through 40 ha. This was due to the progressive addition of carnivorous species with increasing minimum forest size requirements. One large woodlot had more species than the same area subdivided into smaller woodlots. To maintain maximum regional diversity more than three large forests are required. Primary land use priority should be to protect large forests. Second priority should be to maintain a high density of small woodlots.
226 citations
TL;DR: It is suggested that exposure to temperatures in excess of 22° C, as for example during low tides in the summer, might result in a cumulative stress on these populations of mussels by imposing a metabolic deficit which must be recovered at each subsequent high tide.
Abstract: Mytilus californianus regulated its rate of oxygen consumption (VO2) during decline in oxygen tension, but did not acclimate VO2 when held at 58 mm Hg PO2. In spite of a capacity to consume oxygen while exposed to air (the average VO2 in air being equivalent to 0.74xthe standard rate of oxygen consumption in water), these mussels acquired an “oxygen debt” during aerial exposure which was discharged on subsequent reimmersion. During exposure to air the oxygen tension of the fluid in the mantle cavity was rapdly reduced to approximately 40 mm Hg, in animals both in the laboratory and on the shore. Heart rate was also reduced during air exposure, though not to the point of cardiac arrest. The concentration of ammonia in the fluid of the mantle cavity increased during aerial exposure, but the rate of excretion of ammonia was much lower than during immersion. Observations of mussels on the shore at low tide indicated that dehydration of the tissues was not a serious threat, possibly due to the large volume of fluid retained in the mantle cavity. During aerial exposure some end-products of anaerobic metabolism (alanine and malate) accumulated in the posterior adductor muscle. Malate accumulation was rapid during the first hour of exposure; alanine accumulated more gradually. It is concluded that during aerial exposure M. californianus resorts to anaerobiosis in spite of a capacity to extract some oxygen from the atmosphere. This results in a metabolic deficit during each period of low tide which, coupled with the reduced time available for feeding, imposes a physiological stress on mussels distributed on the shore.
209 citations
TL;DR: It is postulated that variation in survival of the very young is brought about by changes in the abundance and nitrogen content of their food plants, and that this in turn is largely influenced byChanges in patterns of rainfall.
Abstract: Species of acridids throughout the world are shown to have very similar habitats and food plants, and to increase and decrease in abundance in response to very similar patterns of weather. Changes in the rate of survival of the very young hoppers from unexplained causes would appear to be the major factor influencing these changes in abundance; parasites and predators apparently have little if any significant effect.It is postulated that variation in survival of the very young is brought about by changes in the abundance and nitrogen content of their food plants, and that this in turn is largely influenced by changes in patterns of rainfall.The hypothesis-already proposed for other phytophagous insects-states that the environment of these insects is basically inadequate in that there is normally a relative shortage of nitrogenous food for the rapidly growing young. Species have adapted to this inadequate environment by producing large "surpluses" of young.When chance combinations of weather stress the food plants, making them a richer source of nitrogen, there is a greatly increased rate of survival of the very young, rapidly leading to explosive increases in abundance-to outbreaks.Some of the implications of applying this hypothesis more generally to the interpretation of the ecology of herbivores are discussed.
207 citations
TL;DR: The forest floor is a major reservoir of organic matter and nutrients for the ecosystem and as such it influences or regulates most of the functional processes occurring throughout the ecosystem.
Abstract: The forest floor is a major reservoir of organic matter and nutrients for the ecosystem and as such it influences or regulates most of the functional processes occurring throughout the ecosystem. This study reports on the nutrient and organic matter content of the forest floor of the Hubbard Brook Experimental Forest during different seasons and attempts to correlate results from studies of vegetation, litter, decomposition, stemflow, throughfall, and soil. An organic matter budget is presented for an undisturbed watershed. Average weight of the forest floor on an undisturbed watershed ranged from 25,500 to 85,500 kg/ha. The weighted watershed average was 46,800 kg/ha. Although the F and H horizons did not vary significantly with time, the L horizon increased significantly during the period June to August largely as a result of a severe hail storm. The order of abundance of elements in the forest floor was Nτ;Ca≷Fe>S>P>Mn>K>Mg>Na>Zn>Cu. The concentrations of Ca, K, and Mn decreased with depth in the forest floor while N, P, S, Na, Fe, Zn, and Cu concentrations increased. N:P ratios were similar in decomposing leaf tissue, the forest floor, litterfall, and net stemflow plus throughfall suggesting a similar pattern of cycling. S was proportional to N and P in decomposing leaf tissue, the forest floor, and litterfall. Net stemflow and throughfall were affected by a relatively large input of SO4=-S from the atmosphere. Residence times for elements in the forest floor were affected by inputs other than litterfall (precipitation, stemflow, and throughfall). Calculation of residence times using all inputs caused smaller values than if litterfall alone was used. While all residence times were reduced, the major differences occurred for K, S, and Na. N and P showed relatively long residence times as a result of retranslocation and immobilization by decomposers. The slow turnover rate because of the strong demand and retention by all biota must account for the efficiency of the intrasystem cycling process for N and P. K showed the shortest residence time. A rapid and efficient uptake of K by vegetation seems to account for the efficient cycling of this element. The patterns of nutrient cycling are several depending on the chemical properties of the forest floor, and nutritional requirements of the biota.
