Showing papers in "Ecological Monographs in 1971"

Competition, Disturbance, and Community Organization: The Provision and Subsequent Utilization of Space in a Rocky Intertidal Community

Abstract: An understanding of community structure should be based on evidence that the growth and regulation of the component populations in the community are affected in a predictable manner by natural physical disturbances and by interactions with other species in the community. This study presents an experimental evaluation of the effects of such disturbances and competitive interactions on populations of sessile organisms in the rocky intertidal community, for which space can be demonstrated to be the most important limiting resource. This research was carried out at eight stations on the Washington coastline which have been ranked according to an exposure/desiccation gradient and subjected to comparable manipulation and observation. Physical variables such as wave exposure, battering by drift logs, and desiccation have important effects on the distribution and abundance of many of the sessile species in the community. In particular, wave exposure and desiccation have a major influence on the distribution patterns of all the algae and of the anemone Anthopleura elegantissima. The probability of damage from drift logs is very high in areas where logs have accumulated along the intertidal. Log damage and wave exposure have complementary effects in the provision of free space in a mussel bed, as wave shock enlarges a patch created by log damage by wrenching the mussels from the substratum at the periphery of the bare patch. Competition for primary space results in clear dominance hierarchies, in which barnacles are dominant over algae. Among the barnacles, Balanus cariosus is dominant over both B. glandula and Chthamalus dalli; B. glandula is dominant over C. dalli. The mussel Mytilus californianus requires secondary space (certain algae, barnacles, or byssal threads) for larval settlement, but is capable of growing over all other sessile species and potentially is the competitive dominant of space in the community.

Succession after Fire in the Chaparral of Southern California

Abstract: Extensive sampling of chaparral with 10—m line intercepts in the San Gabriel and San Bernardino Mountains of southern California revealed site—oriented vegetative characteristics and successional patterns. Of the 78 species encountered, few were widespread and abundant; most were local and infrequent. The most widespread and abundant species were long—lived rootcrown sprouters. Adenostoma fasciculatum (chamise), the most frequently encountered shrub, occurred on 71.4% of the sites and composed one—fifth of all shrubs in the study. The second most common species, Quercus dumosa (scrub oak), appeared on 32% of the sites sampled. Many non—sprouting subshrubs and woody species were restricted to elevations below 3,000 ft (ca. 900 m), sunny exposures, and young stands. Chaparral succession, both in composition and rate of change, is influenced most by aspect, particularly north— and south—facing slopes. Next in importance is the influence of coastal and desert exposure. Elevation is a factor that may compensate for coastal—desert exposure or aspect. Percentage of slope is least important. The rate of succession after fire in coastal chaparral is slowest on south—facing slopes below 3,000 ft. Early stages of shrub succession are characterized by a mixture of chaparral seedlings, resprouts, and seedlings of coastal sage subshrubs. Most of the present—day chaparral on south—facing slopes is a coastal sage—chaparral subclimax due to frequent fire. On fire—free sites a chamise—chaparral climax community develops within 30 years after fire. The fastest succession rate is in coastal chaparral on north—facing slopes above 3,000 ft. The profusion of coastal sage subshrubs is missing, and vigorous, tall—growing sprouting species are abundant. The death of large, short—lived species in stands older than 25 years allows pockets of seral species to develop in the climax scrub oak—chaparral. Chaparral succession is not a series of vegetational replacements, but a gradual ascendance of long—lived species present in the pre—fire stand. The pattern of chaparral succession on desert exposures differs from that on coastal exposures. Slope aspect is less important, but proximity to the Pacific Ocean is more important than on coastal exposures. Fire favors the sprouting species of chaparral over woodland and forest communities bordering the chaparral communities. Fewer chaparral species occur on desert exposures than on coastal ones. Seedling and mature shrub mortality rates are lower in desert than in coastal chaparral. Succession after fire in desert chaparral is slow, and the climax community is composed of large shrub specimens with subshrubs clustered around their skirts and a canopy broken by intershrub spaces. Chaparral stands older than 60 years often are decadent, especially chamise—chaparral. Old stands are characterized by a high proportion of dead wood, little annual growth, and no new seedling development. Various phytotoxic substances may account for the loss of vitality and lack of regeneration. Maintenance of vigorous chamise—chaparral is shown to be dependent on fire. A re—evaluation of current fire—exclusion and suppression practices is needed. The present fire—exclusion policy is probably the least desirable one to insure the perpetuation of chamise—chaparral.

