Showing papers in "Ecological Monographs in 1972"

Development of a New England Salt Marsh

Abstract: The salt marsh at Barnstable, Massachusetts, occupies an embayment into which it has spread during the past 4,000 years. It exhibits all stages of development from the seeding of bare sand flats through the development of intertidal marsh to the formation of mature high marsh underlain by peat deposits more than 20 ft deep. Observations and measurements of the stages of its formation are presented. The geomorphology of the marsh is considered in relation to the factors which have influenced its development, i.e., the ability of halophytes to grow at limited tide levels, the tidal regime, the processes of sedimentation, and the contemporary rise in sea level. The rates at which the early stage of development takes place have been determined by observations during a period of 12 years and the time sequence of later stages by radiocarbon analyses.

Factors Affecting Clutch Size in Arctic Passerines

Abstract: Clutch size and related aspects of breeding biology were investigated in the Lapland Longspur (Calcarius lapponicus) and Snow Bunting (Plectrophenax nivalis) in the North American Arctic, and in allied temperate and subarctic species. Evidence was sought to test Lack's hypothesis that the increase in clutch size with latitude is related to the length of daylight available for the adults to collect food for their young, and that clutch size is ultimately determined by the average maximum number of young for which the parents can find food. The arctic species were studied mainly at 76° N on Devon Island; some additional data were collected elsewhere. Increase in clutch size with latitude was correlated with a decrease in the adults' night rest period from 7 hr at 50° N to 3—5 hr in the Arctic. In the Lapland Longspur in Canada clutches were larger at high latitudes and at localities with early breeding seasons. Clutch size and latitude were not significantly related for those localities where activity of adults attending nestlings is not restricted by daylength. Differences in clutch size were not attributable to geographic or interspecific variation in hatching asynchrony, hatching success, or growth of the young. Hatching of Lapland Longspur and Snow Bunting clutches on Devon Island corresponded closely with the emergence of the adult insects which predominate in the nestlings' diet, but other factors may also influence the timing of the breeding season. The decline in clutch size in these single—brooded species as the season progressed apparently was not related to changes in the environmental food supply. In the multiple—brooded Chestnut—collared Longspur (C. ornatus) in Saskatchewan clutch sizes changes little during the season. Annual differences in clutch size were demonstrated in the Snow Bunting, but their significance is unknown. Although Snow Bunting clutches of seven are rare on Devon Island, more young were fledged from experimental broods of seven than from smaller broods, but the young averaged lighter in weight. Adults feeding large broods made more visits to the nest each day and were lighter in weight than those with small broods, but the visiting rate per young was less in large broods. Much of the variation in clutch size, including the increase with latitude, is related to environmental factors influencing the food—gathering potential of the adults. But this does not mean that clutch size has evolved to a limit set by the environmental food supply, because food—gathering behavior and related morphology have also evolved by natural selection. Clutch size must be determined by the effects that changes in it and other aspects of reproductive strategy have on the probability of survival of both the adults and their offspring.

Role of Temperature and Water in the Ecology of Lungless Salamanders

Abstract: Water economy and thermal relations of plethodontid salamanders were studied in the laboratory and in the field. Laboratory measurements included behavioral responses in temperature and relative humidity gradients, rates of dehydration and dehydration at various relative humidities and soil—moisture levels, and determination of critical thermal maxima by rapid controlled heating to a definite endpoint. Salamanders were acclimated to a combination of three temperatures and two photoperiods: 5°C, 16 hr of light alternating with 8 hr of darkness (LD 16:8); 5°C, (LD 8:16); 15°C (LD 16:8); 15°C (LD 8:16); 25°C (LD 16:8); and 25°C (LD 8:16). Three series of experiments were conducted on 20 populations representing 14 species. Critical thermal maximum increased with an increase in acclimation temperature indicating that the salamander's heat resistance was readily altered by its previous thermal history. Salamanders selected a definite range of temperatures and did not merely avoid extremes in the thermal gradient. Thermal preferenda were relatively stable for each species and were not significantly affected by either acclimation temperature or photoperiod. Rate of dehydration was dependent upon body size, drying power of the air, and ambient temperature. Interspecific differences in dehydration rates appeared to be related in part to differences in size. Species composed of small individuals lost weight faster than species made up of large individuals. As the vapor pressure deficit increased the dehydration rate increased. Dehydration was more rapid at higher temperatures. Rehydration rate increased as the percentage of weight loss due to dehydration increased and was more rapid at higher temperatures. Salamanders absorbed water from soil when soil—moisture tension was as high as 2.8 atm at 25°C. All species absorbed water from unsaturated soil at similar rates that were dependent upon soil—moisture content. Salamanders in the humidity gradient responded positively to differences in the moisture content of the air, and all but one species were more than 70% successful in selecting the highest relative humidity available in the gradient. Interspecific differences were apparent, but were not always correlated with habitat preferences. Plethodon glutinosus did not show any specific adaptation in its thermal responses or water relations that would account for its widespread distribution in the eastern United States. Plethodon ouachitae and P. caddoensis apparently have survived in the Ouachita Mountains due to favorable microhabitats and their ability to burrow deep beneath talus—covered slopes during hot and dry summers. Surface activity of P. caddoensis is limited in the summer by hot and dry conditions in its microhabitat.