190 citations
TL;DR: The determinants of food choice by hummingbirds provide a rationale for viewing factors important in plant competition for pollinator visits.
Abstract: Hummingbirds selected food in choice experiments based primarily on sugar concentration and secondarily on rate of intake and position. Sugar compositions had little effect on food choice, but the preferred sugar compositions appear to be the most common in nectars of plants visited by hummingbirds. Most amino acids in sugar water were not detected at concentrations found in nectars. Higher amino acid concentrations generally resulted in rejection. Hummingbirds did not necessarily select food in the laboratory to maximize feeding efficiency, but under natural circumstances similar choices could result in optimal feeding efficiencies. The determinants of food choice by hummingbirds provide a rationale for viewing factors important in plant competition for pollinator visits.
184 citations
TL;DR: Populations of avian transients were studied at a stopover area in southern Texas during four consecutive migration seasons, fall, 1973-spring, 1975, showing that birds in Zugstimmung and Zugdisposition differ, not only physiologically but behaviorally as well.
Abstract: Populations of avian transients were studied at a stopover area in southern Texas during four consecutive migration seasons, fall, 1973-spring, 1975. We captured individuals by mist net for banding and fat level determination. Concurrently we made observations on behavior of free-flying birds. We worked intensively with a single species, the Northern Waterthrush (Seiurus noveboracensis) while gathering weight fat and behavioral data on other species as well. Many of the patterns of weight change and behavior seen in the Northern Waterthrush were observed in other common passerines which occurred as transients on our study site. Results showed that birds in Zugstimmung and Zugdisposition differ, not only physiologically but behaviorally as well. Individuals of normally non-gregarious species that are in Zugstimmung are gregarious and stay in an area for only a short period. Their habitat needs are broad since these birds are not dependent on the food resources of the area in which they stop while in this physiological state. In contrast, normally non-gregarious migrants in Zugdisposition are hyperphagic and aggressively territorial in defense of resources and may stay at the same site for several days. Their habitat needs are quite specific since they must increase food intake by as much as 40% to build up fat reserves. Not all individuals in Zugdisposition are able to find territories at the same time. Those birds unable to claim territories either continue to migrate or stay in an area as floaters, continually attempting to obtain territories. Weather conditions probably act as a third variable that must be balanced by the individual in a complex optimization strategy with physiological state and success in competition.
182 citations
TL;DR: The NESS measure is shown to be a generalization of Morisita's similarity and is demonstrated to be less biased than other commonly used measures.
Abstract: We propose a new measure of similarity, the normalized expected species shared or NESS. The measure is based on the expected number of species shared between random samples of size, m, drawn from a population. The NESS measure is shown to be a generalization of Morisita's similarity and is demonstrated to be less biased than other commonly used measures. The contribution of dominant and rare species is explicit according to the sample size, m, chosen. For large m, NESS is sensitive to the less common species in the populations to be compared. The NESS measure has been used to cluster a 2-year sequence of subtidal benthic samples taken after a severe disturbance. The NESS measure is responsive to the less common species so that both a temporal progression in community recovery and seasonal variation are revealed.
167 citations
TL;DR: Evidence is presented which supports the hypothesis that bacteria are not as quantitatively important as other components of the detrital food material, and that Simulium and Chironomus do not appear to be selective in their digestion.