Structure of Avian Communities in Selected Panama and Illinois Habitats

Abstract: To elucidate the causal factors responsible for diversity gradients in avian communities, avian populations were studied for 12 months in seven lowland tropical areas in the Republic of Panama and compared with populations in structurally similar habitats in Illinois. Resident (breeding) species made up 38—49% of the species on temperate areas but only 20—36% of the species in similar tropical habitats. There were significantly more species of irregular occurrence in mature tropical habitats. Tropical grassland avifaunas were no higher in diversity (number of species and information measures of diversity) than those of temperate grassland areas, but shrub and forest habitats in the tropics had higher diversity as measured by either diversity measure. The number of species was proportionately higher than the information measure because of the relatively small effect of the many rare species on the information measure. Determination of the biomass and energy relations for the bird populations showed that higher total population size in tropical areas is correlated with smaller bird size and reduced individual energy requirements. When only breeding seasons are compared, the reduced energy requirements are a result of the higher temperatures in tropical areas. Twenty—five to fifty per cent of the increased number of tropical breeding species when compared to similar temperate habitats results from the addition of a new food source, i.e., fruits. Additional species are primarily insectivores. The increase in insectivores seems to be due to additional subdivision of the resources and exploitation of a new kind of insect food, especially by species that depend on relatively large insects. Since energy requirements of tropical and temperate avifaunas are about the same, increased productivity is not related causally to the increased tropical diversity. The stratal distribution of species in several tropical (lowland and montane) and temperate avifaunas indicates that avian communities may subdivide the vegetation profile similarly throughout the world despite sharp differences in the number of species in the various areas. Bark species are about equally numerous in Panama and Illinois forest, but ground, low, medium, and high strata contain increased numbers of species in the tropics. The shift away from classical defended territories in mature tropical habitats seems to be correlated with patchy distribution of food resources in frugivores and ant—following species and reduced food abundances in other species. As a result of this food distribution, the frequency of flocking increased in shrub and forest habitats. In grassland habitats, which experience greater seasonal changes in precipitation, the spacing systems of birds are more similar to those in all temperate habitats studied. Degree of territorial defense against conspecifics and amount of interspecific flocking is inversely related to the distribution of food resources; more patchy or unpredictable food distributions, or both, result in fewer species defending exclusive territories. The major factor related to the increased diversity of tropical avifaunas seems to be the relative stability of food resources resulting from environments that are more or less "equitable" throughout the year. Both within— and between—habitat increases in diversity of avian communities are discussed. The stability—time hypothesis is discussed in light of available data on organization of avian communities.

Genetic, Behavioral, and Reproductive Attributes of Dispersing Field Voles Microtus pennsylvanicus and Microtus ochrogaster

Abstract: To investigate experimentally the relationship between dispersal and population regulation in small mammals, voles were removed continuously from two plots in southern Indiana for 2 years. Three control populations of two Microtus species were monitored over the same period, and animals dispersing onto the experimental areas were compared with resident control animals for the following characteristics: (1) age, weight, and sex; (2) genotype for two polymorphic plasma proteins, leucine aminopeptidase (LAP) and transferrin (Tf); and (3) exploratory, aggressive, and general activity behavior of males. Dispersal was most common during the fall and winter, and in the phase of population increase 59% of male and 69% of female Microtus pennsylvanicus loss from two control populations could be accounted for by dispersal. In contrast, little of the high loss during the population decline could be associated with dispersal. In the late peak and decline periods male M. pennsylvanicus of the Tf—E and LAP—S phenotypes...