Breeding Success of the Common Puffin (Fratercula arctica L.) on Different Habitats at Great Island, Newfoundland

Abstract: Factors contributing to breeding success of puffins were studied on Great Island, Newfoundland, in 1968 and 1969. Puffin burrow density was negatively correlated with distance from the cliff edge and positively correlated with angle of slope. These correlations are biologically significant in that close to the cliff edge, where the angle of slope was steep, breeding success was significantly higher than on adjacent level habitat. In spring both habitats were occupied simultaneously, and nest—site tenacity was equally strong in them. During settlement the frequency of fighting was higher and the peak was reached earlier on slope habitat. Males were heavier on slope than on level habitat just after peak egg laying, although wing lengths were similar. Females were similar on the two habitats. Measurements of eggs from both habitat were the same. Egg—laying dates were also similar, but annual variation was greater on level than on slope habitat, as was variation within a single year. Hatching success was higher on slope habitat, mainly because the incidence of egg disappearance was lower during incubation; also the frequency of infertile eggs was greater on level habitat. Fledging success was higher on slope habitat, and higher on both habitats in 1969. Frequency of chick deaths in the nest and disappearance before fledging was higher on level habitat in both years. Fledging success was higher for early—hatched chicks in both habitats. Total breeding success was higher on slope habitat, and higher in both habitats in 1969. Fledging condition of chicks varied according to the habitat and time period in which they were raised. On the average, body weight at fledging was greater and less variable for birds on slope habitat; early—hatched chicks were heaviest in both habitats. Wing length of young at fledging did not differ. Early—hatched chicks on slope habitat fledged quickest (also quicker than early—hatched chicks on level habitat); late—hatched birds on slope fledged slower than late—hatched birds on level habitat. Age at fledging was greater in 1968 than in 1969 on both habitats. Meal size delivered to chicks by parents was the same on the two habitats, but frequency of feeding was greater on slope than level habitat. Breeding pairs on slope habitat were unable to raise two chicks (artificial twins) to fledging; similarly, one adult could not rear a single chick. Adults feeding chicks on level habitat were attacked and robbed more frequently by gulls than birds on slope habitat, probably because escape (take—off) from an attack was quicker on slope than on level ground. Experiments performed to determine causes of the differential egg and chick loss before fledging in the two habitats showed that during incubation the proportion of eggs displaced to the burrow entrance by incubating birds when leaving the burrow in a hurry was the same, but the rate of panic flights was higher on level habitat. Also, chicks when starved spent more time at the burrow entrance than when fed regularly. It is concluded that the difference in breeding success on the two habitats was due to a higher exposure of eggs and chicks to gull predation on level habitat. The primary cause for this differential exposure was that adults on slope habitat were less vulnerable to gull disturbance during incubation and gull robbery when feeding their chicks. Thus breeding failures resulted from the interactions of food shortage and gull interference. This conclusion was tested by comparing breeding performance of birds at Great Island with birds at two islands where gull interference was absent. Egg and chick survival was greater under "gull—free" conditions. In addition, body weights at fledging were higher and less variable at the colonies without gull interference than at Great Island. The ways in which natural selection acts upon puffins at the breeding colony are considered; a model relating puffin nest distribution and habitat features is presented, and predictions which might be tested are outlined.