Abstract: Bacteriological analyses of the guts of four common lotic invertebrates are described. The results from these analyses suggest thatSimulium andChironomus digest at least half of the bacteria that they ingest in situ, but no evidence has been found for the digestion of bacteria byBaetis or byEphemerella. Moreover,Simulium andChironomus do not appear to be selective, with regard to bacterial type, in their digestion. The limitations of the method are discussed and the relative importance of bacteria compared with other components of the insects' diet is assessed. Evidence is presented which supports the hypothesis that bacteria are not as quantitatively important as other components of the detrital food material.
138 citations
TL;DR: This is the first demonstration of how specific environmental factors affect population density and species diversity of benthic invertebrates in a coral reef-associated habitat.
Abstract: Structural complexity of the habitat significantly increases population density and number of species in assemblages of predatory gastropod molluscs (families Conidae, Muricidae, Mitridae and Vasidae) on intertidal, generally smooth, horizontal limestone platforms fringing tropical Pacific islands. The important topographic features are physical (depressions partly filled with coral rubble) and biotic (thick algal turf binding sand). Higher population density and species richness in areas with than without such natural refuges, and following experimental addition of artificial refuges on portions of habitat lacking them support this hypothesis. Two species of Drupa differ from the other species present in not utilizing refuges during times of physical stress; this is attributed to their depressed shell and broad, tenacious foot. Highest gastropod densities occur in steep-sided depressions and those containing much coral rubble and sand, suggesting that these are important qualities of refuges. We believe this is the first demonstration of how specific environmental factors affect population density and species diversity of benthic invertebrates in a coral reef-associated habitat.
TL;DR: In this article, the authors studied the role of termites in the organic matter decomposition cycle in Pasoh Forest, Malaysia, and found that termites played a very important role in the decomposition process.
Abstract: 1. Density of nests, population number, biomass, nitrogen and carbon content, calorific content and respiration rate of termites were studied at Pasoh Forest, West Malaysia mainly with four dominant species of epigeous nest builders, Macrotermes carbonarius, Dicuspiditermes nemorosus type-a, type-b and Homallotermes foraminifer, to reveal their role in the ecosystem. 2. The density of nests or mounds was 15-41/ha in M. carbonarius, 60-110/ha in the two types of D. nemorosus and 85-165/ha in H. foraminifer. 3. The population number per nest or mound was about 88,000 in M. carbonarius, 45,000 in D. nemorosus type-a, 47,000 in D. nemorosus type-b and 13,000 in H. foraminifer. The population number per hectare was about 1.8x106 for M. carbonarius, 4.3x106 for D. nemorosus type-a, 5.2x106 for D. nemorosus type-b and 2.1x106 for H. foraminifer. 4. The ratio in number of workers to soldiers was 6.4 for M. carbonarius, 19.0 for D. nemorosus type-a, 23.1 for D. nemorosus type-b and 8.9 for H. foraminifer. The ratio in number of adults (workers plus soldiers) to larvae was 1.4 for M. carbonarius, 0.59 for D. nemorosus type-a, 1.76 for D. nemorosus type-b and 3.84 for H. foraminifer. 5. The number of adults per nest of D. nemorosus type-a, type-b and H. foraminifer was linearly correlated with the weight of nest on the log-log coordinates. 6. The ratio of dry body weight to live weight was 0.24-0.30 for workers, 0.19-0.29 for soldiers and 0.15-0.22 for larvae. 7. The ash content of termite body was 26-66% for workers, 2-24% for soldiers and 1-4% for larvae. 8. The carbon content ranged from 45% to 66% of ash-free dry weight and the nitrogen content from 5.6% to 12.6%. 9. The mean calorific value of termite body was 5.3 gcal/mg in workers and soldiers on an ash-free weight basis, but was greater in nymphs and winged reproductives in the nest (6.7-6.9 gcal/mg) owing probably to their large fat storage. 10. The relation of CO2 evolution rate to temperature in these termites was similar to what has been found in other insects. 11. The total biomass of the four termite species was estimated at 6.01 kg ash-free dry weight/ha, equivalent to 0.55 kg nitrogen/ha and 3.09 kg carbon/ha. 12. The role of the fungi cultivated by M. carbonarius on their fungus combs was discussed in relation to the nutrition of termites and the decomposition of leaf-litter with special reference to their nitrogen metabolism. The high nitrogen content of fungus spherules growing on fungus combs seemed to have an important bearing on the nutrition of termites. 13. It was concluded that the termites played a very important role in the organic matter decomposition cycle of Pasoh Forest.