Primary Productivity, Chemo-organotrophy, and Nutritional Interactions of Epiphytic Algae and Bacteria on Macrophytes in the Littoral of a Lake

Abstract: Epiphytic algal and bacterial in situ community metabolism and physiological—nutritional relationships of macrophyte—epiphyte systems were investigated in the littoral zone of a small temperate lake from April 1968 through May 1969. Annual primary productivity, chemo—organotrophy of dissolved organic compounds, and field and laboratory studies of macrophyte—epiphyte interactions were monitored by carbon—14 techniques. Productivity measurements of epiphytic algae on artificial substrates colonized in emergent (Scirpus acutus Muhl.) and submergent (Najas flexilis L. and Chara spp.) macrophytic vegetation sites were compared over an annual period with pigment (corrected chlorophyll a and total plant carotenoids) estimates of biomass. Changes in biomass are not proportional to changes in photosynthetic activity, except during periods of intense productivity. The mean daily productivity of epiphytic algae was higher per unit macrophyte surface area of emergent plants (336 mg C m—2 day—1) than on submerged plants (258 mg C m—2 day—1). Mean daily productivity per unit area of the littoral zone, for all of the macrophytic surface area colonized, was 195 and 1,807 mg C m—2 day—1 in the Scirpus and Najas—Chara dominated sites, respectively. The total annual production by algal epiphytes in the Scirpus and Najas—Chara dominated sites was 2.86 and 35.00 g C m—2 of lake surface year—1, respectively. Estimates of annual net production of macrophytes and epipelic algae, derived from studies undertaken during the same time period as reported in this study, indicate that epiphytic algae were responsible for 31.3% of the total littoral production. The epiphytic algae were responsible for 21.4% of the total annual production for the whole lake when the production of the pelagial phytoplankton was added to that of the littoral communities. In comparison to the pelagial phytoplankton alone, the algal epiphytes fixed an amount of carbon equivalent to 75% of the phytoplankton production over the annual period. These results indicate that algal epiphytes on submerged macrophytes may be one of the dominant primary producers in shallow—water ecosystems and may be comparable to the phytoplankton. Deposition of 14C—monocarbonates during in situ productivity measurements represented 38.5—71.7% of the total intracellular fixed carbon. Acidification of 14C—productivity samples by rinsing with dilute hydrochloric acid (0.001 N) removed 24% of previously incorporated carbon and is not recommended as a routine procedure. Physiological interactions in macrophyte—epiphyte systems were investigated by bioassay procedure. Inorganic iron added at less than 10 mg liter —1, and at 100 mg liter—1 in combination with organic compounds of chelatory or complexing ability, stimulated photosynthesis of epiphytic algae. Bioassay experiments in which vitamins, trace metals, and inorganic phosphorus were added to algal photosynthesis. Chlorophyll a, corrected for pheopigment degradation products, and total plant carotenoid levels are among the highest standing crops reported in the literature (annual maximum of chlorophyll a = 7.3 g m—2; plant carotenoids = 40.7 SPU m—2). Maximum concentrations were found during winter under ice cover. Epiphytic bacterial chemo—organotrophy with glucose and acetate substrates was measured at concentrations of 11—160 mg liter—1 and evaluated through Michaelis—Menten enzyme kinetic analysis. First—order active transport kinetics dominated throughout the annual period. Uptake of acetate (submerged plant site, mean rate = 893 mg liter—1 hr—1 dm—2; emergent plant site, 106 mg liter—1 hr—1 dm—2) was greater than that of glucose (submerged plant site, 586 mg liter—1 hr—1 dm—2; emergent plant site, 54 mg liter—1 hr—1 dm—2). Scirpus acutus was labeled in situ during photosynthesis with natural concentrations of carbon dioxide (as 14C). Epiphytic uptake of 14C—labeled, extracellular products of macrophytic origin was determined. Extracellular release of 14C—labeled organic matter was followed at various depths in the littoral water column. The nature of the extracellular release and the amount of 14C fixed by the macrophyte and transferred into the epiphytic complex suggests nutritional interactions that may be prevalent in other macrophyte—epiphyte systems. Najas flexilis, germinated and grown under axenic conditions in a defined medium, was labeled during photosynthesis and placed into the center section of Plexiglas chambers separated by membrane filters free of organic carbon contamination. Over a 3.75—hr incubation interval, a mean of 7% of the total intracellularly fixed carbon was excreted as 14C—labeled dissolved organic carbon. Cultured algal and bacterial epiphytes, separately and mixed in simulated natural communities, were able to utilize these extracellular products when placed into chamber sections adjoining the labeled Najas. The amount of extracellular products utilized by the mixed algal and bacterial communities changed with time, depending on the composition of the epiphytic community. The results suggest interspecific interactions where competition for specific external metabolites or organic solutes may have existed, or where toxic extracellular products may have accumulated. Laboratory uptake of low concentrations of glucose and acetate—14C at 5°, 11° to 12°, and 21° to 23° C by separate and mixed cultures of algal and bacterial epiphytes showed that uptake was strongly influenced by temperature, except at low temperatures where transport and diffusion mechanisms seemed to be inactivated. A sessile bacterium, Caulobacter, however, showed a highly efficient uptake system for both substrates under cold conditions. Uptake of both substrates by mixed cultures of algae and bacteria showed that bacterial uptake of both substrates by mixed cultures of algae and bacteria showed that bacterial uptake was little influenced at low substrate concentrations by the presence of algae. Epiphytic algal uptake following kinetics of simple diffusion was, however, increased in the presence of bacteria, suggesting uptake of 14CO2 previously respired by the bacteria. Macrophyte—epiphyte metabolism may be an important source of dissolved organic materials and extracellular metabolites and thus may help to sustain high levels of primary productivity and chemo—organotrophy in lakes.