Significance of spider predation in the energy dynamics of forest-floor arthropod communities

Abstract: Spiders were the most important entomophagous predators of a 137Cs-tagged Liriodendron tulipif era decomposer community. Radioisotope techniques were used to quantify the bio- energetic impact of spider predation on the forest-floor detritus food web. Temperature. dependent 137Cs elimination by spiders and 137Cs concentrations in field animals were used in intake-loss equations to estimate ingestion by the spider population. Radiocesium body burdens fluctuated seasonally in response to litterfall and seasonal differences in temperature and precipitation. Ingestion rates, assimilation efficiencies, and respiratory energy losses were used to estimate gross and net production of the forest spider population. Annual mean population density of spiders was 126 individuals/M2. Population-density peaks occurred in fall, early winter, and summer. Mean biomass for the year was 43 mg dry wt/m2; maxima occurred in early winter and spring. Spiders 1-10 mg in size accounted for 59% of total biomass; spiders 10 mg comprised the remaining 24% and 17% of the population, respectively. Predicted values for ingestion, assimilation, and respiration indicate that forest- floor spiders were active throughout a temperature range of 5 -20'C, with 13.30 the optimum for net production by spiders of all size classes. Spiders killed an equivalent of 2.08 kcal prey tissue/M2 per year and ingested 1.68 kcal/m2 per year. Respiratory energy loss equaled 1.23 kcal/m2 per year. Trophic level efficiencies calculated from seasonal energy-budget data were: (1) intake efficiency (prey killed/ingestion), 73-86%; (2) as- similation efficiency (assimilation/ingestion), 90-99%; (3) respiration efficiency (respiration/ ingestion), 58-96%; (4) respiration/assimilation, 63-106%; (5) ecological growth efficiency (net production/ingestion), -5-34%; and (6) tissue-growth efficiency (net production/as- similation), -4-37%.

Foraging Strategy of a Starfish in Relation to Actual Prey Availability and Environmental Predictability

Abstract: The foraging ecology of the asteroid Leptasterias hexactis was studied at five rocky intertidal areas in the San Juan Islands, Washington, for 2—2¾ years. Feeding activity during high tides reaches a high point in mid— to late summer (July and August) and a low point in the winter (January). Three probable factors selecting for this cycle are (1) reproduction, virtually immobilizing the females, during the winter; (2) low food availability in winter compared to summer; and (3) violent winter storms. Persistently reduced low tide feeding during all but autumnal night low tides indicates that some light—related factor(s) select for a tidal cycle of feeding also. Factors believed responsible are desiccation stress and possibly predation by visual predators. A graphic model of foraging behavior is presented. Analysis of the diet of Leptasterias by both numbers and calories of prey consumed indicates that this starfish is a food generalist. Moreover, numbers of prey consumed, when compared to prey available, indicate those prey chosen selectively and those which are avoided. Lastly, calories consumed compared to calories available indicate why particular prey are chosen. Many factors are involved in prey choice including ease of capture, relative sizes of predator and prey, and caloric yield of the prey. Actual availability is defined as that portion of available prey (i.e., prey physically present) which could be consumed by a predator. The factors affecting prey choice, coupled with prey and predator distribution, abundance, and behavior must be considered when determining actual availability of prey. Actual availability coefficients are computed and suggest that (1) hard—to—capture prey are least available; (2) Leptasterias is more selective in summer and autumn, when food is more abundant; and (3) prey are more available to large starfish. Calculations suggest that, under normal conditions, Leptasterias would be severely energy—limited in winter if it foraged at rates similar to those of spring or summer, or both. Thus, food limitation may be partially responsible for reduced feeding in winter. Comparison of numerical patterns of consumption of energy—rich and energy—poor prey indicates that energy—rich prey are most important except in summer when energy—poor prey become the most important prey, presumably because of their tremendous numerical increase and domination. Comparisons between the foraging strategy of this starfish and theoretical models previously proposed support some predictions but not others, indicating that complex natural systems require more comprehensive and precise models. Predictability of resources in time and space probably determines the degree of resource specialization or generalization in animals.