TL;DR: Gross aboveground carbon allocation, leaf growth, and photosynthesis pattern studies were initiated to develop a quantitative understanding of the functional importance of these particular tundra growth forms and support the generalization that species with an evergreen growth form have lower photosynthesis capacities than species with a perennial graminoid, forb, or deciduous shrub growth form.
Abstract: Tundra plant growth forms can generally be characterized as consisting predominantly of low-growing perennial grasses and sedges, perennial herbaceous forbs, dwarf deciduous shrubs, and dwarf evergreen shrubs. Gross aboveground carbon allocation, leaf growth, and photosynthesis pattern studies were initiated to develop a quantitative understanding of the functional importance of these particular tundra growth forms. Photosynthetic capacities of 13 species were determined under standardized exposure conditions using a14CO2 field system and ranged between 5 and 47 mg CO2·g dry wt-1·h-1. These results, in conjunction with detailed leaf growth determinations, support the generalization that species with an evergreen growth form have lower photosynthetic capacities than species with a perennial graminoid, forb, or deciduous shrub growth form. However, these low photosynthetic capacities in evergreen shrubs are associated with relatively extended leaf longevities. Conversely, deciduous shrub forms exhibited high photosynthetic capacities, but were offset by relatively short leaf longevity periods. The perennial grasses, sedges, and forbs showed patterns intermediate to these. As a result, it appears that among tundra species of different growth form, photosynthetic capacity is inversely related to leaf longevity.
TL;DR: Allolobophora rosea (Savigny) was found to be common in mull type soils beneath bramble and it was shown that A. rosea preferentially selects the more organic fractions of the soil for ingestion.
Abstract: Allolobophora rosea (Savigny) was found to be common in mull type soils beneath bramble (Rubus fruticosus L) Burrow construction in this soil type in the laboratory at 44, 100 and 148°C ranged between 133 and 516 mm g-1 fresh wt of worm day-1 Burrowing was affected by both body size and temperature Rates of soil displacement during burrowing were estimated from burrowing rates, burrow dimensions and soil density; depending on body size and temperature they were in the range 809–1,928 mg dry wt of soil g-1 fresh wt of worm day-1 These values were in reasonable agreement with measured egestion rates (range: 1,000–2,000 mg dry wt of egesta g-1 fresh wt of worm day-1) It was concluded that A rosea eats its way through the soil and is adapted to its rapid turnover Gut turnover times were calculated to be between 1 and 25 h Direct observation indicated that feeding was by a “grazing” procedure and it was shown that A rosea preferentially selects the more organic fractions of the soil for ingestion The evaluation of energy budgets for individual small immature, large immature and adult worms at 10°C revealed respiration to production ratios (R/P) of 10, 18 and 41, respectively Assimilation efficiencies (A/C) were always less than 25%
TL;DR: The number of fruit fly pupae taken was shown to be related to the numbers of carabid and staphylinid beetles present, and also to the type of vegetation occuring around each card, and the implication for the effects of predation on potential pest-outbreaks in the crop are discussed.
Abstract: Pitfall trapping was carried out in a field of winter wheat in the Vale of York to determine the levels of abundance of adult carabid and staphylinid beetles, (which formed the bulk of the natural predator complex) in the field. A point quadrat survey was carried out at the same time to assess the vegetation cover round each trap. Predation pressure by the beetles in the field was monitored using fruit fly (Drosophila) pupae as artificial prey. These artificial prey were attached to small cards inserted in the field adjacent to the pitfall traps.The numbers of beetles caught were found to be directly related to the frequency and density of Poa annua L. (annual meadow grass) the only abundant non-crop plant present at the time. More beetles were caught in areas where Poa was abundant than where Poa was scarce. This was probably related to the more suitable environmental factors offered by these of the wheat itself was found to be unrelated to captures.The number of fruit fly pupae taken was shown to be related to the numbers of carabid and staphylinid beetles present, and also to the type of vegetation occuring around each card.The implication of these results for the effects of predation on potential pest-outbreaks in the crop are discussed.
TL;DR: It is concluded that the material stored in C4 bundle sheath cells is at least partially unavailable to herbivores, and that this may contribute to the observed nutritional inferiority of C4 vegetation.