Energy and Nutrient Dynamics of Spider and Orthopteran Populations in a Grassland Ecosystem

Abstract: Population dynamics, energy budgets, and nutrient concentrations were used to develop a compartment model for evaluating energy flow and nutrient fluxes in the spider and orthopteran components of an eastern Tennessee grassland ecosystem. The arthropod community consisted of; herbivores–Melanoplus sanguinipes (Acrididae), Conocephalus fasciatus (Tettigoniidae), and several of the Homoptera—Hemiptera; omnivore–Pteronemobius fasciatus (Gryllidae); and predators–Lycosa spp. (Lycosidae). Weekly estimates of arthropod density and biomass and monthly estimates of vegetation biomass were made during the 1965—69 growing season. Supporting studies included: (1) determination of caloric equivalents; (2) measurements of arthropod metabolism; (3) determination of whole—body concentrations of Na, Ca, and K; (4) estimation of biological turnover rates of these nutrients with radioactive analogues; and (5) field studies of arthropod feeding habits and food consumption. Total net primary production of the grassland ecosystem was 1,274 kcal/m2; 89% of this total was by grass species (Festuca arundinacea and Andropogon virginicus) and 11% by green forbs. Herbivores and omnivores consumed 9.6% (122.9 kcal/m2) of net primary production. Annual net secondary production by the insect community was 32.05 kcal/m2. Total net tertiary production by spiders was 2.26 kcal/m2. Total annual energy flow (= total assimilation) through the community was 75.6 kcal/m2. Herbivores accounted for 79.8% of this total, omnivores 12.2%, and predators 8.1%. Whole—body concentrations of sodium increased with higher trophic position in the food chain: vegetation (0.43 mg/g ash free dry wt = AFDW), prey (1.18 mg/g AFDW), and predators (1.94 mg/g AFDW). Calcium concentrations decreased from vegetation (5.82 mg/g AFDW) to prey (0.85 mg/g AFDW) and remained constant to predators (0.88 mg/g AFDW). Potassium concentrations were much higher in vegetation (14.28 mg/g AFDW) than in either the prey (1.87 mg/g AFDW) or predators (1.96 mg/g AFDW), which were essentially the same. Sodium and potassium behaved similarly in their movement through arthropod food chains. The low concentrations of calcium in arthropod trophic levels and the rapid elimination of this element from each trophic level suggest that calcium is not as limiting as are sodium and potassium in this arthropod community. Herbivores, the dominant members of the arthropod fauna, attained a maximum standing crop of 927 mg/m2 (Melanoplus = 705 mg/m2, Conocephalus = 200 mg/m2, and the Homoptera—Hemiptera = 22 mg/m2). This trophic level was responsible for 85% of the sodium turnover, 76% of the calcium turnover, and 78% of the potassium turnover by the arthropod component of the ecosystem. The omnivore Pteronemobius fed equally well on fresh vegetation and on litter. It reached a maximum biomass of 194 mg/m2 and utilized 10% of the sodium, 22% of the calcium, and 20% of the potassium which passed through the arthropod community. The predator (Lycosa spp.) biomass reached a maximum of 146 mg/m2 in late fall and was responsible for 5% of the sodium, 2% of the calcium, and 2% of the potassium utilized by the arthropod component of the ecosystem. Wolf spiders consumed 21% of total net secondary production. Absence of other predator species in collections from the arthropod community suggests that Lycosa was the dominant invertebrate predator in this grassland ecosystem.