Effects of an Organophosphorus Insecticide on the Phytoplankton, Zooplankton, and Insect Populations of Fresh-Water Ponds

Abstract: Dursban, an organophosphorus insecticide, was applied on June 3, June 18, and July 1 to eight shallow (24 cm) experimental ponds near Bakersfield, California. Four ponds were treated at 0.028 kg/ha (=0.025 lb./acre), four were treated at 0.28 kg/ha, and four were kept as controls. Phytoplankton, zooplankton, and insect populations were sampled on 21 dates between May 20 and August 16. Insect larvae and nymphs were more reduced in numbers than were insect adults, reflecting in part the ability of the latter to emigrate and immigrate. Twenty—four—hour posttreatment samples for the second and third, but not first, treatments showed greater reductions of predaceous Notonectidae, Dytiscidae, Coenagrionidae, larval Hydrophilidae) than of "herbivorous" (Corixidae, Baetidae, adult Hydrophilidae) insect populations. Predaceous insect populations generally recovered to control—pond levels more slowly than herbivorous insect populations. Five weeks after the last insecticide treatment, predaceous insects averaged only 45% and 9% as abundant in low dose and high dose ponds, respectively, as they were in control ponds (P < 0.02); corresponding figures for herbivorous insects were 108% and 206% (P < 0.10). Initially, Cyclops vernalis and Moina micrura were the only crustacean zooplankters present, and both experienced high mortality due to treatments. Recovery in low dose ponds was variable, requiring 1—3 weeks, and in high dose ponds occurred only 3—6 weeks after the final treatment. Populations of Diaptomus pallidus seemed unaffected by the lower rate of treatment, but became large only after Cyclops populations had been reduced by the insecticide or other factors. Ceriodaphnia sp. became abundant in late July or early August in all four control ponds but not in any treated ponds. Herbivorous rotifers, principally in the genera Brachhionus, Polyarthra, Hexarthra, Filinia, and Tripleuchlanis, increased dramatically, often five— to twentyfold, within 1—3 days after Moina and Cyclops populations were decimated by Dursban, but became abundant in control ponds only during the brief absence of Moina in early July. All planktonic rotifers, except Polyarthra, were more abundant in treated than in contro ponds; all benthic—littoral rotifers (e.g., Lecane, Monostyle, Tripleuchlanis, Platyias, Lepadella, Testudinella) were more abundant in control than in treated ponds. The predaceous rotifer Asplanchna brightwelli was 35 times more abundant in treated than in control ponds, feeding primarily on herbivorous rotifers, sometimes on Cyclops, Diaptomus, Moina, and large algae, and rarely on small mayfly (Baetidae) nymphs and chironomid larvae. Asplanchna populations were composed of three morphotypes, ampulliform, cruciform, and campanuliform, the last of which tended to be highly cannibalistic. The "wings" of humps of the cruciform morphotype apparently represent a mechanism for minimizing such cannibalism. The reduction of herbivorous crustaceans by Dursban and the restraint of herbivorous rotifers by Asplanchna predation permitted the rapid increase of phytoplankton populations in treated ponds and, even 6 weeks after the last treatment, the phytoplankton was two and 16 times more abundant in low dose and high dose ponds, respectively, than in control ponds. Blooms of bluegreen algae (Anabaena, Anabaenopsis) developed in three high dose and one low dose pond, and a bloom of the diatom Synedra developed in one low dose pond. The long—spined alga Schroederia setigera seemed favored by high Moina and Diaptomuspopulations and low Cyclops populations. The significance of these results for insect—control programs is discussed.