Abstract: Plants with the C4 dicarboxylic acid pathway of photosynthetic CO2 fixation are generally nutritionally inferior to C3 (Calvin cycle) plants as foodstuff for herbivores. A possible contributing factor to this nutritional inferiority is the concentration, in C4 plants, of large quantities of nutritional material in very tough, thick-walled vascular bundle sheath cells which herbivores may not be able to break down. Experiments with 10 species of grass-hoppers from different areas in the United States revealed large numbers of unbroken bundle sheath cells, contents intact, in fecal pellets produced when the grasshoppers were fed C4 vegetation. We conclude that the material stored in C4 bundle sheath cells is at least partially unavailable to herbivores, and that this may contribute to the observed nutritional inferiority of C4 vegetation.
TL;DR: It seems that epiphytic lichens have potential ecological importance in altering the chemistry of throughfall and stemflow.
Abstract: Epiphytic lichen growth is abundant on the boles and branches of balsam fir trees at high elevations in New Hampshire. These lichens absorb elements needed for growth from solutions flowing over their surfaces and from direct impaction of water droplets. This study describes how epiphytic lichens and fir needles altered the chemistry of simulated rain water solutions under laboratory conditions. Experiments showed: 1) lichens absorbed ammonium and nitrate from solution; the rate of uptake increased with increasing temperature of the solution, 2) lichens lost calcium, magnesium, and hydrogen to the solution, 3) lichen thalli also initially lost potassium, but in time, net movement was reversed back into the thallus, 4) cation movement increased with increasing temperature, and 5) fir needles responded in a manner similar to that of the lichens, but the amount of change was much less. From these results it seems that epiphytic lichens have potential ecological importance in altering the chemistry of throughfall and stemflow.
TL;DR: The life-cycle of the dominant brackish water ostracod Cyprideis torosa has been studied during 4 years and a model is described which permits the evaluation of the duration of development from field data only.
Abstract: The life-cycle of the dominant brackish water ostracod Cyprideis torosa (Jones, 1850) has been studied during 4 years. The species has only one generation anually. Reproduction is fairly similar throughout the years and appears to be tuned in to temperature. The number of adults has one peak every year and can be described by two exponential functions, one for the increase and one for the decrease. Mortality is very similar every year and approximately constant for months. Cyprideis torosa is on top of the food chain: regulation of numbers is probably not external and may be a function of the past of the habitat. A model is described which permits the evaluation of the duration of development from field data only. Predicted values are in good agreement with observed values.
TL;DR: It is concluded that during aerial exposure M. californianus resorts to anaerobiosis in spite of a capacity to extract some oxygen from the atmosphere, which results in a metabolic deficit during each period of low tide which imposes a physiological stress on mussels distributed on the shore.
Abstract: Mytilus californianus regulated its rate of oxygen consumption (VO2) during decline in oxygen tension, but did not acclimate VO2 when held at 58 mm Hg PO2. In spite of a capacity to consume oxygen while exposed to air (the average VO2 in air being equivalent to 0.74xthe standard rate of oxygen consumption in water), these mussels acquired an "oxygen debt" during aerial exposure which was discharged on subsequent reimmersion. During exposure to air the oxygen tension of the fluid in the mantle cavity was rapdly reduced to approximately 40 mm Hg, in animals both in the laboratory and on the shore. Heart rate was also reduced during air exposure, though not to the point of cardiac arrest. The concentration of ammonia in the fluid of the mantle cavity increased during aerial exposure, but the rate of excretion of ammonia was much lower than during immersion. Observations of mussels on the shore at low tide indicated that dehydration of the tissues was not a serious threat, possibly due to the large volume of fluid retained in the mantle cavity. During aerial exposure some end-products of anaerobic metabolism (alanine and malate) accumulated in the posterior adductor muscle. Malate accumulation was rapid during the first hour of exposure; alanine accumulated more gradually. It is concluded that during aerial exposure M. californianus resorts to anaerobiosis in spite of a capacity to extract some oxygen from the atmosphere. This results in a metabolic deficit during each period of low tide which, coupled with the reduced time available for feeding, imposes a physiological stress on mussels distributed on the shore.
TL;DR: The digestive gland of the mollusc was shown to be an important store of Pb, Zn and Cd while Cu was found to be more evenly distributed throughout the tissues of the animal.
Abstract: The distribution of Pb, Zn, Cd and Cu throughout the body tissues of Helix aspersa was determined. The digestive gland of the mollusc was shown to be an important store of Pb, Zn and Cd while Cu was found to be more evenly distributed throughout the tissues of the animal. These results are discussed with relation to previous work concerning heavy metal content in molluscs. The selectivity of the digestive gland for Cd was higher than it was for either Pb or Zn and it is suggested that analysis of the digestive gland of molluscs may be useful in studying levels of Cd at different sites.At a contaminated site the levels of Cd in Helix aspersa were shown to be 13 times greater than at a relatively uncontaminated site.