Dynamics of Black Cherry (Prunus serotina Erhr.) in Southern Wisconsin Oak Forests

Abstract: Black cherry occupies a key position in the dynamics of oak (Quercus spp.) forests in southern Wisconsin. Its relative importance in sapling and small—tree sizes averaged over 50%, and in some stands it was the only species in these strata. Age analysis of 854 cores showed that 58% of all black cherry stems were established between 1931 and 1941. The appearance of large amounts of black cherry in the 1930 decade was the result of drought and livestock—feed shortages. The latter were especially severe in 1934 and 1936 and resulted in large—scale disturbance of forests through grazing and possibly extensive cutting of forests for foliage. The presence of a strong shrub component exerted a major influence on the dynamics of the oak forest. An inverse relationship existed between overstory tree basal area and the importance of shrubs. Although density and cover of tree seedlings were independent of tree basal area and shrub cover, seedling numbers were insufficient for adequate restocking of most stands. In clear—cut forests the shrub layer was extensive, and regrowth of trees was largely confined to stump sprouts. Shrubs in disturbed forests averaged 38,635 stems/acre, 4,535 square inches basal area/acre, and 145.8% cover. In undisturbed forests, shrub competition (average 16,231 stems/acre, 1,036 square inches basal area/acre, and 51.4% cover) largely precluded seedling establishment by tree species, and maximum basal area levels in these forests were not maintained. Growth and survival of black cherry in the understory depended on the complex interaction of environmental factors. Tree overstory basal area and soil available water were the most significant factors controlling its vigor. Suppressed stems of cherry were as old as 60 years. Growth patterns in stem cores showed that stems responded to release after 39 years of suppression. The capacity of black cherry to develop basal sprouts and the occurrence of light intensities greater than 1,200 ft—c in the understory greatly aided its survival in this stratum. The important role of black cherry in the dynamics of the oak forests was based on opportunistic characteristics including widespread dispersal, delayed germination of seeds, and flexible seedbed requirements. Forest conditions, such as the isolation of forests as woodlots, pioneer environmental conditions, and widespread disturbance, predisposed invasion by opportunistic species. Dynamic processes were characterized by general rather than gradient compositional changes. Patterns of replacement were not orderly and predictable, but irregular as a result of chance dispersal and local catastrophe. Although not uncommon in oak forests in the northeastern United States, invasion by Acer saccharum is not occurring in southern Wisconsin. Succession to Acer—Tilia is confined to specific sites. The overall existing pattern is one of increasing diversity typical of many pioneer communities in an early phase of colonization.

Effect of Vegetation Changes on the Fertility of a Newfoundland Forest Site

Abstract: In Newfoundland many sites occupied by Picea mariana forests and Kalmia angustifolia heathland formerly supported an Abies balsamea forest. Stands of each cover type were studied to determine whether these vegetation changes affect the fertility of the sites. They were selected on the basis of similarity of soil conditions; all occurred on well—drained, sandy glaciofluvial soils and had developed after a forest fire about 65 years ago. In the Kalmia heath the raw humus horizon weighed 293 tons/ha and contained 3,070 kg N, 436 kg Ca, 118 kg P, and 99 kg K per hectare. In contrast, the raw humus of the Picea forest weighed 87 tons/ha and that of the Abies forest only 65 tons/ha; nutrient contents were proportionally lower with N showing the largest, and K the smallest, differences between cover types. The annual return of organic matter and nutrients is highest in the Abies forest and lowest in the Kalmia heath. Litter fall is the single most important source in the forests, but annual root mortality contributes most in the Kalmia heath. Additions from the moss layer amounted to about one—tenth of the annual return in the forests. The rate of organic—matter decomposition decreases from Abies to Picea to Kalmia cover type, with accumulations in the raw humus representing 14, 21, and 78 times the annual supply of the present stands, respectively. Mineralization of N and P show the same trend, but Ca and K mineralization are slower in the Kalmia heath only. A comparison of the nutrients in the Abies and Kalmia cover types showed that actual losses of K, and possibly Ca, had occurred from the Kalmia ecosystem during the 65—year period since the fire, and that the quantity of N in the Kalmia ecosystem was about double that in the Abies cover type. A net input of more than 23 kg/ha per year is required to account for this increase. No reliable comparison could be made between the Picea and Abies ecosystems, but the data available do not indicate any obvious fertility changes beyond a greater immobilization of nutrients in the raw humus of the Picea forest.