History of an African Rift Lake and Its Climatic Implications

Abstract: Analysis of a 28—m core from a relict fresh—water lake in Kenya had provided a detailed limnologic and climatic history covering 9,200 years. The core is an incomplete section through the sediments of a submerged crater near the eastern shore of Lake Naivasha. The overall sedimentation rate, 0.33 cm wet sediment per year, is the most rapid on record for a lake whose sediments are essentially autochthonous and organic. A three—stage limnologic history is inferred from the microfossils (particularly diatoms), chemistry, and mineralogy of the core: (A) From before 9,200 B.P. until about 5,650 B.P. a lake significantly larger than the present one existed in the basin. Algal productivity was high, and the water temperature was probably above the present average. The surface waters of this lake were evidently depleted in silica, suggesting some stratification, but the total ion content was not far below today's (B) Between 5,650 B.P. and 3,040 B.P. the lake shrank, aquatic macrophytes increased in abundance near the core site, and the water grew more dilute. The crater became isolated from the main lake and finally dried briefly. (C) For the past 3,000 years a small lake has existed in the basin. It has been frequently smaller and its water sometimes much more concentrated than that of the modern lake. The lake discharged through a southern outlet prior to 5,650 B.P., but since that time has had no surface outlet. Various freshening mechanisms have operated during the past 5,000 years, probably including deflation, burial of alkaline layers, underground seepage, and perhaps ion removal by aquatic plants. The climate during the period of the large lake (Leakey's Gamblian Pluvial period) was much wetter and probably warmer than today, and rainfall at Naivasha was more seasonal. Rainfall was perhaps 65% above the modern average. We find no convincing evidence for an early post—Gamblian wet phase, the Makalian, proposed by earlier workers for this region. A later wet phase, the Nakuran, may be represented by the small, fluctuating lake of the past 3,000 years, but this lake probably never stood as high as the strandline previously assigned to the Nakuran. The climatic inferences from this study are in substantial agreement, but provide interesting points of contrast, with those from other recent investigations in sub—Saharan Africa.

Vegetation Analysis of North and South Edges in a Mature Oak‐Hickory Forest

Abstract: The north and south edges of a mature oak-hickory forest on the New Jersey Piedmont are characterized by local-scale vegetation gradients. These gradients are determined by both exposure-induced microclimatic influences and historical factors. The north edge has been relatively undisturbed since establishment. A narrow vegetative transition is associated with the relatively narrow microclimatic transition within the edge. A low thicket of tree growth (Cornus florida, Prunus avium, Viburnum prunifolium) mingled with woody vines and herbs is found exterior to the original edge. The old edge ends about 10 m within the forest and is characterized by increased densities and basal areas (compared to center) for Quercus spp. and Prunus avium. The original south edge is found about 20 m within the present forest. It is characterized by increased densities and basal areas of Quercus spp. and Viburnum prunifolium. Agricultural abandonment about 1900 accounts for reforestation in front of the old edge. The area immediately in front of the original edge is an open stand in which both Prunus avium and Viburnum prunifolium have increased densities. Exterior to this is a dense strip of medium-sized trees which is characterized by increased densities of Quercus spp. and Prunus avium. The remaining area is composed of small trees (Quercus velutina, Prunus avium) with clumps of woody vines between and upon them. The wide microclimatic transition at one time within the original south edge was transferred to the present edge with the development of a closed canopy within the reforested strip. Few edge effects are found now beyond 20 m within the stand. The segregation of species within and between the edges is more subtle than that between north and south slopes in the region. Species characterized by shade intolerance or good vegetative reproduction, or both, are prevalent at the edges. Many of these species also are associated with secondary succession in forest gaps, but edge responses are stronger than gap responses for most species. These include Fraxinus americana, Prunus avium, P. serotina, Sassafras albidum, and Viburnum prunifolium. Among canopy dominants Quercus velutina shows a stronger edge response than Q. alba or Q. rubra.. Carya ovalis shows no significant edge response, whereas C. ovata displays a strong one. Relatively tolerant species such as Fagus grandifolia, Acer saccharum, and A. platanoides display no edge response. Most tree distributions are more localized than those of their reproductive size classes, presumably as a result of environmental selection acting upon seedlings and saplings within different forest microhabitats such as edges, gaps, and well-stratified areas of the stand. Although the techniques are different, this study represents a local-scale example of direct gradient analysis in that plots (amenable to analysis of variance) are used as microlocational indices of the environmental complex and are matched to known microclimatic gradients.

Origins and Ecology of the Sierran Alpine Flora and Vegetation

Abstract: The alpine flora of the Sierra Nevada has developed relatively recently and largely in situ from western American sources. The Sierra thus provides a good site for an attempt to answer the question: "How does an alpine flora originate?" The primary study area was a transect from the desert near Bishop, California (1,400 m), to Piute Pass in the Sierra Nevada (3,540 m). Upward along the transect the vegetational gradient is Ephedra nevadensis—Tetradymia spinosa desert shrub, Pinus monophylla—Artemisia tridentata open woodland, Pinus jeffreyi open forest, Pinus murrayana forest, Pinus albicaulis—subalpine herbaceous vegetation, and scattered alpine communities. Only 19% of the alpine species at Piute Pass occur in the Arctic, whereas 38% are held in common with the Rocky Mountains. Species endemic to the Sierra (17%) are in genera predominantly from the Californian or Great Basin floras of lower elevations. A number of species have populations in the desert and also at high elevations near the alpine zone. ...