TL;DR: A multiple regression equation including flood frequency and litter depth as variables was used to predict the impact of altered flooding regimes (due to reservoir construction downstream) on spider diversity.
Abstract: Species composition and diversity of a guild of wandering spiders was studied by pitfall trapping over an elevational gradient in an Illinois streamside forest. Differences in flooding frequency and their effect on the litter habitat (removal and/or compression) account for a majority of the variation in the number of species between elevations. Changes in spider communities with elevation over the flooding gradient are indicative of a transition from a harsh to a moderate environment: (1) increased abundance and species diversity; (2) decreased dominance of flood tolerant species accompanied by increased dominance of species with specialized microhabitats found in complex litter; (3) greater similarity in species composition between sites; and, (4) a change in species-abundance curves from a geometric series to a lognormal distribution. The influence of the flooding regime in regulating community structure of spiders is discussed. A multiple regression equation including flood frequency and litter depth as variables was used to predict the impact of altered flooding regimes (due to reservoir construction downstream) on spider diversity.
TL;DR: Chances for survival increase as a snail grows, and the resulting size-specific survival curve dictates hatching size, and no hatchlings are inflated more than others to make them less attractive to predators.
Abstract: Chances for survival increase as a snail grows, and the resulting size-specific survival curve dictates hatching size. Related species tend to hatch at the same size, reflecting similarities in ecological roles. Hatching size depends upon macrohabitat and microhabitat among the Muricidae. Thais emarginata hatches large enough to escape from a major predator (the hermit crab) of newly hatched T. lamellosa. However, Thais hatching sizes reflect a general trend for upper shore muricids to hatch larger than lower shore ones, rather than a response to predators. A given volume of yolk will yield the same volume of hatchlings (regardless of hatching type or number of hatchlings) for all prosobranchs, including those whose embryos feed on nurse eggs. Therefore, no hatchlings are inflated more than others to make them less attractive to predators.
TL;DR: A description of photosynthesis in a single leaf is developed that separates physiological sub-processes and that is practical to apply as an ecological tool and it will be possible to determine the phenotypic plasticity of particular plants with respect to the metabolic sub- processes outlined.
Abstract: A physiologically based steady-state model of whole leaf photosynthesis (WHOLEPHOT) is used to describe net photosynthesis daily time courses in Prunus armeniaca. Net photosynthesis rates are calculated in response to incident light intensity, leaf temperature, air carbon dioxide concentration, and leaf diffusion resistance measured at five minute intervals. The steady-state calculations closely approximate the observed net photosynthesis rates for a broad range of weather conditions and leaf stomatal behavior.
TL;DR: It is suggested that de novo synthesis of photosynthetic enzymes in fully expanded leaves of the sun ecotype following treatment with strong light is the cause of its increased capacity for CO2 fixation.
Abstract: Within the widespread species Solanum dulcamara, contrasting ecotypes were found which are physiologically adapted to the light intensities prevailing in their natural habitats When grown under a high light intensity, an ecotype from a shaded habitat exhibits signs of damage Another one from an exposed habitat has higher rates of photosynthetic CO2 uptake when grown under strong as compared to weak light and does not show damage This differential response becomes even more evident when leaves of both ecotypes are grown to maturity under weak light and are subsequently subjected to strong light for some time The quantum requirement for photosynthesis increases in the shade-, but not in the sun-ecotype The sun type increases its rate of photosynthesis under saturating light intensities after a few days in strong light No significant difference in physical resistances to gas diffusion could be found to explain the highly differing rates of photosynthesis With the increase in photosynthetic capacity in leaves of the sun type, protein content, activity of RuDP carboxylase, and concentration of Fraction I protein increased likewise It is suggested that de novo synthesis of photosynthetic enzymes in fully expanded leaves of the sun ecotype following treatment with strong light is the cause of its increased capacity for CO2 fixation
TL;DR: A conspicuous latitudinal trend was found: the clustering of both landward and seaward boundaries increased with increasing latitude, and evidence that between-species competition influences the locations of zone boundaries was obtained.