Life History and Underwater Studies of a Heterodont Shark

Abstract: The biology of Australian reef populations of the shark Heterodontus portusjacksoni has been studied underwater with SCUBA. Additional life—history data have been obtained from catch records of adults and juveniles and from observations on captive animals. The mature breeding female H. portusjacksoni lays 10—16 eggs which are deposited in rock fissures on shallow reefs; the young emerge approximately 1 year later. The breeding season on the central coast of New South Wales occurs in late winter and spring. This species appears to segregate by sex into separate juvenile, adolescent, and adult populations. A slow growth rate and protracted immaturity is characteristic. Sexual maturity is reached at 8—10 years for males and 11—14 years for females. Most feeding occurs during darkness over both reefs and soft substrates, gut contents reveal that they feed on a variety of benthic invertebrates. Populations of H. portusjacksoni observed on sublittoral reefs consisted of adult sharks, the majority of which were females. A few specific sites, usually caves in which they shelter during the day, are preferred. Resightings of sharks tagged on a reef at Bondi, Sydney, revealed that animals which formed the local population moved freely to and from the reef and also between the several sites on the reef. Reef densities were highest during the breeding season and were correlated with low water temperatures. Emigration from inshore reefs occurs at the end of the breeding season in late September and October. A number of tagged sharks returned to the same reef in the following year and others after periods of up to 2 years. Recaptures made outside the Sydney area indicate that some sharks may travel several hundred kilometers during their migration.

Feeding ecology of the Red-eyed Vireo (Vireo olivaceus) and associated foliage-gleaning birds.

Abstract: The sexes of the Red—eyed Vireo, an abundant insectivorous bird in eastern deciduous woodlands, differed in their foraging heights, with an overlap of only about 35%. The males foraged higher than the females, and non—random sequences of movements were employed to maintain this separation. The foraging level and the nest height of female Red—eyes was similar, whereas the males foraged closer to their singing perches. Thus the foraging efficiency of both sexes was likely greater in accordance with their differing behavior roles. The "small" territory (1.3—1.7 acres) of this species actually consists of a cylinder extending from the forest canopy to the low understory. The associated White—eyed Vireo (Vireo griseus) was generally separated from Red— eyed Vireo by habitat, and the Yellow—throated Vireo (Vireo flavifrons) overlaps in habitat but possesses structural and behavioral differences which indicate different prey preferences. Foraging behavior of migrating Red—eyed Vireos differs markedly from that of breeding birds. Differences were also noted between summer and winter foraging behavior patterns in the White—eyed Vireo. All three vireo species exhibit species—specific patterns of foraging movements. Two other foliage—gleaning insectivorous birds occupying the same forests, the American Redstart (Setophaga ruticilla) and the Acadian Flycatcher (Empidonax virescens), also possess species—specific foraging behaviors (niche—exploitation patterns).

Biomass Turnover, Respiration, and Interpopulation Variation in the Stream Limpet, Ferrissia rivularis (Say)

Abstract: The stream limpet Ferrissia rivularis, which occurs extensively in North America and is ubiquitous in streams of upper New York State, was studied from two distinct populations, one located in the Canandaigua Outlet at Alloway, N. Y. (AL) and the other in Black Creek at Cleveland, N. Y. (BC). These environments differ substantially, that at AL being the more eutrophic. At BC there is one generation per year, but at AL there are two generations per year and more rapid growth rates. Thirteen months is the adult life span for BC limpets, whereas at AL 11 and 3 months are normal for spring and summer adults respectively. At BC 8.4 eggs per limpet are laid, and 34.8 eggs per limpet are laid by spring adults at AL. Biomass and egg production are assessed as total carbon (equivalent to calorific measures) and expressed as biomass—turnover rates (growth and egg production). Egg—production rates can be double those for growth at AL; at BC egg—production rates are usually less than those for growth. This is partly a consequence of greater primary productivity at AL, but may also reflect implied genetic differences. Limpets at BC build up carbon during late summer and early fall; an increase in the C:N ratio (to 4.8) indicates an accumulation of storage compounds. During the winter (lower temperature, solar input, and primary productivity) the C:N ratio decreases, and during spring breeding there is a more marked loss of carbon associated with egg laying. In field—acclimated BC animals, respiration is lowest during the winter; during the spring, respiratory rate is closely correlated with temperature and egg—laying intensity. Oxygen—consumption measurements at 10° and 20°C for all seasons reveal that these limpets show reverse acclimation at low temperature (qualitative and quantitative downward adjustment of metabolism). This acclimation pattern is accompanied by a decrease in Q10 (3.3 to 2.1) which can act to dampen the effects of winter temperature fluctuations. Energy balance (respiration, growth, egg production) is expressed as rates of carbon turnover for the population at BC. Respiration rates are greatest during the summer and spring and reflect increased assimilation due to growth or reproduction or both. The total carbon turnover per year is approximately 1.25 g/m2. Data on energy balance emphasize the adaptive importance of reverse acclimation at times of low energy input.