Developmental and Environmental History of the Dismal Swamp

Abstract: Pollen analysis of several cores from the Dismal Swamp in southeastern Virginia have indicated that the swamp is a relatively young feature, having begun to develop along drainage lows as recently as the late—glacial. Formation of extensive fresh—water marshes along streams appears to have been brought about by general water—table changes controlled by the post glacial rise of sea level. As the sea continued to rise, marsh development proceeded inland and fine—grained organic sediments began to accumulate. By 6,000 years B.P. approximately 50% of Dismal Swamp area had been mantled by fine—grained peat deposits. From 6,000 to 3,500 B. P. peat accumulation continued, but at an appreciably lower rate. The corresponds both to the hypsithermal interval and to a distinct slackening in the rate of sea—level rise. By 3,500 B.P. peat had mantled virtually all of the interfluves and "islands" within the swamp. The pollen diagrams suggest a gradual change from boreal spruce—pine forests during the full—glacial, to s...

Macrobenthos of the Pamlico River Estuary, North Carolina

Abstract: A study of the macrobenthos and its environment in the Pamlico River estuary, North Carolina, included measurements of salinity, temperature, and dissolved oxygen, as well as the particle size and concentrations of organic matter of the sediments. Salinity ranged from 1% to 20%, and temperature from 5° to 31° C. Anoxic conditions in the bottom water over—lying the deeper portions of the estuary occurred in the late summer. Two distinct sediment types were found: a sand substrate in the shallow area and a silty clay substrate in the deep area of the estuary. A preliminary sampling program in July 1968 showed that the macrobenthos was characterized by both low diversity and low density because of unfavorable environmental conditions of salinity and sediment. The statistical sampling design for this study was stratification of the estuary and equal random allocation of samples. Only 18 species were found, and the Shannon—Weaver information diversity index (H) showed low values of 0.66—1.77. In addition, low ...

Structure and Energetics of Three Minnesota Forests

Abstract: Three contiguous ecosystems, an upland oak forest, marginal fen, and cedar swamp, were analyzed along a gentle topographic gradient on the Anoka Sand Plain in east—central Minnesota. The organic structure and aboveground primary productivities of these forests were compared with similar data for other natural ecosystems of the sand plain. Living, aboveground biomass totals of the oak, fen, and swamp forests were 124.6, 98.8, and 159.6 mt/ha, respectively. Aboveground, net annual productivities were 8.9, 7.1, and 10.3 mt/ha, respectively, which compared well with other forest data for the region and with a predicted value based on actual evapotranspiration. Several measures of structure were compared in the analysis. Species richness and equitability were greatest in the marginal fen where biomass and productivity were the least. Richness and equitability were lowest in the oak forest. The highest biomass—to—production ratio was found for the Thuja swamp, although it had the highest annual production. Apparently the high production in the swamp was achieved with a large mass of relatively inefficient foliage concentrated in Thuja occidentalis. The percentages of primary production entering detritus pathways were 52, 62, and 48 for oak, fen, and swamp, respectively. Total detritus, including dead boles, branches, and forest floors, was large in relation to living biomass in all three forests, but was especially important in the fen and swamp systems where deep forest floors had accumulated. Total detritus was 61%, 331%, and 577% of aboveground biomass in the oak, fen, and swamp, respectively. All data were produced in caloric as well as weight units.

Tissue Water Potential, Photosynthesis, C‐Labeled Photosynthate Utilization, and Growth in the Desert Shrub Larrea divaricata Cav.