Abstract: Zonation patterns of salt marsh vegetation were examined at latitudes ranging from 44°40′N at Halifax, Nova Scotia, to 58°50′N at Churchill, Manitoba. It was found that in all areas examined the landward boundaries of the species' zones were more nearly coincident (i.e., more clustered) than their seaward boundaries. A conspicuous latitudinal trend was found: the clustering of both landward and seaward boundaries increased with increasing latitude. Evidence that between-species competition influences the locations of zone boundaries was also obtained. Possible implications of the results in terms of a relationship between intrapopulation polymorphism and latitude are discussed.
TL;DR: Breeding birds were censused along four elevational gradients in the Adirondack Mountains, New York, and the Green Mountains, Vermont and found no convincing cases of altitudinal competitive exclusion between species.
Abstract: Breeding birds were censused along four elevational gradients in the Adirondack Mountains, New York, and the Green Mountains, Vermont. The bird communities of the four gradients were basically similar in species composition, richness and amplitude patterns. Three measures of species diversity decreased with increasing elevation. Low-elevation communities contained higher proportions of rare species and the relative abundances conformed to the broken-stick distribution. At higher elevations the communities showed greater dominance and the dominance-diversity curves approached geometric series. The species characteristic of high-elevation communities had the broadest altitudinal distributions. The upper and lower distributional limits of most species were independent of one another except at “ecotones” where marked changes in vegetation structure occurred. On each mountain, slightly more than half of the species’ limits coincided with ecotones. This is a significantly greater proportion than has been found in similar studies of tropical forest bird communities. In further contrast to tropical communities, we found no convincing cases of altitudinal competitive exclusion between species. Interspecific competition in the past seems to have been translated primarily into differences in habitat selection by temperate forest birds. Many of the differences between temperate forest breeding bird communities and tropical ones can be understood in terms of the migratory nature of most of the temperate species and the lower species richness in temperature forests.
TL;DR: In this paper, the authors measured photosynthesis in leaves ofPhaseolus vulgaris and analyzed the set of equations outlined previously by Tenhunen et al. (1976) and showed that photosynthesis was performed by the leaves of the plant.
Abstract: Photosynthesis was measured in leaves ofPhaseolus vulgaris and analyzed according to the set of equations outlined previously by Tenhunen et al. (1976).
TL;DR: The presence of weasel anal gland secretion on rodent live traps substantially depresses population estimate by greatly reducing the catch of Microtus agrestis.
Abstract: The presence of weasel anal gland secretion on rodent live traps substantially depresses population estimate by greatly reducing the catch of Microtus agrestis. The catch of Apodemus sylvaticus remains almost unaffected.
TL;DR: Field studies of dispersal by first instar gypsy moth larvae indicate that almost all larvae undergo an initial dispersal episode, but in laboratory studies large larvae (from large eggs) disperse more frequently than small larvae ( from small eggs) in the presence of favored food.
Abstract: Field studies of dispersal by first instar gypsy moth larvae indicate that almost all larvae undergo an initial dispersal episode. However, in laboratory studies large larvae (from large eggs) disperse more frequently than small larvae (from small eggs) in the presence of favored food. Large larvae may be better adapted for dispersal. When larvae encounter unacceptable food or are denied food, larvae disperse more frequently and dispersal by small larvae is nearly as frequent as dispersal by large larvae. Factors affecting egg size may contribute to shifts in dispersal patterns of gypsy moth larvae and distribution of populations.
TL;DR: Findings show that gene flow is reduced by pollinator activity over a wide range of spacing parameters but in populations with low spacing means highly localized gene exchange can occur within the colony, corresponding to the “Shifting Balance” view of evolution.
Abstract: The effect of pollinator activity on gene flow in colonies of Viola were examined by measuring pollinator flight distances, the frequency of interplant flights and percent pollination under different plant spacing patterns. Pollinator flight distances were directly proportional to spacing parameters while the frequency of interplant flights and percent pollination were inversely proportional to spacing parameters. These findings show that gene flow is reduced by pollinator activity over a wide range of spacing parameters but in populations with low spacing means highly localized gene exchange can occur within the colony. Isolation of colonies may be expected under these circumstaces and cleistogamy may be the optimal breeding system. However, chasmogamous flowers may be important both in promoting within-colony gene exchange and long distance between-colony gene exchange corresponding to the sexual functions proposed in several recent models. Viola colonies appear to be semi-isolated demes with pollinator service which can bring adaptive genes to high localized frequencies, but which maintains low frequency, long-distance gene dispersal. This pattern corresponds to the "Shifting Balance" view of evolution.