Patterns of Use of a Flood Plain by Zambian Mammals

Abstract: Every year the Kafue River, one of the main tributaries of the Zambezi River in Zambia, floods a broad level area, the Kafue Flats, to a depth of up to 5 m for several months. The flats are 235 km long and up to 40 km wide. The life of the flats is conditioned primarily by the alternating rainy and dry seasons and by the floods. About 80 cm of rain falls from November to April. The Kafue rises slowly during the rains, is highest in May, and falls during the latter part of the dry season. Vegetation is composed primarily of grasses, especially Oryza barthii. Because of the abundant water the primary productivity of the flats is much greater than that of the surrounding woodlands. Secondary productivity also is high. Every year there is an alternation of aquatic and terrestrial faunas. During the floods fish move onto the flats from the Kafue, and most spawning takes place there. Terrestrial species are driven off, but as the floods recede they reoccupy the flood plain and use what is by far the best grazing in the region. Large mammals find shelter in tall stands of grass, small mammals in the thick mat of vegetation that covers much of the ground or in the deeply cracked soil. There is a gradient in use of the flood plain: some species (hippopotamus, otter) always stay near the river at low water, others (lechwe, zebra, wildebeest) go for varying distances onto it, and more than half of the mammals (kudu, squirrel, vervet, aardvark) go onto it little if at all. Failure to use the flood plain seems to be due to absence of suitable habitats or food, rather than exclusion by the floods. The most abundant large mammal on the flood plain is the lechwe, the only terrestrial ungulate that sometimes feeds in the floodwaters. Several shrews and mice, especially Mastomys natalensis, are common on the food plain and breed there during the rains. During the floods they leave the flood plain or take refuge on natural levees along the Kafue. Large populations of water birds are common. Crocodile and monitor live near the water's edge and move in and out with the floods like the hippopotamus. Some snakes are common on the flats, but turtles and frogs are not. Although ants and termites are abundant in the surrounding region, they are largely excluded from the flats by the floods.

Energetics and Population Dynamics of Diaptomus gracilis

Abstract: The population dynamics and energetics of two populations of Diaptomus gracilis have been studied in two Thames Valley reservoirs. The seasonal changes in the standing crop biomass varied from a low of 0.3 Cal/m2 to a high of 7 Cal/m2. Although the population overwintered primarily as adults, reproduction was continuous throughout the year. From the mortality rate the production has been estimated to be 52 and 48 Cal/m2 for the Queen Elizabeth II and King George VI reservoirs, respectively. Feeding and respiratory rates of D. gracilis were measured both in the laboratory and in the field simultaneously with the population dynamics in the reservoir. The feeding rate and the rate of assimilation varied with the species of phytoplankton used as food. Filtering rates varied from 0.1 ml copepod—1 day—1 on bacteria to a high of 2.54 on Diplosphaeria, the latter also having an assimilation efficiency of 78% by D. gracilis. Respiratory rates varied with the season. When the metabolic rate was plotted against body...