Abstract: Tissue water potential is the most important factor throughout the seasons controlling phenological events, photosynthesis, and productivity of Larrea divaricata growing in Deep Canyon near Palm Desert, California. Growth of reproductive structures was initiated at the time of highest tissue water potential and ceased as water potential decreased. Percentage foliation correlated strongly with dawn water potential (r = 0.89). The elongation rate of stems and the rate of node production were both dependent on tissue water potential. Leaf growth and node growth proceeded at varying rates throughout the year, providing a continuous sink for photosynthates. Photosynthesis rates ranged from 9.02 mg CO2 incorporated per day per gram dry weight of leaf tissue in September to an estimated 74.7 mg CO2 in early February. Net photosynthesis and relative productivity correlated very strongly with dawn water potential (r = 0.93 and r = 0.97, respectively). Larrea plants were labeled at 1— to 2—month intervals with photosynthetically incorporated 14CO2to determine the utilization in growth and storage of photosynthate fractions produced at various times throughout the year. Tissue was subsampled at similar intervals, and the activity in various metabolic compounds (sugar, starch, lipid, organic acid, amino acid, protein, cellulose, and cell—wall materials) was analyzed. The utilization of photosynthates in the various fractions was similar in all seasons. No appreciable mobilization into and out of storage materials was apparent. Never dormant, Larrea remains metabolically active and forms new tissue throughout the year. This growth pattern may be an important adaptation allowing Larrea to exist in a wide range of geographical and climatic areas, and, perhaps owing to the species' tropical affinities, it might have been a preadaptation to the desert environment.

Drift and Production of Two Aquatic Insects in a Mountain Stream

Abstract: The relationships between drift rates, population density, production rates, key environmental factors, and movements of adults were studied in two populations of stream insects, the caddisfly Oligophlebodes sigma and the mayfly Baetis bicaudatus. Samples of benthic invertebrates (424 total) were collected every 28 days at four stations on Temple Fork of the Logan River, Utah, from October 1967 to September 1969. Samples of drift invertebrates (181 total) were collected every 14 days at three stations on Temple Fork during the same period. During June—September a day and a night drift sample (681 total) were collected every other day. Drift rates of O. sigma larvae were greatest (5,987 g/year) when biomass in the benthos (2.56 g/m2) and production (4.30 g/m2 per year) were greatest. Total production (dry weight) of O. sigma larvae in the stream (bottom area = 29,487 m2) was 89.0 kg in 1968 and 80.8 kg in 1969. Total production of B. bicaudatus nymphs was 41.3 kg in 1968 and 39.8 kg in 1969. Drift rates of O. sigma larvae were related directly to biomass in the benthos over an entire year. Drift rates of O. sigma and B. bicaudatus were not related directly to density expressed as numbers/area in the benthos. Drift rates were correlated positively and significantly (r = 0.78 and 0.55 for day drift of O. sigma and B. bicaudatus, respectively) with density during the months of June—September for both O. sigma larvae and B. bicaudatus nymphs. Discharge, distance below the spring source of Temple Fork, and densities of competing aquatic insects were other factors of significance in the multiple—regression analyses of factors affecting drift rates of the two insects. The 17 or 18 independent variables used in the multiple—regression analyses accounted for 65% and 55% of the variability in day drift rates of O. sigma and B. bicaudatus, respectively. Adult O. sigma (but not B. bicaudatus) undertook a definite upstream migration estimated at 2—3 km. This flight of adults resulted in a concentrated deposition of eggs in the upper reaches of the stream. The advantage of the upstream flight may be that it stores reproductive products in areas where they are relatively safe from effects of anchor ice during winter and of floods in late winter and early spring.

Computer Analyses of Petersen's Original Data on Bottom Communities

Abstract: Petersen—type bottom communities (a concept based on Petersen's 1914 data) are characterized by constant species which are dominant in terms of numbers and weight. Some workers recently have questioned the existence of these communities, in which quantitative data upon very few of the species present have been analyzed subjectively, and other potentially important species have been neglected. Various computer techniques were used to analyze Petersen's data. For the majority of species only presence—absence data can be used; for quantitative data 88 species from 193 stations were processed. The final methods involved transformed data of numbers and weights, respectively, the Canberra metric coefficient, and a combination of flexible and group—average sorting followed by allocation. The presentation of results is difficult because, even after classification, the complexity of the data–for example, the lists of species of different grades of constancy and abundance which characterize site groups–lies beyond human ability to comprehend adequately. Results are compared with Petersen's and with each other. Petersen's classification compares most closely with ours involving binary data. Our "numbers" and "weights" classifications both reveal Petersen—type communities, but they differ markedly from each other and more markedly still from Petersen's results

Forests of the Catskill Mountains, New York.