Relative Importance of Habitat Variables in Predicting the Distribution of Phytoplankton at the Ecotone of the Antarctic Upwelling Ecosystem

Abstract: The vertical distribution of phytoplankton standing crop, number of species, and community diversity in five transects across the ecotone of the Antarctic Convergence were studied in relation to physical and chemical habitat variables (light, temperature, salinity, density, relative stability, oxygen, phosphate, nitrate, and silicate) and to bacteria and yeasts. Two distinct phytoplankton communities were observed, one north and one south of the convergence. Within the convergence the southern diatomaceous Antarctic community sinks with the formation of Antarctic Intermediate Water and can be traced underneath the northern dinoflagellate subantarctic community by use of indicator species. Chaetoceros bulbosum, Chaetoceros dichaeta, Dactyliosolen antarctica, and Eucampia zoodiacus were used as indicators of the Antarctic community, and Rhizosolenia delicatula, Amphidinium amphidinoides, Oxytoxum variabile, and Phalacroma pulchellum represented the subantarctic community. Submergence of the Antarctic commun...

Life History and Energy Relationships of Hydrophyllum appendiculatum

Abstract: The phenology of marked Hydrophyllum plants in five permanent 1—m2 plots in Brownfield Woods near Urbana, Ill, was observed from March 1966 through August 1966 and from June 1967 through July 1968 The first—year plant which appears above the soil surface in early spring persists during the entire summer under the closed canopy with two to four erect, solid—colored, palmately shaped leaves In autumn, mottled, palmately shaped leaves are formed which then overwinter in the form of a basal rosette The upright, first—year leaves die back with the advent of heavy frosts The plants break dormancy in early spring with subsequent formation of a large basal rosette of mottled, pinnately shaped leaves As the forest canopy closes, solid—colored, palmately shaped leaves and an erect stem are formed Floral buds soon appear Flowering and seed set take place under a closed canopy with plant senescence occurring approximately 2 months after canopy closure Carbohydrates are the major form of food reserves (82% of ovendry weight) in Hydrophyllum seed At least a year is needed after seed dispersal before germination Accumulated degree—hours and the floral bud and flowering stages are closely related in Hydrophyllum Low temperatures are important in rosette formation in both greenhouse and field plants, but photoperiod apparently is not important if temperatures remain moderate Plants will not flower unless they first develop a basal rosette Although only a relatively short vernalization period is essential, longer periods of low temperature will decrease the length of time needed to flower after the plants have broken dormancy Floral buds appeared in photoperiods ranging from less than 12 to over 135 hr, but longer photoperiods shortened the time interval between breaking dormancy and floral bud initiation Hydrophyllum is adapted photosynthetically to canopy closure by producing different types of leaves for different light regimes Plants with only solid—colored, palmately shaped leaves (first—year stage and seed—set stage) are present only under closed canopy conditions Light—compensation point of these plants is 60—80 ft—c, and light—saturation intensity is approximately 700 ft—c their maximum net photosynthetic rates are about 24 mg CO2/dm2 per hour Mottled, pinnately shaped leaves are present on second—year vegetative plants which grow under an open, spring canopy These plants have a light—compensation point of 100 ft—c and light—saturation intensity of 2,500 ft—c Their net photosynthetic rate at light saturation is 85 mg CO2/dm2 per hour Flowering plants, which occur under a closed canopy and usually have both types of leaves, have net photosynthetic rates and light—saturation intensities at intermediate levels between the solid—colored and mottled groups of plants All phenological stages except the seed—set stage demonstrated small but significant decreases in photosynthesis with increasing temperatures in the 15°—27°C range

Ecology of the Water Penny Beetle Psephenus herricki (DeKay)

Abstract: A general theory of distribution suggests that the microhabitat, habitat, and geographic distribution of Psephenus herricki is related to water turbulence. The different life stages typically occur in stream riffles. Adults are found in riffles because they are "attracted" to the moist wave—splashed rocks that stick out of the water. These same rocks provide a mating site and give the female access to the subsurface materials for oviposition. The microdistribution of eggs is a function of the distribution of wave—splashed rocks during oviposition and female oviposition behavior. Oviposition initially accounts for the large numbers of larvae in riffles, but larvae live about 2 years giving them sufficient time to disperse into the runs and pools. Dispersion, however, is negligible due to a thigmokinesis that inhibits vagility when they are wedged in the interstitial spaces of the substrate. This and the distribution of algae on rocks seems to determine the microdistribution of larvae. Riffles contain an abundance of these interstitial crevices due to sorting by stream turbulence. Turbulence and physiography, governing the geographic distribution of riffles, directly influence the geographic distribution of the species.