Abstract: The modern forest of the Catskill Mountain region, New York, particularly the area within the New York State Forest Preserve, was studied and compared with the presettlement forest as determined from surveyors' records. The most notable changes were a marked drop in the proportion of beech (Fagus grandiflora) and hemlock (Tsuga canadensis) and increases in sugar maple (Acer saccharum), red oak (Quercus borealis), and chestnut oak (Quercus prinus). Reproduction and size—class data suggest that in old—growth hemlock stands hemlock is replaced by hardwoods and is not a part of a homogeneous climax forest in spite of its prominence in the presettlement forest. Beech does not give evidence, in the dynamics of the modern forest, of returning to its presettlement dominance. Some pioneer stands are as rich in species and as diverse as are those usually thought of as climax. The comparison of presettlement and recent forests is related to recent discussion of climax concept. See full-text article at JSTOR

Ecology of Alpine Larch (Larix lyallii Parl.) in the Pacific Northwest.

Abstract: Alpine larch (Larix lyallii) grows in or near the timberline zone on high mountains of the inland northern portion of the Pacific Northwest. Unlike other subalpine conifers, which are evergreens, this deciduous larch displays an affinity for cold rocky sites and often grows in tree form higher up on north slopes than even krummholz (shrubby) forms of its associates. Overstory and understory vegetations in alpine larch communities were only indirectly correlated. Vaccinium scoparium, Luzula glabrata, and Phyllodoce empetriformis were the most common understory dominants. The distinctly snowy—cold—timberline nature of alpine larch habitats is emphasized by the presence of Cassiope mertensiana, Phyllodoce glanduliflora, and Abies lasiocarpa krummholz among the 11 most common understory species. Unlike the larch, which is generally restricted to the timberline zone, nearly all associated plants have broader distributions in the subalpine forest proper or above tree limit. Alpine larch is a climax species on a wide variety of sites too severe for the more shade tolerant evergreens to form unbroken stands because of shortness of growing season, rock terrain, avalanches, blizzards, or extreme dryness or bogginess. When alpine larch ascends into what would otherwise be a strictly alpine habitat (above the limits of other conifers), its stands apparently modify the surface environment since subalpine understory species are generally able to ascend with it. Rarely the undergrowth is dominated by tundra species. Alpine larch is superior in invading freshly glaciated sites. The positive correlation of alpine larch to acidic substrates poor in mineral ions is in contrast to the substrate relationship of many other timberline conifers, which are calciphiles.

Interrelations among Plankton, Attached Algae, and the Phosphorus Cycle in Artificial Open Systems

Abstract: The circulation of phosphorus in 200—liter aquaria, continuously supplied with tap water, was analyzed by means of analytical and tracer methods. This open—system design ultimately resulted in a steady—state system whereby the influx of phosphorus to various biological compartments was equaled by a corresponding outflow. This model of phosphorus circulation is believed to apply to small lakes with extensive littoral vegetation during summer stratification, but contrasts with models proposed from other tracer studies on such lakes. The other models are considered to be feasible, but unlikely and based on incorrect analyses of data. Previous estimates of the rate of phosphorus circulation based on tracer analyses are reanalyzed and appear to be of the correct magnitude. The 200—liter system developed two communities of attached and planktonic organisms, with the former rapidly removing a large percentage of the phosphorus from the latter. With this removal any direct relationship between the phosphorus concentration of the open water and the influx concentration was obscured. A major means by which phosphorus was removed from the open water was shown to be trapping of particles by the community associated with the sides of the aquaria. The rate of such removal varied widely, depending on the extent of "littoral" growth and the nature of the particle. These results suggest that a multicompartment analysis of nutrient circulation is significantly more realistic than a simplistic assumption of homogeneity. Considering succession to be the total change in physical and biological conditions over prolonged time, this open—system design developed from a one—community, few—species system into a two—community, several—species system. The rate of nutrient circulation greatly increased with time and developed into a steady state, not an equilibrium system which depended on a continual phosphorus influx to maintain the concentrations and circulation rates.